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### Topic: Enough juice to drive a Darlington transistor? (Read 1 time)previous topic - next topic

#### primate

##### Jul 02, 2011, 09:34 pm
Hi folks, newbie here and working on my first project. I'm trying to build a DC motor controller using the PWM output pins to drive a Darlington transistor (TIP122) using an emitter ground configuration (with an IN4004 and 100nF capacitor across the motor terminals). To be honest, I have not designed hardware for quite a while so I'm a bit rusty (and analog circuits were never my strength) and can use some help.

I'm using an Uno board and I noticed the output pins are rated at 40mA. I'm supplying 12V for the motor and I expect it to draw about 1A and I wanted to make sure the PWM pins provide enough juice at the base to properly drive the transistor. The reference circuit uses a 1K 1W resistor to drive the base and I'm worried that the transistor might be drawing too much current and damage the board. The motor controller is designed for continuous duty.

Any help will be greatly appreciated!

Thanks,
- K.

#### RuggedCircuits

#1
##### Jul 02, 2011, 09:50 pm
With a 1k resistor in series with the base there's no chance you're going to damage your Arduino. Even if the base voltage is 0V (it won't be -- it'll be around 1.5V) the current will be limited to 5V/1k = 5mA.

The TIP122 has a current gain of 1000 so with a 1k series resistor you should be able to get 1A going through your motor.

--
The Ruggeduino: compatible with Arduino UNO, 24V operation, all I/O's fused and protected

#### primate

#2
##### Jul 02, 2011, 10:38 pm

With a 1k resistor in series with the base there's no chance you're going to damage your Arduino. Even if the base voltage is 0V (it won't be -- it'll be around 1.5V) the current will be limited to 5V/1k = 5mA.

The TIP122 has a current gain of 1000 so with a 1k series resistor you should be able to get 1A going through your motor.

--
The Ruggeduino: compatible with Arduino UNO, 24V operation, all I/O's fused and protected

Thanks for the quick reply! Much appreciated.
- K.

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