Simplistic MosFET HV Shunt Regs

[AndrewT]

Measure some Vdrop across components of the working CCS. Write them on a printed copy of your sch.
Use this later to check that the CCS is still working, when you run into more wiring errors.

 

[merlin el mago]

That's a good idea ��, thanks Andrew.

 

[merlin el mago]

Attached pic with measurements.

 

[Salas]

The voltage across the dummy does not compute 30mA though, but 5 times that. Recheck.

 

[merlin el mago]

TP measures minimum 0.310V with trimmer 200R, 6R8 load measures 0.505V = 74mA and have to measure 0.204V for 30mA, have I to change 10R TP resistor or have I to come back to the 500R trimmer or use other trimmer value?

 

[merlin el mago]

I guess to come back to 500R trimmer or to use 1K trimmer, I have to avoid the TP to measure CCS and measure current directly in the load.

 

[Salas]

Seems like #4573 prediction was true. Make the trimmer higher value. Having TP resistor like 1 Ohm or 10 Ohm its no problem, but as you prefer. If you want to jumper.

 

[merlin el mago]

I will try 1K trimmer.

 

[merlin el mago]

What trimmer have I to use to measure 10R TP the right CCS current?

 

[Salas]

Don't know, surely higher than before. If you got the parallel resistor R3 still stuffed there nothing will change much though.

 

[stajo]

Felipe, is that your VDC in, 30 V?

 

[merlin el mago]

@Salas. No, R3 isn't stuffet.

 

[merlin el mago]

Felipe, is that your VDC in, 30 V?

Yes, more or less.

 

[merlin el mago]

With 1K trimmer can't adjust the current of the load to 0.204V, the minimum I can set is 0.406V = 59mA
TP measures 0.069V

 

[Salas]

Jumper the load.

 

[merlin el mago]

ok & adjust current on TP?

 

[merlin el mago]

The bench PSU is jumping 29.5-30.3V

 

[AndrewT]

buy a newer one.

 

[merlin el mago]

I'm poor.

 

[gallon]

The bench PSU is jumping 29.5-30.3V

Modify it with a Salas circuit.