CONTENTSIntroductionStep down chopperStep up chopperClassification of choppersApplicationsReferences
Introduction The conversion of fixed DC voltage to an adjustable DC output voltage, through the use of semiconductor devices is called chopping. A chopper is a static device that converts fixed dc input voltage to a variable dc output voltage directly. It is a high speed on/off semiconductor switch . Chopper systems offer smooth control, high efficiency, fast response and regeneration
DEFINATION:Converting the unregulated DC input to a controlledDC output with a desired voltage level.• It is also known as dc-to-dc converter or DC Chopper
DC supply(from rectifier- DC output LOAD filter, battery, fuel cell etc.) Vcontrol (derived from feedback circuit)
Choppers are of Two Types :1. Step-down choppers. (buck converter)2. Step-up choppers. (boost converter ) In step down chopper output voltage is less than input voltage. In step up chopper output voltage is more than input voltage.
Principle Of Step-down Chopper : Chopper i0 + V R V0 A step-down chopper with resistive load.
• The thyristor in the circuit acts as a switch.• When thyristor is ON, supply voltage appears across the load• When thyristor is OFF, the voltage across the load will be zero.
The average output voltage can be found by :Average Output Voltage tON Vdc V tON tOFF tON Vdc V V .d T tONbut d duty cycle t
Principle Of Step-up Chopper : Chopper i0 + R V V0 D L E A step-up chopper with R-L Load
• When chopper is ON, supply is connected across load.• Current flows from supply to load.• When chopper is OFF, load current continues to flow in the same direction through Diode due to energy stored in inductor ‘L’.
Therefore voltage across load is given by : dIVO V L i.e., VO V dt We clearly see that the output voltage is greater than the input voltage.
Classification Of Choppers• Choppers are classified as : • Class A Chopper • Class B Chopper • Class C Chopper • Class D Chopper • Class E Chopper
Widely used in DC motor . For Speed Controller In Switched mode power supply (SMPS)Battery chargersAlso used in regenerative braking. Class D Electronic amplifiers Switched capacitor filters Variable Frequency Drive