TABLE OF CONTENTS With a contribution by Tom Egel,
Mentor Graphics Corporation
This case study illustrates how VHDL- AMS can be used for the detailed design of a DC-DC switching power supply. For the RC airplane system, a step-down converter is required to convert the 42 V battery voltage used to power the propeller motor to the 4.8 V needed for the on-board servo electronics. In this case study we briefly introduce switched-mode power supply theory, and then perform a detailed design of a simple step-down (buck) converter. We discuss averaging techniques that facilitate analysis of the closed-loop system and use VHDL-AMS simulations to perform system-level design trade-offs.
In this case study, we examine the design of a switching power converter for the RC airplane, outlined in Figure 18-1. Switch-mode power supplies have all but replaced their linear counterparts as the preferred method for converting the supply of DC power from one voltage level to another. This is especially true in today's world of handheld compact electronic systems, where size, weight, efficiency and cost are all critical to the overall system design. All switching supplies use pulse-width modulation (PWM) techniques to achieve efficiency and provide the necessary control of the output voltage as load conditions change. Because of the combination of electronic and magnetic components in a switching power supply, computer simulation plays a vital role in creating a successful design. As we will see, VHDL-AMS is well suited to handle both this mixed-technology aspect and...
