Circuits That Change
Power Supplies & Regulation
13 min · 2 worked examplesFree
Turning an unhelpful voltage into a stable one, and choosing between the simple option and the efficient one.
After this lesson you can
- Choose between a linear and a switching regulator
- Work out how much heat a linear regulator will make
- Say what capacitors a real supply needs around it
Linear regulators
A linear regulator holds its output constant by dropping the surplus voltage across an internal transistor. It is simple, quiet and cheap, and it wastes everything it drops.
Dissipation is (Vin − Vout) × I. Dropping 12 V to 5 V at 500 mA burns 3.5 W as heat, more than most small circuits consume, and enough to need a substantial heatsink.
Efficiency is therefore just Vout/Vin: about 42% in that example. It also has a dropout voltage, a minimum headroom below which regulation fails, so a 5 V regulator with 2 V dropout cannot be run from a nearly flat 6 V battery.
Use linear regulation for small currents, small drops, or where switching noise would be unacceptable, near an ADC or an RF stage.
In the full lesson
- Linear regulators
- Switching regulators
- What a real supply needs around it
Free with an account. Read it, work the examples, answer the questions, then build it in the simulator.