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Simplistic Mosfet HV Shunt Regs
Simplistic Mosfet HV Shunt Regs
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Old 2nd November 2014, 02:55 PM   #4471
Carlp is offline Carlp  United States
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Thanks, AndrewT for the idea and Salas for moving my thread. Can this be done without breaking traces (it's the pcb from the TeaBag group-buy). I don't recall any obvious point to split this, but I'll have a look. Maybe I can de-solder a resistor or two...

I've had another suggestion to unload the output, set the current, then the voltage, then load the output, reset the current, then reset the voltage. I'll try that first since it seems easier.
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Old 2nd November 2014, 03:39 PM   #4472
Carlp is offline Carlp  United States
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Oh, and when unloaded, do I still need to tie F+ to S+ and F0 to S0?
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Old 2nd November 2014, 04:23 PM   #4473
Salas is offline Salas  Greece
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Simplistic Mosfet HV Shunt Regs
Surely they should be connected for the Kelvin circuit to close circuit. BTW when loading it with a dummy to simulate a target load, remember, the calculation is not about exhausting the CCS setting but the expected consumption. You set the CCS +20mA above expected load. That's for HV pre-test to set both CCS and Vout as in the guide.

As for R5 10R T.P. it will drive the set CCS current to its end node anyway even when fed from LV. That is the rail line ending to F+. So you don't need split pcb tracks anything. All you have to do is short F+ to F0 closing circuit to the LV source, be it a 9V battery even. Leave S+ S0 alone. Don't do that test with HV tension.
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Old 2nd November 2014, 05:31 PM   #4474
Carlp is offline Carlp  United States
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OK, looking at the schematic I can now see that the F point is directly tied to the CCS, and disconnected should isolate it for the most part. And how low v would be important. There's a lot going on in the circuit I just don't understand (transistors don't always make sense to me) so I appreciate your patience.
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Old 2nd November 2014, 05:32 PM   #4475
Salas is offline Salas  Greece
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Simplistic Mosfet HV Shunt Regs
Do you have a 9V battery handy?
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Old 2nd November 2014, 06:33 PM   #4476
Carlp is offline Carlp  United States
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I do. I also have a variac and 24v transformer I could whip together into a simple DC source if that's best.
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Old 3rd November 2014, 01:45 AM   #4477
Carlp is offline Carlp  United States
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Tonight based on the suggestion of a knowledgeable friend (knows and has used the SSHV2) I tried tying F+ to S+ and F0 to S0 but no load attached (only load should be the regulator). He suggested setting the CCS to 20mA (for the regulator) then setting output voltage to 300v. Then attaching the real load and adjusting CCS such that 300v at the output, then adding 20mA for the regulator.

When I did this, the test points were showing 0.030v, or 3mA and I couldn't adjust that at all. The output was reading 393v (reflecting my PS raw output minus small losses at 3mA, I assume). Next I'll try tying F+ to F0 and leaving S terminals open, then powering with a 9v battery to check the CCS. Note R4 was adjusting the current fine when I had a load attached. At this point I'm wondering if something may be wrong with the regulator since I understand it should pull 20mA just to operate. I'll also check solder joints and wiring on the board when I work on it tomorrow.

Carl
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Old 3rd November 2014, 05:37 PM   #4478
Carlp is offline Carlp  United States
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Just ran a check over lunch break using a 9v battery and 235R on the output with S+ and S0 disconnected (isolating the CCS). I can't vary the current at all or at most a very tiny amount (maybe a few tenths of milliamps). Voltage dropped by this resistor was about 0.5v.

So can I assume it's the CCS (or maybe both ). I'll look at the solder joints, look for cross-connections, etc. I've had difficulty with the DN2540 in CCS before. Seems it may be a bit fragile. I don't think I used a ground strap when handling them.

Thanks for any additional input!

Last edited by Carlp; 3rd November 2014 at 05:39 PM.
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Old 3rd November 2014, 06:42 PM   #4479
Salas is offline Salas  Greece
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Simplistic Mosfet HV Shunt Regs
I had a broken input section SSHV2 around so I fixed it and measured it to show you. After I changed both 2540s and removed the two associated Zeners, I tied F+ & F0 together (the output connector's far left and right points). Nothing else wired or loaded output wise. Firing it up and adjusting the CCS (TP) trimmer for 45mA at 9V in from a cheap lab PSU, the current draw climbed only by 5mA when at 20V without any dummy. TP checks with DVM were +/-1mA agreeing to the PSU's output current indication. It was drawing in the 150-250mA on 6-9 LV before, no matter the trimmer set.

You look for 1.5-2V VGS across each healthy DN2540 (outer pins) when the CCS is LV powered. The damaged D5, D6 Zeners were measuring like leaky diodes and the damaged MOSFETS were either shorted or like two diodes in series before I chucked them in the dustbin. No visual clues beyond a tiny dimple on the case's front near the drain pin of the shorted MOSFET. Q1 was loose on its sink as I saw plus some over current incidents had taken place during a tube phono build I was told. Still nothing was visually smoked. So do that, just short it like I showed and retry, checking VGS too. When off, see that the trimmer is changing value in Ohm when turned. Its absolutely safe with LV to handle and no side sink for the output MOSFET is needed as no current goes to the shunt section in this way tested.
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Old 4th November 2014, 01:09 AM   #4480
Carlp is offline Carlp  United States
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Thanks, Salas. I had done the check with F pins tied together but didn't report. It was essentially the same as with them loaded with 235R.

But...tonight I re-did the test with a battery showing 9.04v unloaded (7.7v when attached). This time I got adjustment at the TPs from 0.172v to 1.01v or so. That actually sounds right. VGS on Q2 was just a tad over 2v (I couldn't reach the other without worrying about shorting something. I don't know why it wasn't working that way earlier, but it (the CCS at least) now seems OK.
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