This is the final schematic, everything is now tested, and working. Had a little trouble, until I realized I had put a PNP transistor in place of Q6.
Refering to the figure in LAB Power Supply taking shape here is the run down on the last parts.
- is the current limiting circuit on the positive rail. When the voltage across the current sense resistor R1 rises above 0.65V the transistor, Q3, will begin to conduct, stealing base current from the pass transistor. This will make the output voltage fall, until the voltage loss in R1 is back at 0.65V. The value of resistor R1 sets the current limit, using Ohms law it is easy to calculate resistor value for a 1A current limit, (R=U/I), R1=0.65V/1=0.65Ω. The closest value is 0.56Ω, which gives a current of 0.65V/0.56Ω=1.16A.
- is the negative current limiting circuit. Q10 and R14, is the mirror circuits of Q3 and R1. Since the negative rail tracks the positive one, the negative voltage will drop, when the positive current limit kicks in. The positive rail, is not tracking the negative, and the positive voltage, will not drop, when the negative current limiter kicks in. Arguably, there will be no over-current problem, on the positive rail, if the positive current limit is not activated. For completeness, Q6 will turn down the voltage of the positive rail, when the difference between the positive and negative rail becomes large enough to make the voltage at the junction R9, R13 more than 0.65V
Well it seems the power supply is working, I have made a PCB design,
that I will perfect, and publish when done.
Generated on 2018-05-03 01:14:21.906467