Correction For ALL my Logic FET Posts

[gramo]

Ok, sorry about the ammeters/voltmeters every where, I just wanted to make sure I had this right..
**broken link removed**

R1 was added to limit the current from the PIC, as it was exceeding 25mA.

R2 is 5.6K to ensure that Ic through the totempole transistors is kept below 200mA, in this case 180mA max.

Heres the circuit in action

Any further mod's to keep this safe?

 

[geko]

Not withstanding my point above, that you're not really simulating the output from the PIC unless you drive the signal not only to 5Volts but actually pull it to 0Volts when it's supposed to be off.

Otherwise, it's now worthy of a place in a text book.

 

[gramo]

Thanks for your guidance through this, and due to popular demand, heres the new circuit

**broken link removed**

 

[jimg]

So the moral is use an RFD14N05L-ND and save three transistors and a resistor?

 

[gramo]

Well, yes and no. Depends on the application

The normal FET (IRL2203) can handle upto 116Amps, where as the logic FET I have suggested (RFD14N05L-ND) will only handle up to 14Amps.

I'm sure there are better logic FET's out there somewhere, but I'm yet to do a project where I need more than 6Amps (I got to 5.5Amps controlling a DC motor), let alone 14! or 116!!

So yeah, if external component count is not your thing, than go with a logic FET, or else pull out those transistors!

 

[geko]

What I did find interesting was the ten posts following your inclusion of a circuit schematic for the totempole driver.

They debated the merits of a resistor between the PIC and the transistor bases but no one picked up on the fact that it just plain didn't function as you intended; that is to drive the MOSFET gate to the 12 volt supply.

Also worth looking at are MOSFET driver IC's designed for the job. If you're interested have a look at the datasheet for an IR2104, half-bridge driver.

https://www.irf.com/product-info/datasheets/data/ir2104.pdf

 

[jimg]

Would the 568-2345-1-ND at 100A 30V be good for driving directly from a pic? It's a little more pricey at a whole $2.00
It says it's a logic level FET but I can't really tell from the specs.

 

[gramo]

Would the 568-2345-1-ND at 100A 30V be good for driving directly from a pic? It's a little more pricey at a whole $2.00
It says it's a logic level FET but I can't really tell from the specs.

Just remember that the 568-2345-1-ND is surface mount. And they have low stock of the item - it could be popular who knows?

But yeah, it will be fine for logic driving