pwm to voltage conversion.

[hiren_dave]

Hi. friends...

i shown one circuit it gives variable output voltage as per the change in input pulse width.
if input pulse width (on time) will increase than output voltage also increases and vice verse.
how it can be?
how should i design this circuit???

 

[shabbirn]

There are various direct ICs available in the market like LM2907N, LM2907 Frequency to Voltage Converter.
Try with them.

Wish u all the best..

 

[keith1200rs]

Frequency to voltage is not the same as PWM to voltage conversion. For PWM to voltage, a simple resistor charging a capacitor is all that is required.

Keith

 

[hiren_dave]

thanks keith...
i will try.
can you give me a circuit for that?

 

[keith1200rs]

See below. Choose R and C to suit the frequency of the PWM. It is quite a common way of getting an analogue voltage out of a microcontroller without a DAC.

Keith

 

[Sloth]

If you have a DC signal (signal is always higher than ground, no minus voltage), this will do:

https://upload.wikimedia.org/wikipedia/commons/3/3b/RC_Divider.svg

You'll have to remember that you shouldn't put too much load on this circuit though. Or if you do, you need to buffer it with an op amp or such. having a 10k load in Vout, would leave you only half of the actual voltage.

Edit: Keith was faster.

 

[hiren_dave]

thanks keith and sloth...

 

[keith1200rs]

You could do something more complicated with less ripple. For example, charge up a capacitor with a constant current when the PWM is high then a sample & hold of the capacitor voltage on the falling edge and then reset the charging capacitor. However, if you don't mind the smoothing required for a simple CR it actually works very well.

Keith

 

[hiren_dave]

thanks keith...