I'm trying to further my understanding of electronics, so I decided to try to design a fixed voltage regulator capable of supplying an amp or so. I put this together from first principles without referring to any kind of reference on how voltage regulators are usually designed.
My thoughts were:
- Zener and resistor to provide a fixed voltage reference.
- Comparator to detect when the output voltage was above the target threshold.
- Transistor to switch the supply on and off.
- Capacitor to act as a reservoir.
With that in mind, I designed this fixed 5V regulator, which appears to work:
What I did notice, however, is that it has certain limitations which I can't quite derive the cause of:
- The current from V1 (input) roughly equals the current at R2 (output), despite differing voltages. This seems to match the behaviour of linear voltage regulators (is that what I just created?) but I'm not sure why it happens. Why is so much power dissipated from Q2 considering it's just switching on and off?
- When V1 is less than about 7.5V, the output voltage never hits the 5V threshold, but instead hovers around 4V. I have tried this with varying loads but it simply does not function below that input voltage. What is the cause of this?