DC-DC Converters : Basics & Types

Why DC-DC Converters?

DC-DC converter is used to step-up or step-down the input DC voltage as per the load requirement and also main importantly regulates the output voltage for changes in the input voltage and load.

The output voltage regulation can be done by controlling the on/off time period (duty cycle,) of switches inside the converter.

Types of DC-DC Converters

Basically DC-DC converters are categorized into two types

1. Non-isolated DC-DC converters
2. Isolated DC-DC converters

In each category, the DC-DC converter is used to step-up or step-down the input voltage by balancing the power.

Most commonly using DC-DC converters are as follows

Non-isolated DC-DC converters

• Buck converter

Buck converter is used to step-down the input voltage by controlling the switch

• Boost converter

Boost converter is used to step-up the input voltage by controlling the switch

• Buck-Boost converter

Buck-boost converter is used to step-down/up the input voltage based on design by controlling the switch

Isolated DC-DC converters

• Flyback converter

Flyback converter is used to step-down/up the input voltage by controlling the switch with isolation for power rating < 150 W

• Forward converter

Forward converter is used to step-down/up the input voltage by controlling the switch with isolation for power rating < 400 W

• Half-bridge/full-bridge converter

Half or Full bridge converters are used to step-down/up the input voltage by controlling the switches with isolation for power rating < 800 W

• Resonant converter

Resonant converters are used to step-down/up the input voltage by controlling the switches with isolation for power rating > 1 kW. The common architecture of resonant converters is

Resonant converters use resonant control methods and all other DC-DC converters use PWM control methods for controlling the switch.

• Resonant converters are advantageous in DC-DC converters due to provision of
  • Isolation
  • High efficiency – low losses
  • Small size – high power density

• The commonly using resonnat power converters are
  • Phase-shift Full bridge (PSFB)
  • LLC Resonant converter (LLC)
  • Dual Active Bridge (DAB)