LM317 Controlled by PWM and a MOSFET

Hey Guys,

Ive seen a few discussions on the internet relating to how people have used the arduinos PWM signal to change the adjust pin on a LM317 Voltage regulator using a MOSFET.

I know this is usually done through the ratio of a resistor and a potentiometer in a feedback loop, but since a PWM signal can only be changed to emulate a DC Signal for voltage I’m getting quite lost on how driving it into a MOSFET could act as resistance to change this ratio.

I want to regulate my 12v (via Wallwart) into the lm317 to anywhere between 2-10v using the PWM from my arduino so i can digitally set the voltage.

This is one discussion that i have come across.

http://www.protonbasic.co.uk/showthread … entiometer

Any Help is more than appreciated.

The circuit you describe would require feedback because otherwise, there is no way to know just what resistance the MOSFET presents for a given PWM (filtered to a DC voltage) value. Another approach might be to use a digital potentiometer. Google “arduino digital potentiometer” for some ideas. A limitation of this idea is that the voltage on the digital pot resistance element is not supposed to exceed the pot’s power supply voltage, which is typically 5.5 V maximum. In its simplest form, such a circuit would limit your output voltage range to about 1.25 - 7 volts.

Analog Devices now markets the AD5290, which boasts 20-30V supply voltages, but the 5 mA resistance element current limit would have to be observed.

Here is a discussion: http://forums.parallax.com/showthread.p … -regulator