When we need to convert the voltage of the power from direct current, we involve the device called DC-DC converter. As direct current voltages cannot be changed using transformer as in AC current DC-DC converters comes into play. These converters are similar DC version of the transformers. For example, when a 24volt direct current from a lorry power source needs to be decreased to 12volt for the car music system and 12Volt car power sources needs to stepped down to 3volt for mobile phones these electronic devices are applied. Here we simply want to change the voltage with a minimal loss of energy. We can also explain this as extracting maximum efficiency while converting. We have to keep in mind with DC-DC converters is that it is essential to alter the input energy into various impedance levels. Hence, the power delivered out of the converter remains the same as given in with a different voltage with no energy produced within the converter. A perfect converter gives an efficiency of 100% but in practical applications 70% to 95% efficiency are usually got. It is normally obtained with the help of switched mode or chopper circuits whose elements wastes very less power. Pulse-width modulation (PWM) helps with controlling and regulating the voltage output. The method is also implemented for circuits that involves AC, which includes highly efficient AC-DC converter (inverters and power amplifiers), ac-ac power converters, as well as few ac-dc power converters (low-harmonic rectifiers).