Designing a Constant Current Source with Varying Loads


I've designed a constant current source using a current mirror, we need an output of about 50mA. The problem is that we build it and heat has become a problem.The transistors and the R_load are both heating up which decreases beta stabilization (our amperage through our load resistor increases constantly).
Original current source design
I think that by adding an emitter resistor we should be able to beta stabilize but I'm not sure if I'm doing it right.
Current source design with emitter resistor

Best Answer

Given the very large head-room you have available from your primary supply, you should be able to just use the 7805 in current regulator mode:


simulate this circuit – Schematic created using CircuitLab

This would accomodate a wider range of load resistors if you could swap the 7805 out for a chip with a lower reference voltage and lower drop-out voltage.