Simplistic Mosfet HV Shunt Regs - Page 340 - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

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
Reply
 
Thread Tools Search this Thread
Old 27th October 2012, 06:13 AM   #3391
Salas is online now Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
It just sees Q1's Vgs. Hence little volt depending on current mainly. Q1 sees 99% of the HV in-out.
  Reply With Quote
Old 27th October 2012, 02:13 PM   #3392
roger57 is offline roger57  Canada
diyAudio Member
 
roger57's Avatar
 
Join Date: Sep 2006
Location: Edmonton, Alberta
Quote:
Originally Posted by Salas View Post
It just sees Q1's Vgs. Hence little volt depending on current mainly. Q1 sees 99% of the HV in-out.
Thanks for taking the time to answer my questions, I'll keep you posted on what I find.
  Reply With Quote
Old 27th October 2012, 05:19 PM   #3393
roger57 is offline roger57  Canada
diyAudio Member
 
roger57's Avatar
 
Join Date: Sep 2006
Location: Edmonton, Alberta
Quote:
Originally Posted by Salas View Post
Never brought it up with a variac. Just straight with a switch. Maybe the Vref protection Zener latches something when you start from 0? Don't know.
Salas,

To make sure everything was 100%, I replaced every semi device. I verified all resistor values.
Regulator behaves perfectly when bring voltage up from 0V using the variac. However, when I adjust the variac to the AC line voltage I need to get 390V out of the DC supply, and just switch it on, it latches up the regulator. In fact, it doesn't seem to matter what the DC voltage into the regulator is - even 100V switched on instantly latches it up.

Once again, resistive load is 12K, DC voltage set at 375V, voltage across R5 setpoint is 500mV.

The last regulator I built was tested on the same setup (using the same DC input supply), so this is very strange. It's installed in a piece of equipment I don't want to take apart to retest.

Any suggestions...ideas?

Thanks...
  Reply With Quote
Old 27th October 2012, 06:33 PM   #3394
Salas is online now Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
The variac is a coil too in a way, isn't it? If you decouple the reg at its input connector with a 0.1uF across maybe helps in your set up?
  Reply With Quote
Old 27th October 2012, 07:35 PM   #3395
roger57 is offline roger57  Canada
diyAudio Member
 
roger57's Avatar
 
Join Date: Sep 2006
Location: Edmonton, Alberta
Quote:
Originally Posted by Salas View Post
The variac is a coil too in a way, isn't it? If you decouple the reg at its input connector with a 0.1uF across maybe helps in your set up?
OK, I tried that, and it did not help.
I then switched to a higher resistive load - 20K -thinking that maybe reducing load current might cause it to behave differently. No go.

I then built another DC filter supply. Where my bench supply has a CLC filter, on this one just diodes and a filter cap, and I used a smaller 230VAC secondary transformer. Under load this should provide around 300VDC secondary, but good enough to see if this behavior changes. It does not change, exactly the same. Any surge into the regulator causes this latch-up at about 10V.

However I one other test that may suggest something. I bring the voltage up so I have, let's say 280V at the regulator output. Then, I switch off the power and watch the voltage decay. If I switch (I mean switch instantly) the supply input back on before the output gets below about 70V, it goes back to full output with no latch up.
  Reply With Quote
Old 27th October 2012, 07:54 PM   #3396
Salas is online now Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
There is C2 and D3. When we power up, C2 charges with Q6's constant current (2.2mA for say 300VDC out) up to full Vo. D3 keeps 12V across Q6 so it won't see a big voltage even for very short time while C2 comes up. D4,R10,R9 are the voltage reference items that translate Q6's constant current to voltage and bias the Q4, Q5 cascode. I don't have a variac, but I can try see in LT Spice if something holds under a threshold when the reg's Vref is programmed for a certain current via VR11, thus voltage output.
  Reply With Quote
Old 28th October 2012, 01:18 AM   #3397
roger57 is offline roger57  Canada
diyAudio Member
 
roger57's Avatar
 
Join Date: Sep 2006
Location: Edmonton, Alberta
Quote:
Originally Posted by Salas View Post
There is C2 and D3. When we power up, C2 charges with Q6's constant current (2.2mA for say 300VDC out) up to full Vo. D3 keeps 12V across Q6 so it won't see a big voltage even for very short time while C2 comes up. D4,R10,R9 are the voltage reference items that translate Q6's constant current to voltage and bias the Q4, Q5 cascode. I don't have a variac, but I can try see in LT Spice if something holds under a threshold when the reg's Vref is programmed for a certain current via VR11, thus voltage output.
Salas,

After thinking carefully about what I was seeing, and knowing I'd made an identical regulator on the same test setup, I realized there had to be something wrong with the board. I discovered that capacitor C1 was essentially not in the circuit. I used a Wima 0.33uF/630V, with 22mm lead spacing. When I soldered it in place, it was across the same side of the circuit, not bridging across. A bit sloppy, the multiple holes caught me sleeping. It now works perfect at full voltage in on start-up.

Also, I have successfully used a different MOSFET in the Q1 position. I chose this based on similar specifications, and although not identical it is fairly close with slight differences in capacitance.

IXTP08N50D2 IXYS | IXTP08N50D2-ND | DigiKey

I thought it would be worth trying as I really need to have that safety margin on the input voltage. Using a series dropping resistor may be OK, but with voltage surges it could easily get over 400V and any higher dropping resistor would not leave me the 20V margin for the regulator at 375V out.

I ran the regulator with 450V in for about 2 hours and there is no issues, and no noise or oscillation I also switched it on and off about 30 times, to 435V in, about where it will be operating, with no issues.

If possible, can you have a look at this FET and offer your feedback on whether or not this should be stable over the long term? Also, it's a fairly new device, and may not have been available yet when you designed the SSHV2.

Thanks for your help,
Gary
  Reply With Quote
Old 28th October 2012, 01:20 AM   #3398
Salas is online now Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Roger57, I could not see something strange in sim. To recap, those regs would never come to nominal Vout you set if turned on from mains with just a switch? Is that correct?
  Reply With Quote
Old 28th October 2012, 01:25 AM   #3399
Salas is online now Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Ah OK, we cross posted. C1 was not correctly in place then.
  Reply With Quote
Old 28th October 2012, 01:28 AM   #3400
Salas is online now Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
About the alternative 500V IXYS Mosfet, it looks good, even has bit more Vgs than the Supertex one under it its possible, that is good for stability in the CCS. Needs at least 20V across it for its Crss to get low region. Don't prefer to put it in the lower position that sets the current also, it may demand other trimmer values etc. and it will show more reverse capacitance at that low Vds position than the Supertex.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


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?

All times are GMT. The time now is 08:37 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2