• power supply subtelties

    From jlarkin@highlandsniptechnology.com@21:1/5 to All on Fri Jun 24 06:35:32 2022
    I never thought a lot about general-purpose bench type power supplies,
    but now we have to design some.

    A power supply has two knobs (or SCPI commands in our case), voltage
    and current limit.

    A power supply should have low impedance at high frequencies, so after
    whatever current limit circuit is has, there must be a real capacitor.
    When you short a bench supply, you get a spark from the energy in the
    output cap. So for a while, it's not really current limited.

    Our supply will be a buck switcher

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    so we need an LC lowpass filter. It has to kill the 250 KHz ripple but
    allow reasonable programmable voltage slew rates. We'll close a
    feedback loop from the voltage sensor ADC into the bridge PWM drive,
    so the filter has to be well behaved. Maybe we need the R3C3 damper to
    kill the Q of L1C1 so the loop doesn't go bonkers.

    As if that isn't bad enough, the customer load could be most anything,
    a short or a resistor or a box with big input caps. Or a big DC bus.
    Or even a battery. So our filter gets messed with by the customer.

    And a buck switcher is a boost switcher backwards. If the customer
    gadget sources more voltage than our setpoint, we extract power from
    the customer and charge C9 and blow everything up. We can sense the
    +60 and shut off both fets, I guess.

    We also need a well-behaved current-limit loop.

    When I get time, I might prowl the web for old power supply
    schematics, HP or Kepco or whatever, and see what their output caps
    are like and how they managed the voltage/current dynamics. Those
    would be mostly linear supplies, I guess.

    Wild guesses: switch at 250 KHz. Output 0 to 48v at 0 to 6 amps. L1 is
    180 uH. C2 could be 10 to 300 uF. Loop bandwidth 1 KHz.

    We will probably add a secondary lowpass filter with a notch at 250K,
    to un-compromise the main L1C2 filter, but that won't affect than main
    loop dynamics.



    --

    Anybody can count to one.

    - Robert Widlar

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to jlarkin@highlandsniptechnology.com on Fri Jun 24 12:45:41 2022
    jlarkin@highlandsniptechnology.com wrote:
    I never thought a lot about general-purpose bench type power supplies,
    but now we have to design some.

    A power supply has two knobs (or SCPI commands in our case), voltage
    and current limit.

    A power supply should have low impedance at high frequencies, so after whatever current limit circuit is has, there must be a real capacitor.
    When you short a bench supply, you get a spark from the energy in the
    output cap. So for a while, it's not really current limited.

    Our supply will be a buck switcher

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    so we need an LC lowpass filter. It has to kill the 250 KHz ripple but
    allow reasonable programmable voltage slew rates. We'll close a
    feedback loop from the voltage sensor ADC into the bridge PWM drive,
    so the filter has to be well behaved. Maybe we need the R3C3 damper to
    kill the Q of L1C1 so the loop doesn't go bonkers.

    As if that isn't bad enough, the customer load could be most anything,
    a short or a resistor or a box with big input caps. Or a big DC bus.
    Or even a battery. So our filter gets messed with by the customer.

    And a buck switcher is a boost switcher backwards. If the customer
    gadget sources more voltage than our setpoint, we extract power from
    the customer and charge C9 and blow everything up. We can sense the
    +60 and shut off both fets, I guess.

    We also need a well-behaved current-limit loop.

    When I get time, I might prowl the web for old power supply
    schematics, HP or Kepco or whatever, and see what their output caps
    are like and how they managed the voltage/current dynamics. Those
    would be mostly linear supplies, I guess.

    Wild guesses: switch at 250 KHz. Output 0 to 48v at 0 to 6 amps. L1 is
    180 uH. C2 could be 10 to 300 uF. Loop bandwidth 1 KHz.

    We will probably add a secondary lowpass filter with a notch at 250K,
    to un-compromise the main L1C2 filter, but that won't affect than main
    loop dynamics.

    There's a chapter(*) in one of Jim Willams' books about a guy who built
    big SMUish things using a '1/2 pole' rolloff--a bunch of lead-lags that approximated a 10 dB/decade, 45-degree phase shift network. At that
    point it didn't matter what the load capacitance was, the loop was
    always stable. It's probably possible to make a digital version of that.

    Cheers

    Phil Hobbs

    (*) Phil Perkins, "My approach to feedback loop design", Ch 22 of Jim
    Williams, _Analog Circuit Design: Art, Science, and Personalities_

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC / Hobbs ElectroOptics
    Optics, Electro-optics, Photonics, Analog Electronics
    Briarcliff Manor NY 10510

    http://electrooptical.net
    http://hobbs-eo.com

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From jlarkin@highlandsniptechnology.com@21:1/5 to pcdhSpamMeSenseless@electrooptical. on Sat Jun 25 07:30:27 2022
    On Fri, 24 Jun 2022 12:45:41 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    jlarkin@highlandsniptechnology.com wrote:
    I never thought a lot about general-purpose bench type power supplies,
    but now we have to design some.

    A power supply has two knobs (or SCPI commands in our case), voltage
    and current limit.

    A power supply should have low impedance at high frequencies, so after
    whatever current limit circuit is has, there must be a real capacitor.
    When you short a bench supply, you get a spark from the energy in the
    output cap. So for a while, it's not really current limited.

    Our supply will be a buck switcher

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    so we need an LC lowpass filter. It has to kill the 250 KHz ripple but
    allow reasonable programmable voltage slew rates. We'll close a
    feedback loop from the voltage sensor ADC into the bridge PWM drive,
    so the filter has to be well behaved. Maybe we need the R3C3 damper to
    kill the Q of L1C1 so the loop doesn't go bonkers.

    As if that isn't bad enough, the customer load could be most anything,
    a short or a resistor or a box with big input caps. Or a big DC bus.
    Or even a battery. So our filter gets messed with by the customer.

    And a buck switcher is a boost switcher backwards. If the customer
    gadget sources more voltage than our setpoint, we extract power from
    the customer and charge C9 and blow everything up. We can sense the
    +60 and shut off both fets, I guess.

    We also need a well-behaved current-limit loop.

    When I get time, I might prowl the web for old power supply
    schematics, HP or Kepco or whatever, and see what their output caps
    are like and how they managed the voltage/current dynamics. Those
    would be mostly linear supplies, I guess.

    Wild guesses: switch at 250 KHz. Output 0 to 48v at 0 to 6 amps. L1 is
    180 uH. C2 could be 10 to 300 uF. Loop bandwidth 1 KHz.

    We will probably add a secondary lowpass filter with a notch at 250K,
    to un-compromise the main L1C2 filter, but that won't affect than main
    loop dynamics.

    There's a chapter(*) in one of Jim Willams' books about a guy who built
    big SMUish things using a '1/2 pole' rolloff--a bunch of lead-lags that >approximated a 10 dB/decade, 45-degree phase shift network. At that
    point it didn't matter what the load capacitance was, the loop was
    always stable. It's probably possible to make a digital version of that.

    Cheers

    Phil Hobbs

    (*) Phil Perkins, "My approach to feedback loop design", Ch 22 of Jim >Williams, _Analog Circuit Design: Art, Science, and Personalities_

    Here's a possible filter.

    The ESR could be native to some electrolytic caps, but probably added.
    They will get warm from the 250 KHz ripple current from our
    half-bridge switcher, which encourages a big inductor.

