I still don't understand current.

Little Ghostman said:

Eah???

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Hi,

What he probably means is "most generally". One reason would be that we dont know if the power supply can SINK current as well as SOURCE current. IF the power supply can not sink current then it may be ok, such as the Mastech power supply i happen to have. I used a diode for a while, but then realized that i dont need it.
Note also that a diode in series does NOT protect against reverse polarity. If you hook it up wrong something may blow out, either the circuit under test or the power supply itself, or both. The power supply could blow if connected to a battery in reverse. I found out the hard way
Many power supplies can handle a short circuit, but most can not handle a reverse connected external battery (for charging it). At 12v out and a short, no problem, but at 12v out and a -12v battery that's 24v and it cant handle that.
Lucky for me it had a reverse connected parallel diode, and i only connected it for a brief second.
Since then i connected a parallel diode but also a DC fuse in series with it so the fuse blows if there is a reverse connected battery. I wont test it though, just assume it works

MrAl said:

Hi,

What he probably means is "most generally". One reason would be that we dont know if the power supply can SINK current as well as SOURCE current. IF the power supply can not sink current then it may be ok, such as the Mastech power supply i happen to have. I used a diode for a while, but then realized that i dont need it.
Note also that a diode in series does NOT protect against reverse polarity. If you hook it up wrong something may blow out, either the circuit under test or the power supply itself, or both. The power supply could blow if connected to a battery in reverse. I found out the hard way

Click to expand...

See what your saying, as far as I know all my PSU (non home made) can sink current no problem, most of mine are linear as well. I guess it depends on the power supply but I tend not to waste money on crap ones, I had a fire caused by a cheap PSU! Very scary stuff

4 quadrant operation includes V+I+, V-I- (the standard and with the leads reversed). they don't normally include V+I- and V-I+ like an amplifier would. they may be called bipolar supply/amplifiers or 4-quadrant power supplies. They may even be called a voltage source.

e.g. Kepco's BOP series: https://www.kepcopower.com/bopmod.htm

Sourcemeters: (Keithley, Keysight and another manufacturer) that I know of.