normal mosfet vs power mosfet?

I have been googling this for a while now and still don't understand what the difference is? Are they operated the same? does the power mosfet have a higher current rating?

Hi, the main difference is the current capacity, and gate capacitance, this is dictated by the conducting channel in the transistor and it resistance when it is turned ON, this parmeter is called Ron.
Power MOSFETs have much lower Ron than other low power signal types.
This means that when ON the power loss through the MOSFET is minimised.
The physical construction of the semiconductor plays a big role in how this is accomplished.
The link below does a good job of describing the differences.

Hope this helps without going into heavy semiconductor theory.

Tom… :slight_smile:
PS this site if you work through it has some good animations to demonstrate the theory.

Same difference as calling something a NPN or PNP transistor or a power transistor. It's rather subjective as I don't believe there is any official specification that a power transistor is any transistor that handles above a specific voltage/current amount. If there was such an agreement of definition I would suggest a certain maximum power dissipation specification would be best.

A "power MOSFET" tends to come in a package which has a flat metal plate at the back to bolt to your heatsink or piece of scrap Aluminium. Those are necessary if you plan to switch "more than 0.5 Amps". A "normal" MOSFET tends to be available in a 3-legged black plastic thing which might burn out if you go over about half of its rated max current.

The internal design might place hundreds of normal mosfets on a square mm of silicon, and/or use a bigger mosfet for commensurately more current.

To use them, first get the right type. A P-FET is better for high side switching interrupting say a +12V line above your arduino, but that needs a few extra components. An N-FET is available with Vgs in the right range to be fully on while your arduino output pin is "high" and fully off while your arduino pin is "low". Those are better for interrupting a heavy 0V line between your power supply and your load. Take care that your ardino is on the right ground.

So, not all mosfets are the same and be sure to read the datasheet before buying any. Avoid if possible anything which needs more than 5V Vgs to switch it as those would need extra things to avoid the 'half on' state which tends to make it hotter than needbe.

If you wanted to buy something to dabble with, I'd recommend the 1N2700 "normal" nfet. Those are good for switching up to hundreds of mA from an arduino output pin, though a few k ohm resistor between arduino digital out and gate is sensible extra protection. Then you can switch things like a 12V torch bulb at 120mA without worrying about the 200Ohm internal limit in the arduino digital out pins.


Switching, small signal, and Power??

123Splat: Lefty,

Switching, small signal, and Power??

If that is a question I don't understand what you are asking?

TomGeorge: Hi, the main difference is the current capacity, and gate capacitance,

And the price.

Physically, a regular MOSFET will have all three terminals on the top of the die. PowerFets are usually a DMOS variant and use the bottom of the chip as a device terminal.

High power MOSFETs always have the substrate as drain terminal with vertical current flow.

MarkT: High power MOSFETs always have the substrate as drain terminal with vertical current flow.

Not LDMOS. That has the source on the substrate.