DC motor control circuit design and analysis(5)

Two-phase (AC) motors are sometimes used as turntables in precision record players. It is a low-voltage synchronization mechanism.

Figure 21 shows the two-phase motor driver circuit. This circuit can drive an 8 ohm two-phase motor. Up to 3 watts per winding. Frequency ranges from 45Hz to 65Hz. The integrated circuit uses LM377 dual-channel 3-watt audio power amplifier as the driver. The power supply uses plus and minus 11V.

How the circuit works. The left half of the integrated circuit is connected to a Wien bridge oscillator, and the adjustable frequency is adjusted by RV1, with a variable frequency range of 45Hz-65Hz. Amplitude adjustment is controlled by RV2, and bulb LP1 is used to stabilize the amplitude. The output of IC1a directly feeds one phase winding of the motor. The other half of the integrated circuit, IC1b, is used as an 85 phase shifter. C6 and R6 are 85 phase shifters. But at 60HZ, an attenuation factor of ten times must be multiplied, so IC1b must be multiplied by a gain of ten times. Circuit stability is ensured by decoupling networks C3-R4-R5, C4 and C5. The resonant circuit formed by the motor winding and C8 and C9 is tuned to the intermediate frequency value (55Hz).