Simplistic MosFET HV Shunt Regs

[Salas]

Inspect the passives well. Maybe a zap has hit the belly of the caps or something inside them. Push them up half a mm off board for a check.

 

[Jogi]

Q2 replaced, voltage in goes up to 330V, out still 240V, now I can't adjust current anymore, only between 5-6mA, input Voltage then varies between 330-340V...

 

[Jogi]

caps are safe btw

 

[Salas]

Is there Vgs in Q1 and Q2,Q3? (Watch it when you probe). Have you got an LCR to measure the caps for value and dissipation factor?

 

[Jogi]

Caps have 10µ and 0,32, as they should. Dissipation factor I can't measure, also I'm pretty clueless how to measure the Vgs. Maybe I just replace the 840, I've just one left.

 

[merlin el mago]

Vin 12VDC, R5 50 ohms, measured at TP 0.3A = 30mA, it's OK?

 

[merlin el mago]

Caps have 10µ and 0,32, as they should. Dissipation factor I can't measure, also I'm pretty clueless how to measure the Vgs. Maybe I just replace the 840, I've just one left.

Simple measure voltage between Gate & Source

 

[Salas]

Vin 12VDC, R5 50 ohms, measured at TP 0.3A = 30mA, it's OK?

Maybe R4 pot value at 50 Ohm you meant? And 0.3V over T.P. you meant? R5 is a fixed 10 Ohm resistor as it should, yes?

 

[merlin el mago]

Yes, R4 trimmer set to 50 ohms, yes 0.3V over T.P., yes R5 10 ohms fixed resistor.

 

[Salas]

Goes to plan then. Sit C1 and C2 like they don't touch free pads for just a little when you will complete it.

 

[merlin el mago]

OK

 

[Salas]

Look how close to calc you got R4 when I asked it for 30mA CCS. Spot on, I like it.

 

[merlin el mago]

Caps pics, are like you suggested?

 

[Salas]

Good. Especially the little one I am suspect of if its fully down.

 

[merlin el mago]

Makes sense your suspicious because can easily do an unwanted contact. Tomorrow I will finish the rest of reg & check it.

 

[merlin el mago]

Fixed, attached pics with dummy load & real load (Valve Itch)

 

[Salas]

Great! But where are the pics? I did no see any new ones over at Valve Itch thread.

 

[merlin el mago]

Sorry my mistake

 

[Salas]

Fine then. Using a heat sinked Caddock for dummy load testing even, that is top style.

How much raw DCin room does the rectification allow you now?
Was it the small cap doing the monkey business before? What do you think?

 

[Salas]

P.S. You need a tripod or slower camera speed setting.