An ESP32 that resets, a sensor that gives strange readings or Wi-Fi that drops out: the power supply may be the cause, but wiring, software or an incorrect logic level can produce similar symptoms. Check the supply voltage at the board while the circuit is under its real load.
A good supply does more than provide the correct nominal voltage. It must keep that voltage within the limits of the exact board or IC during start-up, current peaks and normal operation.
Start with the circuit requirements
Record the required voltage, the highest current during start-up and operation, and the permitted ripple or voltage dip. Use the documentation for the exact board or IC. For the original ESP32, Espressif recommends a 3.3 V supply capable of at least 500 mA. This is a design requirement for that chip family, not a universal consumption figure for every ESP32 board.
The same applies to relays, motors and displays: measure not only with no load, but also at the load while it is active.
Linear regulator: simple, but check the heat
A linear regulator turns the voltage difference into heat: Ploss = (Vin - Vout) × I. From 9 V to 5 V at 1 A, that is 4 W.
The L7805CV can supply up to 1.5 A under specified conditions. Always check dropout, ambient temperature, thermal resistance, mounting and maximum junction temperature. Use these values to determine whether additional cooling is required.
Switching regulator: check the operating point
A buck converter is often more efficient when the voltage difference is large, but efficiency depends on input voltage, output voltage, load, inductor, diode, PCB layout and temperature. Do not use one universal efficiency figure.
The LM2574 and LM2576 families target approximately 0.5 A and 3 A respectively, subject to the exact datasheet's component, layout and thermal conditions. For more current, for example, see the LM2576D2T-ADJ.
Cables, connectors and decoupling
Measure voltage at the load. Adapter, connector, cable and PCB traces all contribute to voltage drop. Cable type or price alone does not tell you how much voltage will be lost under your load.
Follow the datasheet or reference design for the exact IC or board. Place the specified decoupling capacitors close to the relevant supply pins; do not automatically use the same values in every design.
Practical check
- Determine voltage, peak current and permitted ripple.
- Check the exact datasheet and reference design.
- Calculate linear loss or check buck efficiency at your operating point.
- Size cables, connectors and the thermal path.
- Measure both with no load and under the real load.
Browse adapters and power supplies or DC-DC converters. Not sure what to measure? Start with using a multimeter.