MOSFET Project idea

Other Hardware General Electronics
1

I am looking at building an ignition kill switch for a small petrol engine in a radio controlled model, see my proposed circuit below. I was proposing to use an ATTiny 85 and an IRLZ44N MOSFET

IMG_5112
IMG_51121920×2560 409 KB

The 5V & GND connected to the ATTiny come from the R/C receiver and a signal pulse will go to Pin 2. The signal out to the Gate comes from Pin 3 of the ATTiny, via a 180 Ohm resistor to limit the current with the 10 Kilo Ohm resistor used to pull the Gate to ground when Pin 3 is low.

The Drain is connected to the Ignition unit -ve with the +ve going to Battery +ve. The battery -ve is connected to GND. The Source of the MOSFET is connected to GND also. The ignition unit will draw about 600mA.

To me, it looks as though it should work but my electronics knowledge is limited. My questions are:

    1. Will it work? And
    1. Do I need a heatsink? (my thoughts are no, but will to be guided by the experts)

Thank you in advance for any assistance.

2

Wow, 10 kW must be a very fat resistor! :wink:
I'd write 10k for this resistor and 180R for the other one, not using 'W' because that's for another commonly used unit.

Add a flyback diode across the ignitor or the FET will be killed almost immediately.

3

I had the Ohm symbol in, it was obviously not recognised!

What rating of diode should I use?

4

The rule is to use a diode who’s current rating is equal to at least the current that flows thru the load.

i.e. If the load normally draws 1A, the diode rating should be >= 1A.

5

Thank you for your reply!

6

Other than the addition of a flyback diode, does the circuit look OK?

7

The 10k resistor should be on the other side of the 180ohm resistor.
Leo..

8

I have seen diagrams with the 10k resistor before and after the 180 ohm resistor. I will do as you suggest and thank you for taking the time to reply but can you explain to me why it makes a difference where the resistor is fitted in this case?

9

If the 180R is before the 10k, you are making a voltage divider; even though in this case, the 180R drops a very small amount of voltage.

If the 10k is before the 180R, there is no voltage divider concern and the MOSFET gate sees the full Arduino output voltage.

10

Thanks for clarifying.

11

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.