Overview of Design Examples of AC-DC Non-isolated Buck Converters

In this chapter, as our second installment in the series on AC-DC converter design, we take up design examples of non-isolated buck converters. In the series on the design of AC-DC converters, we previously, under the title “Design Method of PWM AC-DC Flyback Converters“, explained design of AC-DC converters with an isolated flyback design. In this chapter, we shall analyze the circuit operation and design examples of AC-DC step-down converters that do not use a transformer.

Of course, AC-DC converters are not all isolated-type devices. In fact, there are numerous applications that do not require isolation, and by dispensing with the transformer, there are advantages in size, weight, and cost. We begin by considering a circuit example that is easy to visualize. This is a step-down converter generally known as a “buck” converter, and is also called a diode rectifier or asynchronous rectifier. Conceptually, it is the same as a DC-DC buck converter.

Here we also give an overview of this chapter. We first review the basic operation of buck converters, and will be using the above circuit example in explanations ranging from the method of component selection to layout design.

• ・What are Buck Converters? – Basic Operation and Discontinuous Mode vs. Continuous Mode
• ・Selection of Power Supply ICs and Design Examples
• ・Selecting Critical Components: Input Capacitor C1 and VCC Capacitor C2
• ・Selecting Critical Components: Inductor L1
• ・Selecting Critical Components: Current Sense Resistor R1
• ・Selecting Critical Components: Output Capacitor C5
• ・Selecting Critical Components: Output Rectifying Diode D4
• ・EMI Countermeasures
• ・Board Layout and Summary

• AC-DC converter