Pyro channel circuit validation

L

Luca

Active member
Hi, i am building an automated firework launcher with a teensy 4.0, and i wanted to use a mosfet as a switch for activating the ignitor of a firework.
This is the circuit i came up with:
1724932806940.png

I was particularly concerned about which mosfet to use since the digital pins of the teensy operate at 3V3.
I asked chat gpt about it and i sad that either the AO3418 or the SI2302 were ok but i would like a confermation since i can't understand that muth datasheets.
Thanks.
 
I'm certainly not an expert but shouldn't the load be on the high side of the MOSFET, since the switching (gate) voltage is relative to S?

Also, you want to put ~5V into VIN on the Teensy rather than 3.3V. Anywhere between 3.6-5.5 will probably do but not 3.3V.
 
1724935172430.png

You are right, my bad there. However can anyone conferm if the mosfet that the gpt suggested are ok. thanks a lot.
 
Build it like this:

1724947834273.png


Because this is a N-channel mosfet, you must connect the source pin to GND. The load must connect between drain and the +12V power.

The 47 ohm resistor and 0.1 uF capacitor are optional, but they will help against radio interference if you have a long wire that acts like an antenna. These parts are so cheap that you really should use them, even if they may not be strictly necessary. Last thing you want is to have it work when you tested at home and then fail or misbehave when you take it somewhere else for actual usage.

The diode is essential. If the wires are long, they will have some inductance. Not much, but not zero. Without a fast diode to give the current a path to discharge, the transistor could be damaged.

You also need a 330 ohm resistor between Teensy and the transistor gate to limit the current, since it looks like a capacitor.
 
Surely the kick-back suppression (free-wheel) diode doesn't need to be a fast one. All diodes switch _on_ before the forward voltage reaches even 10's of volts - you're not going to see destructive voltage spikes even with a lowly 1N4001. Reverse recovery delays only apply to a diode switching off, such as in a fast rectifier situation. Once you have a free-wheel diode you don't need an RC snubber as well I feel.

I reckon a good amount of decoupling capacitance is important in this circuit as the current pulses are likely to be high to blow an igniter, a few 1000µF perhaps across the 12V supply, rated 16V...
 
You must log in or register to reply here.
Back
Top