How to design a variable voltage supply?

Question

The output voltage should give 0-5 V with the maximum current of 500mA. should use 1 Op-Amp and 1 MOSFET (no commercial regulator chip).
the Voltage is varied using a potentiometer

I tried to do using circuit maker but the voltage step if too big when the potentiometer is varied

Answer 1

how is the voltage varied in your setup? try using a micro adjustment in your voltage selector if you are using resistance to vary the output.

Answer 2

You have at least two choices, both assume that the MOSFET is rated for well more than 500 mA at 5 V:
1. Use the FET as a variable resistance, with gain determined by the op-amp circuit as a gate driver. Not a really good choice, but it could be made to work.
2. Make a buck converter, with the FET as the main switcher and the op-amp as the gate driver. In this circuit, I would assume that the supply voltage is either a rectified ac (from a transformer wall wart) or directly from a battery. Create an astable multivibrator (oscillator) using the op amp with the potentiometer as the fine adjustment. Output of this controlled oscillator drives the FET gate. Be sure to use a suffciently large capacitor on the output of the FET, and be sure to ramp up the output on start-up, so you don't blow the FET while charging the cap initially.

A quick search on buck converters should yield a few example circuits. If you want to be really advanced, you could even make your own very low power single-phase DC-to-AC inverter. Good luck!

Answer 3

I guess there are many ways. I have used a simple Wall adapter and potentiometer playing around.
I not sure this link what you want, but, may give some ideas.
http://www.seattlerobotics.org/encoder/200112/variable.html

Answer 4

I recoment a wheatstone bridge.