FET on PIC output

[grekson]

I found this diagram

on this site and whis to know if you don't need a reverse biased diode like you need when using a BJT to eliminate spikes at startup and shutdown operation.

PS author mention that FETs normaly need voltages higher than 10V at the gait to conduct through drain - source. Do FETs that could be controlled directly from PIC output exsist?

 

[Nigel Goodwin]

You need a diode - risky overwise.

You can buy logic level FET's, so presumably that's one.

 

[ericgibbs]

PS author mention that FETs normaly need voltages higher than 10V at the gait to conduct through drain - source. Do FETs that could be controlled directly from PIC output exsist? n

hi,
This Trench N MOSFET [dual] is logic to gate compatible.

 

[grekson]

Doesn't some FETs have internal diode?

By which data from the datasheet do I search FET compatibile for PIC?
Is this VGS as voltage gate-source. Those values are almost always higher that 5V.
How do I calculate (based on particular FET) how much current could theoreticaly be flowing across drain source?

PS How do you connect this dual channel MOSFET since it has more than 3 pins per channel?

 

[smanches]

All MOSFETS have an integral diode that is formed as part of the MOSFET structure. Though this is basically a by-product of how MOSFETs are designed.

Some MOSFETs also have a integrated Schottkey diode in them for reverse protection.

 

[kchriste]

Doesn't some FETs have internal diode?

Yes, but it is in the wrong part of the circuit. It needs to be connected across the motor. The FETs internal diode is between the motor and ground in your circuit, which is the wrong location to supress the inductive kickback when the FET is turned off.

By which data from the datasheet do I search FET compatibile for PIC?
Is this VGS as voltage gate-source. Those values are almost always higher that 5V.

Look for the RDS(ON) spec. If it is specified at less than 5V, you can drive it directly with your PIC in low speed aplications. Example from the datasheet Eric posted:
RDS(ON) = 14 mΩ @ VGS = 4.5 V (14 mΩ = 0.014Ω)

PS How do you connect this dual channel MOSFET since it has more than 3 pins per channel?

It is two MOSFETs in a single package. There are two connections for each drain. Connect them together. ie: Connect pins 5&6 together as one drain terminal for Q1.