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How will you test a negative supply?+/- 20v and 48v single ended.
Yeah, and the thermal resistance from junction to case is around 0.1 deg/W. With a perfect heat sink, 24V, and 27A, your junction will be 67 deg above ambient. Do you know what the thermal resistance of your heat sink is?Hmm, that's not a bad idea. It would definitely increase the size of the unit to mount some big resistors, but if it helps...
So do you think the module just can't dissipate that much power? Looking at the data sheet it clearly should be derated at operating temp with less than ideal cooling etc, and it looks like I'm near the edge of dc SOA at 24v 27A.
I could go with a few smaller modules I've seen surplus if that would be a better route.
Thanks!
That sounds like an excellent idea.I like to build electronic loads in 10 amp stages. One OP AMP that has its common mode voltage including ground. LM324's work nice. You can build 4
10 amp Cells using Darlinton's or FET's. As explainded before your junction temperature can never be exceeded on your shunt device. It is much easier to cool 4 heatsinks than one large one. I like to keep the sense resistor at 0.1
ohm. This gives a larger feedback signal with out excessive gain that could cause instability. Keep up the good work.
You don't have to match MOSFETs if you only have one per op amp. You do need one sense resistor per stage also. I guess with 0.1Ω @ 10 Amps, you would use 20W resistors. (?)The more I think about it the more I like it. Much easier to cascade, and if one section goes I just loose part of the loading. It shouldn't fail in a runaway fashion. Also, 324's are a tenth the cost of the Burr Brown chips.
The smaller two units have the same heatsink. I'm pretty sure one is big enough for the medium size unit, but I'm going to measure it tomorrow night to be sure. The largest one has a 12x12 lytron double pass coldplate, and I haven't been able to max out it's heat exchanger with residential power.
So, I need an opinion on whether to go with fewer higher power mosfet devices, or more conventional TO247 types. I still need to match them right? If so, I'll just go with the far cheaper 200W devices and inexpensive cement emitter resistors. Thanks!