Fuel Injector Inverter

[quick108]

I have six 0-5V duty cycle signals coming out of an ECU that drive 6 direct injectors. However, I need to invert these signals and was considering the 4049 CMOS chip. Is this a good solution?

Also, I need to change the duty cycle signals to 0-12V. Any suggestions for this?

Thanks,
JP

 

[Nigel Goodwin]

What current do you need?, simple open collector transistor drivers with pullups to 12V will both invert and change the signal to 12V - it's far easier to do this if you're inverting at the same time (as you are).

 

[quick108]

The circuit will be driving six 12ohm solenoids (fuel injectors).

I liked the idea that the single 4049 CMOS chip ($0.30) has 6 drivers which is perfect for this 6 cylinder engine. Otherwise I'd have to run 6 transistors.

Can you elaborate on your idea?

Thanks for the response!
JP

 

[Nigel Goodwin]

A CMOS logic chip can't feed a solenoid, it has no where near the capacity.

Check the relay driver circuit on one of my tutorial pages at

This inverts, and drives the solenoid direct, assuming it's switched in the negative lead. You would need to use transistors with enough gain, and current capacity.

 

[quick108]

What do you think about using ULN2803A?

JP

 

[Nigel Goodwin]

What do you think about using ULN2803A?

You could try it and see, but I suspect it will get too hot?.

 

[quick108]

Sorry, let me clarify I wleft some vital information out.

This signal will not be driving the fuel injector directly, rather it will be going through a controller which is about 62ohms and inductive than the controller will be driving the 12ohm injector.

Do you think heat will now be a problem?

 

[Nigel Goodwin]

Sorry, let me clarify I wleft some vital information out.

This signal will not be driving the fuel injector directly, rather it will be going through a controller which is about 62ohms and inductive than the controller will be driving the 12ohm injector.

Do you think heat will now be a problem?

That should be a lot better, but I would keep an eye on how warm the chip gets - obviously the current is only pulsed, so it's not current all the time.

 

[quick108]

https://www.st.com/stonline/products/literature/ds/1536/uln2803a.pdf

Do I parallel the 12V pull up resistor at pins 13-18? Also, will 1K ohm resistors be good?

Thanks for all the help Nigel!

 

[Nigel Goodwin]

https://www.st.com/stonline/products/literature/ds/1536/uln2803a.pdf

Do I parallel the 12V pull up resistor at pins 13-18? Also, will 1K ohm resistors be good?

Not to feed 62 ohms, do you need to source or sink the power to the controller?, this sort of configuration is really sinking.

 

[quick108]

OK, I am kind of confused on what I hook up to pin 10? Pin 10 is the common for the free wheeling diodes.

The input will be a duty cycled 0-5V signal and I need the output to be a inverted duty cycled 0-12V signal

 

[Nigel Goodwin]

OK, I am kind of confused on what I hook up to pin 10? Pin 10 is the common for the free wheeling diodes.

It goes to the positive supply (12V in your case).

The input will be a duty cycled 0-5V signal and I need the output to be a inverted duty cycled 0-12V signal

But does it need to source or sink current?, the ULN will only sink current.

Think of a switch and a bulb - you can connect the bulb to 12V and the switch down to chassis, this is SINKING current, or you could connect the bulb to chassis and the switch to 12V, this is SOURCING current.

 

[quick108]

Luckily it needs to sink current. Are there any other components I need to wire in to make this circuit work properly?

 

[Nigel Goodwin]

Luckily it needs to sink current. Are there any other components I need to wire in to make this circuit work properly?

No, the ULN should be all you need.