Electronics > Projects, Designs, and Technical Stuff
High Voltage Bench Power Supply Design
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Wolfgang:
... testing the SOAR is a good idea. A test would run a normal load, plus then pulses of the current that would occur when the output is shorted. A very robust load is recommended, just in case the test fails.  >:D
Zero999:

--- Quote from: Wolfgang on January 25, 2019, 10:18:40 am ---
--- Quote from: Zero999 on January 25, 2019, 09:52:54 am ---What's wrong with the FQA8N90C-F109? It's clearly specified for DC linear operation. Refer to figure 9 on page 4 of the data sheet.
https://www.onsemi.com/pub/Collateral/FQA8N90C_F109-D.PDF

--- End quote ---

You're right, I have seen the DC in the SOAR, only I have no trust in parts developped for switching purposes. Fairchild parts also had a DC SOAR, and they blew up nevertheless. In a linear HV PSU, the pass transistor is the most critical part of the circuit. If this shorts out, the full high voltage will appear at the DUT, plus the charge stored in the smoothing cap after the rectifier. This can be many Joules of energy, normally killing your DUT (and hopefully not you too) instantly. I would play extremely safe here.

--- End quote ---
As I said in one of those other threads: never rely on semiconductor or thermionic devices to protect against electric shock. Always assume the output of your power supply has the potential to be at a hazardous voltage, even when it's set to <50V.

It should have overvoltage protection, but even so, it shouldn't be relied on to protect the user from shock, only the DUT.
Wolfgang:
Even if the PSU works just fine, its output voltages can be lethal, as with any HV tool. Use caution even when you set the output at low voltages. Reasons see above.

Old HV slogan:

Your first error is your last error.  >:D
H713:
Perhaps the key aspect here is the fact that I have most of the parts on hand at this time. All of the costly parts (Transformer, filter capacitors, panel meters, chassis, connectors, etc) is stuff I have on hand. Yes, I am aware that this FET is designed for switching. That is why I'm planning to put at least two in parallel, if not more, which should keep it well within the DC SOA. The idea is that each device will be run conservatively enough that even though it's not really designed for linear operation, it should be fine. A circuit breaker or HV fuse on the output will be implemented as well to stop anything too stupid from happening.

The current limit is probably the hardest, but I'll spend some time digging around for a reasonably robust way of doing it.

I pretty much assume (from a safety standpoint, that is) that if the output is capable of producing 500V, then I'm going to treat it as if it always does.

Also, the key aspect is that I recognize the fact that the pass elements could short. That will always be in the back of my mind while I'm using this power supply.
Wolfgang:
What you could do for a safety measure is to implement an adjustable overvoltage crowbar at the output.
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