CY545 Stepper System Controller
www.ControlChips.com
The data outputs from the PROM are then connected to the power driver circuit itself,
generating the proper phase patterns for the motor. Note that such a design not only handles
motors of various phases, but can also implement stepping schemes such as half-step or quad-
step, as well as the standard full-step pattern.
The following paragraphs are meant as a guide to various types of driver circuits, but should not
be used as final driver designs. Detailed switching characteristics, transient suppression, and
circuit protection logic have been omitted for clarity and simplicity.
Unipolar designs are the simplest drivers, and are generally useful when running at less than
600 steps per second. These designs require motors with six or eight leads, since the power
supply is connected to the middle of each winding. The end of each winding is pulled to ground
through a transistor controlled by one of the phase output lines from the data PROM.
Motor performance may be improved by adding a dropping resistor between the power supply
output and the center tap of each winding. This decreases the field decay time constant of the
motor, giving faster step response. The performance increase is paid for by a higher voltage
power supply and heat losses through the dropping resistors. This type of circuit is know as an
L/xR circuit, where the x represents the resistor value relative to the winding resistance. An L/R
circuit would not have any external resistors, while an L/4R circuit would use a resistor of three
times the value of the motor winding resistance. Note that the power supply could be four times
the nominal motor value with this circuit. Also note that this circuit requires only a single voltage
and one transistor per phase.
© 2002 Cybernetic Micro Systems
90
Chapter 19 - Circuits and Examples
ETC [ ETC ]
