Simplistic Mosfet HV Shunt Regs - Page 312

Salas · 28th July 2012, 11:41 AM

GR is especially drifty in this situation. Use BF245A.

studiostevus · 30th July 2012, 09:40 AM

Hi Salas, I fixed my earlier problem. Turned out I had wired the tube rectifier wrongly.
I have the dual mono shunt regs up and running now. A quick listen gave good results, and scope measurement gave a complete flat line, so virtually noise free.

I did notice that the red LED on one of the regs is much brighter than on the other one. CCS and voltage settings are exactly the same (300mA @ 170V), and I have used the components from tea-bag's component GB (I assume they are the same make leds).

As I said, both measure and sound very good. Do you see any problems I am unaware of?

Salas · 30th July 2012, 10:05 AM

Maybe 30mA at 170V? The Led is in series with the voltage reference's CCS in SSHV2. For same reference resistors you must be running the same JFET Var CCS current by Ohm's law in the twin SSHV2 regs to have the same output voltage. Odds are you got different Vref resistors by mistake, one different brightness LED, local oscillation that dims the one. But you got a clean rail you say. What is it for? Have you got more pics?

studiostevus · 30th July 2012, 10:50 AM

Sorry, indeed 30mA at 170V, both CCS and Voltage set with variable resistors.

What do you mean with "For same reference resistors you must be running the same JFET Var CCS current by Ohm's law in the twin SSHV2 regs to have the same output voltage."

Salas · 30th July 2012, 10:54 AM

There are 68K + 68K in series biasing up the cascode error amp BJTs and developing the ref voltage. To have same Vo the Jfet CCS above must be running same Iref. So both leds in the twin regs should be running the same current...

kacernator · 05:23 PM

What do you think about osund difference betwwen IRF840 and IRFP450 at shunt position? IRFP450 has twice transconductance, but also twice capacitance.
Is it the same effect as in position where IRF9610 is?

Thanks.

Salas · 3rd August 2012, 05:29 PM

Will change basic parameters. It could even oscillate, but it takes full analysis to predict. Generally expect: Slower, less bandwidth, less output impedance, steeper impedance rise with frequency.

eboz · 13th August 2012, 04:39 AM

Hi,

I am having a bit of a strange behavior with the original SSHV design. I configured the circuit so that it would output 300vdc, ~12ma with 350vdc, 45ma input. The regulation seems to work fine, except when connecting and disconnecting a multi-meter to either the raw DC supply or to measure the output. What happens, is that the voltage sharply drops from 300v down to about 150v, until the trimmer is adjusted. I can bring the correct voltage back by turning the trimmer one way, and the voltage jumps back up around 200v. Then I can adjust it back to 300v. If I connect or disconnect a meter, either on the raw or output of the regulated supply, it will again jump back down in voltage. I have two multi-meters, and observe the same behavior when connecting either of these meters to the raw or output voltages. I even have two of these SSHV1 boards, and both of them behave the same way. I'll attach the schematic and board layout.

Regards,
-MW

Salas · 13th August 2012, 09:47 AM

Make R10 4K7, see if its stabler.

AndrewT · 13th August 2012, 10:06 AM

How hot does R9 become? Be careful it has a lot of volts across it !

3rd August 2012, 05:05 PM	#3116
kacernator diyAudio Member Join Date: Jan 2008	SSHV1 What do you think about osund difference betwwen IRF840 and IRFP450 at shunt position? IRFP450 has twice transconductance, but also twice capacitance. Is it the same effect as in position where IRF9610 is? Thanks. Last edited by kacernator; 3rd August 2012 at 05:23 PM.

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28th July 2012, 11:41 AM	#3111
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	GR is especially drifty in this situation. Use BF245A.

30th July 2012, 09:40 AM	#3112
studiostevus diyAudio Member Join Date: Oct 2009 Location: Brunei	Hi Salas, I fixed my earlier problem. Turned out I had wired the tube rectifier wrongly. I have the dual mono shunt regs up and running now. A quick listen gave good results, and scope measurement gave a complete flat line, so virtually noise free. I did notice that the red LED on one of the regs is much brighter than on the other one. CCS and voltage settings are exactly the same (300mA @ 170V), and I have used the components from tea-bag's component GB (I assume they are the same make leds). As I said, both measure and sound very good. Do you see any problems I am unaware of?

30th July 2012, 10:05 AM	#3113
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Maybe 30mA at 170V? The Led is in series with the voltage reference's CCS in SSHV2. For same reference resistors you must be running the same JFET Var CCS current by Ohm's law in the twin SSHV2 regs to have the same output voltage. Odds are you got different Vref resistors by mistake, one different brightness LED, local oscillation that dims the one. But you got a clean rail you say. What is it for? Have you got more pics?

30th July 2012, 10:50 AM	#3114
studiostevus diyAudio Member Join Date: Oct 2009 Location: Brunei	Sorry, indeed 30mA at 170V, both CCS and Voltage set with variable resistors. What do you mean with "For same reference resistors you must be running the same JFET Var CCS current by Ohm's law in the twin SSHV2 regs to have the same output voltage."

30th July 2012, 10:54 AM	#3115
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	There are 68K + 68K in series biasing up the cascode error amp BJTs and developing the ref voltage. To have same Vo the Jfet CCS above must be running same Iref. So both leds in the twin regs should be running the same current...

3rd August 2012, 05:29 PM	#3117
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Will change basic parameters. It could even oscillate, but it takes full analysis to predict. Generally expect: Slower, less bandwidth, less output impedance, steeper impedance rise with frequency.

13th August 2012, 09:47 AM	#3119
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Make R10 4K7, see if its stabler.

13th August 2012, 10:06 AM	#3120
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	How hot does R9 become? Be careful it has a lot of volts across it !