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Boost Converter Example

Step-up DC-DC converter with current mode control.

Overview

The boost converter steps up DC voltage, commonly used in: - Battery-powered devices - Solar MPPT front-end - PFC rectifiers - LED drivers

Specifications

Parameter Value
Input Voltage 12V DC
Output Voltage 48V DC
Output Power 100W
Switching Frequency 100 kHz
Inductor 68 µH
Output Capacitor 100 µF

Circuit Files

  • boost_basic.ipes - Open-loop boost converter
  • boost_current_mode.ipes - Average current mode control
  • boost_pfc.ipes - PFC application

Theory

Operating Principle

Switch ON: - Inductor charges from input - Output capacitor supplies load

Switch OFF: - Inductor energy transfers to output - Voltage steps up

Key Equations

Voltage Conversion Ratio: $\(\frac{V_{out}}{V_{in}} = \frac{1}{1-D}\)$

Right-Half-Plane Zero: $\(f_{RHPZ} = \frac{(1-D)^2 R_{load}}{2\pi L}\)$

Minimum Inductance (CCM): $\(L_{min} = \frac{D(1-D)^2 R_{load}}{2 f_s}\)$

Design Considerations

Right-Half-Plane Zero (RHPZ)

The RHPZ limits control bandwidth: - Cannot cross over above fRHPZ - Typically limits bandwidth to fRHPZ/5

Input Current

Continuous input current (advantage for battery/solar): $\(I_{in,avg} = \frac{I_{out}}{1-D}\)$

Exercises

  1. Voltage Gain: Verify Vout vs D relationship
  2. RHPZ Effect: Measure loop gain, observe phase drop
  3. Current Ripple: Compare with buck converter
  4. Soft-Start: Implement duty cycle ramping