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    Of course we don't know how much load capacitance we'd ever see; could
    be a farad. I was thinking that we're measuring the current, so we can
    use that info to help compensate big caps. Maybe differentiate it and
    squirt into the loop or something. After/if I wake up I might close
    the loop and play with that.

    I have the Williams books; I'll look that up.


    Version 4
    SHEET 1 1348 680
    WIRE -112 96 -160 96
    WIRE -48 96 -112 96
    WIRE 144 96 32 96
    WIRE 288 96 224 96
    WIRE 432 96 288 96
    WIRE 528 96 432 96
    WIRE 672 96 608 96
    WIRE 720 96 672 96
    WIRE 880 96 800 96
    WIRE 1040 96 880 96
    WIRE 1088 96 1040 96
    WIRE 1248 96 1088 96
    WIRE 1344 96 1248 96
    WIRE 288 144 288 96
    WIRE -160 176 -160 96
    WIRE 672 192 672 96
    WIRE 736 192 672 192
    WIRE 880 192 880 96
    WIRE 880 192 800 192
    WIRE 432 208 432 96
    WIRE 1088 208 1088 96
    WIRE 1248 224 1248 96
    WIRE 288 256 288 208
    WIRE 880 256 880 192
    WIRE -160 384 -160 256
    WIRE 288 384 288 336
    WIRE 432 384 432 272
    WIRE 880 384 880 320
    WIRE 1088 384 1088 288
    WIRE 1248 384 1248 288
    FLAG 288 384 0
    FLAG -160 384 0
    FLAG 1088 384 0
    FLAG 1248 384 0
    FLAG 432 384 0
    FLAG 1040 96 OUT
    FLAG -112 96 GEN
    FLAG 880 384 0
    SYMBOL ind 128 112 R270
    WINDOW 0 -33 52 VTop 2
    WINDOW 3 -38 53 VBottom 2
    SYMATTR InstName L1
    SYMATTR Value 50µ
    SYMBOL cap 272 144 R0
    WINDOW 0 51 21 Left 2
    WINDOW 3 48 50 Left 2
    SYMATTR InstName C1
    SYMATTR Value 1m
    SYMBOL res 272 240 R0
    WINDOW 0 51 44 Left 2
    WINDOW 3 46 75 Left 2
    SYMATTR InstName Resr
    SYMATTR Value 250m
    SYMBOL res -64 112 R270
    WINDOW 0 -33 55 VTop 2
    WINDOW 3 -41 54 VBottom 2
    SYMATTR InstName Rgen
    SYMATTR Value 100m
    SYMBOL voltage -160 160 R0
    WINDOW 0 32 11 Left 2
    WINDOW 3 38 73 Left 2
    WINDOW 123 41 42 Left 2
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V1
    SYMATTR Value SINE(0 1 1K)
    SYMATTR Value2 AC 1
    SYMBOL res 1072 192 R0
    WINDOW 0 -78 35 Left 2
    WINDOW 3 -68 66 Left 2
    SYMATTR InstName Rload
    SYMATTR Value 100
    SYMBOL cap 1232 224 R0
    WINDOW 0 -81 2 Left 2
    WINDOW 3 -68 37 Left 2
    SYMATTR InstName Cload
    SYMATTR Value 1m
    SYMBOL cap 416 208 R0
    WINDOW 0 56 21 Left 2
    WINDOW 3 51 49 Left 2
    SYMATTR InstName C3
    SYMATTR Value 10µ
    SYMBOL res 512 112 R270
    WINDOW 0 -39 65 VTop 2
    WINDOW 3 -47 59 VBottom 2
    SYMATTR InstName Rshunt
    SYMATTR Value 25m
    SYMBOL ind 704 112 R270
    WINDOW 0 -30 34 VTop 2
    WINDOW 3 -2 95 VBottom 2
    SYMATTR InstName L2
    SYMATTR Value 10µ
    SYMBOL cap 800 176 R90
    WINDOW 0 67 63 VBottom 2
    WINDOW 3 40 -4 VTop 2
    SYMATTR InstName C2
    SYMATTR Value 40n
    SYMBOL cap 864 256 R0
    WINDOW 0 48 20 Left 2
    WINDOW 3 49 49 Left 2
    SYMATTR InstName C4
    SYMATTR Value 5µ
    TEXT -16 288 Left 2 !.ac dec 20 100 300k
    TEXT -24 328 Left 2 ;Power Supply Filter
    TEXT -16 360 Left 2 ;JL Jun 24 2022
    TEXT 728 272 Left 2 ;250 KHz
    TEXT 752 304 Left 2 ;trap

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to jlarkin@highlandsniptechnology.com on Mon Jun 27 08:00:18 2022
    jlarkin@highlandsniptechnology.com wrote:
    On Fri, 24 Jun 2022 12:45:41 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    jlarkin@highlandsniptechnology.com wrote:
    I never thought a lot about general-purpose bench type power supplies,
    but now we have to design some.

    A power supply has two knobs (or SCPI commands in our case), voltage
    and current limit.

    A power supply should have low impedance at high frequencies, so after
    whatever current limit circuit is has, there must be a real capacitor.
    When you short a bench supply, you get a spark from the energy in the
    output cap. So for a while, it's not really current limited.

    Our supply will be a buck switcher

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    so we need an LC lowpass filter. It has to kill the 250 KHz ripple but
    allow reasonable programmable voltage slew rates. We'll close a
    feedback loop from the voltage sensor ADC into the bridge PWM drive,
    so the filter has to be well behaved. Maybe we need the R3C3 damper to
    kill the Q of L1C1 so the loop doesn't go bonkers.

    As if that isn't bad enough, the customer load could be most anything,
    a short or a resistor or a box with big input caps. Or a big DC bus.
    Or even a battery. So our filter gets messed with by the customer.

    And a buck switcher is a boost switcher backwards. If the customer
    gadget sources more voltage than our setpoint, we extract power from
    the customer and charge C9 and blow everything up. We can sense the
    +60 and shut off both fets, I guess.

    We also need a well-behaved current-limit loop.

    When I get time, I might prowl the web for old power supply
    schematics, HP or Kepco or whatever, and see what their output caps
    are like and how they managed the voltage/current dynamics. Those
    would be mostly linear supplies, I guess.

    Wild guesses: switch at 250 KHz. Output 0 to 48v at 0 to 6 amps. L1 is
    180 uH. C2 could be 10 to 300 uF. Loop bandwidth 1 KHz.

    We will probably add a secondary lowpass filter with a notch at 250K,
    to un-compromise the main L1C2 filter, but that won't affect than main
    loop dynamics.

    There's a chapter(*) in one of Jim Willams' books about a guy who built
    big SMUish things using a '1/2 pole' rolloff--a bunch of lead-lags that
    approximated a 10 dB/decade, 45-degree phase shift network. At that
    point it didn't matter what the load capacitance was, the loop was
    always stable. It's probably possible to make a digital version of that.

    Cheers

    Phil Hobbs

    (*) Phil Perkins, "My approach to feedback loop design", Ch 22 of Jim
    Williams, _Analog Circuit Design: Art, Science, and Personalities_

    Here's a possible filter.

    The ESR could be native to some electrolytic caps, but probably added.
    They will get warm from the 250 KHz ripple current from our
    half-bridge switcher, which encourages a big inductor.

