Better not. They don't seem to like your own board version. Maybe a fat Schottky for D3 the most.
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.
Thanks, I did check the Jfet, they are ok on both boards. I was thinking to increase value of R9, R10 to 100K or more? or increase R8? currently I use 82K for R9, R10 and 2.7K for R8.
When you want less Vout trimming response then R9,R10 should be made less but the max Vout is also going to lessen some.
Higher R8 lowers the bias and dissipation in the cascoded BJTs. The TO-126s.
Higher R8 lowers the bias and dissipation in the cascoded BJTs. The TO-126s.
Unexplainable sensitivity to adjustments is often a sign of oscillations.
Did you change wiring or decoupling caps in your setup between then and now?
Jan
Did you change wiring or decoupling caps in your setup between then and now?
Jan
I never changed anything since. I measured the total resistance of R12 // R11 is around 40 ohm after I re-adjusted the R11 for 420V. I think that's why it behaves sensitive when adjusting. I will try 300R for R12 and 200R for the trimmer and see.
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.
Attachments
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?
In this case we can't be guessing which exact parts could have been hit, you should follow the troubleshoot steps example from post one link. Ccs first, shunt section next.
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