Just make sure the negative terminal is floating relative to the connected computer’s ground! 
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and thats the reason why most lab bench PSUs are galvanically isolated. need a ± voltage source: take 2 PSus and define ground in the middle
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Watched a youtube about connecting two power supplies together for +/-, that makes sense.
The Bus Pirate is powered from the bench supply USB high speed charging port. I assume they share a ground. If I just swap +/- is that the same as a true negative voltage, or just reversed polarity? Are those the same thing? I think they need to share a common ground, otherwise the + is just going to short to the USB -.
From electronic_eel’s VOUT protection testing. When subject to 6 volts the protected circuit drops back to 0 volts. This is not what I saw during testing. It stayed at about ~5.4 volts. So, I’m guessing something is wrong and the TVS diodes are actually what is kicking in.
This also seems to confirm it. I will do additional testing on the second board to see if it is a build issue or implementation issue.
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Confirmed on second board. The protected VOUT is not dropping to 0 during over voltage.
Now to figure out why.
Edit:
+9V is solid on both boards: +9 on one and +9.34 on the other.
-5 is however only reaching -4volts on both boards. I need to study how that impacts the circuit.
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what benchtop supply do you use? in the worst case you grab a second supply and rig a labwire->USB adapter somehow (i got a few pigtails with various ends, too for exactly the same reason when i need to PSU-power something while debugging)
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Just an aliexpress cheapy, don’t recommend it the interface is awful. I’ll borrow a second supply or visit my friends lab this weekend.
was mainly asking to know what it could do or not. also: easy to verify if the - side of the USB and the regulated voltage are connected by beeping it out
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Appears they are, 0 ohms resistance.
Don’t start me on my cussing the power supplies on Amazon.com, etc. It is very hard not to curse here about it.
If you want to guarantee the isolation you need, get a couple or more of these. I can usually find them somewhere. Zoro says it is out of stock.
This WILL NOT supply 40A, like it says. I bet that is just a very old and fondly remembered LM317 circuit, so it can only do about 1 to 1.5 DC amps. BUT, it is excellent at isolation (look at the isolation transformer). I use these a lot. And, of course, you can switch the leads to get your negative voltage or connect a lead of two of these and get a double (+/-) power supply.
I can’t trust anything else.
Functional Devices-Rib
DC Power Supply, 120V AC, 1.5/28V DC, 40A, Track
Mfr # PSM19A24DAS
Zoro # G0394331
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A long time back, I purchased a TekPower TP-3005D-3. It was about $200, but provided:
- Two output power:
+,-, and floating ground on each- 0-30 V fixed, or 0-5 A fixed
- Digital displays of V and A for each
- Toggles to switch from independent / series / parallel outputs
- A third power output at fixed 5V, 3A max (later models exposed this as a USB port)
I’ve been happy with this unit for many years. Might be worth investing in one if you use them a lot.
Downside: It’s a big box.
Upside: It’s a big box, with massive components.
Check reviews online for technical details (ripple, etc.) … I don’t know enough to speak on it.
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I’m going to purchase some BP6 next month. Should I wait for the BP7? If it comes in like 2 months, it’s worth the wait
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Get a 5 or 6. 7 is stalled. The protection circuit isn’t working. The people who know it best are occupied with real life, so it’s on hold for now. It’ll probably pick back up in the winter, but it’s not moving forward at the moment.
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