March 14, 1997

Circuit controls slew for stepper drive

J Jayapandian, IGCAR, Tamil Nadu, India

The circuit in Figure 1 provides slewing control for stepper motors that you use in sophisticated applications, such as monochromator movements in optical experiments. The LM331 VFC plays a vital role in this circuit. The constant 10V dc from the IC9596 voltage reference routes to the VFC through the DG303 CMOS switch. The DG303's configuration is such that the VFC initially receives 0V through the grounded 33-kilohms resistor. When the Inhibit pin goes high, the switch provides the 10V reference level to the 100-nF capacitor at the VFC input. The RC combination of 100 kilohms and 100 nF provides a slewing input to the VFC and thus produces a slewing frequency at the VFC's output. The VFC's output is the basic clock for the stepper-motor drive-control circuit. The design produces a 0- to 2-kHz slewing clock; you can modify the RC values to obtain other ranges. (DI #1988)

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