How to use MOSFET for Hide Side Switching

 

I've crafted a circuit designed for high-voltage (up to 100V) and high-current (up to 33.6A) applications, specifically for switching loads on the high side. The carefully selected P-Channel MOSFET, Q1, boasts low ON resistance. To safeguard against exceeding the maximum gate-source voltage (VGS), I've incorporated R1 and R2. Another option involves including a Zener diode across the Gate and Source. In addition, a small signal N-Channel MOSFET, Q2, effectively controls the ON/OFF switching of the N-Channel MOSFET. When the ON/OFF control is low, Q2 remains OFF. Conversely, when it's high, Q2 activates, thereby reducing the P-Channel gate voltage via R2 and effectively limiting the current.

Relay Circuits

Momentary Relay Activation Circuit

The relay will energize momentarily until the capacitor is fully (or partially) charged.

Protection Diodes for Relays

The relay coil produces brief high-voltage spikes when switched off. These voltage spikes can destroy transistors and ICs in the circuit. To prevent damage, a protection diode must be placed across the relay.