Question

Describe how the dc voltage at the buck chopper output varies when the duty cycle of the switching control signal is increased.

Answer 1

The average output voltage value of a buck chopper is related to the duty cycle, Duty cycle (D) which is defined as the conduction time of the transistor switch during one full switching cycle. If VN is the supply voltage, and the "ON" and "OFF" times for the transistor switch are defined as: to and to, then the output voltage VouT is given as Buck Converter Duty Cycle OUT = IN CON+ OFF The buck converters duty cycle can also be defined as tON+toFF Total Time T D YOU or Vour DV VIN From the above equation the output voltage can be varied by varying the duty cycle.So the larger the duty cycle, the higher the average DC output voltage. From this we can also see that the output voltage will always be lower than the input voltage since the duty cycle, D can never reach one (unity) resulting in a step-down voltage regulator. Voltage is regulation is obtained by varying the duty cycle and with high switching speeds, up to 200kHz. smaller components can be used thereby greatly reducing a switches power supply's size and weight