Simplistic MosFET HV Shunt Regs

[vgeorge]

Both of them? There is your problem.
It happened to me once when doing initial tests, but that was due to a wrong connection when trying different transistors.

 

[merlin el mago]

The other 0,58V

 

[vgeorge]

This one is ok. Change the first one.

 

[merlin el mago]

ok

 

[merlin el mago]

Still 17Vout

My SA1381 was well conected.

I suspect SK117GR, how can check it?

 

[vgeorge]

Did you replace the sa1381?
Did you measure (hfe) the replaced part to check that it was ok or not?

 

[merlin el mago]

New measure as the old 0,15V

 

[vgeorge]

Then maybe 117 is gone. GS voltage of 117 should be around 1.5V. If gone you should check his zener also.

 

[merlin el mago]

VGS 117 is 0,15V, D1 Zener also 0,15V

 

[vgeorge]

This seems low.
Maybe this is your problem.
I can' t think of anything else. If you want, I can take some readings on my board tomorrow.

 

[merlin el mago]

Thanks for your help George.

 

[merlin el mago]

The 1K trimmer is damaged measure always 1K I will change for the Vishay precision 1260W tol. 5%.

 

[merlin el mago]

Isn't the 1K trimmer

 

[AndrewT]

How long have you been building Salas style regulators?
Do you know how they work?

Then why are you dabbling in HV stuff?

 

[vgeorge]

VGS 117 is 0,15V, D1 Zener also 0,15V

I measure 0.61V on mine.
Did you change the 117?

 

[merlin el mago]

I measure 0.61V on mine.
Did you change the 117?

No I didn't change, do you wat that I change & measure the VGS?

 

[euro21]

Zener distroyed?
Take it out temporary.

 

[vgeorge]

If you change it, measure idss to see if dead or not.
According to datasheet, vgs should be -.2 to -1.5V.
You can adjust current, so front stage is OK, and we have checked that 840 and ksa1381 are not damaged, there is nothing else to go wrong. If you replace the 117, check d3 too. It could have gone south too.

 

[merlin el mago]

Zener distroyed?
Take it out temporary.

I taked it out but still 15-17Vout

If you change it, measure idss to see if dead or not.
According to datasheet, vgs should be -.2 to -1.5V.
You can adjust current, so front stage is OK, and we have checked that 840 and ksa1381 are not damaged, there is nothing else to go wrong. If you replace the 117, check d3 too. It could have gone south too.

OK I used the 117 supplied with the mini-kits without measuring the Idss now I will use one near 4mA of Idss also I will check D3. I disconnect D3 schematic that is D1 in the GB pcb that I have but still 15-17Vout.

 

[vgeorge]

If all the other semis are ok as you say, I can not think of anything else.