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| Qa3qa3qa3:
Hi, can anyone help explain how the attached voltage regulator works ? Input is 240vdc output is 170vdc and 140vdc, it doesn't look like a shunt regulator, the circuit is faulty and i don't know how it works so i can troubleshoot it. Thanks |
| james_s:
It's a linear voltage regulator of fairly conventional design except it's regulating the negative side which is unusual. T1001 is the pass transistor which carries the load. IC1005 is a voltage reference and T1002 controls drive to the pass transistor by comparing a sample of the output voltage from the divider comprised of R1011 and R1012 with the reference voltage. The 140V output is not regulated, it's simply dropping the 170V output with a string of resistors, burning the excess voltage off as heat. What is the symptom of the fault? |
| srb1954:
--- Quote from: james_s on May 02, 2023, 05:02:12 pm ---It's a linear voltage regulator of fairly conventional design except it's regulating the negative side which is unusual. T1001 is the pass transistor which carries the load. --- End quote --- Regulating the negative side has the advantage that the pass transistor collector is at ground potential and can simply be heat sunk to the grounded metalwork without insulation. This circuit looks as though it has been designed down to a cost as the rest of the circuit is possibly a little bit simpler than what could be implemented in a positive side regulator. |
| Qa3qa3qa3:
Thank you so much, that really helped .. this is a part of the power supply circuit of a hameg 203-5 scope, I believe I directly screwed one of the TO220 packages down to the metal chassis of the unit, which was supposed to be insulated. Now the 170 rail is down to 25 volts and of course the unit is not working. I injected 170v from an external source to the rail and traces showed up and everything is normal. Now im trying to figure out what is wrong with the circuit. |
| james_s:
My guess is that T1001 failed open and now the load is being carried by R1005. You'll have to start testing parts though, there aren't very many of them. |
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