Electronics > Projects, Designs, and Technical Stuff
Simple DIY Linear PSU
xavier60:
--- Quote from: panoss on March 14, 2020, 09:48:48 pm ---Input voltage: 12V.
RL=20 Ohms.
Q2:
Ve=11.67V
Vb=10.83V
Vc=11.58V
Q3:
Ve=11.66V
Vb=11.59V
Vc=10.30V
--- End quote ---
The voltages for Q2 look about right. 0.84V B-E voltage means it is being driven hard for its size which is expected.
Voltages for Q3 only make sense if the Vc and Ve are swapped? B-E voltage of 1.29V means that it's being stressed also.
Looks like output voltage setting is higher than what's available. Try decreasing the setting.
You need to get the proper transistors for it. Don't test at more than 500mA for now.
When it's happily regulating, the Base of Q1 should drop to a lower voltage and the CV op-amp's input voltages will be the same as each other.
xavier60:
The D45H11 and 2x TIP35C combination in my bench supply project have a total current gain of about 10,000.
Q1 only needs to sink about 1mA for 5 amps of output.
There needs to be another 3 or so milliamps reserve to drive Q2 deep into saturation as the regulator approaches its dropout state of about 0.9V.
I have some minor changes in mind that will allow the regulator to work better with low input voltages. I would like to see it working properly first of all.
panoss:
--- Quote from: xavier60 on March 14, 2020, 10:14:10 pm ---
--- Quote from: panoss on March 14, 2020, 09:48:48 pm ---Input voltage: 12V.
RL=20 Ohms.
Q2:
Ve=11.67V
Vb=10.83V
Vc=11.58V
Q3:
Ve=11.66V
Vb=11.59V
Vc=10.30V
--- End quote ---
Voltages for Q3 only make sense if the Vc and Ve are swapped? B-E voltage of 1.29V means that it's being stressed also.
--- End quote ---
Vb=11.59V Ve=11.66V
Vb-e=-0.07V
That is, b is lower than e for 0.07V. (So Q3 is in cutoff?)
You made a mistake: you swapped Ve with Vc (Vb=11.59V Vc=10.30V , this is a difference of 1.29V)
xavier60:
Q3 is NPN. Its Collector should connect to the input rail and should always be more positive than its Emitter which should connect to the output rail.
panoss:
Indeed...you 're right Xavier...I had swapped C & E in Q3 and Q4... (omg... :palm:.. I 'm gonna hide in some cave...In Eagle, I had connected Q3 and Q4 to a PNP package...:palm: )
Ok, I corrected it:
RL=no load, Vout=11.39V
RL=20 Ohms, Vout=10.82V
RL=10 Ohms, Vout=10.55V
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