CHOPPEFtED DC MOTOR DRIVE USING MOS AND BIPOLAR POWER TRANSISTORS

Document Type : Original Article

Authors

1 Military Technical College Cairo - Egypt.

2 Zagazig University - Banha Branch Shoubra Faculty of Enr,ineering, Cairo - Egypt.

3 Zagazig University - Banha Branch, Shoubra Faculty of Enr,ineering, Cairo - Egypt.

Abstract

A four quadrant DC chopper circuit is presented applying a combination of MOS and bipolar power transistors as the main power elements. This circuit uses two MOS switches to take all required high frequency (up to 100 KHz) switching in the four quadrant operation. Two bipolar transistors are used in the return path of current as fast contactors to select the required quadrant of operation. Using of this scheme greatly reduces cost than the case of using four MOS switches. Moreover separate fast recovery diodes can be used as freewheeling diodes instead of relatively slower integral body-drain diode of the power MOSFET which cause restrictions on ON state switching speed. In the following work, the detailes of design of power circuit to feed a 20 A- 18V separately excited DC motor is given. Analytical dependence of overall efficiency on operating frequency and battery voltage is discussed. Results show that frequency has a little effect so that a 100 kHz frequency seems to be practically possible with this configuration. Under such high frequency the armature leakage reactance alone is sufficient to draw smooth continuous current to give good motor operating characteristics.

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