# How to identify high side switch or low side switch? Is the circuit a high side or low side switch? Why?

I am in progress of analyzing a schematic. I have a major doubt and confusion.

The below circuit is for measuring the current and if the current reaches the threshold value the Mosfet will get switched off so it will cut the power between battery and the vehicle for protection. In this circuit they have used two MOSFETS for switching.

Are the below Mosfets connected as high side switches or low side switches?

I searched on Google and I got many results. I understood the concept but when I compare it with the circuit I am getting confused because both the sources are connected together.

Please explain which type and why when it comes to two mosfets.

Please tell me if it is high side or low side and why and also how to identify it.

simulate this circuit – Schematic created using CircuitLab

Figure 1. Examples of high-side and low-side switching.

• High and low in this case refers to the voltage rails - typically V+ being high and GND being low.
• High-side switches usually have their loads connected to the GND rail.
• Low-side switches usually have their loads connected to the V+ rail.

Low-side switching is popular because interface to microcontrollers, etc., is simple and allows a low-voltage control signal to switch a high voltage load.

Your circuit is badly drawn (battery voltage + at the bottom when convention is to have more positive voltages towards the top of the schematic) so you'll have a little more difficulty working it out. Can you?

High-side switches the load from +V. (closer to +V than the load)

Low-side switches the load from GND or -V. (closer to GND or -V than the load)

Simple, no?

So now, do you think Q7/Q8 is on the high-side? Or low-side?

Q7/Q8 are acting together back-to-back to make a bidirectional switch. Almost every discrete MOSFET has a parasitic body diode so can only block current in one direction. You can see them in the symbol for the MOSFET.