Controlling external PS via PWM

I need to be able to control an external 12V, 1A DC power supply via a PWM pin on the Arduino. Depending on the voltage of the PWM pin, the output of the circuit should be 0 to 10(or 12)V. I will be powering a simple LED strip that runs at 12V/200mA. With lower voltage and current I should be able to dim the strip to get exactly what I want. I'm hoping to use an op amp or some other component to do the work. Will an LM675 do the trick or is there something else I can use?

Thanks!

Depending on the voltage of the PWM pin

Voltage on this pin is only ever 0V or 5V.
http://www.thebox.myzen.co.uk/Tutorial/PWM.html

With lower voltage and current I should be able to dim the strip to get exactly what I want.

Current yes voltage not so, you need a certain amount to turn on the LED.

Grumpy_Mike:

Depending on the voltage of the PWM pin

Voltage on this pin is only ever 0V or 5V.
http://www.thebox.myzen.co.uk/Tutorial/PWM.html

Sorry, I meant that I could smooth out the PWM signal to get an analog signal using an RC filter. So if I ran the PWM pin at 50%, it would output 2.5V.

Grumpy_Mike:

With lower voltage and current I should be able to dim the strip to get exactly what I want.

Current yes voltage not so, you need a certain amount to turn on the LED.

I've tested this manually with a pot and the dimming will work exactly how I want. I just need a way to do it automatically with the Arduino.

And you have rejected the idea of simply using PWM directly to dim the array?

MarkT:
And you have rejected the idea of simply using PWM directly to dim the array?

The array requires 200mA which is too much for the Arduino pin to handle.

The array requires 200mA which is too much for the Arduino pin to handle

Yes but withe the addition of a transistor or a FET it could give you a PWM at 12V with as much current as you want.

Grumpy_Mike:

The array requires 200mA which is too much for the Arduino pin to handle

Yes but withe the addition of a transistor or a FET it could give you a PWM at 12V with as much current as you want.

That's exactly what I'm looking for. The transistor or FET would be controlled by the PWM pin and would be connected to an external power supply. right?

Yes that is right.
Output pin to 1K resistor, other end of resistor to the base. Emitter to ground, collector to -ve of your LEDs +ve of your LEDs to 12V.