i want to design ecus
@umery2k75
thanks for bringing me in!
Now, as for the voltage and current specs for output drivers, I've replaced original driver with BD912 which is rated for 15A and 100V. I think 15A is a bit of an overkill, since I'm using high impedance injectors - around 15 ohm, which at average automotive power supply draw around 1A of current.
100V I choose because I wasn't sure if original ECU has flyback voltage protection. Didn't know either about what voltage can flyback generate. Some sources said it was in 60V range, and some other quoted much higher. I went with 100V and assumed that there must be some sort of protection around them. Factory shouldn't be so dumb even back then not to put some.
It turned out that it works flawlessly with this driver.
Now there are other types of injectors - low impedance, which are in 2 ohm range, and they can draw much more current. However, they are operated in different manner. ECU should first allow them full current, until they open, and then limit it to lower value for the time injector is open. When operated in this way, injectors are opened faster, which results in better overall performance.
You should be able to drive injectors with about anything that is fast enough (which I assume all semiconductors are - only mechanical devices like relays are ruled out of course
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Injector opening times are in millisecond range, which varies from engine to engine, but for petrol injected are for example 1.7msec at idle. Pulse width can go to full duty cycle at wide open throttle.
I suppose that it would be very useful for you to take a look at Megasquirt project (just google for it!) as you can use it for ideas, to get better understanding about how fuel injection works, and it could even provide complete solution for you.