Simplistic MosFET HV Shunt Regs

That part is a classic cascode for CCS, it was around, later I saw it analyzed in Morgan Jones 4th edition book also. A very good book to get, recommended. There is nothing much to it, you just put it where you would put an anode resistor and you turn its trimmer to fix a current. If it will not work that will only be if something is damaged. Good thing its also workable in low voltage so you can model and fix it safely. You can use an Led instead of a tube in that modeling and some 20V supply. Or a small resistor. That's all there is to it.

Salas,

I have been doing some modeling with the CCS, with 12VDC only (my line amp still at friend’s place), loaded with a 620R resistor.

Playing around, with 12VDC in, loaded with 620R, the best range of the CCS I can get is 20.9mA to 5.8mA, with R3 = 1K (R4 = 500R trimmer)......further increase of R3 value did not change the range much.
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Would you give a hint what combination of R3 and R4 I should try, to get a range of 10mA to say about 25-30mA when loaded with a VT25A please??

Thankyou, and Happy New Year!!
 
Use 30VDC or something about there. Low VDC modeling is just to verify your circuit works in safe experimenting. The real max mA you will evaluate on the real amp voltages.

In my amp, I am using 1 x SSHV2, TP set at 50mA, feeding a pair of these CCS, with R3 = 330R and R4 = 500R trimmer, with 248VDC, I can onlt get max about 9.0mA with the CCS.

What values for R3 and R4 should I try next please??

Happy New Year :)
 
I have been doing some modeling with the CCS, with 12VDC only (my line amp still at friend’s place), loaded with a 620R resistor.
As you have already been told - use the Ohm law to evaluate your setup. The CCS needs some voltage across it to work. In your setup the CCS is connected in serial with 620 Ohm resistor. Best estimation of the CCS compliance voltage is around 3V across it. So, for the 620Ohm resistor there is only 12-3=9V left. The 9V/620Ohm=14.5mA - it is the biggest current in this setup, tunung CCS to higher current will only make it in no-working state. Lowering the resistance or increasing the voltage can help you in achieving bigger current.
Would you give a hint what combination of R3 and R4 I should try, to get a range of 10mA to say about 25-30mA when loaded with a VT25A please??
As you can see above the current range depends not only on CCS parameters, but on external circuit also if the external circuit forces the voltage across the CCS out of compliance range. That is why you have been told to open a new thread for that discussion. In your case the current in your amplifier depends not only on CCS, but on biasing method, other parts values, B+, schematic, ... i.e., discussion becomes not about the CCS, but about your amplifier.
 
""...The CCS needs some voltage across it to work. In your setup the CCS is connected in serial with 620 Ohm resistor. Best estimation of the CCS compliance voltage is around 3V across it. So, for the 620Ohm resistor there is only 12-3=9V left. The 9V/620Ohm=14.5mA - it is the biggest current in this setup, tunung CCS to higher current will only make it in no-working state. Lowering the resistance or increasing the voltage can help you in achieving bigger current....""

All these are more than just Ohm law....and they do not agree with what I my modeling....

Poty...thankyou for your reply...but no thanks....please do not answer to my post anymore...

Have a happy new year instead please.
 
I bought a pair of boards last year after having great success with them previously.

I have just populated both boards and am trying to get them working but unfortunately neither board is working as it should;

Both boards have 200V LCLCRCRC supply feed.

Board 1 - only reading 20-30V at the input. CCS is working OK, but something is causing nearly all supply voltage to be dropped across the last PS resistor. I replaced the DN2540 but no luck.

Am I looking for a fault here? Or as I can adjust current properly is the fault further down stream?

Board 2 - CCS is only ever fully on and passes over 100mA which is causing the smoke to escape from various components. So this would be a fault in the CCS? I will replace the DN2540 here too and see.

I assume these issues may of come up here before, but have been trawling this thread for a few hours and have not found an answer yet. I will edit post if I do though!

Thanks in advance
 
... something is causing nearly all supply voltage to be dropped across the last PS resistor.
How have you checked the CCS? If it is definitely OK, then maybe the last PS resistor has wrong value? Or the CCS current was set too high?
... CCS is only ever fully on and passes over 100mA
Check with low voltage source first - it is less devastating sort to say. It seems DNs are go...
 
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I bought a pair of boards last year after having great success with them previously.

I have just populated both boards and am trying to get them working but unfortunately neither board is working as it should;

Both boards have 200V LCLCRCRC supply feed.

Board 1 - only reading 20-30V at the input. CCS is working OK, but something is causing nearly all supply voltage to be dropped across the last PS resistor. I replaced the DN2540 but no luck.

Am I looking for a fault here? Or as I can adjust current properly is the fault further down stream?

Board 2 - CCS is only ever fully on and passes over 100mA which is causing the smoke to escape from various components. So this would be a fault in the CCS? I will replace the DN2540 here too and see.

I assume these issues may of come up here before, but have been trawling this thread for a few hours and have not found an answer yet. I will edit post if I do though!

Thanks in advance

Check the CCSs individually under a low voltage supply first. Its a safe procedure for fault finding. Check if you got the 0.33uF cap on wrong pads or touching extra pads with its barrel. Can short the output if metal jacketed.