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Hi Russ,
I want to get 850 mA out of my Placid HD. I used 2.5" tall heat sinks as well as another large heatsink bridge that I custom designed, to further reduce the heat. I set VR1 to output 850 mA and then waited a bit. I started to see smoke. Now when I check the voltage output, I can only get approx. 2.5V at that VR1 setting. Lowering VR1 lowers the output voltage, but no matter how many times I adjust VR2, nothing changes.
Did I burn something out? Do I need to order another Placid HD?
Any help is appreciated. Thank you.
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Hi toast, thanks for the link.
After reading, it seems that it would be a better idea to find another series reg that can handle what I want. I was looking into AMB's Sigma 11, which appears to be a better solution.
My concern is that getting the Placid HD up to 850 mA will make it run extremely hot, and I really don't want to be producing so much heat in the case (since there's two other HD BPs in there!). If the Sigma 11 runs cooler, then that's what I'll go for.
If I do want to try getting more current out of the Placid HD, from what I read, it appears I should make the following changes:
C1: 22,000 uF
R2: O.5R
c2: 220 uF (?)
Is that correct?
Thanks for the help!
PS - It appears I fried QN2. The middle leg was blackened.
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Very likely it dies because you were testing it with no load without accounting for the power the shunt transistor would have to stand, and so the shunt transistor had to shunt the entire current and died.
Placid HD can handle that load, but if you testing it you need to provide a dummy load resistor so that the shunt transistor does not have to drop the whole thing.
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How much Ohms and which maximum power rating can you recommend for the dummy load resistor? |
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Originally Posted by: Corpius  How much Ohms and which maximum power rating can you recommend for the dummy load resistor? With not intent at being rude, you must study Ohm's law.
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Right, I got it.
I = V/R
fi.
850mA = 5.25V / R
R= 5.25 / 0.85 = 6.17 ohm
Power:
5.25 x 0.85 = 4.46 W |
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