ignition coil diriver sinking too much current?
Ben Solon, Sun Apr 08 2012, 07:39PMhaving nothing better to do for the last few days, i have built both a small zvs induction heater(note to NEVER try to insulate 2 to-220s on the same heatsink EVER again!) and a ignition coil driver. the problem is in the latter.
this is such an easy project nothing should have gone wrong... it is 12v and runs with a 555 and mosfet/igbt. the power section works just fine, but i have fried 5 555's and a couple to-92's. pictured above is the 2n3906 from a bjt halfbridge intended to take the load off of the 555. as you might guess, because the 06 exploded, it is the sinking that is the problem.
first i tried the resistor with an anti-paralleled diode/resistor pair, and then the npn/pnp bridge. the 555 overheated in the first setup, and then the bjt exploded in the second. what is happening here!?
Re: ignition coil diriver sinking too much current?
Patrick, Sun Apr 08 2012, 08:01PM
Post a schematic please. remember a 555 can source and sink current form pin3. I need to see a pic though to be sure of what your talking about.
Patrick, Sun Apr 08 2012, 08:01PM
Post a schematic please. remember a 555 can source and sink current form pin3. I need to see a pic though to be sure of what your talking about.
Re: ignition coil diriver sinking too much current?
Ben Solon, Sun Apr 08 2012, 08:49PM
i cant print one up very fast, and i have used many 555's before. its just the resistor/diodes from 6 to 3. 3 is the output, and it oscilates how it should. i know there was nothing wrong with how it was wired, it was with the current capabilities. if you still need a schematic, i can link you to sections of other circuits:
555 section:
dead-time circuit:
or,
halfbridge of bjt's:
actual switch: just an igbt sinking power from an ignition coil
Ben Solon, Sun Apr 08 2012, 08:49PM
i cant print one up very fast, and i have used many 555's before. its just the resistor/diodes from 6 to 3. 3 is the output, and it oscilates how it should. i know there was nothing wrong with how it was wired, it was with the current capabilities. if you still need a schematic, i can link you to sections of other circuits:
555 section:
dead-time circuit:
or,
halfbridge of bjt's:
actual switch: just an igbt sinking power from an ignition coil
Re: ignition coil diriver sinking too much current?
Proud Mary, Sun Apr 08 2012, 10:32PM
The back EMF - the inductive kick-back - from an ignition coil is considerably greater than that of a flyback, as shown in Uzzors' circuit. Also, the time constant of an ignition coil primary is much greater than that of a flyback primary.
Proud Mary, Sun Apr 08 2012, 10:32PM
The back EMF - the inductive kick-back - from an ignition coil is considerably greater than that of a flyback, as shown in Uzzors' circuit. Also, the time constant of an ignition coil primary is much greater than that of a flyback primary.
Re: ignition coil diriver sinking too much current?
Ben Solon, Mon Apr 09 2012, 02:51AM
The kickback on the drain was measured at 280v peak, and the time constant is much larger so I don't run it in the kHz range. It's something like 1-10 bps.
Ben Solon, Mon Apr 09 2012, 02:51AM
The kickback on the drain was measured at 280v peak, and the time constant is much larger so I don't run it in the kHz range. It's something like 1-10 bps.
Re: ignition coil diriver sinking too much current?
Proud Mary, Mon Apr 09 2012, 05:07PM
Perhaps you might try running the timer/buffer elements and the output transistor from electrically seperate supplies - except for a common earth. A battery for the 555 and bjts perhaps, and your usual psu for the output.
The three terminal regulator in the Uzzors circuit might not react very well to the 280V spikes you mention.
Proud Mary, Mon Apr 09 2012, 05:07PM
Perhaps you might try running the timer/buffer elements and the output transistor from electrically seperate supplies - except for a common earth. A battery for the 555 and bjts perhaps, and your usual psu for the output.
The three terminal regulator in the Uzzors circuit might not react very well to the 280V spikes you mention.
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