peak and hold fuel injector driver

[mrhrholden]

Hi i am new to pic programming and i am wanting to make a PIC16f84A peak and hold injector driver circuit.
The injectors are .7ohm @ 12volts .7/12=17.14amps this current it too great. it only needs to saturate the injector for 500us and then osilate 5k-10k 50% duty for current limiting.
The Peak and Hold current look like this 17amp for 500us then 8amps
we need to current limit as the injector over heat with 17amp full saturation.

I am using PortA as 4 inputs and PortB as 4 Outputs.
But i need the pic16f84 to trigger the mosfet like this, Peak switch on for 500us then pwm 5k-10k hertz 50% duty for current limiting.
and when the signal is removed from input Port A input the output PortB must switch off and then wait for another input signal. all 4 Inputs and Outputs must be separate from each other.

any help will be much apreciated
thank you
Mark

[mackrackit]

Welcome to the forum.

Hi i am new to pic programming

OK, the first thing you need to do is get some LEDs. Hook them up as outputs and make them bkink. Got to start somewhere.

Then we will take a look at PWM.

all 4 Inputs and Outputs must be separate from each other.

That is the trick. You will want a PIC with hardware PWM. Not sure if there is one with four channels.

[Melanie]

You could share a single PWM and use an external AND gate for each channel, but even with the best will in the world, monitoring 4 channels, you could easilly get upto a 20uS Delay using a PIC - this could affect your engine timing significantly. Dump the PIC. You could do this with a splattering of discrete logic far better with nanosecond accuracy.

[mrhrholden]

Hi Dave i have all ready got a program setup that when you press a input button on portA it lights up an led on the output portB.

just need to do some peak and hold in the middle there thats what i am not to shure on.

Hi Melanie in a engine things happen pretty slow compared to electronics the pulse coming out of the Engine managment computer into the Injector driver box. When the engine is idling the ECU output is 1ms earth pulse and when the engines at 8000rpm it has a 8ms earth pulse, The milli second time is how long the injector is open for.


Melanie i am very keen about you idea or using discrete logic components for nanosecond timing. Could you maybe point me in the right direction with a diagram o somthing? that would be much apreaciated

Thank you

Mark

[Acetronics2]

Hi,

I Really believe our Friend Skimask is the best here for injectors driving ...

his realizations have already reached top levels ...

Alain

[mackrackit]

Mark,
At least you have a start. By your first post I figured you have not done anything yet and was wanting to start big. My apologies.

Alan is correct, skimask is the best solution to this problem.

[skimask]

I Really believe our Friend Skimask is the best here for injectors driving ...

Thanks for the vote, but I'm all with Melanie on this one.
Use some ready made injector driver chips. They've already been road proven, road tested, and so on and so on. Did I mention they're already made?
Can't think of any off the top of my head, but they are all over out there.