BUCK CONVERTER

The three basic switching power supply topologies in common use are the buck, boost and buck-boost. These topologies are non-isolated, i.e. the input and output share a common ground. The power supply topology refers to how the switches, output inductor and output capacitor are connected. Each topology has unique properties. These properties include the steady state voltage conversion ratios, the nature of the input and output currents, and the character of the output voltage ripple. Another important property is the frequency response of the duty cycle to output voltage transfer function.

We are employing the buck converter for this project. The buck converter is one of the most fundamental topology of any switching power supply configuration. It is basically a forward mode regulator and is also the basic building block for all the forward mode topologies.

The basic circuit of a buck converter is shown in the above figure. When the switch Q1 is turned on, the input voltage is applied to inductor L1 and the power is then delivered to the output. Inductor current can also build up according to Faraday’s Law as shown below:

V_L = L (di/dt)

When the switch is turned off, the voltage across the inductor reverses and the free-wheeling diode D1 becomes forward biased. This allows the energy stored in the inductor to be delivered to the output where the continuous current is then smoothed by the output capacitor. Typical waveforms for a buck converter are shown in the below figure.