P Channel Mosfet problems (FET EXPERTS) :D

[TKS]

Hi,

I made a simple powerswitch using a Pmosfet and a transistor,
basicly what it does is it takes away the power from 4injectors wich run my bike. In that way i can kill the engine for a short time and shiftup.

The problem i find is that it works well until i reach third!
if i upshift from 1 to seconds it goes well but when i enter third everything dies.
I think that then the mosfet is blocking anything! and not listening anymore to its gate.

When i cut the power to the mosfet and reengage it. it works allright again...

anyone any clue???

1) what happens if the injector (electromagnet) fires a high voltage to the fet???

2)the mosfet has an internal diode, can it be used parallel with the fet itself??
i mean if there is a flow of voltage trough the diode and i switch the fet on what happens then???

Tks

 

[picbits]

You need a fast external clamping diode with a minimum rating of the current being drawn by the load.

 

[TKS]

can you explain what is happening.... so in series witht he load.

problem is that then it consumes 0,6volts... wich results in voltage drop / more reaction time of the injector.

Tks

 

[Roff]

Post a schematic of your circuit.

 

[TKS]

Hi Ron,

This is the schematic, i used a solenoid buit in reallife its an injector.

The lower 10K resistor is managed and pulsed by the bikes Engine Management.

The upper one is my disable injectors pic output.

The 200ohm resistor in series with the load is to fool the MCU else it will detect that there is no voltage and register a fault on the injectors.

What do you think???

I have now added an Zener across the injectors....

but haven't tested it with it.

Tks