MOSFET and PWM question

[Spadez]

Hi.

I was looking to use LM317's to change the voltage to a pump, but infact I am going to look at software PWMing them via MOSFET. If this does not work at a high frequency I will reduce the frequency until it may be on for a few seconds even.

The pumps are 12V with around 1A start up current. What mosfet would be a good choice for this?

Thank you.

 

[ronv]

An IRF540 would work. It is cheap and available almost everywhere. Maybe a little overkill, but hey.

 

[birdman0_o]

What will generate the PWM?

 

[Spadez]

A PIC microcontroller.

 

[crutschow]

The IRF540 requires 10V on the gate for proper switch operation and thus is not suited to being driven by a PIC output. To operate from 5V logic levels, you need a logic-level MOSFET such as this.

 

[Spadez]

Thank you for the reply. I just brought two of these:

IRL520 HEXFET POWER MOSFET, IRF on eBay (end time 11-Dec-10 19:16:25 GMT)

Is it correct that these can turn on a 12V ~1A load using the PIC as the driver? From what I can see on the datasheet it seems to say to but I would just like to confirm it before I intergrate it into my circuit.

 

[crutschow]

Thank you for the reply. I just brought two of these:

IRL520 HEXFET POWER MOSFET, IRF on eBay (end time 11-Dec-10 19:16:25 GMT)

Is it correct that these can turn on a 12V ~1A load using the PIC as the driver? From what I can see on the datasheet it seems to say to but I would just like to confirm it before I intergrate it into my circuit.

Did you not read my previous reply?

The datasheet shows that the IRL520 requires 10V gate voltage to fully turn on as a switch. To turn it on from a PIC you will need to add a transistor driver to supply this 10V (or 12V if you have that available) to the IRL520's gate.

 

[Spadez]

Your previous reply talks about the IRF540 needing 10V. In your post you describe the IRF520 as a logic level MOSFET so this is what I brought. I am now thoroughly confused.

 

[crutschow]

Your previous reply talks about the IRF540 needing 10V. In your post you describe the IRF520 as a logic level MOSFET so this is what I brought. I am now thoroughly confused.

My apologies. I was looking at 520 and thinking 540. Certainly the IRF520 should work. Must be too early in the morning for my brain.

 

[Spadez]

Awesome, because they arrived this morning

 

[crutschow]

That was quick. If you have any problems using them, let us know and someone will be sure to help.