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    Of course we don't know how much load capacitance we'd ever see; could
    be a farad. I was thinking that we're measuring the current, so we can
    use that info to help compensate big caps. Maybe differentiate it and
    squirt into the loop or something. After/if I wake up I might close
    the loop and play with that.

    I have the Williams books; I'll look that up.


    <snip circuit>

    Interesting. I use notch filters in feedback loops for resonant
    actuators. They're the bomb for that, because the resonance is usually
    simple and isolated, so notching it out lets you use a much wider
    feedback BW.

    I've played with them for switchers, but have never used one because
    they don't work that well with harmonic-rich waveforms (especially
    highly asymmetric ones). I'm usually happier keeping the extra two
    poles at high frequency.

    Cheers

    Phil Hobbs



    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC / Hobbs ElectroOptics
    Optics, Electro-optics, Photonics, Analog Electronics
    Briarcliff Manor NY 10510

    http://electrooptical.net
    http://hobbs-eo.com

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Fred Bloggs@21:1/5 to jla...@highlandsniptechnology.com on Mon Jun 27 06:40:43 2022
    On Friday, June 24, 2022 at 9:35:47 AM UTC-4, jla...@highlandsniptechnology.com wrote:
    I never thought a lot about general-purpose bench type power supplies,
    but now we have to design some.

    A power supply has two knobs (or SCPI commands in our case), voltage
    and current limit.

    A power supply should have low impedance at high frequencies, so after whatever current limit circuit is has, there must be a real capacitor.
    When you short a bench supply, you get a spark from the energy in the
    output cap. So for a while, it's not really current limited.

    Our supply will be a buck switcher

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    so we need an LC lowpass filter. It has to kill the 250 KHz ripple but
    allow reasonable programmable voltage slew rates. We'll close a
    feedback loop from the voltage sensor ADC into the bridge PWM drive,
    so the filter has to be well behaved. Maybe we need the R3C3 damper to
    kill the Q of L1C1 so the loop doesn't go bonkers.

    As if that isn't bad enough, the customer load could be most anything,
    a short or a resistor or a box with big input caps. Or a big DC bus.
    Or even a battery. So our filter gets messed with by the customer.

    And a buck switcher is a boost switcher backwards. If the customer
    gadget sources more voltage than our setpoint, we extract power from
    the customer and charge C9 and blow everything up. We can sense the
    +60 and shut off both fets, I guess.

    We also need a well-behaved current-limit loop.

    When I get time, I might prowl the web for old power supply
    schematics, HP or Kepco or whatever, and see what their output caps
    are like and how they managed the voltage/current dynamics. Those
    would be mostly linear supplies, I guess.

    Wild guesses: switch at 250 KHz. Output 0 to 48v at 0 to 6 amps. L1 is
    180 uH. C2 could be 10 to 300 uF. Loop bandwidth 1 KHz.

    We will probably add a secondary lowpass filter with a notch at 250K,
    to un-compromise the main L1C2 filter, but that won't affect than main
    loop dynamics.

    I didn't go thru the analytics, but the output Z for the buck is proportional to sqrt(L/C) or something. Low impedance at high frequency requires only small C. It's up to the user to do their own decoupling anyway. It's a lost cause to try to do that
    with a general purpose power supply. I analyzed more than few HP bench tops ( 30 years ago) and don't recall them do anything arcane, manufacturing success correlates strongly with simplicity.




    --

    Anybody can count to one.

    - Robert Widlar

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Fred Bloggs@21:1/5 to Phil Hobbs on Mon Jun 27 06:45:34 2022
    On Friday, June 24, 2022 at 12:45:51 PM UTC-4, Phil Hobbs wrote:
    jla...@highlandsniptechnology.com wrote:
    I never thought a lot about general-purpose bench type power supplies,
    but now we have to design some.

    A power supply has two knobs (or SCPI commands in our case), voltage
    and current limit.

    A power supply should have low impedance at high frequencies, so after whatever current limit circuit is has, there must be a real capacitor.
    When you short a bench supply, you get a spark from the energy in the output cap. So for a while, it's not really current limited.

    Our supply will be a buck switcher

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    so we need an LC lowpass filter. It has to kill the 250 KHz ripple but allow reasonable programmable voltage slew rates. We'll close a
    feedback loop from the voltage sensor ADC into the bridge PWM drive,
    so the filter has to be well behaved. Maybe we need the R3C3 damper to
    kill the Q of L1C1 so the loop doesn't go bonkers.

    As if that isn't bad enough, the customer load could be most anything,
    a short or a resistor or a box with big input caps. Or a big DC bus.
    Or even a battery. So our filter gets messed with by the customer.

    And a buck switcher is a boost switcher backwards. If the customer
    gadget sources more voltage than our setpoint, we extract power from
    the customer and charge C9 and blow everything up. We can sense the
    +60 and shut off both fets, I guess.

    We also need a well-behaved current-limit loop.

    When I get time, I might prowl the web for old power supply
    schematics, HP or Kepco or whatever, and see what their output caps
    are like and how they managed the voltage/current dynamics. Those
    would be mostly linear supplies, I guess.

    Wild guesses: switch at 250 KHz. Output 0 to 48v at 0 to 6 amps. L1 is
    180 uH. C2 could be 10 to 300 uF. Loop bandwidth 1 KHz.

    We will probably add a secondary lowpass filter with a notch at 250K,
    to un-compromise the main L1C2 filter, but that won't affect than main
    loop dynamics.
    There's a chapter(*) in one of Jim Willams' books about a guy who built
    big SMUish things using a '1/2 pole' rolloff--a bunch of lead-lags that approximated a 10 dB/decade, 45-degree phase shift network. At that
    point it didn't matter what the load capacitance was, the loop was
    always stable. It's probably possible to make a digital version of that.

    National invented a more than few unconditionally stable circuit topologies for their voltage regulator and power op amp product families. They go back to Widlar's day.


    Cheers

    Phil Hobbs

    (*) Phil Perkins, "My approach to feedback loop design", Ch 22 of Jim Williams, _Analog Circuit Design: Art, Science, and Personalities_

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC / Hobbs ElectroOptics
    Optics, Electro-optics, Photonics, Analog Electronics
    Briarcliff Manor NY 10510

    http://electrooptical.net
    http://hobbs-eo.com

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to Fred Bloggs on Mon Jun 27 10:59:40 2022
    Fred Bloggs wrote:
    On Friday, June 24, 2022 at 12:45:51 PM UTC-4, Phil Hobbs wrote:
    jla...@highlandsniptechnology.com wrote:
    I never thought a lot about general-purpose bench type power
    supplies, but now we have to design some.

    A power supply has two knobs (or SCPI commands in our case),
    voltage and current limit.

    A power supply should have low impedance at high frequencies, so
    after whatever current limit circuit is has, there must be a real
    capacitor. When you short a bench supply, you get a spark from
    the energy in the output cap. So for a while, it's not really
    current limited.

    Our supply will be a buck switcher

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    so we need an LC lowpass filter. It has to kill the 250 KHz
    ripple but allow reasonable programmable voltage slew rates.
    We'll close a feedback loop from the voltage sensor ADC into the
    bridge PWM drive, so the filter has to be well behaved. Maybe we
    need the R3C3 damper to kill the Q of L1C1 so the loop doesn't go
    bonkers.

    As if that isn't bad enough, the customer load could be most
    anything, a short or a resistor or a box with big input caps. Or
    a big DC bus. Or even a battery. So our filter gets messed with
    by the customer.

