⒈Compose switch circuit

When the input signal ui is at a low level, the transistor V1 is in an off state, the current of the light-emitting diode in the photocoupler B1 is approximately zero, and the resistance between the output terminals Q11 and Q12 is large, which is equivalent to the switch being "opened"; At high level, v1 is turned on, and the light-emitting diode in B1 is turned on. The resistance between Q11 and Q12 becomes smaller, which is equivalent to the switch being "on". This circuit is turned on at high level because Ui is low State. Similarly, because there is no signal (Ui is low level), the switch is turned on, so it is low-level on state.

2. Make up a logic circuit

The circuit is an AND gate logic circuit. The logical expression is P = AB. The two photosensitive tubes are connected in series. Only when the input logic levels A = 1 and B = 1, the output P = 1. Similarly, it can also form an "OR gate", a "NOR" Gate "," NOR gate "and other logic circuits.

3. Make up isolated coupling circuit

The circuit is shown in Figure 4. This is a typical AC-coupled amplifier circuit. The current-limiting resistor R1 of the light-emitting circuit is appropriately selected so that the current transfer ratio of B4 is a constant, which can ensure the linear amplification of the circuit.

4. Make up high voltage regulator circuit

The driving tube needs to use a transistor with a higher withstand voltage (the driving tube in the figure is 3DG27). When the output voltage increases, the bias voltage of V55 increases, and the forward current of the light-emitting diode in B5 increases, which reduces the voltage between the poles of the phototransistor. While keeping the output voltage stable.

⒌Composed of automatic control circuit for hall lighting

A is four sets of analog electronic switches (S1 ~ S4): S1, S2, and S3 are connected in parallel (which can increase the driving power and anti-interference ability) for the delay circuit. When it is connected to the power, it drives the bidirectional thyristor through R4 and B6. VT, VT directly control the hall lighting H; S4 and an external photoresistor Rl constitute an ambient light detection circuit. When the door is closed, the normally closed reed switch KD installed on the door frame is affected by the magnet on the door, and its contacts are opened, and S1, S2, and S3 are in the data open state. In the evening, the owner went home to open the door, the magnet was far away from KD, and the KD contact was closed. At this time, the 9V power supply is rectified and charged to C1 via R1, and the voltage across C1 rises to 9V quickly. The rectified voltage causes the light-emitting tube in B6 to emit light through S1, S2, S3, and R4 to trigger the triac to conduct, and VT also conducts On, H lights up to achieve automatic lighting control. After the door is closed, the magnet controls KD, the contacts are disconnected, the 9V power supply stops charging C1, and the circuit enters a time-delay state. C1 begins to discharge to R3. After a delay, the voltage across C1 gradually drops below the turn-on voltage (1.5v) of S1, S2, and S3. S1, S2, and S3 return to the off state, causing B6 to turn off and VT to turn off. , H goes out to realize the function of delaying the light off.