Power MOSFET to switch a high current

[cks3976]

Dear All,

I want to implement a power switch using an power MOSFET. Specs are : Vin: 12VDC and IDS: 10A. Gate trigger shall be initated by a Microcontroller (3.3V).
I can think of following implementations:

Option 1: 12V source voltage will be connected to the Source of the P-channel MOSFET and the Voltage-out will be on the drain. Connect the microcontroller trigger to a Charge pump and use this to turn the power MOSFET On. VGS_threshold of the MOSFET is around 22V.

OR,

Option 2: 12V source voltage will be connected to the drain of an N-channel MOSFET, while grounding the source. Gate of the MOSFET will be directly driven by the microcontroller (3.3V/ 5V). During Gate current ON, the MOSFET will conduct and 12V will not be switched to the output stage. And when the gate current is OFF, the MOSFET is turned off and the output will get 12V (reverse logic).

Please help me in underststaning whether above logcs are correct, if not how can I implemet the switch for above specs.

Thanks a lot

 

[barry]

Your second method will accomplish only the dramatic, and rapid, failure of the mosfet, as there is nothing to limit the current through it. If you can put your load in the Drain path, then this will work (i.e., one side of the load connected to +12, the other side of the load to the drain.)

If your load must be connected to ground, then your first method (P-channel) must be used. VGS of the MOSFET is not 22V, that sounds like the ABSOLUTE MAXIMUM, not the threshold; usually the threshold is in the 2-5 volt range. I wouldn't bother with a charge pump to turn on the P-channel MOSFET, I'd use an NPN bipolar to drive the gate to ground(through an appropriate resistor). There is lots of information on the internet about this type of circuit (search 'high-side drive'). You might need a totem-pole gate drive, depending on your required speed.

 

[mtwieg]

As barry says, if your load must be ground referenced, then you'll need a P channel FET (you could use a high side N FET but it would be much more complicated...).

Here's an effective, simple method for driving a high side P FET from a logic signal:


However, keep in mind this circuit, as is, does not implement any limiting on the Vgs of the P FET. This shouldn't be a problem if your source voltage is only 12V though (most power P FETs can tolerate up to -20V), but you'll want to make sure.

 

[cks3976]

Folks.. thanks a lot. this really helped me a lot. I ran pSpice simulation of mtwieg's circuit and that worked Barry... thanks for nice explaination...however I was planning to use a limiting resistor on both drain and source. But since my load must be ground referenced, I cannot connect the two ends of load to 12V and drain point. Hence I use Option 1 and NPN transistor driver for Gate...

 

[ea.arun]

also be careful with the selection of P-MOS whose RDSon is high compared to N-MOS since your curent fairly high.......
calculate the static power dissipated across the mosfet and determine the maximum RDSon allowed.......

EA