Intro

Now there are many integrated solutions (chips), that specially designed for switching powering, but today we'll take a look at the simple basic solution, that can commutate power with using only discrete components – several MOSFET's and resistors.

Structural Block Diagram

Typically load switches switch positive rail, so we will do the same.

Electrical Schematic

*R2 could be changed to shortcut

The main switching element is P-CH MOSFET, when

• Vg = Vs CLOSED
• Vg = 0V  OPEN

Additional N-CH MOSFET give a chance to invert control logic and work with push-pull GPIO control with VIN higher than MCU VCC (e.g. 5V).

Simulations

The following simulations performed in MicroCap 12 ((Analysis -> Dynamic DC...) Alt+4 shortcut). LEDs with current-limiting resistors only for work demonstration purposes.

MCU_GPIO = 0V (LOW) → DISABLED

When control signal is LOW (about 0V) the output voltage is near zero (load not powered).

MCU_GPIO= 3.3V (HIGH) → ENABLED

When control signal is HIGH (about Vgs threshold of X2 (for logic controlled about 1V min)) the output voltage is near zero (load not powered).

Real Prototype

*X1 transistor is physically upside down

* Pull-up resistors 4.7k for other purposes, don't pay attention to them

Tests

Input Voltage

VIN = 5V

❎ Switch disabled

✅ Switch enabled

And here is how it works in real time:

Results

Conclusions

This simple schematic typically used for control power (switch) of low-voltage (typically 3.3V-5V) small power loads (typically up to 3A) Using standard widespread SOT-23 MOSFETs and 0603/0805 resistors make a schematic far enough small for DIY devices Discrete components give a chance to not use ICs in short supply In comparison to the integrated power switch solution this schematic doesn't have: current limitation; output discharging; reverse current blocking; soft start (this feature can be added by placing cap between X1 gate and source).