Confused about flyback options

[scottieb]

Hi all,

Finally got round to putting my ECU together and after reading various bits of the wiki and vems build manuals I'm a bit confused about the flyback options.

Some diagrams might help at this point:



From left to right: (I have only show one channel for clarity)

The first diagram is what I understand a the 'Low voltage flyback' topology. this seems to be what is fitted to my board, assuming the flyback terminal (pin 23) is wired to Injector +V

The second diagram is the equivalent of the flyback circuit withe the external transient diode wired in

The third diagram is the an alternative arrangement mainly to test my understanding of the whole thing. If you removed the two diodes and replaced them with a single transient diode, would this not be the ultimate flyback configuration? as far as I can tell the only thing the two standard flyback diodes would be redundant if you did it this way?

Also, there is a transient diode soldered to the pcb between +V and GND5 is this intended to replace the external flyback diode or is it there to protect the electronics?

So which do I need, the external flyback, the internal flyback, or both?

Thanks in advance.

Scott

[rob@vems.co.uk]

The flyback as is will work (on the right), but its not too hot at closing the injectors.
So the next step (middle one) is the one we use, and yes, the final one might work, but it would mean re-working the automated board assembly process and as this is a consumer unit we have to consider the fact that someone might just wire the thing directly to live which is not what we'd want.

Belt and braces.

That transient diode in the power supply circuit is designed to protect the board, from nasty voltage spikes, reversing the power by mistake and when someone shorted out the injectors on their system is blew and took out the fuse.

[scottieb]

ok, cheers Rob, so what I need is all the ER2J Diodes in place, the internal flyback diode and the externat one wired to +V intectors?

Also can I put the Flyback transorb inside the case?

Regards,

Scott

[rob@vems.co.uk]

Yeah the transient diode can happily sit inside the case.