    And a buck switcher is a boost switcher backwards. If the
    customer gadget sources more voltage than our setpoint, we
    extract power from the customer and charge C9 and blow everything
    up. We can sense the +60 and shut off both fets, I guess.

    We also need a well-behaved current-limit loop.

    When I get time, I might prowl the web for old power supply
    schematics, HP or Kepco or whatever, and see what their output
    caps are like and how they managed the voltage/current dynamics.
    Those would be mostly linear supplies, I guess.

    Wild guesses: switch at 250 KHz. Output 0 to 48v at 0 to 6 amps.
    L1 is 180 uH. C2 could be 10 to 300 uF. Loop bandwidth 1 KHz.

    We will probably add a secondary lowpass filter with a notch at
    250K, to un-compromise the main L1C2 filter, but that won't
    affect than main loop dynamics.
    There's a chapter(*) in one of Jim Willams' books about a guy who
    built big SMUish things using a '1/2 pole' rolloff--a bunch of
    lead-lags that approximated a 10 dB/decade, 45-degree phase shift
    network. At that point it didn't matter what the load capacitance
    was, the loop was always stable. It's probably possible to make a
    digital version of that.

    National invented a more than few unconditionally stable circuit
    topologies for their voltage regulator and power op amp product
    families. They go back to Widlar's day.

    Sure, as far back as (iirc) the 80s I used to use a fair number of
    LM6361As that were like that. It rather involves putting the
    compensation cap in the output stage, so that the capacitive loading
    appears in parallel with it.

    Since JL is rolling his own, it might be possible to do that. It's
    tougher to do with an internally-compensated regulator that somebody
    else designed.

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC / Hobbs ElectroOptics
    Optics, Electro-optics, Photonics, Analog Electronics
    Briarcliff Manor NY 10510

    http://electrooptical.net
    http://hobbs-eo.com

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From jlarkin@highlandsniptechnology.com@21:1/5 to pcdhSpamMeSenseless@electrooptical. on Mon Jun 27 07:57:09 2022
    On Mon, 27 Jun 2022 08:00:18 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    jlarkin@highlandsniptechnology.com wrote:
    On Fri, 24 Jun 2022 12:45:41 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    jlarkin@highlandsniptechnology.com wrote:
    I never thought a lot about general-purpose bench type power supplies, >>>> but now we have to design some.

    A power supply has two knobs (or SCPI commands in our case), voltage
    and current limit.

    A power supply should have low impedance at high frequencies, so after >>>> whatever current limit circuit is has, there must be a real capacitor. >>>> When you short a bench supply, you get a spark from the energy in the
    output cap. So for a while, it's not really current limited.

    Our supply will be a buck switcher

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    so we need an LC lowpass filter. It has to kill the 250 KHz ripple but >>>> allow reasonable programmable voltage slew rates. We'll close a
    feedback loop from the voltage sensor ADC into the bridge PWM drive,
    so the filter has to be well behaved. Maybe we need the R3C3 damper to >>>> kill the Q of L1C1 so the loop doesn't go bonkers.

    As if that isn't bad enough, the customer load could be most anything, >>>> a short or a resistor or a box with big input caps. Or a big DC bus.
    Or even a battery. So our filter gets messed with by the customer.

    And a buck switcher is a boost switcher backwards. If the customer
    gadget sources more voltage than our setpoint, we extract power from
    the customer and charge C9 and blow everything up. We can sense the
    +60 and shut off both fets, I guess.

    We also need a well-behaved current-limit loop.

    When I get time, I might prowl the web for old power supply
    schematics, HP or Kepco or whatever, and see what their output caps
    are like and how they managed the voltage/current dynamics. Those
    would be mostly linear supplies, I guess.

    Wild guesses: switch at 250 KHz. Output 0 to 48v at 0 to 6 amps. L1 is >>>> 180 uH. C2 could be 10 to 300 uF. Loop bandwidth 1 KHz.

    We will probably add a secondary lowpass filter with a notch at 250K,
    to un-compromise the main L1C2 filter, but that won't affect than main >>>> loop dynamics.

    There's a chapter(*) in one of Jim Willams' books about a guy who built
    big SMUish things using a '1/2 pole' rolloff--a bunch of lead-lags that
    approximated a 10 dB/decade, 45-degree phase shift network. At that
    point it didn't matter what the load capacitance was, the loop was
    always stable. It's probably possible to make a digital version of that. >>>
    Cheers

    Phil Hobbs

    (*) Phil Perkins, "My approach to feedback loop design", Ch 22 of Jim
    Williams, _Analog Circuit Design: Art, Science, and Personalities_

    Here's a possible filter.

    The ESR could be native to some electrolytic caps, but probably added.
    They will get warm from the 250 KHz ripple current from our
    half-bridge switcher, which encourages a big inductor.

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    Of course we don't know how much load capacitance we'd ever see; could
    be a farad. I was thinking that we're measuring the current, so we can
    use that info to help compensate big caps. Maybe differentiate it and
    squirt into the loop or something. After/if I wake up I might close
    the loop and play with that.

    I have the Williams books; I'll look that up.


    <snip circuit>

    Interesting. I use notch filters in feedback loops for resonant
    actuators. They're the bomb for that, because the resonance is usually >simple and isolated, so notching it out lets you use a much wider
    feedback BW.

    I've played with them for switchers, but have never used one because
    they don't work that well with harmonic-rich waveforms (especially
    highly asymmetric ones). I'm usually happier keeping the extra two
    poles at high frequency.

    Cheers

    Phil Hobbs

    This is my current thinking. I can get my AC feedback from a local
    node that I can control the dynamics of, and get DC fb from the nasty
    remote sense. The notch filter really helps kill 250 KHz and above,
    and its impedance actually helps the control loop a little.

    https://www.dropbox.com/s/wf8rq1ziypt1vjn/ACDC_sense.jpg?dl=0

    https://www.dropbox.com/s/g4qba0cjly7blbq/PS_Filt_3.jpg?dl=0

    https://www.dropbox.com/s/m6pg94dxrmencq3/PS_Filt_3.asc?dl=0

    And I thought power supplies were simple.

    I guess my HF filter could be un-notched too, with a bigger L maybe.
    I'll try that.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Don@21:1/5 to Fred Bloggs on Mon Jun 27 15:35:54 2022
    Fred Bloggs wrote:
    jlarkin wrote:
    I never thought a lot about general-purpose bench type power supplies,
    but now we have to design some.

    A power supply has two knobs (or SCPI commands in our case), voltage
    and current limit.

    A power supply should have low impedance at high frequencies, so after
    whatever current limit circuit is has, there must be a real capacitor.
    When you short a bench supply, you get a spark from the energy in the
    output cap. So for a while, it's not really current limited.

    Our supply will be a buck switcher

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    so we need an LC lowpass filter. It has to kill the 250 KHz ripple but
    allow reasonable programmable voltage slew rates. We'll close a
    feedback loop from the voltage sensor ADC into the bridge PWM drive,
    so the filter has to be well behaved. Maybe we need the R3C3 damper to
    kill the Q of L1C1 so the loop doesn't go bonkers.

    As if that isn't bad enough, the customer load could be most anything,
    a short or a resistor or a box with big input caps. Or a big DC bus.
    Or even a battery. So our filter gets messed with by the customer.

