Adjustable power supply simulator/reality

Question

Hi im a student of computer engineering and im currently doing a project of a adjustable power supply it should be doing 0-30V but im getting some problems with the word adjustable haha,i got this circuit, it takes away every part of the PS that does not work with the adjust of the voltage.

On proteus this circuit runs fine, my teacher gave a circuit and there was some flaws, i searched on books for similar circuits because im tied to the components that i have, so more complex circuit and other components are not an option.

The simulation runs ok, RV1 does the main adjustment and RV2 the fine, but i cannot get this circuit to work on real life, im using a linear power supply to test and i get some short circuit protection to work some times, the circuit on the protoboard is just as on proteus, revised by tree people, there is no shorts or any mistake.

Is there anything that i am missing here? Im going by what proteus tells me on the simulation with some probes and other simulation tools, maybe this is the mistake.h

Answer 1

In a shameless bid for rep points, I'll expand on my comment.

The circuit is very simple, but not very good. Its biggest problem is that its output impedance is fairly high. In other words, its output voltage will vary with load resistance, which is what allows your fine adjustment to produce results. Ideally, of course, a voltage source will not vary with load, so your circuit is actually a demonstration of why an emitter-follower isn't all that great for this purpose.

That said, it does show the basic principles, or it should.

The circuit itself seems as though it ought to (approximately) work, but you may have read the TIP31 pinout wrong. Using the ordinary orientation/left-to-right reading, the pinout is BCE, not the CBE or EBC you might expect.

Answer 2

That looks like a decent stab at an emitter follower based regulator, with internal feedback (transistor beta). Assuming it is operating correctly, the output voltage should be around 0.7v or so less than the base voltage. I'm not sure what your RV2 is supposed to be doing. If the regulator is working correctly, it should have no effect on the output voltage. If you need a fine adjustment, then you should move RV2 so that it will adjust the transistor base voltage, possibly by placing it in series with the output of RV1. The only possible issue I can think of offhand is maybe you need to ensure a minimum load, though in your current circuit RV2 should provide this. Perhaps try a smaller load resistor and see what happens?

Also, can you take measurements of all the major circuit nodes (namely, the pins of Q1 and D1) and post these?