Book Analog Interfacing to Embedded Microprocessors
voltage drop. The power dissipated by the opamp at any time is given by
P = ( V - Vm) I
where V is the supply voltage, Vm is the motor coil voltage, and I is the coil
current.
A linear drive like this requires a negative supply voltage. It is possible to
build a bridge-driver using two opamps that operates from a positive supply
and works like the H-bridge, driving one side of the coil positive or negative
with respect to the other.
The L297 (Figure 7.19) from SGS-Thompson is a stepper-controller IC. It
provides the on-off drive signals to an H-bridge driver such as the L6201 or
to a discrete transistor driver design. The L297 controls current in the motor
Figure 7.18
Linear constant-current drive.
Motors 179
Figure 7.19
SGS-Thompson L297.
windings using chopping. It has an internal oscillator, comparators, and chop-
ping logic
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