    And a buck switcher is a boost switcher backwards. If the customer
    gadget sources more voltage than our setpoint, we extract power from
    the customer and charge C9 and blow everything up. We can sense the
    +60 and shut off both fets, I guess.

    We also need a well-behaved current-limit loop.

    When I get time, I might prowl the web for old power supply
    schematics, HP or Kepco or whatever, and see what their output caps
    are like and how they managed the voltage/current dynamics. Those
    would be mostly linear supplies, I guess.

    Wild guesses: switch at 250 KHz. Output 0 to 48v at 0 to 6 amps. L1 is
    180 uH. C2 could be 10 to 300 uF. Loop bandwidth 1 KHz.

    We will probably add a secondary lowpass filter with a notch at 250K,
    to un-compromise the main L1C2 filter, but that won't affect than main
    loop dynamics.

    I didn't go thru the analytics, but the output Z for the buck is proportional to sqrt(L/C) or something. Low impedance at high frequency requires only small C. It's up to the user to do their own decoupling anyway. It's a lost cause to try to do that with a general purpose power supply. I analyzed more than few HP bench tops ( 30 years ago) and don't recall them do anything arcane, manufacturing success correlates strongly with simplicity.

    Fred, you confirm my intuition about how responsibility for proper
    power supply operation ultimately rests with its user. On the other
    hand, the use of a ground return for current sense remains nonintuitive.

    The use of ground symbols in schematic diagrams (actually
    just a convenience for avoiding more lines in the drawing)
    lulls us into thinking that they're all at the same
    potential. That’s the essence of the fantasy ... but far
    from the truth. Until room-temperature super-conductors
    become a common reality, "grounds" are connected by
    wires, PCB traces, or sheets of metal - all of which have
    both resistance and inductance. So much for the fantasy!

    - Bill Whitlock

    Danke,

    --
    Don, KB7RPU, https://www.qsl.net/kb7rpu
    There was a young lady named Bright Whose speed was far faster than light;
    She set out one day In a relative way And returned on the previous night.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From jlarkin@highlandsniptechnology.com@21:1/5 to bloggs.fredbloggs.fred@gmail.com on Mon Jun 27 08:47:33 2022
    On Mon, 27 Jun 2022 06:40:43 -0700 (PDT), Fred Bloggs <bloggs.fredbloggs.fred@gmail.com> wrote:

    On Friday, June 24, 2022 at 9:35:47 AM UTC-4, jla...@highlandsniptechnology.com wrote:
    I never thought a lot about general-purpose bench type power supplies,
    but now we have to design some.

    A power supply has two knobs (or SCPI commands in our case), voltage
    and current limit.

    A power supply should have low impedance at high frequencies, so after
    whatever current limit circuit is has, there must be a real capacitor.
    When you short a bench supply, you get a spark from the energy in the
    output cap. So for a while, it's not really current limited.

    Our supply will be a buck switcher

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    so we need an LC lowpass filter. It has to kill the 250 KHz ripple but
    allow reasonable programmable voltage slew rates. We'll close a
    feedback loop from the voltage sensor ADC into the bridge PWM drive,
    so the filter has to be well behaved. Maybe we need the R3C3 damper to
    kill the Q of L1C1 so the loop doesn't go bonkers.

    As if that isn't bad enough, the customer load could be most anything,
    a short or a resistor or a box with big input caps. Or a big DC bus.
    Or even a battery. So our filter gets messed with by the customer.

    And a buck switcher is a boost switcher backwards. If the customer
    gadget sources more voltage than our setpoint, we extract power from
    the customer and charge C9 and blow everything up. We can sense the
    +60 and shut off both fets, I guess.

    We also need a well-behaved current-limit loop.

    When I get time, I might prowl the web for old power supply
    schematics, HP or Kepco or whatever, and see what their output caps
    are like and how they managed the voltage/current dynamics. Those
    would be mostly linear supplies, I guess.

    Wild guesses: switch at 250 KHz. Output 0 to 48v at 0 to 6 amps. L1 is
    180 uH. C2 could be 10 to 300 uF. Loop bandwidth 1 KHz.

    We will probably add a secondary lowpass filter with a notch at 250K,
    to un-compromise the main L1C2 filter, but that won't affect than main
    loop dynamics.

    I didn't go thru the analytics, but the output Z for the buck is proportional to sqrt(L/C) or something. Low impedance at high frequency requires only small C. It's up to the user to do their own decoupling anyway. It's a lost cause to try to do that
    with a general purpose power supply. I analyzed more than few HP bench tops ( 30 years ago) and don't recall them do anything arcane, manufacturing success correlates strongly with simplicity.


    HP did often include a big final electrolytic cap that could be
    jumpered in or out.

    We want fast programmable voltage slew rates, clean fast current
    limiting, and stable remote sense no matter how far away or how stupid
    the wiring and the load may be. We could expect the load to be some
    decent fraction of a mile away.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From jlarkin@highlandsniptechnology.com@21:1/5 to Don on Mon Jun 27 08:50:54 2022
    On Mon, 27 Jun 2022 15:35:54 -0000 (UTC), "Don" <g@crcomp.net> wrote:

    Fred Bloggs wrote:
    jlarkin wrote:
    I never thought a lot about general-purpose bench type power supplies,
    but now we have to design some.

    A power supply has two knobs (or SCPI commands in our case), voltage
    and current limit.

    A power supply should have low impedance at high frequencies, so after
    whatever current limit circuit is has, there must be a real capacitor.
    When you short a bench supply, you get a spark from the energy in the
    output cap. So for a while, it's not really current limited.

    Our supply will be a buck switcher

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    so we need an LC lowpass filter. It has to kill the 250 KHz ripple but
    allow reasonable programmable voltage slew rates. We'll close a
    feedback loop from the voltage sensor ADC into the bridge PWM drive,
    so the filter has to be well behaved. Maybe we need the R3C3 damper to
    kill the Q of L1C1 so the loop doesn't go bonkers.

    As if that isn't bad enough, the customer load could be most anything,
    a short or a resistor or a box with big input caps. Or a big DC bus.
    Or even a battery. So our filter gets messed with by the customer.

    And a buck switcher is a boost switcher backwards. If the customer
    gadget sources more voltage than our setpoint, we extract power from
    the customer and charge C9 and blow everything up. We can sense the
    +60 and shut off both fets, I guess.

    We also need a well-behaved current-limit loop.

    When I get time, I might prowl the web for old power supply
    schematics, HP or Kepco or whatever, and see what their output caps
    are like and how they managed the voltage/current dynamics. Those
    would be mostly linear supplies, I guess.

    Wild guesses: switch at 250 KHz. Output 0 to 48v at 0 to 6 amps. L1 is
    180 uH. C2 could be 10 to 300 uF. Loop bandwidth 1 KHz.

    We will probably add a secondary lowpass filter with a notch at 250K,
    to un-compromise the main L1C2 filter, but that won't affect than main
    loop dynamics.

    I didn't go thru the analytics, but the output Z for the buck is proportional
    to sqrt(L/C) or something. Low impedance at high frequency requires only
    small C. It's up to the user to do their own decoupling anyway. It's a lost >> cause to try to do that with a general purpose power supply. I analyzed more >> than few HP bench tops ( 30 years ago) and don't recall them do anything
    arcane, manufacturing success correlates strongly with simplicity.

    Fred, you confirm my intuition about how responsibility for proper
    power supply operation ultimately rests with its user.

