Buck converter or regulator
The following section explains the buck converter or regulator in details.
Basic buck converter or regulator:
- The fundamental circuit for a step down converter or buck converter consists of an inductor, diode, capacitor, switch and error amplifier with switch control circuitry.
- The circuit for the buck regulator operates by varying the amount of time in which inductor receives energy from the source.
- In the basic block diagram the operation of the buck converter or buck regulator can be seen that the output voltage appearing across the load is sensed by the sense / error amplifier and an error voltage is generated that controls the switch.
- Typically the switch is controlled by a pulse width modulator, the switch remaining on of longer as more current is drawn by the load and the voltage tends to drop and often there is a fixed frequency oscillator to drive the switching.
Buck converter operation
- When the switch in the buck regulator is on, the voltage that appears across the inductor is Vin - Vout.
- Using the inductor equations, the current in the inductor will rise at a rate of (Vin-Vout)/L.
- At this time the diode D is reverse biased and does not conduct.
- When the switch opens, current must still flow as the inductor works to keep the same current flowing. As a result current still flows through the inductor and into the load.
- The diode, D then forms the return path with a current Idiode equal to Iout flowing through it.
- With the switch open, the polarity of the voltage across the inductor has reversed and therefore the current through the inductor decreases with a slope equal to -Vout/L.