I've been working on this circuit for some time... I'm not sure if I've used the correct MOSFET (IRF510) device:

http://electro-geek.blogspot.com/2009/05/thermoelectric-temperature-controller.html

I want a TTL 5V control on the MOSFET that can handle up to 5 amps.

Anyone know if this is the right MSOFET for the task?

 

Hello,

You will need the "logic level" gate version of the mosfets.
Here is a page from IRF with some examples:
http://www.irf.com/whats-new/nr090428.html

Greetings,
Bertus

 

No, it will not turn on with 5 volts applied. You need a logic-level FET like the IRL520 - http://www.hobbyengineering.com/H1586.html

These FET's will turn on with +5 applied - note that a TTL level is perhaps 3.8 volts, so a CMOS gate is best to drive the device.

 

beenthere - thanks for the info, I think that is exactly what I need...

I'm assuming PWM to the MOSFET is better than driving it with a particular voltage?

 

Hello,

PWM is more efficient than linear.
PWM can be made "manual" (with opamps) or by an microcontroller.
Linear would make the mosfet very hot.

Greetings,
Bertus

 

Bertus -

A couple of questions:

1. by "manual", do you mean analog? I currently use an opamp between the microncontroller and the MOSFET. I think this is changing the PWM signal from the microcontroller into a linear voltage. I am generating a LOT of heat.

2. I could run the MOSFET straight from the microcontroller with PWM (picaxe). But I was told that:

"One note, there is capacitance in the gate of the FET that must be considered in the PWM drive signal. Therefore if the FET is being driven at a high frequency, a low impedance circuit must be used to turn the FET on and off rapidly to minimize the time that the FET is in the transition region between being fully on and fully off"

Can this be considered a decent low impedance circuit to get this rapid on/off?

http://sites.google.com/site/elektrogeekproject/circuit1

 

Hello,

You need to remove the 0.1μF capacitor at the gate.
Put a resistor of 220 Ohms between the output of the microcontroller and the gate of the mosfet.

Greetings,
Bertus