# Buck Converter Efficiency

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#### Rory34

I'm wondering how to calculate the duty cycle of a buck converter?

#### ron simpson

Example: you have 10V and want to buck it down to 5V, use 0.5 duty cycle.

#### salmanshu322

duty cycle is basically the measure of on time vs off time. output voltage by input voltage give you efficiency. duty cycle give you the percentage of power use.

#### simon mugo

The duty cycle is a ratio of output voltage against input voltage. When given an output voltage of 20v and an input voltage of let us say 100 volts then the duty cycle is 20/100.

#### bertus

Hello,

The duty cycle does not tell all about the efficiency.
The losses in the parts are not taken into account.
The switching element (most times a mosfet) has a resistance.
Also the used inductor will introduce losses.

Bertus

#### Papabravo

To calculate the efficiency, you need to compute the ratio of the output power with respect to the input power. The immutable rule of DC-DC conversion schemes of any type is that the output power will ALWAYS be less than the input power. Sometimes it will be much less.

Edit: Here is an example from a simulation on an open loop buck converter. The figure of 89% is typical for rudimentary circuits. We can do better, but things get more complicated quickly.