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Old 5th May 2010, 02:06 PM   #1061
Salas is offline Salas  Greece
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Quote:
Originally Posted by housing View Post
Hello Salas,

I have completed and tested the build of Simplistic Mosfet HV Shunt Regs

After the regulator is turned on and adjusting the VR, I got about 252 volts that slowly creeps to about 269 volts in an hour's time and settles down within +-0.5 volt. The voltage across the 33R is 1.803 and I assume that it's working perfectly. Am I right?

I also roughly measure the AC output ripple that's less than 0.5 mV using Fluke 189 but it's fluctating very rapidly (I know this is crude). Is the circuit oscillating? Should I use back IRFP9240 as the PMOS?

Thanks in advance for any response.

All the best,
housing
Shows 54mA constant current, the JFET comes to thermal stability and settles IDSS so the Vref comes up with time. Looks normal.

You can't tell its oscillating if there is no certain frequency caught. Is there a dummy load on its output?
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Old 5th May 2010, 02:11 PM   #1062
housing is offline housing  Hong Kong
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Originally Posted by Salas View Post
Shows 54mA constant current, the JFET comes to thermal stability and settles IDSS so the Vref comes up with time. Looks normal.

You can't tell its oscillating if there is no certain frequency caught. Is there a dummy load on its output?

Thanks Salas.

Yes, it's loaded with 5 pieces of 47K 20W resistors in parallel, 9.73K by measurement.
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Old 5th May 2010, 03:21 PM   #1063
Salas is offline Salas  Greece
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Originally Posted by regal View Post
A shunt regulator won't hold a constant voltage (it will drift with the mains.)

Two things you can do without a scope.

1. See if you have this sort of oscillation on your mains.
2. Hold an am radio up to the regulator board and see if you here interferance, if you do there is an oscillation problem.
Why drift with the mains? It has its own voltage reference, plus its CCS ''firewall''. The drift is thermal, then stops. No.2 is an all time classic.
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Old 5th May 2010, 04:50 PM   #1064
housing is offline housing  Hong Kong
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Why drift with the mains? It has its own voltage reference, plus its CCS ''firewall''. The drift is thermal, then stops. No.2 is an all time classic.
Yes, it's thermal drift. I'll try to improve it soon by adding mini heatsink to the 2SK170 and changing the VR to 15 ppm vishay trimpot. I've used 5 ppm S106K (?) 135K (2 x 200K S104K + 2 x 70K S102K) resistor as voltage reference.
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Old 5th May 2010, 05:07 PM   #1065
Salas is offline Salas  Greece
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Best is a low ppm resistor instead of trimpot if the application will be fixed after measuring the set trimpot value. The JFET will always slide a bit more IDSS with time until its equilibrium, its inherent to translate enough in a large voltage Norton source, but a mini sink on it may help it do it less. Shoot for the final voltage value as nominal. If it was a Zener it would be much more noisy and its filter cap would be a large electrolytic due to low impedance. Both detrimental to subjective tests. Don't use carbon composition resistors as reference under the JFET, even if they are nice in signal even if Riken and the like. They are large ppm and noisy relatively. You did well to use low ppm.
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Old 5th May 2010, 05:43 PM   #1066
housing is offline housing  Hong Kong
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Quote:
Originally Posted by Salas View Post
Best is a low ppm resistor instead of trimpot if the application will be fixed after measuring the set trimpot value. The JFET will always slide a bit more IDSS with time until its equilibrium, its inherent to translate enough in a large voltage Norton source, but a mini sink on it may help it do it less. Shoot for the final voltage value as nominal. If it was a Zener it would be much more noisy and its filter cap would be a large electrolytic due to low impedance. Both detrimental to subjective tests. Don't use carbon composition resistors as reference under the JFET, even if they are nice in signal even if Riken and the like. They are large ppm and noisy relatively. You did well to use low ppm.
Thanks Salas for your advice.
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Old 8th May 2010, 11:24 AM   #1067
regal is offline regal  United States
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Why drift with the mains? It has its own voltage reference, plus its CCS ''firewall''. The drift is thermal, then stops. No.2 is an all time classic.
According to Broskie, shunt regulators will drift with the mains. In other words if you plug in a 1500W heater on the same circuit as the shunt reg the reg wil still kill ripple but the output voltage will drop.

If your shunt reg doesn't do this I'd be very surprised but enthused because I have a hybrid amp with a dc servo that is very touchy to any changes in B+.

Can you measure the output of your reg by turning on a heater and monitoring the B+ voltage to see if it moves? Now your mains may be such that it doesn't shift when turning on a high wattage device plugged into the same circuit so you would need to check that to.
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Old 8th May 2010, 11:26 AM   #1068
housing is offline housing  Hong Kong
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Originally Posted by regal View Post
According to Broskie, shunt regulators will drift with the mains. In other words if you plug in a 1500W heater on the same circuit as the shunt reg the reg wil still kill ripple but the output voltage will drop.

If your shunt reg doesn't do this I'd be very surprised but enthused because I have a hybrid amp with a dc servo that is very touchy to any changes in B+.

Can you measure the output of your reg by turning on a heater and monitoring the B+ voltage to see if it moves? Now your mains may be such that it doesn't shift when turning on a high wattage device plugged into the same circuit so you would need to check that to.

Hi Regal,

This is defintiely thermal drift. I have tested it with a swinging fan blowing against the PCB and the voltage dropped 5 volts almost instantaneously.
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Old 8th May 2010, 11:29 AM   #1069
regal is offline regal  United States
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Originally Posted by housing View Post
Hi Regal,

This is defintiely thermal drift. I have tested it with a fan and the voltage dropped 5 volts almost instantaneously.
Big fan or little fan? Could be your mains dropped when the fan turned on?

Still interested in hearing reports on if the voltage changes with the mains.


Sounds to me that you need a bigger heatsink if blowing a little air on it causes that much change in voltage.

Last edited by regal; 8th May 2010 at 11:35 AM.
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Old 8th May 2010, 11:37 AM   #1070
housing is offline housing  Hong Kong
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Originally Posted by regal View Post
Big fan or little fan? Could be your mains dropped when the fan turned on?

Still interested in hearing rports on if the voltage changes with the mains.


Sounds to me that you need a bigger heatsink if blowing a little air on it causes that much change in voltage.
Mains dropped when the fan turned on? That's impossible. I have a 100Amp 3 phase 220V supply. Moreover the drop in the HV shunt regulator then remains at about 265 volts.

That doesn't concern the heatsink. It's about thermal equilibrium. It's the Jfet's Id that's sensitive to temperature change and it's inherent in the circuit.
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