Trouble powering 12V fan with MOSFET

Basically I want to automatically regulate the speed of a 12V fan on a microcontroller using an N-channel MOSFET (IRF-510), but I'm having trouble making the fan go on full speed.

Before even trying to use a microcontroller, I attempted to power the fan on just using 5V on the gate, drain connected to one end of the fan, 12V from a computer PSU connected to the other end, and everything connected to common ground (source and ground of PSU).

Can someone tell me what I am doing wrong? If I simply connected the PSU directly to the fan you can definitely tell it wasn't on full speed before. I'm assuming its an issue with the amperage from the drain to the fan?

What can I do to remedy this issue? The IRF-510 should have sufficient maximums to power on the fan. Link to the transistor I'm using: http://www.vishay.com/docs/91015/sihf510.pdf

What you need is a logic level gate mosfet. The gate needs to be fully on or the resistance of the drain/source is not at its least so causes heat.
My favourite small mosfet is NTD5867NL. It works with 5v on the gate and handles a few amps with ease. They are cheap. I bought mine from RS Components.
There are others but make sure they are fully on at 5v on the gate.

Weedpharma

weedpharma:
What you need is a logic level gate mosfet. The gate needs to be fully on or the resistance of the drain/source is not at its least so causes heat.
My favourite small mosfet is NTD5867NL. It works with 5v on the gate and handles a few amps with ease. They are cheap. I bought mine from RS Components.
There are others but make sure they are fully on at 5v on the gate.

Weedpharma

Okay, I will definitely check this one out. Would it work well with PWM to regulate the speed of the fan?

Logic level MOSFET.

zoomkat:
Logic level MOSFET.

https://www.sparkfun.com/products/10213

Thanks! Can you explain the difference between logic level mosfet and power mosfets?

FYI, there's a chart in the spec that shows what's a happening:

It will only allow about 1A. Spec reading is good for the soul, but sometimes it's something of an art. :slight_smile:

Cheers,
/dev

There is no difference, a logic level MOSFET is a power MOSFET. Its just that its one that only
requires 4.5V or so on the gate to switch on. 10V is much more common. MOSFET in these
forums always means power MOSFET in practice.

A power MOSFET is basically one with a body diode and a low on resistance (an ohm or less,
usually). Small logic MOSFETs are often symmetrical with source and drain equivalent,
in a power MOSFET the source and drain are completely different.

> What's the difference?

Err... they are fully turned on with logic levels of 3-5V. Again, from the spec for the suggested FQP30N06L:

You can see that the 4th curve from the top (for Vgs=5.0V), and a Vds=11V, it will allow ~60A. Ha! Let's just say it's fully turned on, and looks like a 0.035 resistor. :slight_smile:

Cheers,
/dev

I could suggest an interface using an NPN and a couple of resistors you may have and then rig that up to switch the IRF FET with.