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From: john larkin <JL@gct.com>
Newsgroups: sci.electronics.design
Subject: Re: power supply discharge
Date: Mon, 30 Sep 2024 08:33:42 -0700
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On Mon, 30 Sep 2024 18:42:08 +0800, Sylvia Else <sylvia@email.invalid>
wrote:

>On 30-Sept-24 1:21 am, john larkin wrote:
>> On Sat, 28 Sep 2024 10:21:46 -0700, john larkin <JL@gct.com> wrote:
>> 
>>> On Sat, 28 Sep 2024 09:44:44 -0400, legg <legg@nospam.magma.ca> wrote:
>>>
>>>> On Fri, 27 Sep 2024 08:07:29 -0700, john larkin <JL@gct.com> wrote:
>>>>
>>>>>
>>>>> Given a benchtop power supply, you can turn the voltage up and then
>>>>> down, and it goes down. Most have a substantial amount of output
>>>>> capacitance, and can be driving an external cap too. So something
>>>>> pulls the output down.
>>>>>
>>>>> I guess that there are no standards for this, but I've never seen a
>>>>> supply that just hangs high when it's cranked down.
>>>>>
>>>>> I'm designing some programmable multi-channel power suplies and that
>>>>> is one of many tangled issues in the project.
>>>>
>>>> Twiddling the adjustment knob on a bench supply doesn't
>>>> represent a dramatic change - and most adjustible
>>>> supplies don't load their output terminals with a
>>>> lot of capacitance.
>>>
>>> I've measured a few, and got output terminal capacitance of a few
>>> hundred to maybe 2000 uF.
>>>
>>> People here might measure some random power supplies. I leave them off
>>> and connect to a 50 ohm sinewave-output function generator and find
>>> the -3 dB point. One could use a square wave and scope the slopes too.
>>> Keeping the amplitude low will avoid turning semi junctions on.
>> 
>> Come on guys, quit pontificating and start measuring.
>> 
>
>At this stage in the process, you seem to have some odd constraints. Why 
>the specific h-bridge driver? Why non-isolated?
>
>Sylvia.

What I suggested is that a few people grab their bench power supplies
and see what sort of output capacitance they have.

The simplest way is to crank the voltage up and short the ouput and
see how much it sparks. Or measure the capacitance, even.

That quad TI driver is cheap and available and seems to have good
protections. TI makes good stuff and keeps it in production
approximately forever.

Non-isolated because that's simple and gets more channels on a small
board. The launch customer says that power supplies don't usually need
to be grounded because everything is grounded on an airplane.