Photoelectric control attenuation circuit a

Phototransistor, also called phototransistor , is also a commonly used photosensitive device. Its characteristics are the same as photoresistors and photodiodes.
It can adjust its own impedance according to the intensity of light. It is widely used in photoelectric coupling and some special circuits. Figure
6-2 shows the optocoupler attenuation circuit. In the circuit shown in (a), the phototransistor in the photoelectric controller and the 500 kfl resistor form a
series voltage dividing circuit. When the impedance of the phototransistor becomes smaller, the attenuation of the circuit The amount increases. In the circuit shown in Figure (b), if
the positions of the fixed resistor and the photosensitive device are exchanged , the impedance of the photosensitive transistor becomes smaller and the attenuation decreases. The circuit shown in Figure (c) is a practical circuit of the circuit shown in Figure 6-2 (b) .