Weird HP 6012A Power Supply Fault

On Mon, 10 Jul 2006 11:36:38 GMT, Chris Quayle Gave us:

Well, if you have it set to "sense" on the back (if it has such an animal), the voltage sense wires must be in place and be used. If the switch is set to internal, it regulates at the output taps. The sense is for more precise voltage control AT the device under test.

Anyway... That *could* be one cause for a trip. Though it seems unlikely in this case.

The way to set current limit is with the output leads shorted at a low voltage set point. The limit value would show up on the meter.

This supply is overkill for practically any home hobby job. Mice to have, but you should have a smaller PS (perhaps even more accurate) for most bench work.

Ours in the lab was only 30V at about 3 Amps max, but it was fully programmable so I could set high line, low line, and nominal input voltages (inputs to my device), and test a product for function at those points,.

Sounds like the internal watchdog circuitry might be a bit hosed. Normally it senses voltage on a shunt in the output line to monitor current.

Ebay has manuals if yours didn't come with one.

Thanks - The weirdness may be intentional. After looking at it some more, the logic board seems to be ok, with a 1.7uS mosfet on pulse at the start of the pwm period and a 1uS off pulse at the end. The pulses are transformer coupled to the mosfet gates. The transformer has a centre tapped secondary, one side used via a diode and other parts to drive the gate on, with the other side used to drive a transistor to short the gate capacitance, thereby ensuring fast turn off. AFAICS, the only way that the thing could ever work with the above is if it's using the mosfet gate capacitance to store a charge to hold the fet on during the pwm on period, which has a max of 25 uS. I guess it's feasable, especially as the resistance in the gate circuit is much higher than expected at 270K. No clue about this in the manual at all.

Problem is that the original mosfets don't have a commercial equivalent, just the 4+4 hp part number. Have tried 4 x MRFP450, which should be enough to do the job power wise, but they don't work. It's too usefull a psu to just scrap, so will probably redesign the driver etc to get it going, even if some functionality is lost. Your right about overkill though - the whole design is pretty laboured and the 6012B (Have manuals for both) even more so. It's 1984 vintage, so we give them the benefit of the doubt :-)...

Regards,

Chris