    We have to answer the phone when something doesn't work as expected.
    So we prefer to design a power supply that is maximally tolerant of
    customer wiring and loads.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to jlarkin@highlandsniptechnology.com on Mon Jun 27 15:37:08 2022
    jlarkin@highlandsniptechnology.com wrote:
    On Mon, 27 Jun 2022 08:00:18 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    jlarkin@highlandsniptechnology.com wrote:
    On Fri, 24 Jun 2022 12:45:41 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    jlarkin@highlandsniptechnology.com wrote:
    I never thought a lot about general-purpose bench type power supplies, >>>>> but now we have to design some.

    A power supply has two knobs (or SCPI commands in our case), voltage >>>>> and current limit.

    A power supply should have low impedance at high frequencies, so after >>>>> whatever current limit circuit is has, there must be a real capacitor. >>>>> When you short a bench supply, you get a spark from the energy in the >>>>> output cap. So for a while, it's not really current limited.

    Our supply will be a buck switcher

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    so we need an LC lowpass filter. It has to kill the 250 KHz ripple but >>>>> allow reasonable programmable voltage slew rates. We'll close a
    feedback loop from the voltage sensor ADC into the bridge PWM drive, >>>>> so the filter has to be well behaved. Maybe we need the R3C3 damper to >>>>> kill the Q of L1C1 so the loop doesn't go bonkers.

    As if that isn't bad enough, the customer load could be most anything, >>>>> a short or a resistor or a box with big input caps. Or a big DC bus. >>>>> Or even a battery. So our filter gets messed with by the customer.

    And a buck switcher is a boost switcher backwards. If the customer
    gadget sources more voltage than our setpoint, we extract power from >>>>> the customer and charge C9 and blow everything up. We can sense the
    +60 and shut off both fets, I guess.

    We also need a well-behaved current-limit loop.

    When I get time, I might prowl the web for old power supply
    schematics, HP or Kepco or whatever, and see what their output caps
    are like and how they managed the voltage/current dynamics. Those
    would be mostly linear supplies, I guess.

    Wild guesses: switch at 250 KHz. Output 0 to 48v at 0 to 6 amps. L1 is >>>>> 180 uH. C2 could be 10 to 300 uF. Loop bandwidth 1 KHz.

    We will probably add a secondary lowpass filter with a notch at 250K, >>>>> to un-compromise the main L1C2 filter, but that won't affect than main >>>>> loop dynamics.

    There's a chapter(*) in one of Jim Willams' books about a guy who built >>>> big SMUish things using a '1/2 pole' rolloff--a bunch of lead-lags that >>>> approximated a 10 dB/decade, 45-degree phase shift network. At that
    point it didn't matter what the load capacitance was, the loop was
    always stable. It's probably possible to make a digital version of that. >>>>
    Cheers

    Phil Hobbs

    (*) Phil Perkins, "My approach to feedback loop design", Ch 22 of Jim
    Williams, _Analog Circuit Design: Art, Science, and Personalities_

    Here's a possible filter.

    The ESR could be native to some electrolytic caps, but probably added.
    They will get warm from the 250 KHz ripple current from our
    half-bridge switcher, which encourages a big inductor.

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    Of course we don't know how much load capacitance we'd ever see; could
    be a farad. I was thinking that we're measuring the current, so we can
    use that info to help compensate big caps. Maybe differentiate it and
    squirt into the loop or something. After/if I wake up I might close
    the loop and play with that.

    I have the Williams books; I'll look that up.


    <snip circuit>

    Interesting. I use notch filters in feedback loops for resonant
    actuators. They're the bomb for that, because the resonance is usually
    simple and isolated, so notching it out lets you use a much wider
    feedback BW.

    I've played with them for switchers, but have never used one because
    they don't work that well with harmonic-rich waveforms (especially
    highly asymmetric ones). I'm usually happier keeping the extra two
    poles at high frequency.

    Cheers

    Phil Hobbs

    This is my current thinking. I can get my AC feedback from a local
    node that I can control the dynamics of, and get DC fb from the nasty
    remote sense. The notch filter really helps kill 250 KHz and above,
    and its impedance actually helps the control loop a little.

    https://www.dropbox.com/s/wf8rq1ziypt1vjn/ACDC_sense.jpg?dl=0

    https://www.dropbox.com/s/g4qba0cjly7blbq/PS_Filt_3.jpg?dl=0

    https://www.dropbox.com/s/m6pg94dxrmencq3/PS_Filt_3.asc?dl=0

    And I thought power supplies were simple.

    I guess my HF filter could be un-notched too, with a bigger L maybe.
    I'll try that.

    I sometimes do the split AC/DC feedback thing wrapped round a cap
    multiplier. It does need a buffer to break the sneak path from the
    output reservoir cap to the output via the RC diplexer.

    The ESR on the 1000 uF cap is probably on the high side. I'm using some
    nice 220 uF alpos with 25 mohm ESR.

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC / Hobbs ElectroOptics
    Optics, Electro-optics, Photonics, Analog Electronics
    Briarcliff Manor NY 10510

    http://electrooptical.net
    http://hobbs-eo.com

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From John Larkin@21:1/5 to pcdhSpamMeSenseless@electrooptical. on Mon Jun 27 14:33:49 2022
    On Mon, 27 Jun 2022 15:37:08 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    jlarkin@highlandsniptechnology.com wrote:
    On Mon, 27 Jun 2022 08:00:18 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    jlarkin@highlandsniptechnology.com wrote:
    On Fri, 24 Jun 2022 12:45:41 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    jlarkin@highlandsniptechnology.com wrote:
    I never thought a lot about general-purpose bench type power supplies, >>>>>> but now we have to design some.

    A power supply has two knobs (or SCPI commands in our case), voltage >>>>>> and current limit.

    A power supply should have low impedance at high frequencies, so after >>>>>> whatever current limit circuit is has, there must be a real capacitor. >>>>>> When you short a bench supply, you get a spark from the energy in the >>>>>> output cap. So for a while, it's not really current limited.

    Our supply will be a buck switcher

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    so we need an LC lowpass filter. It has to kill the 250 KHz ripple but >>>>>> allow reasonable programmable voltage slew rates. We'll close a
    feedback loop from the voltage sensor ADC into the bridge PWM drive, >>>>>> so the filter has to be well behaved. Maybe we need the R3C3 damper to >>>>>> kill the Q of L1C1 so the loop doesn't go bonkers.

    As if that isn't bad enough, the customer load could be most anything, >>>>>> a short or a resistor or a box with big input caps. Or a big DC bus. >>>>>> Or even a battery. So our filter gets messed with by the customer. >>>>>>
    And a buck switcher is a boost switcher backwards. If the customer >>>>>> gadget sources more voltage than our setpoint, we extract power from >>>>>> the customer and charge C9 and blow everything up. We can sense the >>>>>> +60 and shut off both fets, I guess.

    We also need a well-behaved current-limit loop.

    When I get time, I might prowl the web for old power supply
    schematics, HP or Kepco or whatever, and see what their output caps >>>>>> are like and how they managed the voltage/current dynamics. Those
    would be mostly linear supplies, I guess.

    Wild guesses: switch at 250 KHz. Output 0 to 48v at 0 to 6 amps. L1 is >>>>>> 180 uH. C2 could be 10 to 300 uF. Loop bandwidth 1 KHz.

