Simplistic MosFET HV Shunt Regs

[AndrewT]

The Gate draws no current if the FET is working properly.
In this case there should never be any DC voltage across the gate stopper.

The LED has you scratching your head. Measure the voltage across it.

 

[buzzforb]

20mV. No Vdrop across R11 or r12. It seems to me that it is the Jfet.

 

[Salas]

You need Vbe first for the fet to tick.

 

[buzzforb]

Replaced both bjt's. No change and no light from led. Layout is correct. Cathode of led i attached to tpop of 68k resistor. No voltage at output. Im dying here

 

[Salas]

Did you change fet also?

 

[Tea-Bag]

Replaced both bjt's. No change and no light from led. Layout is correct. Cathode of led i attached to tpop of 68k resistor. No voltage at output. Im dying here

Just relax. Walk away and do something else while your trouble shooting braincells recharge

 

[Salas]

First HV thing to do and that being SSHV2 on own inverted PCB ain't the easiest job. Tell you what, if it ain't gonna badge on reasonable debugging, continue with the pre, run it on additional RC cell to nominal B+ and wait, we gonna put PCBs out reasonably soon 'cause the protos hit 100%. OTOH, Mike, have we got one spare proto for Buzz? I think all are out already? No?

 

[buzzforb]

Did you change fet also?

840 or 170? No output voltage would suggest a short after ccs, correct. If detach sense wires from main rails, i shoul dread full voltage, correct.

 

[buzzforb]

Just relax. Walk away and do something else while your trouble shooting braincells recharge

How bout a cup of tea!

 

[Salas]

840 or 170?

170

 

[buzzforb]

170 replaced. 20 mv across output. 20mv across led. Nothing else registers anything.

 

[buzzforb]

If i detach sense wires, i should read input voltage, correct.

 

[Salas]

Don't its possible it will burn semis.

 

[Salas]

P.S. Give us a close up picture from top and copper side, maybe we spot something.

 

[buzzforb]

Here ya go

 

[buzzforb]

Lets talk theory of operation perhaps understanding better will help me solve it.could you explain functioning of the entire Vref area including bjts and jfet.

 

[Tea-Bag]

OTOH, Mike, have we got one spare proto for Buzz? I think all are out already? No?

Nope, sent them all overseas last year.
If anyone's got a spare , its you

 

[Salas]

Lets talk theory of operation perhaps understanding better will help me solve it.could you explain functioning of the entire Vref area including bjts and jfet.

Because the traces are printed as top side, when the DN2540 that I can see is rotated VS real PCB, other things must be reversed also. Are the CCS zeners so?

The CCT is explained when presented, its all in that post.

 

[Salas]

Nope, sent them all overseas last year.
If anyone's got a spare , its you

Got two for double mono.

 

[buzzforb]

The CCS is working perfectly and providing 40mA or 400mV across test point of R5. The problem is happening with Vref section.