Although you could control its Id with a proper value trimmer, its VGS (off) is considerably higher to can work good enough under just one Vbe provided for VDS here. You need a low noise 0.5V-0.7V VGS (off) type. So to be beyond the Ohmic region entering the saturation region already under such low VDS.
Hi, Salas
Thanks for the wonderful reg. I build two 420V version for my preamp quite a while back. It's been working fine since but recently it developed problem. The output voltage suddenly dropped below 400V, that made relays in my SS power amp start acting. I re-adjusted the trim port, and it went to 420V as expected. But a few days late it will do the same again. I noticed when I tried to adjust the trim port, it's very sensitive , just a micro little touch, the output voltage will increase by 10V or more , this makes adjustment very difficulty. I use 1 reg per channel. The other reg behaves the same so I'm reluctant to think the trim pot could be the problem.
Thanks for the wonderful reg. I build two 420V version for my preamp quite a while back. It's been working fine since but recently it developed problem. The output voltage suddenly dropped below 400V, that made relays in my SS power amp start acting. I re-adjusted the trim port, and it went to 420V as expected. But a few days late it will do the same again. I noticed when I tried to adjust the trim port, it's very sensitive , just a micro little touch, the output voltage will increase by 10V or more , this makes adjustment very difficulty. I use 1 reg per channel. The other reg behaves the same so I'm reluctant to think the trim pot could be the problem.
I just change R12 to 220 ohm and leave R11 as it is. A quick simulation shows that the trimmer is about at its middle position for the 420V output I wanted.
So, I just paralleled another 470 ohm resistor with R12 , and now I feel much better when I adjust. I also feel less Vout drifting as temperature increases.
So, I just paralleled another 470 ohm resistor with R12 , and now I feel much better when I adjust. I also feel less Vout drifting as temperature increases.
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Hi Salas, I have a problem with 2 shunts, they worked perfectly for a week, but today when I turned everything on I didn't go out from either of them, the LEDs light up very slowly, q1 and q2 start to get hot after a few minutes, before they got lukewarm after hours, this happened when I connected all the GNDs together, that of the heaters and those of the shunts, before I kept them separate for each channel, what could have gone wrong?
I did the test, I really believe they are faulty, I have a 350mA VGS and an 800mA idss, I am waiting for spare parts and I will replace them, I will let you know thanks in the meantime