    We will probably add a secondary lowpass filter with a notch at 250K, >>>>>> to un-compromise the main L1C2 filter, but that won't affect than main >>>>>> loop dynamics.

    There's a chapter(*) in one of Jim Willams' books about a guy who built >>>>> big SMUish things using a '1/2 pole' rolloff--a bunch of lead-lags that >>>>> approximated a 10 dB/decade, 45-degree phase shift network. At that >>>>> point it didn't matter what the load capacitance was, the loop was
    always stable. It's probably possible to make a digital version of that. >>>>>
    Cheers

    Phil Hobbs

    (*) Phil Perkins, "My approach to feedback loop design", Ch 22 of Jim >>>>> Williams, _Analog Circuit Design: Art, Science, and Personalities_

    Here's a possible filter.

    The ESR could be native to some electrolytic caps, but probably added. >>>> They will get warm from the 250 KHz ripple current from our
    half-bridge switcher, which encourages a big inductor.

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    Of course we don't know how much load capacitance we'd ever see; could >>>> be a farad. I was thinking that we're measuring the current, so we can >>>> use that info to help compensate big caps. Maybe differentiate it and
    squirt into the loop or something. After/if I wake up I might close
    the loop and play with that.

    I have the Williams books; I'll look that up.


    <snip circuit>

    Interesting. I use notch filters in feedback loops for resonant
    actuators. They're the bomb for that, because the resonance is usually
    simple and isolated, so notching it out lets you use a much wider
    feedback BW.

    I've played with them for switchers, but have never used one because
    they don't work that well with harmonic-rich waveforms (especially
    highly asymmetric ones). I'm usually happier keeping the extra two
    poles at high frequency.

    Cheers

    Phil Hobbs

    This is my current thinking. I can get my AC feedback from a local
    node that I can control the dynamics of, and get DC fb from the nasty
    remote sense. The notch filter really helps kill 250 KHz and above,
    and its impedance actually helps the control loop a little.

    https://www.dropbox.com/s/wf8rq1ziypt1vjn/ACDC_sense.jpg?dl=0

    https://www.dropbox.com/s/g4qba0cjly7blbq/PS_Filt_3.jpg?dl=0

    https://www.dropbox.com/s/m6pg94dxrmencq3/PS_Filt_3.asc?dl=0

    And I thought power supplies were simple.

    I guess my HF filter could be un-notched too, with a bigger L maybe.
    I'll try that.

    I sometimes do the split AC/DC feedback thing wrapped round a cap
    multiplier. It does need a buffer to break the sneak path from the
    output reservoir cap to the output via the RC diplexer.

    The ESR on the 1000 uF cap is probably on the high side. I'm using some
    nice 220 uF alpos with 25 mohm ESR.

    Cheers

    Phil Hobbs

    I need that ESR to tame the phase shift at node MID, so we can close a reasonable loop. It will probably be an actual resistor.

    --

    If a man will begin with certainties, he shall end with doubts,
    but if he will be content to begin with doubts he shall end in certainties. Francis Bacon

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to John Larkin on Tue Jun 28 12:34:30 2022
    John Larkin wrote:
    On Mon, 27 Jun 2022 15:37:08 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    jlarkin@highlandsniptechnology.com wrote:
    On Mon, 27 Jun 2022 08:00:18 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    jlarkin@highlandsniptechnology.com wrote:
    On Fri, 24 Jun 2022 12:45:41 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    jlarkin@highlandsniptechnology.com wrote:
    I never thought a lot about general-purpose bench type power supplies, >>>>>>> but now we have to design some.

    A power supply has two knobs (or SCPI commands in our case), voltage >>>>>>> and current limit.

    A power supply should have low impedance at high frequencies, so after >>>>>>> whatever current limit circuit is has, there must be a real capacitor. >>>>>>> When you short a bench supply, you get a spark from the energy in the >>>>>>> output cap. So for a while, it's not really current limited.

    Our supply will be a buck switcher

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    so we need an LC lowpass filter. It has to kill the 250 KHz ripple but >>>>>>> allow reasonable programmable voltage slew rates. We'll close a
    feedback loop from the voltage sensor ADC into the bridge PWM drive, >>>>>>> so the filter has to be well behaved. Maybe we need the R3C3 damper to >>>>>>> kill the Q of L1C1 so the loop doesn't go bonkers.

    As if that isn't bad enough, the customer load could be most anything, >>>>>>> a short or a resistor or a box with big input caps. Or a big DC bus. >>>>>>> Or even a battery. So our filter gets messed with by the customer. >>>>>>>
    And a buck switcher is a boost switcher backwards. If the customer >>>>>>> gadget sources more voltage than our setpoint, we extract power from >>>>>>> the customer and charge C9 and blow everything up. We can sense the >>>>>>> +60 and shut off both fets, I guess.

    We also need a well-behaved current-limit loop.

    When I get time, I might prowl the web for old power supply
    schematics, HP or Kepco or whatever, and see what their output caps >>>>>>> are like and how they managed the voltage/current dynamics. Those >>>>>>> would be mostly linear supplies, I guess.

    Wild guesses: switch at 250 KHz. Output 0 to 48v at 0 to 6 amps. L1 is >>>>>>> 180 uH. C2 could be 10 to 300 uF. Loop bandwidth 1 KHz.

    We will probably add a secondary lowpass filter with a notch at 250K, >>>>>>> to un-compromise the main L1C2 filter, but that won't affect than main >>>>>>> loop dynamics.

    There's a chapter(*) in one of Jim Willams' books about a guy who built >>>>>> big SMUish things using a '1/2 pole' rolloff--a bunch of lead-lags that >>>>>> approximated a 10 dB/decade, 45-degree phase shift network. At that >>>>>> point it didn't matter what the load capacitance was, the loop was >>>>>> always stable. It's probably possible to make a digital version of that.

    Cheers

    Phil Hobbs

    (*) Phil Perkins, "My approach to feedback loop design", Ch 22 of Jim >>>>>> Williams, _Analog Circuit Design: Art, Science, and Personalities_

    Here's a possible filter.

    The ESR could be native to some electrolytic caps, but probably added. >>>>> They will get warm from the 250 KHz ripple current from our
    half-bridge switcher, which encourages a big inductor.

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    Of course we don't know how much load capacitance we'd ever see; could >>>>> be a farad. I was thinking that we're measuring the current, so we can >>>>> use that info to help compensate big caps. Maybe differentiate it and >>>>> squirt into the loop or something. After/if I wake up I might close
    the loop and play with that.

    I have the Williams books; I'll look that up.


    <snip circuit>

    Interesting. I use notch filters in feedback loops for resonant
    actuators. They're the bomb for that, because the resonance is usually >>>> simple and isolated, so notching it out lets you use a much wider
    feedback BW.

    I've played with them for switchers, but have never used one because
    they don't work that well with harmonic-rich waveforms (especially
    highly asymmetric ones). I'm usually happier keeping the extra two
    poles at high frequency.

    Cheers

    Phil Hobbs

    This is my current thinking. I can get my AC feedback from a local
    node that I can control the dynamics of, and get DC fb from the nasty
    remote sense. The notch filter really helps kill 250 KHz and above,
    and its impedance actually helps the control loop a little.

    https://www.dropbox.com/s/wf8rq1ziypt1vjn/ACDC_sense.jpg?dl=0

    https://www.dropbox.com/s/g4qba0cjly7blbq/PS_Filt_3.jpg?dl=0

    https://www.dropbox.com/s/m6pg94dxrmencq3/PS_Filt_3.asc?dl=0

    And I thought power supplies were simple.

