With this solution you can fast open low z injectors and fast close(30V flyback) but with 25% pwm(low energy losses on flyback transistor). Hold time is 1ms.
Schematic:
- diode : I use by500-1000 (cheap, fast)
- I put zener diode on vems board 30V transient protection diode (1k5E30 diode from WebShop)
- so when pwm is activated, current flow throo active flyback, but when injector needs to close, 30V high voltage flyback inside VEMS does the clamping
Same schematic, but drawn in a slightly confusing way:
When pwm last, flyback voltage is 0.3-1.5V(depending of schottky diode and mosfet(irf9540))
Bad thing is, you must have one of thise flyback for every injector.
PCB
Assembled board(missing 2 zener diodes, i bought two too few)
That board was tested on lpg injectors(landi renzo, 0.9ohm) and working well.