PWM to RC network question

[jprg]

Hi all,
I need to caculate voltage inside a RC network that is being driven from a PWM unit.

Square wave has duty cycle of 10% and frequency of 1 kHz. It drives a NPN transistor that in turn drives the RC network. I guess that it makes an integrator.

Thanks

 

[jprg]

Would I need to get into Fourier series and a bunch of calculus to calculate this?

I don't even need an exact number. Is there an easy way to get an approximation on this without actually building the circuit and measuring the voltage?

Thanks

 

[betwixt]

pretend the drive is always low and work out the voltage, then pretend it is always high and work out the voltage. The actual reading will be between the two and proportional to the PWM mark/space ratio. For example 50% m/s ratio will give half the difference.

Brian.

 

[jprg]

Hi Brian,
Thanks for your reply.
What I am confused about is that if I model the charging circuits for on and off states, using Thevenin equivalent circuit, the Thevenin resistance will be different between the two.
For the on state, I get voltage of 3.722V and resistance of 248.
For the off state, I get voltage of 15V and resistance of 1000.
To put it in other words, the RC time constants will be different for on and off states.
Would the resulting voltage still be proportional to the on/off ratio?

Thanks.