    I guess my HF filter could be un-notched too, with a bigger L maybe.
    I'll try that.

    I sometimes do the split AC/DC feedback thing wrapped round a cap
    multiplier. It does need a buffer to break the sneak path from the
    output reservoir cap to the output via the RC diplexer.

    The ESR on the 1000 uF cap is probably on the high side. I'm using some
    nice 220 uF alpos with 25 mohm ESR.

    Cheers

    Phil Hobbs

    I need that ESR to tame the phase shift at node MID, so we can close a reasonable loop. It will probably be an actual resistor.


    Better be a honking big pulse rated job, then. A short could
    potentially dump

    0.5 * 57V **2 *0.001F = 1.65 J

    into that poor little resistor in under a millisecond. Toasty!

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC / Hobbs ElectroOptics
    Optics, Electro-optics, Photonics, Analog Electronics
    Briarcliff Manor NY 10510

    http://electrooptical.net
    http://hobbs-eo.com

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    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From jlarkin@highlandsniptechnology.com@21:1/5 to pcdhSpamMeSenseless@electrooptical. on Tue Jun 28 10:13:39 2022
    On Tue, 28 Jun 2022 12:34:30 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    John Larkin wrote:
    On Mon, 27 Jun 2022 15:37:08 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    jlarkin@highlandsniptechnology.com wrote:
    On Mon, 27 Jun 2022 08:00:18 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    jlarkin@highlandsniptechnology.com wrote:
    On Fri, 24 Jun 2022 12:45:41 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    jlarkin@highlandsniptechnology.com wrote:
    I never thought a lot about general-purpose bench type power supplies, >>>>>>>> but now we have to design some.

    A power supply has two knobs (or SCPI commands in our case), voltage >>>>>>>> and current limit.

    A power supply should have low impedance at high frequencies, so after >>>>>>>> whatever current limit circuit is has, there must be a real capacitor. >>>>>>>> When you short a bench supply, you get a spark from the energy in the >>>>>>>> output cap. So for a while, it's not really current limited.

    Our supply will be a buck switcher

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    so we need an LC lowpass filter. It has to kill the 250 KHz ripple but >>>>>>>> allow reasonable programmable voltage slew rates. We'll close a >>>>>>>> feedback loop from the voltage sensor ADC into the bridge PWM drive, >>>>>>>> so the filter has to be well behaved. Maybe we need the R3C3 damper to >>>>>>>> kill the Q of L1C1 so the loop doesn't go bonkers.

    As if that isn't bad enough, the customer load could be most anything, >>>>>>>> a short or a resistor or a box with big input caps. Or a big DC bus. >>>>>>>> Or even a battery. So our filter gets messed with by the customer. >>>>>>>>
    And a buck switcher is a boost switcher backwards. If the customer >>>>>>>> gadget sources more voltage than our setpoint, we extract power from >>>>>>>> the customer and charge C9 and blow everything up. We can sense the >>>>>>>> +60 and shut off both fets, I guess.

    We also need a well-behaved current-limit loop.

    When I get time, I might prowl the web for old power supply
    schematics, HP or Kepco or whatever, and see what their output caps >>>>>>>> are like and how they managed the voltage/current dynamics. Those >>>>>>>> would be mostly linear supplies, I guess.

    Wild guesses: switch at 250 KHz. Output 0 to 48v at 0 to 6 amps. L1 is >>>>>>>> 180 uH. C2 could be 10 to 300 uF. Loop bandwidth 1 KHz.

    We will probably add a secondary lowpass filter with a notch at 250K, >>>>>>>> to un-compromise the main L1C2 filter, but that won't affect than main >>>>>>>> loop dynamics.

    There's a chapter(*) in one of Jim Willams' books about a guy who built >>>>>>> big SMUish things using a '1/2 pole' rolloff--a bunch of lead-lags that >>>>>>> approximated a 10 dB/decade, 45-degree phase shift network. At that >>>>>>> point it didn't matter what the load capacitance was, the loop was >>>>>>> always stable. It's probably possible to make a digital version of that.

    Cheers

    Phil Hobbs

    (*) Phil Perkins, "My approach to feedback loop design", Ch 22 of Jim >>>>>>> Williams, _Analog Circuit Design: Art, Science, and Personalities_ >>>>>>
    Here's a possible filter.

    The ESR could be native to some electrolytic caps, but probably added. >>>>>> They will get warm from the 250 KHz ripple current from our
    half-bridge switcher, which encourages a big inductor.

    https://www.dropbox.com/s/enuvum2gt0nzbf2/Isol_PS_1.jpg?raw=1

    Of course we don't know how much load capacitance we'd ever see; could >>>>>> be a farad. I was thinking that we're measuring the current, so we can >>>>>> use that info to help compensate big caps. Maybe differentiate it and >>>>>> squirt into the loop or something. After/if I wake up I might close >>>>>> the loop and play with that.

    I have the Williams books; I'll look that up.


    <snip circuit>

    Interesting. I use notch filters in feedback loops for resonant
    actuators. They're the bomb for that, because the resonance is usually >>>>> simple and isolated, so notching it out lets you use a much wider
    feedback BW.

    I've played with them for switchers, but have never used one because >>>>> they don't work that well with harmonic-rich waveforms (especially
    highly asymmetric ones). I'm usually happier keeping the extra two
    poles at high frequency.

    Cheers

    Phil Hobbs

    This is my current thinking. I can get my AC feedback from a local
    node that I can control the dynamics of, and get DC fb from the nasty
    remote sense. The notch filter really helps kill 250 KHz and above,
    and its impedance actually helps the control loop a little.

    https://www.dropbox.com/s/wf8rq1ziypt1vjn/ACDC_sense.jpg?dl=0

    https://www.dropbox.com/s/g4qba0cjly7blbq/PS_Filt_3.jpg?dl=0

    https://www.dropbox.com/s/m6pg94dxrmencq3/PS_Filt_3.asc?dl=0

    And I thought power supplies were simple.

    I guess my HF filter could be un-notched too, with a bigger L maybe.
    I'll try that.

    I sometimes do the split AC/DC feedback thing wrapped round a cap
    multiplier. It does need a buffer to break the sneak path from the
    output reservoir cap to the output via the RC diplexer.

    The ESR on the 1000 uF cap is probably on the high side. I'm using some >>> nice 220 uF alpos with 25 mohm ESR.

    Cheers

    Phil Hobbs

    I need that ESR to tame the phase shift at node MID, so we can close a
    reasonable loop. It will probably be an actual resistor.


    Better be a honking big pulse rated job, then. A short could
    potentially dump

    0.5 * 57V **2 *0.001F = 1.65 J

    into that poor little resistor in under a millisecond. Toasty!

    Cheers

    Phil Hobbs

    It kills efficiency too. AoE X-chapters has nice data on exploding
    various resistors.

    The other approach is to use an LCLC filter with an effective
    bandwidth in the KHz region, and let it flail the phase all it wants
    up there, as long as it doesn't wreck our maybe 350 Hz control loop.

    Something roughly like

    https://www.dropbox.com/s/95jmjayj0cykykg/PS_Fast_Filt_1.jpg?raw=1

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