The circuit diagram given here is of a stepper motor driver using MC3479 from Motorola. The MC3479 is specifically designed for driving a 2 phase stepper motor in bipolar mode and is available in standard DIP and surface mount packages.The IC is compatible to TTL and CMOS inputs and has selectable HIGH/LOW output impedance. The output can deliver up to 350mA each of two coils of a 2 phase stepper motor. The state change of the output occurs at the low to high transition of the input clock pulse. The new output will depend on old output and the state of the digital inputs. The output L1 to L4 are high currents outputs, which when connected to a two phase stepper motor forms two full bridge formations.
Resistors R1 & Rb, Zener diode D1 and IC2 MC14049UB are the additional components used in the circuit. R1 is a pull up resistor and Rb is used to set the maximum output sink current. Zener diode D1 provides back emf protection.
- Assemble the circuit on a good quality PCB.
- The supply voltage (+V) can be 7 to 16V DC depending on the stepper motor used.
- Maximum possible current per coil is 350mA.
- Value of the resistor Rb can be obtained from the equation Rb = (Vm – 0.7V)/Ibs.
- Where Ibs = Iod X 0.86.( Vm is the supply voltage itself and Iod is the current per coil).
- Pin10 (CW/CCW) is used to select clock wise or counter clock wise rotation.
- Pin 7 (clock) is the clock input pin.
- Pin 9 (full/half step) is used to select between full and half steps.
- Pin8 (OIC) is used for output impedance control.