Design of a 300W DC/DC crank pulse generator for 12V and 24 V systems

Abstract

Today a modern vehicle incorporate hundreds of electronic devices, each one demanding a steady voltage supply. The vehicles electric network is supplied through the internal generator and like all electric networks the voltage level may vary during different loads. One of the largest power consumers in a vehicle is usually the starter motor, pulling several kilowatts of power during the start up and thereby adding a significant voltage drop to the electric network. These drops are called crank pulses and are defined for a couple of different cases in ISO standards. Other nodes in the network needs to be tested under these conditions and for this purpose power supplies with variable output that can simulate these voltage levels are being used. In this project a simple and cheap dc/dc converter is designed to meet the basic criterions to allow testing of nodes being subjected to crank pulses. The resulting design is based on a buck converter controlled by an Atmel AVR MEGA168 microcontroller and allows testing of resistive 12V loads in the interval 30W to 300W and resistive 24V loads in the interval 50W to 300W. The design and components are chosen based on performance, price and avaliability with a resulting component cost of less than SEK 1000 + VAT.