MicroSquirt.com read only forum (Jan.15,2018)

I'm in the process of making a mod to the fuel pump drive on my MS II V 3.0 board and would appreciate some clarification.(Obviously my knowledge of electronic circuitry is rudimentary)
In this circuit, transistor Q2 provides ground for the pump when the processor provides voltage through FP-1 and R16.What is the function of transistor Q19 ? The zenor diode D4 is there simply to protect against voltage spikes from the pump circuit.(Correct?)
Once I can fully understand this circuit I'll feel better about modding it to provide +12V to the pump which is required due to the requirements of my Bosch injection system (currently L-Jet)
Thanks

MurrayA4,

Q19 drains the current from the base of Q2 (shutting it off) if the voltage drop across R40 gets too high. So it is there to limit the current through Q2.

D4 protects against voltage spikes (that are > 22 Volts) when the fuel pump relay shut off.

Lance.

Thanks

The existing circuit can be used to supply 12v to the pump already, it depends on how you wire your fuel pump relay.
My pump requires a 12v supply and I use the standard fuel pump transistor circuit. A relay must always be used anyway as the puny transistor could never supply enough current for the pump.

James

Yes James I will be supplying my pump through a relay which is part of my cars existing OEM circuit.My need for +12V on pin 19 of the DB37 is to be able to use my existing wiring and ECU connector.This has already been done successfully on the V 2...board and now I want to reproduce it on the V3 board.
The schematic below demonstrates the fix for the older board,now I'm attempting to mimic its logic on the V3 driver circuit.