Products > Test Equipment
Lab Power Supply Turn ON and OFF Characteristics
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mawyatt:
Since there's been some discussions on various Lab Power Supply Turn ON and OFF misbehavior, thought a thread dedicated to such might be in order.

https://www.eevblog.com/forum/testgear/power-supply-for-home-lab-do-i-really-need-a-rs/

First off, think creating a setup and parameters that can be utilized for comparisons is necessary, so we'll start off with a proposed setup for evaluating the Turn ON and OFF characteristics.

1 ) Use 50Ω Load Resistor (usually available to everyone as a discrete resistor, or BNC termination type, or directly within the DSO).

2 ) Use General Purpose 10X DSO probe.

3 ) Use 20MHz DSO Bandwidth limit.

4 ) Set Power Supply Voltage to 8V.

5 ) Set Power Supply Current Limit to 40mA.

6 ) Set DSO to 0.5V/Div for full scale with 4V.

7 ) Trigger DSO on Rising Edge Single Shot for Turn ON Behavior (Falling Edge for Turn OFF Behavior)

8 ) Use Power Supply Enable ON/OFF to activate the output.

9 ) Capture DSO waveforms at various Time Scales starting with 50ms/Div, add additional Time Scales and identify such to show more details such as fast initial glitch (100us/Div) and slow settling (200ms/Div). 

10 ) Annotate waveform displays with details.

11 ) Main purpose is to show Voltage/Current Overshoot (if any) at Lab Supply Turn ON and Turn OFF.

Voltage/Currrent overshoot at Turn ON and/or OFF is our main concern with a Lab Supply, others may have additional concerns, but for now let's stay focused on the Turn ON/OFF Supply behavior.

Hopefully this will yield a means to compare various Power Supply characteristics with a more uniform test procedure/parameter setup.

Anyway, comments, recommendations, additions welcome with goal to yield a set of expert agreed upon setup and test parameters to allow various Lab PS evaluations.

Best
Kleinstein:
With a 8 V supply  and possibly higher it is not a good idea to use the scope internal 50 ohms. Depending on the scope this may already be damaging from overload, especially over longer time.

The transients from a lab supply are usually slow enough that the exact probing ( 1:1 or 1:10 probe or Z0 probe) does not matter. The load may make a small difference.

8 V and 50 ohm would be 160 mA. So a setting to 40 mA would have the supply in CC mode.
So one would more tend towards a high load resistor (e.g. 100 or 220 ohm) and a slightly higher current limit like 100 mA or 500 mA.
Not so sure why 8 V. More relevant may be 5 V or 3.3 V as a supply to quite some low voltage circuits that may care about an overshoot.

nctnico:

--- Quote from: Kleinstein on October 06, 2024, 02:29:19 pm ---With a 8 V supply  and possibly higher it is not a good idea to use the scope internal 50 ohms. Depending on the scope this may already be damaging from overload, especially over longer time.

--- End quote ---
Agreed. For simplicity, a 47 Ohm resistor might be a better choice as this is a standard E12 series value
Fungus:

--- Quote from: Kleinstein on October 06, 2024, 02:29:19 pm ---With a 8 V supply  and possibly higher it is not a good idea to use the scope internal 50 ohms. Depending on the scope this may already be damaging from overload, especially over longer time.

--- End quote ---

"5) Power Supply Current Limit to 40mA"

But yeah, a 47 Ohm resister seems more sensible.
Fungus:

--- Quote from: Kleinstein on October 06, 2024, 02:29:19 pm ---So one would more tend towards a high load resistor (e.g. 100 or 220 ohm) and a slightly higher current limit like 100 mA or 500 mA.

--- End quote ---

This, too.
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