Simplistic Mosfet HV Shunt Regs - Page 310

studiostevus · 22nd July 2012, 02:56 PM

aarghhh.... I don't have a suitable load resistor so can't test this Sunday. It'll have to wait until tomorrow.

Btw, PSUD2 tests it at 178V (which is too low for me, but still higher than I see when I hooked up the SSHV2)

Screen shot 2012-07-22 at 4.55.40 PM.png

Salas · 22nd July 2012, 03:59 PM

Did you have long non twisted wire between C3 and reg's input connector when you tested?

studiostevus · 22nd July 2012, 04:02 PM

yes, maybe 40cm

Salas · 22nd July 2012, 04:05 PM

Stick a capacitor across the input connector to decouple. Twist the wires if feasible. Also are your 100 Ohm gate resistors really near to the Supertex Mosfets gates and with short pin in your layout?

studiostevus · 04:38 PM

Unfortunately didn't help.

I noticed, though, that I am able to trim both the CCS and the voltage between
-CCS: 95ma to 130ma
-Voltage: 127V to 111V

So I think the reg is working properly....
the gate resistors are within 1cm (or less)

Salas · 22nd July 2012, 04:35 PM

It helped, because you couldn't trim anything before. Your low input voltage thing is you need a different transformer. This one sags a lot and/or your coils are too resistive for 30mA CCS not to drop much voltage.

studiostevus · 22nd July 2012, 04:45 PM

You are probably right, but usually PSUD2 is quite spot-on:

I am using a transformer from a reputable source in Germany, multiple members have used it before without problems.

The chokes are specified by the same source as 330Ohm. I have modeled this correctly in PSUD2.

I did some further calculation, and think I could live with 170V input voltage (then I could have 150V output voltage which would work in my application). However I still don't understand this extreme sagging...

Salas · 22nd July 2012, 05:02 PM

Is the Tx internal resistance and chokes Rdc you feed to PSUD verified by measurement?

RollE2k · 24th July 2012, 08:57 AM

Salas, would there be any trouble using ~5-10cm wires from the Q3-spot on the PCB to mount the FET a little to the side?

Salas · 24th July 2012, 09:14 AM

Quite possibly, can't predict because it was never designed or tested like that. In any such a test I would move the gate resistor from PCB right at the pin (restore continuity at PCB also), hook scope on rail for oscillation stake out, and start at lower voltage if possible.

22nd July 2012, 04:32 PM	#3095
studiostevus diyAudio Member Join Date: Oct 2009 Location: Brunei	Unfortunately didn't help. I noticed, though, that I am able to trim both the CCS and the voltage between -CCS: 95ma to 130ma -Voltage: 127V to 111V So I think the reg is working properly.... the gate resistors are within 1cm (or less) Last edited by studiostevus; 22nd July 2012 at 04:38 PM.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Regs - Shunt vs Series	richie00boy	Solid State	42	14th March 2013 06:45 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

22nd July 2012, 02:56 PM	#3091
studiostevus diyAudio Member Join Date: Oct 2009 Location: Brunei	aarghhh.... I don't have a suitable load resistor so can't test this Sunday. It'll have to wait until tomorrow. Btw, PSUD2 tests it at 178V (which is too low for me, but still higher than I see when I hooked up the SSHV2) Screen shot 2012-07-22 at 4.55.40 PM.png

22nd July 2012, 03:59 PM	#3092
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Did you have long non twisted wire between C3 and reg's input connector when you tested?

22nd July 2012, 04:02 PM	#3093
studiostevus diyAudio Member Join Date: Oct 2009 Location: Brunei	yes, maybe 40cm

22nd July 2012, 04:05 PM	#3094
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Stick a capacitor across the input connector to decouple. Twist the wires if feasible. Also are your 100 Ohm gate resistors really near to the Supertex Mosfets gates and with short pin in your layout?

22nd July 2012, 04:35 PM	#3096
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	It helped, because you couldn't trim anything before. Your low input voltage thing is you need a different transformer. This one sags a lot and/or your coils are too resistive for 30mA CCS not to drop much voltage.

22nd July 2012, 04:45 PM	#3097
studiostevus diyAudio Member Join Date: Oct 2009 Location: Brunei	You are probably right, but usually PSUD2 is quite spot-on: I am using a transformer from a reputable source in Germany, multiple members have used it before without problems. The chokes are specified by the same source as 330Ohm. I have modeled this correctly in PSUD2. I did some further calculation, and think I could live with 170V input voltage (then I could have 150V output voltage which would work in my application). However I still don't understand this extreme sagging...

22nd July 2012, 05:02 PM	#3098
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Is the Tx internal resistance and chokes Rdc you feed to PSUD verified by measurement?

24th July 2012, 08:57 AM	#3099
RollE2k diyAudio Member Join Date: Nov 2007	Salas, would there be any trouble using ~5-10cm wires from the Q3-spot on the PCB to mount the FET a little to the side?

24th July 2012, 09:14 AM	#3100
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Quite possibly, can't predict because it was never designed or tested like that. In any such a test I would move the gate resistor from PCB right at the pin (restore continuity at PCB also), hook scope on rail for oscillation stake out, and start at lower voltage if possible.