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High Efficiency Motor Drive Circuit

IP.com Disclosure Number: IPCOM000052262D
Original Publication Date: 1981-May-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Roalson, HJ: AUTHOR

Abstract

A high efficiency AC motor drive circuit is produced by minimizing the supply voltage required to produce the required peak-to-peak output voltage swing.

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High Efficiency Motor Drive Circuit

A high efficiency AC motor drive circuit is produced by minimizing the supply voltage required to produce the required peak-to-peak output voltage swing.

The amplifier shown in Fig. 1 shows the circuit designed to produce the improved efficiency. Current sources 10 in the collector circuit of the input transistors 22 make it possible to drive the output very close to the supply voltage VS. Also precise bias control to center the output between the supply rails is important to achieve maximum voltage swing. Transistors 12, 20 and 22 are Darlington devices.

A further source of power dissipation is the DC current that flows through the motor 14. Since the DC impedance of motor 14 is normally very low, any DC offset in the output voltages will produce a current that can increase power dissipation significantly. The amplifier in Fig. 1 shows the two bias circuits 16 in block form, and the details of these bias circuits are shown in Fig. 2. This circuit will easily reduce the offset voltage to a very low level, thereby nearly eliminating the DC current flow.

Another problem encountered in the design of a power amplifier is power sequencing. If power is applied to the amplifier with the load connected, a transient current will flow through the motor as the two sides of the amplifier reach equilibrium. This is due to the fact that the two sides will not be identical and any voltage offset could cause currents to flow that would permane...