Building a Simple 9V Boost Converter for a Spark Plug

[ben123324]

hi, i am pretty new with electronics, and i can't find any simple boost converter circuts on the enternet. i would like to make the circut THE MOST SIMPLE i can, with the fewest possible parts. for a power source, i have 9v-1w. for the output power, i would like to send a thin spark from 1 electrode to the other about 1/8"-1/4" apart as a substitute as a spark plug. schematics, diagrams, photos, links all would be helpful, but keep in mind that about all i can do is solder, and go to raioshack.
thanks,
Ben

edit: here is a simple curcut i found(http://en.wikipedia.org/wiki/File:Boost_circuit.png), and i understand everything but the switch. how would i get a switch that switches the flow of electricity off-on that fast?

 

[Zryn]

That diagram of a switch shows the basic principle of 'on and off', however in practice people use a MOSFET.

A MOSFET comes in an IC package, and is controlled by a PWM (square wave generator) IC, which supplies a voltage that turns the MOSFET on and off periodically with a desired frequency and duty cycle. Depending on the application, the PWM IC voltage may not be large enough to active the MOSFET, so a Gate Driver IC acts as an interim amplifier/control IC. Looking more into these three items should give you an abundance of information on how to create a robust electronic switch.

 

[mheslep]

Linear Technologies application notes are very good, probably the best of their kind. See, e.g.
http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1002,C1223,P1209,D4120
http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1042,C1031,C1061,P1266,D4176

or anything written by LT engineer Jim Williams

 

[Mike_In_Plano]

The biggest bear for you, is to have a decent transformer / inductor. Time to get an old car ignition coil.
The kind you want is old-style. It will be about the size of a soda can with an insulated section coming out the top and two terminals, one on either side of the insulated terminal.
A fair going price is $10-$15, but old mechanics and junk yards might let you have one for the asking (their just dirtier).

Now, the lovely thing is that no sooner than you get this evil device, you can start making sparks with common junk from around the house. A nine volt battery, some tape, aluminum foil, and something to use for a wire - like wire or even foil.

Make a ball of aluminum foil that is just a bit too large for the high voltage socket. Wrapped an exposed portion of your wire around the foil ball, and shove them into the socket. If it becomes a problem later, you can retrieve the foil with a screw.
Then, tape the wire to the side of the insulator, so that it doesn't tug out of the hole.
Adjust the wire to be about .2" from your negative terminal.

Now, put a couple of wires on your terminals and bring them out where you can tap them with the battery. Just tap and release, and you should get a spark.

To get a nasty, steady stream of sparks, you can go as crude as using a relay to break the connection, or be a little more cool and use a 200V MOSFET. In either case, the handy man's second secret weapon, the NE555 timer is you're best bet for turning things on and off. I'd try for about 2ms on and wait about 20ms off. This will give things a little time to cool and not eat your battery up so quick.

Enjoy!

Mike

 

[mheslep]

The biggest bear for you, is to have a decent transformer / inductor. Time to get an old car ignition coil.
The kind you want is old-style. [...]

Eh, careful there. The inductor has to be sized to the intended switching regulator frequency and power.

From the Linear Technology http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1042,C1031,C1061,P1266,D4176" :

WARNING
Before reading this section, be aware that the intent of the author is not to insult, but rather to relate in an attention getting manner a list of goofs that, in many cases, he personally has had to own up to.
[...]
5. Fred’s Inductor (Or Transformer)
Inductors are not like lawn mowers. If you want to borrow the one out of Fred’s drawer, make sure it’s the
right value for your application. A 50μH inductor with 50V applied will have a current increasing with time at the rate of 1A per microsecond. It doesn’t take a calculator to see that things can get out of hand quickly during the 25μs period of a 40kHz switcher. Likewise, if “Fred’s inductor” is 50 millihenries, it will probably saturate at such low current levels that it is useless, not to mention the fact that the transient response can be measured on a Simpson VOM. Use the formulas in the application note to get a ball park inductance value before starting a breadboard.

 

[Bob S]

If you put an 0.01 uF capacitor across the switch in this circuit

http://en.wikipedia.org/wiki/File:Boost_circuit.png

you will have the primary of the standard ignition circuit in automobiles prior to ~1970. The ignition coil has about a primary:secondary turns ratio of 1:100. The primary will generate ~300 volts across the switch, and the secondary ~30,000 volts. See thumbnail.

Bob S