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What can I use to drive high current in my electronics?

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Author Topic: What can I use to drive high current in my electronics?  (Read 322 times)
240gunny
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Posts: 3
« on: May 03, 2011, 06:36:39 PM »
I am building a 20 channel automatic fireworks ignition system as a summer project. I have a PIC processor that can source or sink only 25 mA. What can I use to supply a high current (500mA+) to the rocket igniters using the microcontroller pin? I would rather stay away from relays because each relay is rather expensive.

Can regular BJT transistors handle high current? I have a lot of 2N3904 NPN transistors laying around.. Im fairly new to electronics I only just finished one year of electrical engineering at college.

Also, I heard its wise to use a 100n ceramic cap with your ICs in circuits to reduce noise. Is this true? Do i put it in parallel or series with the IC's VDD pin?
For more details email me if you want! Thanks-
found this-- would this work?

https://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_119802_-1
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Jacko
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Posts: 3
« Reply #1 on: May 03, 2011, 07:34:48 PM »
You could use SCRs (Silicon Controlled Rectifiers)(Thyristors)
I don't think the 2N3904 will handle the current sufficiently well. A 2N3055 certainly would.
Have a look at the BMFA website, in their Model Rocket section for more ideas.
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Sadek
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Posts: 2
« Reply #2 on: May 03, 2011, 08:00:29 PM »
Use a pass Transistor and The fed the processor output to the base of that transistor.
Yes you can use 3609 NPN transistor.
It can handle upto 2A  of current with proper heat sink
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squeegee
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Posts: 9
« Reply #3 on: May 03, 2011, 08:19:56 PM »
Yes, it is wise to fit a 100 nF capacitor in parallel with each IC's power pin to ground; ie. Vdd to Vss.
It is also a good idea to fit it right at (or adjacent to) the power pin. This not only inhibits noise getting in to the IC but also helps it to switch cleanly without current transients along and on the power lines.

You need to add a series pass transistor to raise the current delivery potential of the circuit.
A ZTX 651 will pass 2A which should be a reasonable safety margin.
You connect the collector to the +ve supply rail; the base from your IC output pin, and the emitter to the load which needs 500 mA. Shorting the emitter to ground when in a high state will destroy the transistor.
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Doug_Aldridge
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Posts: 10
« Reply #4 on: May 03, 2011, 08:38:21 PM »
If you have time and not money, use the 2N3904s.  If you use three in parallel, they will handle 600 ma.  I assume the fireworks fuse burns out pretty quick, so you are not going to get any significant buildup of heat no matter what you decide.  i.e. no heat sinks required.  If I was doing this project, I would probably spec in a quad or more power driver IC.  Much less wiring.
100 nf is a waste of time.  If you are concerned about noise, spec in .1 or .33 mfd ceramics, from Vcc to ground, close to the chip.
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