sine wave amplitude to control pwm

[harps]

hello : )

I am trying to design a circuit that will allow me to use the amplitude of a sine wave as a control signal (10khz from a sound card) to control the duty cycle of a PWM generator.

The idea I have so far, is sort of like this:

Sine wave AC (control signal) > full wave rectify to DC > to vary pwm generator duty cycle.

ive done some measurements of the voltages and I've added them to a draft schematic below.

Im not sure what I can do to connect this together to make it work, any ideas would be great, as im a bit stuck.

heres a pic:

In the end I used 1N4148 diodes to rectify the AC signal to DC. (when i took voltage measurments)

thanks for any help : )

UPDATED PICTURE*
cant seem to delete the old attachment below

 

[panic mode]

that PWM circuit is not easily converted to do what you expect. this is simpler:
http://www.solorb.com/elect/solarcirc/pwm2/

you can simply get rid of potentiometer and the two resistors around it and bring DC control signal directly to pin6.

you will need to scale your DC signal to get proper range (we could add another opamp to get that gain, or repurpose one used as virtual ground).

your rectifier is not good. lower side of your AC input is on wrong terminal.

 

[harps]

Thanks panic mode for your reply .

is this a high frequency PWM circuit? As i need it to be well above human hearing range.

i think it may be 400hz ? not 100 percent sure. : /

 

[panic mode]

you can make it anything you like, the key is how the PWM is obtained. with circuit like this you get separate oscillator and comparator so hacking is easier (you can modify one part without affecting rest of the circuit). beside oscillator has single capacitor, you can easily replace it to get it into particular range...

 

[crutschow]

...........
is this a high frequency PWM circuit? As i need it to be well above human hearing range.

i think it may be 400hz ? not 100 percent sure. : /

You need to be >20kHz to be above the human hearing range.