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High side switching vs low side switching

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shortbus=

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Not true. A high side switch will be a P channel with the source being the source of a positive constant voltage.
A low side switch will be an N channel with the source connected to ground, thus switching it off will isolate the ground.

The high side switch can be used to power the entire circuit on and off. A low side switch can do similar but can cause problems with floating grounds when switched off.
A low side switch is great for switching bulbs on and off due to the fact most N channel FETs have a lower Rds on, but if you want to switch an ampliying stage for example can lead to a world of hurt.

What you said is not completely true either.

Nmos is the most widely used type, for both high and low side.

A low side switch is the easiest type to use to control anything that only needs on and off. Or a motor that doesn't need to be reversible.

Pmos usually has a lower Rds and voltage drop. Though some of the newer generation Nmos are getting close to the Pmos values.

Nmos is the normal low side switch, because it can be controlled with a positive voltage on the gate. Pmos needs to have a lower voltage than the Vsd to turn it on. Meaning that in a low side switch, with drain at 0V/common, you need ~ -10V to completely turn it on.
 

ChrisP58

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Most Helpful Member
The terms high-side and low-side have nothing to do with what the switching device is, but only where it is with respect to the load. A high-side switch will be between the positive supply and the load, and a low-side switch will be between the load and the negative (or ground) supply.

The switching device itself can be almost anything. Nmos, pmos, PNP, NPN, relay, a mechanical switch, thermostat, etc.
 

WTP Pepper

Active Member
Pmos usually has a lower Rds and voltage drop. Though some of the newer generation Nmos are getting close to the Pmos values.

Not from my experience they don't.

As for the rest, I think I already said as much.
 
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