So your CCS input section is healthy double checked. Now calculate a test load equal in current draw to your real HV load. Pre-set your TP while still under LV for +20mA that HV test load draw. Then you will be ready to repeat your normal HV test as in the guide. Its possible your TP will climb a bit when the Vin-Vout will be higher than 9V during the HV test. You may then reset it or allow +5mA to 10mA extra if sinks heat still feels comfortable. You don't need more than 15-20V drop across the reg, the margin is there to anticipate possible mains sag without risking a drop out in regulation.
Not sure I understand entirely, but here's what I did. I assumed an output v of about 7v and my target total current of 60mA (including the regulator current). I set the current before including a load to 60mA, then attached a 100R load (it's what I had on hand but it's pretty close given my assumptions which calcualted to a 116R resistor). Checked the TP and found about 42mA, and the drop across the 100R output resistor was about 4v. More importantly, as I adjusted the current via R4, I could only get to about 45mA and the voltage drop stayed about the same no matter what I did with R11. The battery itself had ultimately dropped below 8v, so maybe that had an effect - I know batteries drop current capacity at some point, and the voltage had dropped a bit.
Tonight I was able to try again with HV. Checked at LV to make sure it was still set to 40mA. My goal is 300v at about 20mA for the circuit (one channel) and 20mA for the regulator. At 300v I used a load of 13.3k/10W resistor (closest I had to 15k).
When I turned on the HV supply (360v into the SSHV2), I checked current and found it 32mA. Checked output voltage and it was 360v. Same as the input. I'm still unable to vary the current via R4, and can't set voltage via R11. Given my voltage, it seems like 5mA must be going through the regulator.
I assume this must mean the regulator circuit is the problem?
When I turned on the HV supply (360v into the SSHV2), I checked current and found it 32mA. Checked output voltage and it was 360v. Same as the input. I'm still unable to vary the current via R4, and can't set voltage via R11. Given my voltage, it seems like 5mA must be going through the regulator.
I assume this must mean the regulator circuit is the problem?
When input and output voltages are equal the CCS won't function properly. That section was verified good during the LV check nonetheless. Thus the shunt voltage part must be having a defect. There are two BJTs and a JFET there. The BJTs must be showing normal Vbe (0.6-0.7V) in circuit, and the JFET must be producing low and trimmer controlled current. About 2.2mA for 300V. A healthy JFET of its type must be producing an Idss of 2.6-6.5mA (current draw) when removed and checked with 9-10V VDS, (+) on pin D, when G+S are shorted to battery (-).
Another test tip is, as the circuit is off power, Q5 between E,B pins on Ohm meter with red probe on E should be reading in the hundreds of Ohm and changing reading when turning the R11 trimmer. When a blown Q5 could read a couple of Ohm near short. Q4 should be reading in the hundreds of kilo Ohm on same test probing (the trimmer is not involved in Q4).
Resistance E-B on Q5 is in the hundreds (350R or so somewhere in mid trim) and changes with changing R11. Q4 reads something like 20M ohm in circuit! I'll try to pull the JFET soon and test IDSS.
I checked the board for parts, orientation and solder joints and re-flowed a few solder joints, then re-connected the board (using same 13.3k load resistor). This time, I'm now able to adjust current (now set at 40mA) and output voltage is about 245v. Unfortunately I still can't adjust the output voltage, but at least the CCS is working under HV. For the first time Q1 heatsink got a little warm after a few minutes on.
I checked the board for parts, orientation and solder joints and re-flowed a few solder joints, then re-connected the board (using same 13.3k load resistor). This time, I'm now able to adjust current (now set at 40mA) and output voltage is about 245v. Unfortunately I still can't adjust the output voltage, but at least the CCS is working under HV. For the first time Q1 heatsink got a little warm after a few minutes on.
Well, Salas, you got it right. Q4 was backward. Writing was quite faint and I'd mounted it on a small heat sink, so it took de-soldering it to see. I feel silly. So now I can adjust both current and voltage. Current seems to have a pretty wide range regardless of voltage, but voltage seems to have a max that depends on the current. Set at 40mA I can only get about 270 or 280v out of it, while if I increase the current I can squeeze more voltage out.
Looks like I'm about ready to re-calibrate it for my breadboarded circuit. Thanks so much for your patience and willingness to help.
Looks like I'm about ready to re-calibrate it for my breadboarded circuit. Thanks so much for your patience and willingness to help.
Congrats on fixing it. I would expect the output voltage max not to be hindered before approaching a load consumption only 5mA less than the CCS setting although 20-30mA difference is advised for better output impedance spec. See to leave no less than 15-20V margin between raw DC fed to the regulator and the regulator's output level when you will calibrate it. Upping constant current set will be dropping more voltage on any pre-filter resistance.
From the question, does this mean that the Reg is dissipating a total of 45 Watts? That's a lot of power dissipation for a high voltage shunt Reg
Anyway, If this is so, then for a temperature rise of say, 25*C above room ambient temp, you'll require a heatsink that's rated at 25/45 = 0.55 degree centigrade/W in free air (0.55*C/W) - just pick a suitable shaped sink that'll dissipate at this rate - it won't be 'small' either.
At a nominal room temp of 50*C, this 0.55 needs to be derated a bit (about 10 <-> 15%) as heatsinks are generally rated at a temp of 80*C.
Joshua, I hope that 45 watts is a misprint!
Anyway, If this is so, then for a temperature rise of say, 25*C above room ambient temp, you'll require a heatsink that's rated at 25/45 = 0.55 degree centigrade/W in free air (0.55*C/W) - just pick a suitable shaped sink that'll dissipate at this rate - it won't be 'small' either.
At a nominal room temp of 50*C, this 0.55 needs to be derated a bit (about 10 <-> 15%) as heatsinks are generally rated at a temp of 80*C.
Joshua, I hope that 45 watts is a misprint!