Need LogicLevel FET

turrican

Hello,

i am just started working with the Prop.
I want to switch 12V high currents (up to 20Amps) with the propeller. Ive done this before with a AVR and a 5V-Logic-Level-FET.
But with the prop this wont work (i think because of the 3,3V Logic-Level).

Its very important that the FET works as a fast switch because its used for driving magnetic-solenoid-valves of an diesel-engines (so timing is very important!)


if anyone has an idea which FET to use or how to solve this problem in another way i will be very happy


Thanx

Anubisbot

HI
have you tried to pull up the signal line with a resistor to 5V.

Anubisbot

turrican

Thank you for the fast response!

Yes, i tried it, in 99% of cases it behaves like expected, but on the rest 1% it doesnt (especially at reset/bootup) it switches randomly!

So i thought if someone knows a FET which is 3.3V Logiclevel-compatible it will solve the problem!

Phil Pilgrim (PhiPi)

For a MOSFET of that capacity, I'd use a MOSFET driver. Micrel makes a number of these devices. They can run on 5V (some as high as 18V) and typically need only a 2.4V input to register as a "high". (But check the datasheet for the device you want to use.) They're designed for driving high-capacitance loads, such as MOSFET gates.

-Phil

turrican

Thank you for that link, i just had a look at the page and i think the 5015-Driver will fit!

The only thing is the slow response-time, but i will check this directly in the circuit (maybe this will not be a problem in my design!)

Let me say that i think choosing the propeller was a good choice (even if i miss some functions) not only because of the chip - but even because of this forum! Very fast help and good comments!

TransistorToaster

You could also try to make a circuit to drive the gate with an optoisolator like the 4n35. Be sure to check the propagation delay, I recall several microseconds. There are faster and newer ones out there for certain.