DC motor control circuit

Wide application of the servo motor, almost all automatic control systems need to use. In home appliances, such as VCRs, laser disc players are all important and indispensable component.

1. The working principle of a simple servo motor

DC motor control circuit

Figure 22 shows the servo motor of the most simple applications. RV1 potentiometer driven by a servo motor. Electrical current can choose no more than 700mA, voltage 12 ~ 24V in any of the servo motor. Figure in RV1 and RV2 is connected into the Wheatstone (Wheatstone) bridge. IC LM378 is a dual 4-watt power amplifier, also constitute a motor drive in bridge mode differential amplifier.

When RV2 any changes will undermine the balance of the bridge, so RV1-RV2 produce a difference between the voltage to be amplified and sent to the motor. Motor will rotate, drag potentiometer RV1 to a new location, so that the bridge again to reach a new equilibrium. So, RV1 RV2 to track the movement.

DC motor control circuit

Figure 23 is a block diagram form, draw a speed sensor for servo motor system that can be used as precise speed control dial player schematic. Motor body using traditional belt drive turntable. Dial edge of the reflection with the provisions of interval graph structure. Speed meter with photoelectric surveillance and detection. Optical velocity meter output signal proportional to the speed dial. The optical velocity meter output signal phase and frequency, and oscillator phase and frequency standard comparison, with its error signal controls the motor drive circuit. Therefore, the turntable's speed to maintain the accuracy on the rated speed. Rated speed of the shift, by operation of switch control. The control circuit, has made a dedicated integrated circuit manufacturers.

2. Digital Proportional Servo Motor

DC motor control circuit

One of the best types of servo motors, is to use digital proportional remote control system. In fact these devices are composed of three parts: use of integrated circuit, servo motor, reduction gear box potentiometer body. Figure 24 is a block diagram of such a system. Drive circuit input is 15ms and the pulse width period is 1 ~ 2ms pulse signal drive. Input pulse width of the mechanical output of the position control servo. For example: 1ms pulse width, position in the far left; 1.5ms in the location, 2ms in the most right position.

Three columns for each input pulse for simultaneous transmission. All the way to trigger a fixed 1.5ms pulse width pulse generator. An input trigger pulse generator, the Third Way into the pulse width comparison circuit. Gear box output to the RV1, control of variable width pulse generator. The three pulse width also sent to the comparator, the way to determine the direction of motor drive circuit. Another way to give width expansion to control the servo motor speed, so fast driving machine location RV1 input pulse width output to follow any changes.

The servo motor-type remote control system commonly used in the multiple. Figure 25 shows the four digital proportional control system waveforms.

DC motor control circuit

As can be seen from the figure is the serial data input, through the decoder control signal ceded their own ways. 4ms each frame contains synchronization pulses, immediately behind the four variable-width (1 ~ 2ms) Order of the "road" pulse. Decoder will be transformed into parallel form of four pulses can be used to control servo motor.

3. Digital servo motor circuit

Digital servo motor control unit, you can buy ready-made integrated circuits. For example ZN409CE or NE544N-type servo motor amplifier integrated circuits. Figure 26 and Figure 27 shows the typical application of the two integrated circuits.

DC motor control circuit

DC motor control circuit

Map component values for the entry of the pulse width of 1 ~ 2ms, the frame is about 18ms pulse width case.

Figure 28 is applicable to the servo motor-based General Test Circuit. Servo power supply battery typically 5V. Input pulse delivered by a standard servo plug servo circuit. Frame pulse width of 13-28ms; with the regulation and control RV1. RV2 conditioning control pulse width of between 1-2ms. Fine-tuning with RV4 median 1.5ms. Output level adjusted by the RV3.

DC motor control circuit

Two integrated circuits CMOS7555 too basic type, power supply voltage can be as low as 3V still work. IC1 is no stable multivibrator to generate frame time pulse, its output trigger IC2. The IC2 is a monostable circuit to generate the output test pulse.