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LM317 HV PSU
LM317 HV PSU
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Old 5th December 2017, 01:11 AM   #1
Ripcord is offline Ripcord  United States
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Default LM317 HV PSU

Just wondering if anyone has built this and how much heat sink the IRF820 will need. Thanks.
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Old 5th December 2017, 01:15 AM   #2
audiowize is offline audiowize  United States
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The IRF820 is going to handle the brunt of the voltage drop. How much current do you plan to draw, what's your raw B+, what will be your regulated voltage?
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Old 5th December 2017, 02:34 AM   #3
Ripcord is offline Ripcord  United States
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I don't have a specific application in mind. I was thinking about laying out a pcb for it and was wondering if I should put the IRF underneath the pcb, to bolt to a bigger heatsink, or if a smaller on board type, like the one attached, would work.
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Old 5th December 2017, 02:40 AM   #4
audiowize is offline audiowize  United States
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For a phono preamp, your heatsink is OK. For a power amp, not so much.
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Old 5th December 2017, 05:18 AM   #5
ErikdeBest is offline ErikdeBest  Switzerland
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LM317 HV PSU
In this circuit there will be about 8V over the LM317 (12V zener - Vgs for enhancement mosfet).

Power dissipated on IRF820 is
(Vin-Vout-8)*I

example:
Vin 350
Vout 300
Current 100mA

(350-300-8)*0.1 = 3.8W

Power dissipated on Lm317: 8V * 0.1A = 0.8W

missed the 33 ohm resistor. At 100mA thiw will dissipate 0.33W, and the LM317 about 0,5W.
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Old 5th December 2017, 06:41 AM   #6
dotneck335 is offline dotneck335  United States
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I think this is a better design for a high voltage/high current regulator.
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Old 5th December 2017, 07:47 AM   #7
ErikdeBest is offline ErikdeBest  Switzerland
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LM317 HV PSU
Hi dotneck335

why do you think that?

what I dont like much about the 317 in this application is that a 317 requires 5mA, some say 10mA load, to regulate well. At 300V output that is 1.5W (5mA), a potentiometer that can take that is quite big, expensive and probably not very reliable. There is a recent thread on the LT3080 - I would probably use that device if I were to build one of these regulators.
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Old 5th December 2017, 01:22 PM   #8
Kay Pirinha is offline Kay Pirinha  Germany
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Quote:
Originally Posted by dotneck335 View Post
I think this is a better design for a high voltage/high current regulator.

High current - yes, with the drawbacks that the power devices' emitter balancing resistors are missing and that there's no overload protection at all.


High voltage - no, the input voltages mustn't exceed the LM317's/LM337's ratings.


Best regards!
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Old 5th December 2017, 05:02 PM   #9
dotneck335 is offline dotneck335  United States
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Quote:
Originally Posted by Kay Pirinha View Post
High voltage - no, the input voltages mustn't exceed the LM317's/LM337's ratings.Best regards!
The LM317/337 datasheet does NOT indicate a maximum input OR output voltage---only that the DIFFERENCE must be less than 40 volts.
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Old 5th December 2017, 05:06 PM   #10
scottjoplin is offline scottjoplin  Wales
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You are right but the problem is that at power up the output capacitor appears as a near short to 0V
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