Mosfet drive circuit for ignition coil - Page 1
Forum section: electronics / beginners

author: Plow
author_rank: Newbie
timestamp: March 13, 2024, 07:36:59 pm
content: The first attached picture is a schematic for "version 1", the second is a photo of "version 2". It's a simple mosfet driver running from a signal generator.The question I have is how is the schematic changed between version 1 and version 2? I can see a capacitor being added but I do not know where or for what purpose.It's taken from a Serbian youtube channel here.

author: Zero999
author_rank: Super Contributor
timestamp: March 14, 2024, 01:47:37 pm
content: I haven't seen the video.The attached schematic is poor. A pointless opto-coupler and two diodes which do nothing.Replace the opto-coupler and diodes with a MOSFET driver such as the TC4427.https://ww1.microchip.com/downloads/en/DeviceDoc/20001422G.pdf

author: Terry Bites
author_rank: Super Contributor
timestamp: March 14, 2024, 04:28:21 pm
content: Clearly it has, but how is another question.

author: MathWizard
author_rank: Super Contributor
timestamp: March 16, 2024, 11:47:58 am
content: Is the supply voltage for the controller and LCD, and opto and gate, really connected to the mosfet drain ? Maybe they can be separate supplies, and then the opto might isolate the controller IC, if the mosfet blows up from gate to drain.I'm not looking at that right, but if there is 2 high side supply rails, them maybe the opto could still help isolate the IC (IDK how easy it is to short them side to side when they fail)

author: soldar
author_rank: Super Contributor
timestamp: March 17, 2024, 06:56:57 am
content: In consideration for those of us with slow, metered connections, please reduce and compress the graphics files you post. You can reduce the files to less than 1/20th of their size and still be perfectly readable.As has already been said, the schematic looks like a very poor design and I would not bother trying to build it. A simple 555 astable and a few components will do the same job. Like, for instance:https://www.electroschematics.com/555-ignition-coil-driver/In this circuit I believe C3 would better go to the collector of Q2.

author: CaptDon
author_rank: Super Contributor
timestamp: March 17, 2024, 01:48:26 pm
content: If C3 were connected across the primary to the collector of Q2 the resonant ringing would probably kill Q2. I think I would be tempted to place a damper diode across Q2 to prevent negative spikes during the off time of Q2. C3 can source a bit of current during the inrush cycle stabilizing the voltage drop across the supply resistor. C3 can also act as a high frequency path to ground to complete the spark current path. I prefer a totally isolated primary and secondary for this type of work. Some ignition coils are wound like the example, some are isolated. When properly phased the primary flyback voltage can boost the spark voltage by another 300 to 500 volts peak which is also the peak across the collector. Some of the old horizontal output transistors from the old C.R.T. televisions work great for these spark generator circuits and some even have an internal damper. They have one drawback, low HFE of 10 to 20 at high current. They were usually driven from a small 'horizontal output driver transformer' which provided a big current pulse at about 1 volt peak.

author: langwadt
author_rank: Super Contributor
timestamp: March 17, 2024, 02:56:02 pm
content: you can skip all the driver stuff and add some protection, using something like thishttps://efi-parts.co.uk/product/coilpack-with-built-in-ignitor/

author: Zero999
author_rank: Super Contributor
timestamp: March 17, 2024, 07:07:33 pm
content: Note to everyone:the original poster of this thread has been banned. Hence theemoji under their name.I don't know why. Going from his posts, he's not done anything wrong, although it's possible the bad ones have been removed. Another possibility is it's a glitch in the forum software or an error on the part of the moderation team.Perhaps this thread should be locked, to save others wasting their time, or if it's an error, then the original poster unbanned.

author: kevin.gibbs
author_rank: Regular Contributor
timestamp: March 26, 2024, 03:38:34 pm
content: If you are meaning the 4700µF x 25V capacitor - it is on a 12V supply for better stability.