# Average voltage in PWM?

I have a doubt regarding average PWM voltage. Let's take a buck convertor with Vin=10V, Vout=5V. With this we can determine the duty cycle of PWM needs to be 50%. Thus means the MOSFET of the buck is switched on for half of the time and switched off for remaining time.

How can we say that output voltage will be 5V. It needs to be a varying voltage from 0 to 12V, since the voltage is being turned on and off by PWM. Why are we using the average voltage?

• So this must be a perpetual motion PWM? 10V goes to 12V… Jun 24 at 21:45
• Are you aware of how the inductor and freewheel diode works? The switcher provides bursts of current to charge the inductor and the output filtering capacitor holds the output end at constant voltage. Post a circuit for analysis if you want. Jun 24 at 21:54
• A buck converter is basically a pwm switch followed by a filter to remove the pwm and leave us with the average dc voltage. Think of it like a water tap going into a pipe. The mass of water serves to filter or average the water flow. Whilst the tap way be turned on/off at various duty cycles, the result at the end of the pipe is a continuous flow of water - it might fast or slower depending on the duty cycle. Jun 24 at 21:55
• "PWM" is not necessarily the same as "buck converter." PWM without an inductor (and possibly a capacitor) is NOT a buck converter. Jun 24 at 21:56
• electronics.stackexchange.com/questions/367574/… Jun 25 at 11:40

$$f_c = \frac{1}{2 \pi \sqrt{L C}}$$
If you now can guarantee that your PWM switching frequency is much higher than your cut-off frequency $$\f_c\$$, you will essentially have an almost DC output.