Title of Invention

A DEVICE FOR SYNCHRONOUS RECTIFICATION OF THE OUTPUT OF AN AUTOMOBILE ALTERNATOR

Abstract

A device for the synchronous rectification of the output of an automobile alternator, comprising a set of comparators, for sensing the line voltage of the said alternator, the comparators deriving the zero crossings of the lire voltages from the sensed outputs thereof; a one shot, a multiplexer controlled from the one-shot, and a mosfet driver, the one shot being driven by the comparators through the multiplexer and the zero crossing voltages starting the said one shot for deciding the ON state duration of the MOSFET; a demultiplexer through which the one shot output is steered MOSFET driver ,said demultiplexer being controlled from the driver, one-shot.

Full Text

This invention relates to a device for synchronous rectification of the output of an automobile alternator. By "synchronous rectification" is meant that the device proposed herein enables MOSFETS to be switched on and off at a frequency equal to that of the generated AC output of the said aI ternator which is required for supplyinq power to the automobile electrical load and also for charging the battery . While MOSFETs have been used for AC to DC conversion, there are several means adopted for the purpose and known to the art; however, these means suffer from the following disadvantages. (1) Current transducers are required for identifying the instant of turning ON the MOSFET switch; and the presence of current sensors adds to the system cost. (ii) The duration for keeping the MOSFET switches ON in the individual phases could be different in different phases on account of the controller configuration. Such operation will lead to imbalance in the operation of the alternator leading to a large current ripple in the DC output current. the controller is a disadvantage from the standpoint of system integration for tnass production through large-scale integrated circuits dedicated for this application. On the other hand, the device proposed herein has the following advantages! (i) The control1er implementaion does not depend on phase currents (li) The timing device is the same for all the phases (iv) There is no need for current sensors for satisfictory operation of the controller (v) The need for sensing the rectified d.c. voltage at the bridge output terminals for controlling the MOSFETs in the bridge is obviated, (vi) The turn-on intervals for the MOSFETs are derived from a one-shot ( a single circuit block) and steered to the different switches through enabling circuits, eliminating a possible source imbalance in alternator operation. Various other features of this invention will be apparent from the following further description thereof The device, according to this invention, for synchronous rectification of the output of an automobile alternator, comprises a set of comparators for sensing the line voltage of the said alternator, the comparators deriving the zero crossings of the line voltages from the sensed inputs thereof; a one-shot; a multiplexer and demultiplexer controlled from the one-shot, said one-shot being driven by the comparators through the multiplexer; a MOSFET driver, the one-shot output being steered through the demultiplexer to the MOSFET driver; and aMOSFET bridge connected to the MOSFET driver. This invention will now be described by reference to the accompanying drawings which illustrate in Fig.l the wave form of the alternator currentusing the known diode rectifier Fig.2 the wave form of the alternator current using the device proposed herein, high lighting the absence of zero interval in the phase current wave form which is present in the wave form in Fig. 1 and Fig.3 iIlustrating the layout of one of possible embodiments of the device proposed herein. The sensed inputs to the set of comparstors E are the terminal voltages of the alternator at A B C. The comparators derive the zero-crossings of the line voltages from the sensed Inputs and drive the one-shot O through a multiplexer M. The appropriate zero-crosaing voltages start the one-shot which decides the ON state duration of the MDSFETS of the bridge. The control for the multiplexer M is in turn derived from the one-shot. The one-shot output is steered to the appropriate MOSFET through a demultiplexer D which is also controlled from the same one-shot. The terms and expressions in this specification are of description and not of limitation, since various other embodiments of the device proposed herein are possible without departing from the scope and ambit of this invention. We Claim: 1. A device for synchronous rectification of the output of an automobile alternator, comprising a set of comparators for sensing the line voltage of the said alternator, the comparators deriving the zero crossings of the line voltages from the sensed inputs thereof; a one-shot; a multiplexer and demultiplexer controlled from the one-shot, said one-shot being driven by the comparators through the multiplexer; a MOSFGT driver, the one-shot output being steered through the demultiplexer to the MOSFET driver; and aMOSFET bridge connected to the MOSFET driver. 2. A device for synchronous rectification of the output of an automobile alternator substantially as herein described with reference to, and as illustrated in. Figs 2 and 3 of the accompanying drawings.

Documents:

2656-mas-98 abstract-duplicate.pdf

2656-mas-98 abstract.pdf

2656-mas-98 claims-duplicate.pdf

2656-mas-98 claims.pdf

2656-mas-98 correspondence-others.pdf

2656-mas-98 correspondence-po.pdf

2656-mas-98 description (complete)-duplicate.pdf

2656-mas-98 description (complete).pdf

2656-mas-98 drawings-duplicate.pdf

2656-mas-98 drawings.pdf

2656-mas-98 form-1.pdf

2656-mas-98 form-19.pdf

2656-mas-98 form-26.pdf