Go Down

Topic: Trouble powering 12V fan with MOSFET (Read 2136 times) previous topic - next topic

smoras

Feb 01, 2015, 01:42 am Last Edit: Feb 01, 2015, 02:26 am by smoras
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

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

smoras

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?

zoomkat

Google forum search: Use Google Search box in upper right side of this page.
Why I like my 2005 Rio Yellow Honda S2000  https://www.youtube.com/watch?v=pWjMvrkUqX0

smoras

Logic level MOSFET.

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

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

-dev

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.  :)

Cheers,
/dev
Really, I used to be /dev.  :(

MarkT

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.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

-dev

> 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.  :)

Cheers,
/dev
Really, I used to be /dev.  :(

runaway_pancake

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.
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

Go Up