I've been looking at the schematic of a popular product that has two options as
the power source. One source is a Vin point (pin or DC jack) that goes to a 1117-5V regulator, the other is a USB port. The USB +5V line joins the 1117 output via a Schottky diode.
Does this mean that the 1117 has no problem with this arrangement - that is, with power coming from another source to its output pin?
On 9/30/2024 4:37 AM, Pimpom wrote:
I've been looking at the schematic of a popular product that has two
options as the power source. One source is a Vin point (pin or DC
jack) that goes to a 1117-5V regulator, the other is a USB port. The
USB +5V line joins the 1117 output via a Schottky diode.
Does this mean that the 1117 has no problem with this arrangement -
that is, with power coming from another source to its output pin?
Short the LDO's input to GND and consider how it will (mis)behave.
On 30-09-2024 05:51 pm, Don Y wrote:
On 9/30/2024 4:37 AM, Pimpom wrote:Sure, this issue is often brought up while discussing regulators.
I've been looking at the schematic of a popular product that has two
options as the power source. One source is a Vin point (pin or DC
jack) that goes to a 1117-5V regulator, the other is a USB port. The
USB +5V line joins the 1117 output via a Schottky diode.
Does this mean that the 1117 has no problem with this arrangement -
that is, with power coming from another source to its output pin?
Short the LDO's input to GND and consider how it will (mis)behave.
Apparently the makers of the product (Arduino, various versions) seem to
feel that the input of the LDO getting shorted while being powered via
USB is not likely enough to bother with.
Anyway, what I'm thinking about is how the LDO's internal circuit reacts
to being reverse fed a voltage at the output pin without having an input
but *without* the input being shorted to ground.
On 30-09-2024 05:51 pm, Don Y wrote:
On 9/30/2024 4:37 AM, Pimpom wrote:Sure, this issue is often brought up while discussing regulators.
I've been looking at the schematic of a popular product that has two
options as the power source. One source is a Vin point (pin or DC
jack) that goes to a 1117-5V regulator, the other is a USB port. The
USB +5V line joins the 1117 output via a Schottky diode.
Does this mean that the 1117 has no problem with this arrangement -
that is, with power coming from another source to its output pin?
Short the LDO's input to GND and consider how it will (mis)behave.
Apparently the makers of the product (Arduino, various versions) seem to
feel that the input of the LDO getting shorted while being powered via
USB is not likely enough to bother with.
Anyway, what I'm thinking about is how the LDO's internal circuit reacts
to being reverse fed a voltage at the output pin without having an input
but *without* the input being shorted to ground.
If *designing* in this sort of configuration, I tend to be more paranoid about the types of "stuff" that will inevitably get connected to the
"input connector" -- especially if you opt for the ubiquitous "barrel connectors". There, it seems that the typical user just hunts for *an* adapter (wall wart) that "fits", mechanically. Consider that many such devices are generic and don't even declare the device to which they
are *intended* to be mated (People's Wall Wart Company #773), the
user has very little by way of guidance.
On 30-09-2024 05:51 pm, Don Y wrote:
On 9/30/2024 4:37 AM, Pimpom wrote:Sure, this issue is often brought up while discussing regulators. Apparently the makers of the product (Arduino, various versions) seem to feel that the input of the LDO getting shorted while being powered via USB is not likely enough to bother with.
I've been looking at the schematic of a popular product that has two options
as the power source. One source is a Vin point (pin or DC jack) that goes to
a 1117-5V regulator, the other is a USB port. The USB +5V line joins the >>> 1117 output via a Schottky diode.
Does this mean that the 1117 has no problem with this arrangement - that is,
with power coming from another source to its output pin?
Short the LDO's input to GND and consider how it will (mis)behave.
Anyway, what I'm thinking about is how the LDO's internal circuit reacts to being reverse fed a voltage at the output pin without having an input but *without* the input being shorted to ground.
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