Power and Motor Electronics
Batteries and supplies, switching converters and thermal design, and driving motors and actuators.
Every circuit needs power, and some of them need a lot of it: a motor, a heater, a bank of LEDs. This guide covers where the power comes from (cells, adapters, linear and switching regulators), how to convert it efficiently and keep it cool, and how to drive the loads that need more current than a microcontroller pin can give (DC motors, steppers, servos and solenoids). It builds on Electronics Fundamentals, especially transistors and diodes, and the finished designs in Design, Testing and Troubleshooting put it to use.
Start here: what do you need?
| I need to… | Go to |
|---|---|
| choose a battery or estimate how long it will last | Batteries and Power Supplies |
| power a project from USB, a wall adapter or a bench supply | Batteries and Power Supplies |
| choose a linear regulator, or find out why it is hot | Batteries and Power Supplies |
| design a buck or boost converter, or pick its inductor and capacitors | Power Electronics: Buck, Boost and Thermal Design |
| work out efficiency, losses and heat in a converter | Power Electronics: Buck, Boost and Thermal Design |
| drive a DC motor with PWM, or reverse it with an H-bridge | Driving Motors and Actuators |
| drive a stepper, a servo or a solenoid, and protect against flyback | Driving Motors and Actuators |
| measure motor current, or limit it at start-up | Driving Motors and Actuators |
A suggested order
Start with the supply, then the converters, then the loads: motors need a good supply to work well.
- Batteries and Power Supplies: Cell chemistries, battery life, linear and switching regulators, bench supplies and current limiting.
- Power Electronics: Buck, Boost and Thermal Design: How switching converters work, choosing the inductor and capacitors, feedback dividers, efficiency and losses, heat and layout, with worked designs.
- Driving Motors and Actuators: Driving DC motors, steppers, servos, solenoids and relays from a microcontroller: PWM, H-bridges, MOSFETs, flyback protection and current sensing.
Quick reference: formulas
| Topic | Formula | Page |
|---|---|---|
| Linear regulator heat | P = (Vin − Vout) × I | Batteries and Power Supplies |
| Battery runtime | hours ≈ mAh × 0.8 ÷ mA | Batteries and Power Supplies |
| C-rate | C = I ÷ capacity (2 A on a 5 Ah pack: 0.4 C) | Batteries and Power Supplies |
| Buck duty cycle | D = Vout ÷ Vin | Power Electronics: Buck, Boost and Thermal Design |
| Buck inductor ripple | ΔI = (Vin − Vout) × D ÷ (f × L) | Power Electronics: Buck, Boost and Thermal Design |
| Efficiency | η = Pout ÷ Pin | Power Electronics: Buck, Boost and Thermal Design |
| Conduction loss | P = I² × RDS(on) | Power Electronics: Buck, Boost and Thermal Design |
| Junction temperature | TJ = TA + P × θJA | Power Electronics: Buck, Boost and Thermal Design |
| PWM average voltage | Vavg = D × Vsupply | Driving Motors and Actuators |
| Motor back-EMF | V = Ke × ω | Driving Motors and Actuators |
Calculators
- LM317 Adjustable Regulator Calculator: Output voltage, resistor values and heat in an LM317.
- Battery Runtime and Pack Calculator: Battery life from capacity and load, and series and parallel pack sizes.
- Ohm’s Law and Power Calculator: Any two of voltage, current, resistance and power give the other two.
- PCB Trace Width and Current Calculator: Trace width for a current and temperature rise.
Safety
- Lithium cells can catch fire if shorted, punctured or overcharged. Use protected cells, a proper charger and a fuse, and do not charge unattended.
- Motors store energy. A stalled motor can draw many times its running current, and the flyback spike when it is switched off can destroy a driver: fuse the supply and add flyback protection.
- Hot parts. Regulators, MOSFETs and inductors can burn: check the heat before closing an enclosure.
- Mains. Do not build or open mains-powered supplies unless you are qualified; use a certified adapter.
The other Electronics guides
- Electronics Fundamentals: The circuit basics every maker needs: Ohm’s law, resistors, capacitors, inductors, diodes, transistors and switches, with worked examples.
- Analog Circuits and Sensing: Op-amps, comparators and timers, and how to read, amplify and filter sensor signals: thermistors, RTDs, load cells and 4-20 mA loops.
- Digital Electronics and Microcontrollers: Logic gates, counters and timing, and the hardware around a microcontroller: power, reset, clocks, GPIO, level shifting, the ADC and buses.
- Design, Testing and Troubleshooting: Reading datasheets, keeping a design quiet, measuring a circuit, finding faults with flowcharts, and complete worked projects.
- PCB Design and Layout: schematic to layout, stack-up, routing, return paths and design checks.
FAQ
Should I use a linear regulator or a buck converter?
A linear regulator is simple and quiet, but wastes the voltage difference as heat. Above a watt or so of dropped power, or when running from a battery, use a buck converter; see Power Electronics.
How do I pick a motor driver?
Match the supply voltage and the stall current of the motor, with margin, and choose a driver with built-in flyback and current limiting for a first design; the page Driving Motors and Actuators has the details.
Why does my project reset when the motor starts?
The motor’s start-up current pulls the supply down. Use a separate or better-decoupled supply, a bulk capacitor and a flyback diode; see EMC and Noise at Board Level.
References
- Erickson, R. W. and Maksimović, D., Fundamentals of Power Electronics, 3rd ed., Springer.
- Battery University, BU-100 to BU-300 series on battery types and charging.
- Horowitz, P. and Hill, W., The Art of Electronics, 3rd ed., Cambridge University Press.
- Manufacturer datasheets and application notes for the parts you use: they give the limits, pinouts and example circuits.
Last reviewed: October 2026. Values are typical: check the datasheets of the parts you use, follow the electrical code for mains work, and do not work on live mains equipment unless you are qualified.