PWM Filter for fan input

[Jakethepython]

I have a small 12 VDC fan that i am running from a PWM out of PIC24 Micro. It is being switched through a MOSFET on the Low side. The problem is normally the system is running as 12VDC  Some applications will require a 24VDC input. I have a voltage sense that will put my PWM to 50% creating an average voltage of 12 VDC. The 24 volt spikes are killing the fan though. what is the best way to go about smoothing the voltage out of the PWM to be DC voltage.

[S. Petrukhin]

I have a small 12 VDC fan that i am running from a PWM out of PIC24 Micro. It is being switched through a MOSFET on the Low side. The problem is normally the system is running as 12VDC  Some applications will require a 24VDC input. I have a voltage sense that will put my PWM to 50% creating an average voltage of 12 VDC. The 24 volt spikes are killing the fan though. what is the best way to go about smoothing the voltage out of the PWM to be DC voltage.

PWM always has the same amplitude, equal to VCC but different filling, i.e. the time during which this voltage is connected to the load. To reduce this amplitude, you can use the LC filter as an integrator or LL / CC divider, calculating the reactance.

[Jakethepython]

You're English is fine. The only problem with an LC filter based on Frequency is that it will always chop the voltage so when i have a 12V amplitidue it will make it seem like a 6  volt. Unless I am doing something wrong.
Thanks in advance
Jake

[S. Petrukhin]

You're English is fine. The only problem with an LC filter based on Frequency is that it will always chop the voltage so when i have a 12V amplitidue it will make it seem like a 6  volt. Unless I am doing something wrong.
Thanks in advance
Jake

I made a little mistake-RC filter. Not every PWM can withstand the load on the LC. See how class D amplifiers generate output voltage. You can even use a TDA amplifier with a standard datasheet circuit to generate the desired DC voltage using PWM. And any step-down pulse converter.

[David Hess]

An LC filter will do what you want.  Essentially PWM driving an LC filter is the output stage of a buck switching converter with an output voltage equal to the input voltage times the duty cycle.