capacitor and inductor in boost converter

hi. just wanna ask, what is the function of capacitor and inductor on boost converter to increase the output voltage? thanks :)

Answer 1

[Mahmoud Saleh]

Basically, without them the output of the converter whether it is voltage or current will be square wave, on/ off. Most of loads can not handle such waves. In order to smooth out the current an inductor is used and to smooth out the voltage a capacitor is used. Therefore, basically the inductor and the capacitor act as a filter.

This square wave, if you analyze it using Fourier, its multiple of cosines and sines with different frequencies added up together to form the square wave. In order to filter the high frequency waves, an LC filter is used.

[Alex Wang]

I think you are half right.

It's easier to explain it from the energy perspective.

The capacitor in the boost converter is for filtering purpose (The voltage across capacitor could not change suddenly).

The inductor is where the "Boosted Energy" comes from. During switch ON stage, the source will charge the inductor. Once the switch is closed, inductor will release its all energy along with the source to the load side. The release of energy (Negative diL/dt) will make the voltage across inductor to become negative. And on the load side, Vout=Vin-vL. And since vl is negative during switch OFF, it will result in Vout > Vin.

Usually a proper value of L and C is selected based on system requirments (continous conduction mode, voltage ripple limt, current ripple limit...)

Hope this helps

[Mahmoud Saleh]

I agree with Alex. However, there is a minor correction, the inductor used to boost the voltage not the energy. The energy can't be boosted. as you step up the voltage, you simultaneously step down the current. Energy cannot be created or destroyed "Law of Conservation of Energy."