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Series Pass Regulator question..

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randolfo

New Member
I have a question regarding series pass regulator. How you would know if the collector to emitter is shorted on emitter-follower transistor output assuming that there is 30 V power supply ? What voltage you would likely measure in the output ? Thank you... :D
 
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MikeMl

Well-Known Member
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NPN transistor? The series pass transistor is basically an emitter follower. The collector is at the unregulated, filtered voltage out of the rectifier/filter(~33 to 40V). The emitter is at the regulated output voltage(30V?). The base is at one Vbe (~0.7V) higher than the emitter voltage (30.7V)

PNP, everything is upside down.
 

randolfo

New Member
clarification..

if the load is 25 V (regulated voltage) and you measured 30 V at the output , what could you say about the emitter follower transistor ? is it shorted ? or there is other explanation why the output becomes 30 V ? please clarify.. thank you. Please see attached schematics...
 

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ericgibbs

Well-Known Member
Most Helpful Member
if the load is 25 V (regulated voltage) and you measured 30 V at the output , what could you say about the emitter follower transistor ? is it shorted ? or there is other explanation why the output becomes 30 V ? please clarify.. thank you. Please see attached schematics...

hi,
If the Vin is 30V and Vout is 30V I would say the series pass transistor is shorted, measure the base voltage.?

Whats the value of that load resistor R5.?

Whats the voltage across the zener.??
 
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mneary

New Member
There are several possibilities.

1) Q1 shorted
2) Q2 open or bad soldering
3) DZ open or bad soldering
4) R3 open or bad soldering
5) R4 wrong value, too low (or shorted)
6) Q2 backwards
7) common ground on power source and regulator not connected together.
 
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