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Simple car ignition coil driver problems

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speedshop

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Hi I thought I'd have a go at building this very simple circuit using an IGBT to drive a Car ignition coil.

So far I've had no luck getting it to work, with T1 failing after a couple of seconds running. The IGBT side seems fine and never fails. I've tried numberous things such as replacing T1 with a 1 amp mosfet, a 240 volt mosfet and altered the resistors all to no avail.

This is the circuit I am trying to use:


The components are:
R1 1K 1Watt
R2 1K 1Watt
R3 50R
D1 1N4007
D2 1N4007
D3 400v zener 1.5KE400
T1 2n7000 mosfet
T2 IRGB6860KPBF

So why is the T1 blowing, even when a 1 amp / 240 volt item used?
 

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klystron

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Filter the 12 v supply to the T1 driver part of the circuit with a series inductor to block any "spikes" on the 12 V line
 

speedshop

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OK thanks for the advice, I'll try putting an inductor in line. I think I have some 12 volt car accesory power supplies I can 'borrow' one from.

I wanted to use an IGBT for simplicity and loose as many components as possible. I have found a Velleman kit and could have built that using darlington transistors, but it seems there are lot of parts compared to the IGBT circuit. I've taken some coil on plug lead units apart and impressed with the simplicity of them
 

speedshop

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Engines run at comparitive low speeds, so switching speed isn't that important.

Tried a 100uH inductor same as in the bosch set up also tried a 1.3 amp mosfet in T1, exactly the same - it blew in a second. The IGBT is fine.

This should be really simple so I'm annoyed as its proving such a problem
 

betwixt

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Engine speed is almost irrelevant, it's the transistor switching speed tpetar means. The high voltage is generated by rapidly pulsing the primary current, if the rise and fall are slow it dramatically reduces the output voltage. However, I don't think this is the issue that is damaging T1. Can you confirm that the contact breaker is only connecting the gate to ground and is not injecting any voltage into the FET?


Brian.
 

LightDiodeDesigns

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The "Maplins'" coil-ignition system used to give 8 sparks per spark, easily done with a bit of MCU magic or some TTL shift registers... I remember the kit had an awesome capability for making old coils (especially) produce 5cm sparks, **broken link removed** If there is a circuit there for I can't find it but for £10, I'd have one again just for fun!
NEAL
 

tpetar

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The "Maplins'" coil-ignition system used to give 8 sparks per spark, easily done with a bit of MCU magic or some TTL shift registers... I remember the kit had an awesome capability for making old coils (especially) produce 5cm sparks, **broken link removed** If there is a circuit there for I can't find it but for £10, I'd have one again just for fun!
NEAL

Its classic Capacitive Discharge Ignition, but its commercial not DIY. I have lots of CDI/Multispark circuit if You need.




Speedshop say:

Engines run at comparitive low speeds, so switching speed isn't that important.
Tried a 100uH inductor same as in the bosch set up also tried a 1.3 amp mosfet in T1, exactly the same - it blew in a second. The IGBT is fine.
This should be really simple so I'm annoyed as its proving such a problem

Simply compare Your circuit with circuit what I post and you will see solution. Your circuit have some mistakes.
I hope you soon realize where you're wrong, before You kill several T1, or destroy other parts.

Fast diode BYX84, together with LC combination 100mH and 10nF protect T1 transistor.



For replacement of BOSCH1012 in circuit what I give You can use any of following :
BU323, BU920, BU921, BU922, BUV37B (TOP3), BUW29, BUW81, BUX37, MJ10012, MJ10013, MJ10014, TIP662, TIP665, 2SD683, 2SD685

For replacement of T1 in circuit what I post You can use :
BC160, BC161, BC287, ON607, 2N2905,....

For replacement of BYX84 (SOD-57) fast diode You can use:
BY226, BY227, BY399, BYW54

Zener diodes are in DO-34 case with minimal declared power is 1,3W.
 
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LightDiodeDesigns

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I've played with coils and signal generators on a bench, literally just with a 2A PSU (and caps!), a big PNP and a a zener some *big* TO case PNP's.. My original maplins-amplifier came with the circuit diagram, in about 1993 it was though.... It transformed my Vauxhall Viva.. Leaving the coil lead off once there were 6" sparks!

Would you consider adding a bit of MCU to the design? Have a 12F PIC (or whatever 8pin or anything really) that switches the driver transistor 3 times for every spark, or something a bit clever you know (I think Alpha do something with a similar name?)... The more switches make it a longer spark and burn even more fuel if possible, but at higher revs it'd have to cut out some ticks.... You could even add a rev limiter easily...
Just a thought
NEAL :D
 

speedshop

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Simply compare Your circuit with circuit what I post and you will see solution. Your circuit have some mistakes.
I hope you soon realize where you're wrong, before You kill several T1, or destroy other parts.

I assumed the diode in the 2n7000 would protect it? Are you saying I should add an extenal fast diode?
 

dr pepper

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If T1 is switching very fast then its dv/dt rating might be exceeded, but if you tried a device rated over an amp with the 50r resistor in seried this shouldnt have blown.

Is the gate driven by an inductive pickup, such as a ford system?, if so there might be some issue with voltage spikes, or possibly the whole thing is oscillating at radio frequencies.

A vdr or zener volatge clamp at the input would help protect from volatge spikes, and if oscillation is an issue then you need some means to limit the frequency response of the circuit.
 

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