Re: power supply discharge

On Sat, 28 Sep 2024 22:28:07 -0700, Joerg <news@analogconsultants.com>
wrote:

On 9/27/24 8:07 AM, john larkin 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.
 

>
Often the only internal load is the resistive divider for the regulator
loop feedback.
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>

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 have some. They drop very slowly when there isn't much load on the output.

Customers might whine if they ask for 10 volts and see 30. Amd that
may be mostly held up by their capacitive load.

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>

I'm designing some programmable multi-channel power suplies and that
is one of many tangled issues in the project.
 

>
A synchronous buck architecture should work quite well if you need to
slew fast. I've used that on a driver that had to modulate a hard
capacitive load at several kHz and above 100V.

I'm doing some multichannel non-isolated supplies that will be sync
buck, using multiple TI DRV8962 chips.

One problem is that a sync buck can become a boost in the wrong
direction, and start charging my +48 supply. If it hits, say, 55
volts, I'll disable the switcher chips, and the outputs can hang. I
need to discharge the outputs. I'm thinking about 20 mA of depletion
fet per channel.