Trouble with transistors

So I am trying to use an Arduino pin to turn on a transistor that is acting like switch for a motor. The transistor needs 1 amp but I know the Arduino is not capable of supplying that much current. So I need to either switch transistors (would rather not) or step up the current. I believe a transistor can be used to increase current could I used another transistor if so how do I know which transistor to use? The ones I have are: CEN2N4 126, 2N3904 and the 2N7000. Will any of those get the job done?

Maybe you post what transistor you are trying to use, and the schematic of your circuit; it could be that you don’t necessarily need a secondary transistor to switch it. Regardless, knowing the specs of the transistor will help determine all of that, anyhow, if you do need a secondary one.

At the same time - it might be better just to get a completely different device (likely a logic-level mosfet) - but to know which one, we would also need specs for your motor.

Okay so the transistor I want to use for the switch on the motor is F22AB TIP31C.

I am kind of stuck with it at the moment. I will go back to radio shack and try to find a transistor that meets my specs tomorrow but they have a limited selection. I need a transistor that can be turned on by the arduino and can also handle the current from a 12v battery. From what I understand they typically run around 1.5 A. However, to be safe, I bought the F22AB which can handle 3A because I dont know how much amperage my motor and pump are going to draw from the battery. Actually, I was going to use two AA's to power the 12v motor cause the guy at radio shack said I could get more torque from it if I did that but the pump will run off of a 12v battery.

Now I am using the arduino to time the two motors so they come on and off in intervals which I set, hence why I am using transistors.

Also, I happen to have a few 741's lying around. Could I use one of them to amplify the current coming out of the arduino? Maybe in a voltage to current configuration? Would I need a second stage to safeguard the arduino?

You'ld get better information if you tell us the voltage and current rating of the motor. I wouldn't have much faith in "the guy at Radio Shack" if he advises using 2 AA cells to replace a 12v battery. And you should be aware that the torque required from the motor (and hence the current) depends on the load presented by the pump and has nothing to do with the battery you use.

Three ratings are needed when you design a circuit to control a motor.
Motor stall and running current plus motor voltage.

Would you measure the motor winding resistance?

Hey ! No need to bash RadioShack. Fir over 75 years they have made electronic components available to hobbyists and professionals alike by selling them right in your neighborhood. Nobody evrr expected the guy behind the counter to know anything more than what he had in stock and which store had what he didn't. I'd use a mosfet to PWM the motor .Spsrkfun sells the FQP30N06 for $ 0.99.

For just switching the motors on and off you could just use a relay or, as Raschemmel suggests a logic level MOSFET if you want to vary the speed with PWM.

The transistor you have doesn't need 1 A base current, that's its rated maximum. It will however need about 150 mA to switch 1.5 A and that is too much for the arduino.

Russell

You could that transistor if you made a darlington configuration. Google it ("darlington") (but I would use a mosfet)

You're better off going to RadioShack and picking up a Tip 120 or 122, depending what they have. They cost about $1-2 there, can drive up to 5A if you put a heat sink on them, and work great if with PWM.

They do have a tendency to get hot, so you may want to also buy a heatsink while you're there.

Take a look at this tutorial, it should answer all of your questions.

The downfall of only using a single transistor to control your motor is that you can only move in one direction. If you need bi-directional control, you're best off purchasing an H-Bridge from SparkFun/Adafruit/MicroCenter/Pololu that can drive at least 2A.

Last thing, you should get an external power supply that isn't connected to your Arduino. If you try and share power between your board and the motor, you'll find that the motor (being an inductive load) draws more power when you start moving it, and can pull power away from the Arduino, causing it to reset and do other funny things to drive you mad.

xxmamakinxx: You're better off going to RadioShack and picking up a Tip 120 or 122, depending what they have. They cost about $1-2 there, can drive up to 5A if you put a heat sink on them, and work great if with PWM.

They do have a tendency to get hot, so you may want to also buy a heatsink while you're there.

Bad idea to use a darlington when you can get a logic mosfet for less than $1. https://www.sparkfun.com/products/10213

Darlingtons always drop ~1.5volt. More when current increases. That is 1.5watt per ampere motor current. A heatsink is always needed, and the motor gets 1.5volt less. A logic mosfet is the same price, generally does not need a heatsink, and drops only a fraction of a volt. Leo..