The simplistic Salas low voltage shunt regulator

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#3,461
merlin el mago said:
It's not clear, when you said 5V across R1 is the dummy load right?
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Oh - that's the trouble! The 5V should be across R1, which is the current-setting resistor.

The dummy load goes in the place of the Heater of the 6922. The voltage across the dummy load should be 0,3 x R(dummy).

The dummy load value is not too important, it's just to check that the current is correct.

When you connect the 6922 the voltage should be about 6,1 to 6,2V - BUT you may need to make small changes to R1 until it is correct.
 
#3,462
Rod Coleman said:
Please ignore the Quanghao drawing, unless you want to change to a much lower power supply, and use this totally different circuit!

If you have a 17-18V supply, 9,2V across the LEDs, you should be OK. Just check for 5V across R1, then change the value of R1 until you get 0,29 to 0,30A
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With R1 15R & dummy load 16R I read 1.99V across the dummy load & 1.85V across R1
 
#3,463
If you get 1.85V across R1, and you have 9.17V across LEDs, then the FET gate voltage is 7V. That does not sound right!

One possibility is that the circuit is oscillating. This can give confusing readings on a DVM! Do you have a big capacitor on the supply voltage, right near the circuit?
 
#3,465
Rod Coleman said:
If you get 1.85V across R1, and you have 9.17V across LEDs, then the FET gate voltage is 7V. That does not sound right!

One possibility is that the circuit is oscillating. This can give confusing readings on a DVM! Do you have a big capacitor on the supply voltage, right near the circuit?
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Yes
 

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#3,466
Rod Coleman said:
Quanhao schematic is NOT OK. There is likely to be stability problems, if you build the circuit like that.

I notice that Quanghao is attempting to sell filament regulators on his site, using design elements copied from my DIY kit filament regulators (he bought one last month to get a closer look). I should make it clear that, although he is using my description "Gyrator + CCS" filament regulator, this circuit is not designed by me, nor am I able to support it. AND, If the snapshot above is used in the regulator, there is VERY likely to be trouble from oscillation, and other effects as well.

The parts of the design taken from my kits were used without the politeness of asking if it was OK.
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Typical Quanghao move. I would like to add another warning to everybody. Quanghao often makes mistakes in his schematics. If you can get over the ethical issues and will get boards/kits from Quanghao, make sure you check the schematic thoroughly.
 
#3,468
OK to have PSU/diodes separate, but please take care that you have 1000uF near to Q1.

If the circuit is stable (is not oscillating), you should have 4V (approx) across GATE- to SOURCE of the IRF9610.

If you have 7V here, I suspect FET trouble, or oscillation. If you bring a AM-radio nearby (tuned to a weak station), do you hear the radio crackling, when the circuit is powered ON?
 
#3,470
Rod Coleman said:
OK to have PSU/diodes separate, but please take care that you have 1000uF near to Q1.

If the circuit is stable (is not oscillating), you should have 4V (approx) across GATE- to SOURCE of the IRF9610.

If you have 7V here, I suspect FET trouble, or oscillation. If you bring a AM-radio nearby (tuned to a weak station), do you hear the radio crackling, when the circuit is powered ON?
Click to expand...

Is not 1000uF is 100uF 25V.

I have 7.3V gate-source irf9610
 
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