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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.
English (United States)
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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
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...