SWITCHING POWER SUPPLIES FOR SPECIAL VEHICAL APPLICATIONS Adriana FLORESCU 1) , Alexandru Vasile 1) , Luigi Vladareanu 2) , Dumitru Stanciu 1) 1) “Politehnica” University of Bucharest, Electronics, Telecommunications and Technology Information Faculty, Bd. Armata Poporului 1-3, Sect. 6, 77206 - Bucharest, Romania 2) Institute of Solid Mechanics of Romanian Academy, C-tin Mille 15, Bucharest 1, 010141, Romania Abstract: The paper presents switching power supplies with MC34063 and μA78S40 monolithic switching regulator subsystems and DC-DC step-up converter that can be used in special vehicle applications. General description of MC34063 and μA78S40 operation modes, mathematical design and PSpice under ORCAD simulation of the whole switching power supply, a numerical example and the practical implementation are included. Some practical considerations are also presented. 1. INTRODUCTION The use of switching regulators is becoming more pronounced over that of liniar regulators because the size reductions in new equipment designs require greater conversion efficiency. Another major advantage of the switching regulator is that it has increased application flexibility of output voltage. The output can be less than, greater than or of opposite polarity to that of the input voltage. The MC34063 and µA78S40 monolithic switching regulator subsystems are intended for use and control dc to dc converters. These devices achieves regulation by varing both the on-time and the total switching cycle time (mixed PWM+PFM control) of the output switch Q 1 , representing a significant advancement in the ease of implementing highly efficient and yet simple switching power supplies [1]. The paper presents switching power supplies with MC34063 and µA78S40 monolithic switching regulator subsystems using a DC-DC step-up converter that makes the output voltage V out greater than the input voltage V in . 2. GENERAL DESCRIPTION OF SWITCHING REGULATOR SUBSYSTEMS The MC34063 (fig.1a) is a monolithic control circuit containing all active functions required for dc to dc converters regulation. This device contains an internal temperature compensated Reference Regulator that provides 1,25V, comparator Comp, controlled duty cycle oscillator OSC with an active peak current limit circuit, driver Q 2 and a high current output switch Q 1 . This series was specifically designed to be incorporated in step-up, step-down, step up/down and voltage inverting converter applications. These functions are contained in an 8-pin dual in-line package. The µA78S40 (fig.1.b) is identical to the MC34063 with addition of an on-board catch diode and un uncommitted operational amplifier. This device is an 16-pin dual in-line package which allows the reference and the noninverting input of the comparator to be pinned-out. These additional features greatly enhance the flexibility of this part and allow the implementation of more sophisticated applications [5]. a) b) Fig.1. Functional block diagrams for a) MC34063 and; b) µA78S40 monolithic switching regulator subsystems 9th WSEAS International Conference on AUTOMATION and INFORMATION (ICAI'08), Bucharest, Romania, June 24-26, 2008 ISBN: 978-960-6766-77-0 109 ISSN 1790-5117