Simplistic mosFET HV Shunt Regs

[Salas]

But you can adjust down? Try next value R9,R10 i.e. 27k, if still no good, 33k.

How you use the IXTP? As Q1 or in both positions? If not, what is your Q2?
Measure Vgs for Q1 and Q2.
What value TP resistor you use?

 

[Adams_Leo]

I was using both for the ccs,i have tried 27K,but still did not work,the Vgs -1.87V and cannot adjust more,for TP resistor ,i have tried 5R,and 2.5R and 1.0R,but still limited about 104ma

 

[Salas]

I see higher Id range is possible in the charts. But not at -2V Vgs area. Q2 probably holds Q1. Do you have a DN2540 to replace for Q2?

 

[Salas]

About output voltage range, also depends on how much current the JFET can feed to the 22 or 27k, and if there is spare current in the reg for its subsystems. Is it too heavy output loaded maybe?

 

[Adams_Leo]

Yes,if we use DN2540 for Q2,rhat means the current limit lower 2540 IDSS

 

[francoiacc]

Good evening looking for help. I spent couple of frustrating days on the circuit but still not working! The issue is that I have no output at all, the led doesn't light on and on the CCS output I have no current. I started troubleshooting the CCS, this is what I did:
1. connected F+ and F0
2. disconnected zener D1 and D2 across Q1 and Q2
3. 9V input to the CCS with 0,4A wall supply
4. Q1 (DN2540N5) VGS is around 2V
5. Q2 (DN2540N5) VGS is 0V
6. disconnected Q3 (IRF840)
7. tested again voltage across Q1 and Q2 and still same voltages: Q1 VGS around 2V, Q2 VGS=0V

Tested Q1 and Q2 they looks fine

Board made by me from the SSHV2 PDF using easyeda.

Any good idea?

 

[Salas]

Hi,

Q2 needs replacement because no VGS means broken when assuming the board is correct.

 

[francoiacc]

I replaced Q2 with a new one same result! I assume there is something else wrong. The PCB is a copy of the one in the SSHV2 PDF, you can see it attached, I checked it and to me looks fine. What can be wrong????

 

[Salas]

Maybe Q1's sink touches ground? Insulate Q1 from sink if its not.

 

[francoiacc]

Maybe Q1's sink touches ground?

Tested, Q1 sink not touching ground.

 

[Salas]

R4 works? DMM shows R value going up and down across it? (test when powered off)

 

[francoiacc]

R4 works? DMM shows R value going up and down across it? (test when powered off)

Yes, it ranges between 0 and 100Ohm measured across R3

 

[Salas]

Why up to 100 and not to ~200? Is it not a 500R trimmer (parallel to 330R resistor)?

 

[francoiacc]

Why up to 100 and not to ~200? Is it not a 500R trimmer (parallel to 330R resistor)?

The schema I have is a 200R Trimmer in parallel to a 220R. May be I have an old one!

 

[Salas]

Its OK there are two. One in the original description, one in the PDF. Adjusted for parts availabilty.

 

[Salas]

Is Q1's back insulated from the sink anyway? That's the HV carrying MOSFET of the cascode.

 

[francoiacc]

So, should I replace R3 and R4? I have R1 and R2 100K, are they ok?

 

[francoiacc]

Is Q1's back insulated from the sink anyway? That's the HV carrying MOSFET of the cascode.

Yes, it is insulated

 

[Salas]

Has a nylon grommet for the screw too?

 

[Salas]

Is Q2 placed face to face with Q1?