Derpy Load: Is my dummy load design any good?

[T4P]

Sliver TIM again? That stuff is quite electrically conductive no matter what they say

[skipjackrc4]

Arctic Silver Ceramique is supposedly non-conductive, so you may look into that.  I am eagerly awaiting your results as I plan to do something similar in my upcoming load design. 

What would everyone's opinion be on sandwiching the transistors between 2 CPU coolers?

[tom66]

Tests of various thermal pastes:
http://dansdata.com/goop.htm

You may be surprised 

[LEECH666]

Always used the standard white goop for semiconductors so far (Amasan brand, probably not that well known outside of Gemany). Seems to work fine for CPUs and other power semiconductors. The test from the page tom66 linked seem to confirm that the standard white goop is sufficient.

Man why am I awake ... :S

[dr_p]

Blackdog suggested in this post that the IRFP064N might be a good candidate for a power MOSFET in a dummy load. I checked the datasheet for the device and VGS(th) max seems to be around 4V. I reckon from the threshold value that this FET could be used as a logic level device then? (Even tho it's not specifically called a logic level MOSFET in the datasheet).

Cheers,
Florian

Gate-Source Threshold Voltage (VGSth) is the minimum voltage that allows the FET to conduct ( some!! ) electricity. The datasheet says 2...4V and I think they mean it varies from part to part, but no more than 4V and no less than 2V. With only 2 to 4V it has just crossed in the linear region (not fully on). When VGSth rises some more (rise = the Overdrive Voltage), the FET reaches the fully-on state.

Notice how RDSon is given on VGS=10V, not at 4V?

added on EDIT:

[...]With the initial planned 4 sink units this will leave me with ~200mA for the op amps.
Should be enough ...

I would expect 20-30mA tops.

[LEECH666]

Updated schematic ...

[say]

It's been a while LEECH. Have you produced a prototype yet?
I have been struggling to build one myself but the heatsink issues didn't let me proceed further. Would love to hear from you soon.

[LEECH666]

Uh there is always some stuff (xmas, new year, health, motivation, etc.) that keeps interrupting me, and I am lazy sometimes. Sometimes I need a push in the right direction.

These two threads are related to this project. Just in case you haven't read them alread and in case you're wondering what I've been doing.

https://www.eevblog.com/forum/beginners/ltspice-frustration/
https://www.eevblog.com/forum/beginners/trouble-adjusting-op-offset-voltage/

Cheers,
Florian

[Spikee]

Cmon leech finish that thing already   

[LEECH666]

I knoooooooow, xD.

[LEECH666]

Okay so I finally* managed to build up a (sort of) prototype on breadboard and it seems to work reasonably well. I've been able to draw 3A at 30V from my Manson NRP-3630 PSU (36V/3A), however I am a bit puzzled by the discrepancy of the 'set' voltage and the current actually drawn from the PSU. For example - at the moment the set voltage is set to roughly 0.33V. If I measure the voltage across my 0.100R shunt resistor, I get the same voltage.

Nevermind, looks like I have some heavy losses on my bread board that probably explain the discrepancy.

Measuring between the GND near the 0.100R shunt and my main GND "node" (a few centimeters away) shows a 90mV drop ...

Guess it's perf board time again ...

(* - Damn you Borderlands 2 and your addictive gameplay! )