Mosfet fire work circuit -

[zotdoc]

I would like to set up an array such that row "a 1...12" controls the positive wire to a set of loads (1...144) and column "b 13...24" controls the negative wire to the same set of loads , such that each load could be turned on individually. The loads are each 3 short segments of small guage nichrome wire in parallel, powered by 3 8V golf cart batteries, such that when they turn, they glow red hot and/or melt to ignite fireworks fuses. I am thinking of using power mosfets as the switch for the array, as I have some logic boards that should power them directly and a friend has written software for them. The row of the array would be controlling the + side of the battery and the column of the array would control access to the - side of the battery. Each mosfet would need to be turned on and off at very low frequency and stay on for up to 15 minutes. This will allow me to take the 24 outputs from my logic boards and using them two at a time, control 144 firework events, each shooting three firework devices. I am a hobbiest with no electronic expertise and would like input as to weather this idea is feasable from someone who has some experience. Thanks to anyone in advance.

 

[cadstarsucks]

I would like to set up an array such that row "a 1...12" controls the positive wire to a set of loads (1...144) and column "b 13...24" controls the negative wire to the same set of loads , such that each load could be turned on individually. The loads are each 3 short segments of small guage nichrome wire in parallel, powered by 3 8V golf cart batteries, such that when they turn, they glow red hot and/or melt to ignite fireworks fuses. I am thinking of using power mosfets as the switch for the array, as I have some logic boards that should power them directly and a friend has written software for them. The row of the array would be controlling the + side of the battery and the column of the array would control access to the - side of the battery. Each mosfet would need to be turned on and off at very low frequency and stay on for up to 15 minutes. This will allow me to take the 24 outputs from my logic boards and using them two at a time, control 144 firework events, each shooting three firework devices. I am a hobbiest with no electronic expertise and would like input as to weather this idea is feasable from someone who has some experience. Thanks to anyone in advance.

Nothing wrong with that at all, a very common practice actually. About the only thing is that you can not drive the high side FETs directly off of logic outputs. You will need level translation, even if it is only a small FET and a pull up resistor.

D.

 

[zotdoc]

Thanks. I apologize for my ignorance, but I assume that by "high side FETs" you mean the one's connected between the + side of the battery and the loads , and the low side fets are those connected between the ground side of the battery and the load? Or am I more lost than I think? Could I use P type mosfets for the high side and n type for the low side and avoid the level translation?

 

[kchriste]

but I assume that by "high side FETs" you mean the one's connected between the + side of the battery and the loads , and the low side fets are those connected between the ground side of the battery and the load?

That's correct.

Could I use P type mosfets for the high side and n type for the low side and avoid the level translation?

You'll still need level translation because the logic will be running at a lower voltage (5V most likely) than your fireworks fuses. But using P channel FETs will make the level translation circuitry simpler if you don't want to use a special high driver IC for N channel FETs....
That said, it may still be cheaper to go the high driver IC / N channel FET route because high current N channel FETs are cheaper and easier to find than P channel ones. How much current will the fireworks fuses draw?

 

[cadstarsucks]

That's correct.

You'll still need level translation because the logic will be running at a lower voltage (5V most likely) than your fireworks fuses. But using P channel FETs will make the level translation circuitry simpler if you don't want to use a special high driver IC for N channel FETs....
That said, it may still be cheaper to go the high driver IC / N channel FET route because high current N channel FETs are cheaper and easier to find than P channel ones. How much current will the fireworks fuses draw?

Ummm... That I would not know...I guess I'm a bit spoiled, when I want one I just go next door and pull it out of stock I often hack together little things I might need out of the SMT parts. As for PFETS I think one of my favorites is a little dual 2A@20V 1.8V gate in a SOT23-6...I would have to look at work but I think that is the one we get for around $0.20 in qty

I was assuming he was talking about PFETs since it would cost so much to do add the drivers to NFETs. I think if there is a problem getting PFETs it would be better to use a booster or another battery for the 24V gate drive, 2 10Ks to a small NFET to gnd and the high side NFET gate with a diode to 12V at the center of the 2 10Ks

I think that one is it...it lists for more but the common channel has it for $0.40 each in single piece qty... we are getting them for half that in reels

D.