NPN Switch Strong Ground

All,

I am trying to use an Arduino to control some functions in a car. For this particular function, I need the Arduino to sink .4 amps to control cutouts on the exhaust of the car. The open and close of the cutouts is controlled by seeing ground. I know the IO pin can only provide a max of 40 mamps.

I want to use an NPN (2N2222A) to accomplish this. I want to make sure my thinking is correct. I want to connect the open wire of the cutouts to the collector of the NPN, base to the Arduino and the emitter to ground. When I apply 5V to the IO pin, will the NPN short and cause the cutout to see the ground?

Thanks

OP Image:

You will probably need to reduce the resistor value if you want that much collector current. Or better yet, use a mosfet instead.

Right idea, wrong part. A 2N2222 transistor is limited to about 800 mA or less, not even close to 4 Amps unless you are planning to put transistors in parallel and balance the currents somehow.

Perhaps you want to use a 2N3055 transistor, or a logic-level MOSFET.

I cannot tell from the text or from the picture, but if the load is inductive (e.g. a motor or a solenoid) then there should also be a shunt diode to protect the transistor.

I read the OP as saying 0.4A. I'd be pretty surprised is a small exhaust cutout valve needed 4A

vaj4088:
Right idea, wrong part. A 2N2222 transistor is limited to about 800 mA or less, not even close to 4 Amps unless you are planning to put transistors in parallel and balance the currents somehow.

Perhaps you want to use a 2N3055 transistor, or a logic-level MOSFET.

I cannot tell from the text or from the picture, but if the load is inductive (e.g. a motor or a solenoid) then there should also be a shunt diode to protect the transistor.

Load is .4A (400mA), not 4A.

How is the Arduino being powered?

Sorry, I missed seeing the decimal point. 2N2222 could work but resistor value may need to change. Also, I still wonder about an inductive load.

OP wrote .4Amp. Should have written 0.4Amp or 400mA. Dots are sometimes overlooked.

A 2N3055 is a useless dinosour.
A 2N2222 is borderline for 400mA.
A TIP120 or some other darlington would work here.
A logic level mosfet would be best.

Yes, a back EMF diode from collector to 12volt could be needed to protect the transistor.

Potentially dirty (spikes) 12volt from a car could be unhealthy for the Arduino.
Leo..

I would vote for the darlington, as then you don't have to worry about adding a zener to protect a
MOSFET's gate oxide (automotive environments are unforgivingly noisy and a single voltage spike is all it
takes to puncture a MOSFET's gate oxide).

saximus:
OP Image:

You will probably need to reduce the resistor value if you want that much collector current. Or better yet, use a mosfet instead.

Am I looking at a 5V SLA just for the Arduino, and the exhaust flappy thing getting 12V that's not shown?

MarkT:
I would vote for the darlington, as then you don't have to worry about adding a zener to protect a
MOSFET's gate oxide (automotive environments are unforgivingly noisy and a single voltage spike is all it
takes to puncture a MOSFET's gate oxide).

A darlington might be safer, but it still needs a kickback diode with an inductive load.
Leo..

Indeed, I should have mentioned it - this is always the case for highly inductive loads like this.