Simplistic Mosfet HV Shunt Regs

[quanghao]

Originally Posted by albertli

Salas,

The voltage on my SSHV1 is drifting lately. The supply voltage is 217v. It starts at about 100v at the output then slowing drifts the way up to around 145v ( this is my desire voltage for the 26 B+ ) then drifting up and down. I have tried changing the 350, 840 and even all 4 12v zeners with no avail. Will it be the problem on the 9610 / or the 170 ??

Albert

your problem is due to IRF 840, MJE 350. Because IRF 840 dead, will Mje overwork-it's very hot, so hot when Mje voltage begins to descend.

So you need to immediately MJE 840 and 350.

thanks

[CSlee]

Just about to fire up, need a couple of caps though..

Is C1 value 330nF critical for the zobel? I have plenty of 220nF and 470nF.

Cheers

[triode_al]

As I reported some instability some time back, I today set myself to some part changes.

I changed the pot, I changed the set resistor: replacing the MJE had success.

With a new MJE350 it worked well, flat on 2 mV/cm. For a little time.
because . . . when I changed the voltage (200 ohms multiturn potmeter; 2SK170GR/110K) then all at once the problem stated a bit again: now there is again a little bit of instability around 10 mV peakpeak.

Is my conclusion right that the MJE350 cannot stand tweaking the voltage [even though it is a few volts to the turn)?

I now have a 12V BE zener; maybe 4V1 is better (the max Vbe being 5 V)? I'm afraid I fried another MJE already. NOW - - I'm chicken.

[triode_al]

Erratum.
While I was away for over half an hour it has settled again, though there is a very mild drift of +/- 2 mV, now it is stable in time. No jolts.
The output voltage went up from 200V to 203 in the mean time, that is of probably the 2SK170 doing its own figuring out how to respond to the warming up of the earth.
Like it is it can be used in a preamp again.

(I tested with a lab supply 220V-240V, 750 ohms source resistor, that is a good setting to take the current limit out of the test.)
albert

[albertli]

Originally Posted by Salas

Yes.

Salas,

I have both 170 replaced, but sorry to let you know they're still the same. It drifts very minor at start and I almost can tune to my desired voltage, then it drifts the way up to the supply voltage 217v. I even tried to tune it back down to 145v, then suddenly the voltage free fall to around 41.5v and stop.
I also have the 2 zeners at 9610 replaced, but won't help. I took the 9610 out from the board and checked them with the new one. The readings seemed normal.

Albert

[Salas]

Albert, is it a PCB or P2P SSLV1?

[Salas]

Originally Posted by CSlee

Just about to fire up, need a couple of caps though..

Is C1 value 330nF critical for the zobel? I have plenty of 220nF and 470nF.

Cheers

Not very critical. Prefer the 470nF from those you got.

[Salas]

Originally Posted by albertli

I even tried to tune it back down to 145v, then suddenly the voltage free fall to around 41.5v and stop.
I also have the 2 zeners at 9610 replaced, but won't help. I took the 9610 out from the board and checked them with the new one. The readings seemed normal.

Albert

My mind went to the tiny trimmer wiper now. Maybe a resistor in trimmer's place after you check the set value?

[Salas]

Originally Posted by triode_al

when I changed the voltage (200 ohms multiturn potmeter; 2SK170GR/110K) then all at once the problem stated a bit again:

Originally Posted by triode_al

(I tested with a lab supply 220V-240V, 750 ohms source resistor, that is a good setting to take the current limit out of the test.)
albert

Better use a resistor instead of your trimmer for making sure too? Weird behavior when you tweaked it at a point.

[albertli]

Originally Posted by Salas

Albert, is it a PCB or P2P SSLV1?

It's quanghao's PCB. It worked from start, but it happened all in a sudden.