GATE Electrical Engineering - Complete Master Library

 

 Page 22 – Step Down Chopper (Buck Converter)

                                        

1️⃣ What is a Step Down Chopper?

A Step Down Chopper (Buck Converter) is a DC-DC converter that produces an output voltage lower than the input voltage.

✔ Output Voltage < Input Voltage
✔ Used for DC motor speed control
✔ High efficiency converter

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2️⃣ Circuit Operation

• Switch ON: Load connected to supply → Current increases
• Switch OFF: Freewheeling diode conducts → Current decreases

Switching frequency is very high to maintain smooth DC output.

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3️⃣ Output Voltage Derivation

During ON time (T_ON):

V_o = V_in

During OFF time:

V_o = 0

Average Output Voltage:

V_o(avg) = (T_ON / T) × V_in

Since,

Duty Cycle (D) = T_ON / T

V_o(avg) = D × V_in

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4️⃣ Important Characteristics

• 0 ≤ D ≤ 1
• Output voltage controlled by duty cycle
• Continuous and Discontinuous conduction modes
• Ripple depends on L and switching frequency

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 GATE Important Points

• Derivation of V_o(avg)
• Waveform understanding
• Current ripple calculation
• Effect of inductance
• Continuous vs Discontinuous Mode

Very Important: Buck converter is most commonly asked DC-DC converter in GATE.