# Step Up Chopper vs Step Down Chopper-Difference between Step Up Chopper and Step Down Chopper

The chopper is a high speed on/off switch. This page on compares Step Up Chopper vs Step Down Chopper describes difference between Step Up Chopper (i.e. Boost converter) and Step Down Chopper(i.e.Buck converter).The page describes operation of both the circuits.

In both the chopper circuits, switch connects source with the load and diconnects at very fast speed or rate. Hence chopped output is derived from constant dc supply voltage.

## Step Up Chopper-Boost converter

Figure-1 depicts circuit of Step Up Chopper. As it increases input voltage, hence it is also known as boost converter.

The Operation of the Step Up chopper is as follows:
• When the chopper is in ON state, the switch path is closed and current flows. Hence inductor connected in series stores energy during this ON period.
• When the chopper is in OFF state, the switch path is open. Inductor current does not reduce instantaneously and it flows through the diode and load during this OFF period.
• Due to above, voltage across the load exceeds the source voltage Vs. Hence the circuit is referred as step up chopper.
• The equation for average load voltage for this boost converter is given by following:
Vo = ( T/Toff )* Vs = (1/1-α)*Vs
Where,
α is duty cycle
T =Ton + Toff

## Step Down Chopper-Buck converter

Figure-2 depicts circuit of Step Down Chopper. As it decreases input voltage, hence it is also known as buck converter.

The Operation of the Step Down chopper is as follows:
• When the chopper is in ON state, load voltage is equal to the source voltage.
• When the chopper is in OFF state, the load current flows through the diode. As a result load terminals are short circuited by the diode. Hence load voltage is zero during the OFF period.
• Due to above, load current increases during ON period and decreases during OFF period. Hence chopped DC voltage is available at the load. Hence the circuit is referred as step down chopper.
• The equation for average load voltage for this buck converter is given by following:
Vo = { Ton/(Ton+Toff) }* Vs = α*Vs
Where,
α is duty cycle
T =Ton + Toff