Re: [TCML] Frequency

[Henry Hallam <henry@xxxxxxxxxxxxxxxx>]

To some extent, you're just transferring the problem.  Maybe the 555
won't blow but the drive transistor on the isolated side still will,
and perhaps the optical receiver.  These parts are cheap, just buy a
few and if they blow, figure out the problem and replace them.
Really, a good back-EMF diode across the LV winding should be enough
to protect most drive electronics.  A snubbing capacitor across the
winding will also help but (like a series resistor) it will make the
drive pulse edges less sharp and therefore reduce your output voltage.

Still not sure why you aren't using the 120V light dimmer circuit that
is so simple and reliable.

If you want specific advice please post a schematic diagram of the
setup you're intending to use.

Good luck,
Henry


On Sun, Oct 11, 2009 at 11:30 AM, Rhys Sage <rhys_sage@xxxxxxxxx> wrote:
> I did some research and found the circuit I'd found online is basically OK. There are some things that need changing though.
>
> One thing I'll do for simplicity is to make the pulse generator run off a 9v battery and produce an optical pulse which a receiver will pick up to apply the current to the coil. I did discover the ignition coils need a bridging resistor and capacitor combination to reduce spikes that might damage the power supply. Similarly a diode will be needed in series to prevent blowback.
>
> I had to get a book on 555 circuits - I couldn't blindly trust the information I'd found online.
>
> The ignition coil I have is marked E70. The packet has a barcode of 841266025075. It was cheap and something I'll be using for testing. I will need one of the $40 accel supercoils to get my 50KV ionisation pulse - that's a different circuit however. I'll need a 25KV coil to charge the main capacitor though and that's what the 555 circuit is all about.
>
> I've been on hold for quite a while what with not being so sure about a downloaded circuit diagram and because of all the add-ons and extra features people say it needs. I'm avoiding most of those by optically isolating the circuit. Thus, if anything blows, it won't be the control circuitry!
>
>
>
>
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-- 
Henry Hallam

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