Variable Voltage Using PWM and Low Pass Filter

Question

I am trying to control a steady DC output voltage using a Micro controller with a PWM duty cycle. With the current schematic, the Voltage on Vout is pulsing along with the Mosfet at what ever the duty cycle is. I know that this is the result of Load being grounded only when Mosfet is "on", but can not figure out how to get around this. I want a smooth, controllable Vout that uses the same ground as the Fet. I know this is a noob question but any help will be appreciated. Also, I don't want to be picky but for me pictures really do speak a thousand words.

Current Schematic

Simulation

EDIT

What I'm really looking for is a way to use a low-pass filter to smooth a PWM voltage. This smoothed out voltage will then be used to power a 1 ohm load. I know how to create a PWM voltage and a low pass filter, but not how to implement both to power something. Since I'm new to circuits, a simple schematic drawing will be very helpful.

Answer 1

you have to read theory of DC/DC (buck or boost) converters. http://www.learnabout-electronics.org/PSU/psu31.php

Answer 2

Here's one viable approach.. the buffer simulates the micro output. The output in this case is 0-Vdd = 0-5V and that is filtered and buffered and amplified by 1.6 to give 8V. I used 1kHz for this, but you can adjust resistor and cap values to suit. For precision, you can use an actual buffer and give it a separate reference supply. The op-amp type will depend on your requirements, but probably would be a rail-to-rail in and out capable of handling the desired output voltage.

Edit: If you're actually wanting a 1 ohm load, you'll also need a hefty power stage followingt hte op-amp. This is a separate question, really. The PWM gets you the analog voltage, but you want a really high current, so that voltage requires a power analog buffer stage.

P.S. You should be able to run the simulation on this.

^{simulate this circuit – Schematic created using CircuitLab}

Answer 3

The problem in your design is basic:

1. The series filtering resistors are too large, and they add inefficiencies. Use an inductor instead and thus filter with an LC circuit instead of RC.
2. The series filtering capacitors need to go to ground, not to the drain of the mosfet.
3. Once inductance is added, a freewheeling diode needs to be added to prevent spurious oscillations and large voltages generated when the MOSFET would open.