This is the circuit of a power supply with adjustable output voltage and current, and I wish to understand how it works:
R1 T1 VD5 - they form a voltage divider which provides a voltage referrence that is applied through a voltage divider formed by R3 to the input of a common collector amplifier formed by T2, T3 and T4. This allows us to set a desired output voltage by varying the base voltage on T2.
R6 is used to create a voltage drop, to measure the output current, which is set by R8. To limit the current, T5 loweres the referrence voltage.
What I don't understand:
Is C3 used to filter fluctuations which occur too fast for the zener to react?
What is the purpose of R4 and R5? And what is the purpose of R7, C4 and C5?
How exactly does T1 work? And why does the LED only come on when the current limit is reached? It looks to me that it should be on all the time.
Sorry for my english. And I hope my questions aren't too dumb.
PS: Is it possible to replace the output transistors T2, T3 and T4 with a MOSFET?