DC motor drive circuit composed of dual power amplifier KD28

The figure below is a DC motor forward and reverse light control circuit composed of dual power amplifier KD28. VD1 and VD2 (2CUx2) are photodiodes. Since R1~R4=10kΩ, the voltages at points A and B are both 4.5V (1/2VCC). When a small flashlight is used to illuminate VD1, VD1 is turned on to make the voltage at point A higher than the voltage at point B. The voltage at pin ③ of the two outputs of KD28 is higher than 1/2Vce, and the voltage at pin ⑤ is lower than 1/2Vce, and the motor M rotates forward. On the contrary, if VD2 is turned on by light, the voltage at point B is higher than the voltage at point A, the output at pin ③ is lower than 1/2Vce, and the output at pin ⑤ is higher than 1/2Vce, and the motor M obtains a reverse polarity voltage and reverses. The circuit requires that the performance of VD1 and VD2 should be consistent. R1 and R2 in parallel with the photodiode stop the motor in static state, and the effective working voltage of the motor is about 2V lower than the power supply voltage.