On Sun, Dec 05, 2010 at 05:06:16PM -0500, Dave wrote: > That's simple! :-)
Dave, please be aware that the first circuit at: http://www.rmcybernetics.com/projects/DIY_Devices/homemade_ignition_coil_driver.htm is seriously oversimplified. If a 2N3055 is used, as shown, the 100v collector breakdown voltage (BVcbo) won't get the best out of an ignition coil. It is common for the primary back-emf to be 400v in a kettering system, so limiting it to 100v is only 25% of what's usual. (Something like a BUW76 (350v), 2SC2333 (500v), or 2SC3153 (900v), would be better.) Relying on the snubber (RC1) to protect a low voltage transistor like the 2N3055 is very risky, because the back-emf from an arbitrary ignition coil will be unknown. Even if using a BUW76, I'd connect a transient suppression diode across its collector and emitter. (Somthing like a 1.5KE250, or 300v if you're game.) If a MOSFET is substituted for the 2N3055, as suggested there, it will not be turned off, because there is no pull-down on the emitter of T1. A low resistor value would be needed to provide a high di/dt in the coil, to generate a high flyback voltage. Better would be to reverse the drive, with a pull-up resistor, and the transistor pulling the gate low through a small gate resistor. A decent gate driver circuit needs a few more components. If not confident of high voltage design skills, I'd google for an electronic ignition circuit or two, to see how they protect their power transistor. (OK, IIRC, many of them use a small inverter to generate 400 Vdc, then use something like an SCR to dump into the ignition coil primary. Still, there might be some which give good ideas.) A flywheel diode is enough protection when fitted across an inductive load such as a relay coil, but that would defeat the generation of high voltage in this case, because a high di/dt would not be achieved. To obtain something which works from that site, it appears necessary to buy. They say "We sell an ignition coil driver module which has built in protection against most spikes that would damage a driver." Implicit in that is an admission that the simplistic circuits displayed do not do that. (At least, AIUI.) That's just some thoughts, which might help save some wasted time. ;-) Erik ------------------------------------------------------------------------------ What happens now with your Lotus Notes apps - do you make another costly upgrade, or settle for being marooned without product support? Time to move off Lotus Notes and onto the cloud with Force.com, apps are easier to build, use, and manage than apps on traditional platforms. Sign up for the Lotus Notes Migration Kit to learn more. http://p.sf.net/sfu/salesforce-d2d _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
