Switching-Mode Power Supply Design Tutorial; Part 3: Simple Switching Topologies

Focus:

Part 3 of this tutorial explains operation of the following switching topologies: heater control, switched-capacitor converter (a.k.a. charge pump converter) switched-inductor converter and buck converter. Simplified circuits consisting of a voltage source and a switch in combination with one or more components (resistor, capacitor, inductor, or diode) are presented for each topology. Efficiency issues are briefly discussed. Key parameters related to switching waveforms are introduced and tips for making calculations with pulse and periodic waveforms are given. Formulas and rules-of-thumb are given for determining parameters such as inductance, capacitance, output overshoot, and output ripple. The state-plane concept is introduced and used to explain turn-on and turn-off behavior of the buck converter, and also to explain hysteric control (also known as bang-bang or ripple control) of a buck converter. The overall usefulness of state-plane analysis in switched-mode power supply design is discussed. The pros and cons of hysteretic control and why pulse-width modulation control is more popular are also discussed.

What you’ll learn:

• How to understand the basic operation of switching regulators
• How to understand basic concepts and analytical techniques used in switched-mode power supply (SMPS) design
• How to understand the value of the state-plane in analyzing switched-mode power supply designs

Notes:

This section is Part 3 of 3. For a description of Part 1, see the How2Power Design Guide under "Power Supply Function" and "DC-DC Converters." For a description of Part 2,see the How2Power Design Guide under "Power Supply Function" and "Voltage Regulators."

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Author & Publication:

Jerrold Foutz, SMPS Technology, Oct 07 2007

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