Boost Converter

A boost converter is a step-up DC-DC converter that produces an output voltage higher than its input voltage. They are essential in solar PV systems and hybrid electric vehicle powertrains to step up low battery voltages.

Core Concept

During the ON state of the MOSFET, the input source charges the inductor directly. The diode is reverse-biased, isolating the output capacitor, which supplies the load alone.

During the OFF state, the inductor voltage adds to the input voltage. This combined voltage forward-biases the diode to recharge the capacitor and supply the load.

The output voltage increases as the duty cycle approaches 1. The input current is continuous, making it ideal for battery and solar sources.

Key Formulas

Voltage ratio Vo / Vin = 1 / (1 - D). Inductor ripple current dI = (Vin * D) / (L * fs). Capacitor ripple voltage dVc = (Io * D) / (C * fs).

Given:\nVin = 12 V, Duty cycle D = 0.6.\n\nFormula:\nVo = Vin / (1 - D)\n\nSteps:\n1 - D = 0.4\nVo = 12 / 0.4 = 30 V\n\nFinal Answer:\nThe output voltage is 30 V.

Exam Tip: GATE trap: A practical boost converter cannot achieve infinite output voltage at D=1. Parasitic resistances in the inductor and switch cause the voltage to collapse at extremely high duty cycles.

Performance Parameters

• Voltage Gain: Always greater than or equal to 1.
• Input Current: Continuous, reducing electromagnetic interference.
• Output Current: Pulsating, requiring a large output filter capacitor.
• Switch Voltage Stress: Equals the maximum output voltage Vo.
• Right Half Plane Zero: Exists in the control transfer function, complicating feedback loop design.

Quick Revision

• Steps up DC voltage.
• Inductor is in series with the input.
• Input current is continuous.
• Output current is discontinuous.
• Switch connects inductor to ground.
• Exam trap: Calculating average switch current as identical to input current. Average switch current is strictly Iin multiplied by D.