Simplistic MosFET HV Shunt Regs

[king4joy]

I try to use small sinks just try to get the board into the amp box...seems not quite possible especially if I may use 1 board per channel in the future...just hope that this board with remote sensing, I can get by with putting the board in the PSU box (with about 0.5 meter wires connecting) without too much negative...

 

[vgeorge]

Seems you have to adjust your SSHV2 for two channels at 70mA then.
Maybe you could use the chassis as a sink for the 840, in order to save space inside?

 

[AndrewT]

What voltage is on the drain of these high voltage FETs?
The backplate of these FETs are able to be touched and prodded and wires dropped on etc.

 

[vgeorge]

The first fet drain is at Vin.
I didn' t took temperature readings, but with 50mA and 200V there was no problem touching the sink for extended period.

 

[AndrewT]

With 200V on the drain and the drain being within the thickness of the electrical isolator of the heatsink, be very careful about where you put tools and fingers.

 

[king4joy]

should we use two pieces of the isolator for high voltage??

 

[AndrewT]

The high voltage of itself is not a problem.
It's the accidental shorting of the copper backplate to anything at a different voltage that is the problem. Extra insulators cannot cure that.
The screwdriver tip will still span the gap from backplate to heatsink. The Finger can still touch the 200V.

 

[luvdunhill]

Plastic devices are the best choice here.

 

[Tea-Bag]

Plastic devices are the best choice here.

Luvdunhill, what are you refering to - caps or insulators?

 

[luvdunhill]

Transistors.

 

[merlin el mago]

Old SMHV shunt regulator

I'm doing in a quanghao board the old SMHV, it uses irf9610 for CCS, MJE350 and irf8410.

Vin is 285VDC and I only get 0Vout, LED's are all ligthning so I think IRF9610 is OK but I don't know how I have to start to fix the issue.

Thanks for help

 

[Salas]

Check vgs on both mosfets. Should be ~4V. Also check the Jfet.

 

[merlin el mago]

IRF9610 9.3V
IRF840 3.5V
2SK170BL 0.59V

 

[Salas]

Are you sure its 9.3V for 9610 between G & S (outer pins)?

 

[merlin el mago]

Now 9.5V, see pic

 

[Salas]

Looks much. But maybe because you got very large Vin-Vout right now. Can be bust. Check all your orientations, check if the system draws any current, change the easy ones, like MJE, FET, first.

 

[merlin el mago]

OK i will start with sk170, mje350 and let you know. Thanks for help Nick.

N.B. SK170BL I have 6.60-6.78 range and 8.16-8.98 range, wich range will be better?

 

[Salas]

Low range.

 

[merlin el mago]

220R gate resistor IRF9610 fired

 

[Salas]

You got a problem there. Change the Mosfet, its gate resistor, keep you rectification smoothing capacitor near input.