IGBT ignition coil driver

[mmcl055]

Argh!!!

I just replaced the first transistor connected to RB3 and then things started working; The gate on the IGBT was switching from 0-6 volts.

But then after a while that stopped working and it now will only switch between 0 - 0.7V on the base of that transistor.

So I'm guessing one or both of those transistors have blown?

I'm sooo fed up with this thing. I think I'll have a beer and calm down.

 

[mmcl055]

It's not because I'm using BC547's which have a max base-emitter voltage of 6V is it?

 

[Rleo6965]

It's not because I'm using BC547's which have a max base-emitter voltage of 6V is it?

No. BC547 have a base resistor as current limit. I think BC547 was shorted due shorting of transistor on its collector. That transistor have no resistor protect its collector emitter current when BC547 turn on or conduct. So when that transistor have shorted, it will also short BC547. I guess.

You can try again your circuit and try to removed that transistor. I think it will work again without that transistor.. or wait for steve confirmation.

 

[(*steve*)]

Oh dear.

I just saw this:

You have the circuit and the ignition coil both powered from the long end of a pair of inductive cables.

You should have (at the very least) separate connections to the battery (as far as you can). You may still need to filter the 12V to the driver.

Rleo 6965, you will note that both transistors cannot be on simultaneously.

 

[Rleo6965]

Ooops. Sorry steve.

Your right. Transistor only conduct if BC547 was turn off . that is BC547 collector was pull up by 1k resistor.

 

[Rleo6965]

@mmcIO55

How about placing a 3Amp fuse on +12V supply wire. This is to protect your circuit in case of short circuit and shorted transistors.

 

[mmcl055]

Oh dear.

I just saw this:

You have the circuit and the ignition coil both powered from the long end of a pair of inductive cables.

You should have (at the very least) separate connections to the battery (as far as you can). You may still need to filter the 12V to the driver.

Ok cool. It will have seperate connections when on the bike anyhow.

However the circuit doesnt seem to work without the coil even. Its possible it was damaged earlier when testing with the coil thou.

Later today ill rebuild the driver part of the circuit on a breadboard; working on the vero is killing me.

Thanks for your help guys.

 

[Rleo6965]

Can you tell us which components was damaged. So, we can help analyse.

 

[mmcl055]

I've highlighted the transistor which was definitely broken. I'm not sure of the state of the other one but will rebuild and test after work tonight and let you know how I go.

Thanks

 

[mmcl055]

I just modeled the circuit in an online modling tool and it give's surprising results. It looks like the IGBT gate is high when the switch representing the output from RB3 is open.

You can view the circuit here

 

[(*steve*)]

As I suggested earlier. Do your next lot of tests with a reverse biased diode across the coil.

This will suppress the spark, but it will enable you to switch the ignition coil on and off without danger to the IGBT. When you've got this working right (the IGBT shouldn't get hot), you can move on to following GonzoEngineer's solution for the snubber.

You need to protect the 12V connection to the IGBT driver. I would suggest a series inductor, a capacitor to ground and a zener (18V should be fine) across the capacitor. You can connect the 47 ohm resistor for your other 12V connection to the junction of the L, C, and Zener. The zener in the regulator circuit is now superfluous. The R and the C to the regulator serve to decouple the regulator from the driver's moderate current spikes.

Sorry I can't draw it right now.

 

[(*steve*)]

It looks like the IGBT gate is high when the switch representing the output from RB3 is open.

Yep, that's exactly true.

 

[mmcl055]

OK Steve, thanks again for explaining all that!

I'll get to work on your suggestions later tonight.

 

[Rleo6965]

Yes its at high or approximately 1V on gate of IGBT. You have a 33 ohm as current limit. But pulse signal must short as required by ignition coil. Longer pulse will cause overheat of IGBT and got shorted.

You mentioned that BC547 was shorted. I assume the cause of damage was a long trigger pulse from PIC RB3. I suspect that you have damaged IGBT, open 33 ohm Resistor, shorted CE upper transistor, shorted diode on collector BC547 and BC547 itself. Can you post what components was damaged. This will confirm if you need to reprogram PIC length of turn on time or trigger time.

This the reason that i recommend 3a fuse to protect your circuit in case of failure.

Note: PIC RB3 high pulse will be inverted when it reach gate of IGBT. That is, your triggering IGBT at PIC RB3 low pulse.



Pardon steve. Just curious.

 

[mmcl055]

But pulse signal must short as required by ignition coil. Longer pulse will cause overheat of IGBT and got shorted.

I think this^^^ has finally sunk into my thick head.

The test code I currently have on the PIC toggles RB3 when I trip the hall sensor with a piece of metal. i.e the pulse on RB3 could be many seconds long.

Which probably explains everything. I'll reprogram to trigger a 4ms pulse whenever I trip the hall sensor instead. 4ms is the recommended dwell time for the coil.

 

[Rleo6965]

Do you know how many volts you expect on IGBT collector ( - coil terminal )? If its 300V, place 6 pcs zener 1N4757 in series . Cathode on collector of IGBT and anode to ground. This will act 300V zener in IGBT collector to protect it from ringing or spike voltage of – coil when IGBT turn off. Just place it like the 1N4007 in your first post. Hope this add more protection of your circuit.

 

[twister]

I still think that the original circuit should work. Just replace the 300 ohm with a 500 ohm, to protect the pic, and remove the capacitor. My circuit needs a gate return resistor to ground. I don't know if your type of transistor does or not. I use any large size resistor.
Also I don't use that diode across the transistor, Mine has one built in the transistor. I think yours does too. I don't use a snubber diode either.
The transistor that you are using only needs 4.33 volts to be completely on. If the pic puts out that much voltage it will work. If not, just use a pull up resistor to 12 volts of around 10k.
4m seconds on times seems like too short to me, but maybe you're right. You will know when you measure the voltage out. My coil needs a resistor of 7 ohms. Some coils have a resistor built in. It should say on the coil if it has one. My car switch throws 12v to the coil, but only when the starter is engaged, then current goes back thru the resistor and I think it is only 6 or 8v on the coil.

 

[(*steve*)]

I still think that the original circuit should work

Ignoring everything else that you've written...

It won't.

Look at the Vge Vs, Ice graph on the top of page 4 of the datasheet. (this was the subject of the second, third, and fourth posts in this thread that you may not have read.

Much of the other stuff you wrote was wrong too (other than perhaps the note about the diode since this device does have a built in fast diode).

 

[mmcl055]

BTW I'm taking a wee break from this since I'm fed up with it and it looks like around 5 PIC's are partially stuffed from playing with this circuit.

When motivation comes back to me next week I'll get back into it.

Thanks for all your help guys.

 

[twister]

Ignoring everything else that you've written...

It won't.

Look at the Vge Vs, Ice graph on the top of page 4 of the datasheet. (this was the subject of the second, third, and fourth posts in this thread that you may not have read.

Much of the other stuff you wrote was wrong too (other than perhaps the note about the diode since this device does have a built in fast diode).

If the pic is able to sink the pull up resistor voltage, his original circuit will work with my suggestions. That's how my circuit works with only a measly slotted optical switch. Most of what I wrote is right! If he would have used the resistor on the gate, that I suggested, he wouldn't have ruined 5 pics.