https://www.dropbox.com/scl/fi/191fe4xtipoxkr66g6y81/Cap_CV.jpg?rlkey=2gohwv8ksdc9z19znisalle6r&raw=1

So the 10u cap is better at all voltages, but the ratio is like 5:1 at
0 volts but only 2:1 at 10 volts.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Tuesday, November 7, 2023 at 2:50:11 PM UTC-8, john larkin wrote:

https://www.dropbox.com/scl/fi/191fe4xtipoxkr66g6y81/Cap_CV.jpg?rlkey=2gohwv8ksdc9z19znisalle6r&raw=1

So the 10u cap is better at all voltages, but the ratio is like 5:1 at
0 volts but only 2:1 at 10 volts.

That's a curve of dQ/dV versus V_bias, I presume?
That's the significant value when you're bypassing a DC bias voltage source. The capacitance could also be considered to be the total charge Q(V)/V versus V_peak, which would represent an
AC current through the capacitor to ground better than dQ/dV does.

Capacitance being an intrinsically linear property, the graph alone is ambiguous.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Tue, 7 Nov 2023 17:03:51 -0800 (PST), whit3rd <whit3rd@gmail.com>
wrote:

On Tuesday, November 7, 2023 at 2:50:11?PM UTC-8, john larkin wrote:

https://www.dropbox.com/scl/fi/191fe4xtipoxkr66g6y81/Cap_CV.jpg?rlkey=2gohwv8ksdc9z19znisalle6r&raw=1

So the 10u cap is better at all voltages, but the ratio is like 5:1 at
0 volts but only 2:1 at 10 volts.

That's a curve of dQ/dV versus V_bias, I presume?
That's the significant value when you're bypassing a DC bias voltage source. >The capacitance could also be considered to be the total charge Q(V)/V versus V_peak, which would represent an
AC current through the capacitor to ground better than dQ/dV does.

Capacitance being an intrinsically linear property, the graph alone is >ambiguous.

It's the small-signal capacitance, literally measured as the time
constant with DC bias and a small square wave from a 50 ohm source.

I didn't trust my AADE c-meter with big caps like this. My Boonton
only goes up to about 1 nF.

As a power rail bypass, this is the number that I want.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Wed, 8 Nov 2023 10:23:18 +0000, piglet <erichpwagner@hotmail.com>
wrote:

On 07/11/2023 22:49, john larkin wrote:

https://www.dropbox.com/scl/fi/191fe4xtipoxkr66g6y81/Cap_CV.jpg?rlkey=2gohwv8ksdc9z19znisalle6r&raw=1

So the 10u cap is better at all voltages, but the ratio is like 5:1 at
0 volts but only 2:1 at 10 volts.

Cool! Thanks, some manufacturers are coy about those graphs.

So at 10V two 2.2uF would be almost as good as a single 10uF?

It looks that way. I suspect that the root cause is the higher
capacitance in a given package forces thinner dielectric films,
increasing the voltage stress per volume of dielectric.

Also, different dielectric compositions may be used.

Joe Gwinn

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Wed, 8 Nov 2023 10:23:18 +0000, piglet <erichpwagner@hotmail.com>
wrote:

On 07/11/2023 22:49, john larkin wrote:

https://www.dropbox.com/scl/fi/191fe4xtipoxkr66g6y81/Cap_CV.jpg?rlkey=2gohwv8ksdc9z19znisalle6r&raw=1

So the 10u cap is better at all voltages, but the ratio is like 5:1 at
0 volts but only 2:1 at 10 volts.

Cool! Thanks, some manufacturers are coy about those graphs.

So at 10V two 2.2uF would be almost as good as a single 10uF?

piglet

Yes, less inductance too.

Our original question was whether it's always better to use a cap with
a bigger nameplate capacitance as a bypass. Probably yes. In this one
case, the 10u always wins.

I have some power pours that have noise from switching regs, in the
hundreds of KHz range, 1.2 to as much as 10 volts DC. They are
filtered by a ferrite bead and a lot of 1 uF bypass caps. The bead is
a short at these frequencies. The fix is to use a real 47uH inductor
and change the caps to 10u.

https://www.dropbox.com/scl/fi/wt737ji10ap0o9beq6177/T660B_pcb.jpg?rlkey=bazxur2vfdt0765wmqy088lt3&raw=1

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Wed, 08 Nov 2023 10:41:45 -0800, john larkin <jl@650pot.com> wrote:

On Wed, 8 Nov 2023 10:23:18 +0000, piglet <erichpwagner@hotmail.com>
wrote:

On 07/11/2023 22:49, john larkin wrote:

https://www.dropbox.com/scl/fi/191fe4xtipoxkr66g6y81/Cap_CV.jpg?rlkey=2gohwv8ksdc9z19znisalle6r&raw=1

So the 10u cap is better at all voltages, but the ratio is like 5:1 at
0 volts but only 2:1 at 10 volts.

Cool! Thanks, some manufacturers are coy about those graphs.

So at 10V two 2.2uF would be almost as good as a single 10uF?

piglet

Yes, less inductance too.

Our original question was whether it's always better to use a cap with
a bigger nameplate capacitance as a bypass. Probably yes. In this one
case, the 10u always wins.

I have some power pours that have noise from switching regs, in the
hundreds of KHz range, 1.2 to as much as 10 volts DC. They are
filtered by a ferrite bead and a lot of 1 uF bypass caps. The bead is
a short at these frequencies. The fix is to use a real 47uH inductor
and change the caps to 10u.

https://www.dropbox.com/scl/fi/wt737ji10ap0o9beq6177/T660B_pcb.jpg?rlkey=bazxur2vfdt0765wmqy088lt3&raw=1

Note that upper-left and lower-right are the little side-firing
3-color LEDs that were discussed in another thread.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 07/11/2023 22:49, john larkin wrote:

https://www.dropbox.com/scl/fi/191fe4xtipoxkr66g6y81/Cap_CV.jpg?rlkey=2gohwv8ksdc9z19znisalle6r&raw=1

So the 10u cap is better at all voltages, but the ratio is like 5:1 at
0 volts but only 2:1 at 10 volts.

Cool! Thanks, some manufacturers are coy about those graphs.

So at 10V two 2.2uF would be almost as good as a single 10uF?

piglet

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)