Simplistic Mosfet HV Shunt Regs - Page 269 - diyAudio
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Old 30th January 2012, 11:46 PM   #2681
Salas is online now Salas  Greece
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Is IRF840 having its source on ground's side? Difficult to picture bcs sandwiched. That's voltage section for instance.
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Old 30th January 2012, 11:54 PM   #2682
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Metal backing to inside of pcb putting source at ground.

Am i right that no voltage is found across outputs because the current is not finding ant impedance that would cause Vdrop. I have larger than 500R pot. Could that be causing problem?

I have it set to read 500r across pot.

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Old 31st January 2012, 12:03 AM   #2683
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To develop voltage, the JFET's current should flow to the 68K resistors through the LED. The trimmer sets that current. Is its middle leg connected to its side leg?
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Old 31st January 2012, 12:07 AM   #2684
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Yes. I will try another. Is it possible toreverse a pot? Never considered that?
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Old 31st January 2012, 12:10 AM   #2685
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The trimmer must travel from zero to max between Jfet's S pin and LED. If you reverse, still working as rheostat though, it should increase Vo anticlockwise.
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Old 31st January 2012, 01:03 AM   #2686
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last worrisome post for the night. Could the 840 have been blown in the intial smoking and be causing problems? It is the only thing that remains unchanged. I even changed the LED. Still just getting 20mV across output, LED and Jfet Vds. 160mV Vbe of bottom bjt.
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Old 31st January 2012, 01:10 AM   #2687
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Very possible 840 is out. Should give about 4V Vgs if healthy.
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Old 31st January 2012, 01:31 AM   #2688
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Aha! Naturally it was the last thing. It was actting as short?
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Old 31st January 2012, 01:36 AM   #2689
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Could be. If it will work by changing it, possibly.
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Old 31st January 2012, 06:08 AM   #2690
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To be sure, and in the end saves time, is to take out all the semis and check them. Zeners and leds sometimes, could go south also.
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