Internal structure and detection method of photocoupler

Photocoupler - also known as optical coupler or optocoupler, it is a relatively new electronic product, now it is widely used in computers, audio and video... various control circuits. Since the light-emitting diode and phototransistor inside the optocoupler only convert the voltage or current changes of the circuit before and after into light changes, there is no electrical connection between the two, so it can effectively cut off the potential connection between circuits and achieve reliable isolation between circuits.

1. Detection of photocouplers To determine whether a photocoupler is good or bad, you can measure the forward and reverse resistance of its internal diode and transistor in the circuit. There are three more reliable detection methods. 1. Comparison method Remove the suspected problematic photocoupler and use a multimeter to measure the forward and reverse resistance of its internal diode and transistor, and compare it with the measured value of the corresponding pin of a good photocoupler. If the resistance value is significantly different, it means that the photocoupler is damaged.

2. Digital multimeter detection method The following uses PCIll optocoupler detection as an example to illustrate the digital multimeter detection method. The detection circuit is shown in Figure 1. During the detection, insert the + terminal ① and the - terminal ② of the diode in the optocoupler into the c and e jacks of the digital multimeter respectively. At this time, the digital multimeter should be set to the NPN gear; then connect the c pole ⑤ pin of the phototransistor in the optocoupler to the black test lead of the pointer multimeter, and the e pole ④ pin to the red test lead, and set the pointer multimeter to the Rxlk gear. In this way, the deflection angle of the pointer multimeter pointer, which is actually the change of photocurrent, can be used to judge the condition of the optocoupler. The greater the rightward deflection angle of the pointer, the higher the photoelectric conversion efficiency of the optocoupler, that is, the higher the transmission ratio, and vice versa; if the needle does not move, it means that the optocoupler is damaged.

3. The photoelectric effect judgment method still takes the detection of ICIll optocoupler as an example, and the detection circuit is shown in Figure 2. Set the multimeter to Rxlk resistance block, and
connect the two pens to the output terminals of the optocoupler, ④ and ⑤ respectively. Then, connect a 1.5V battery and a 50-100 ohm resistor in series, and connect the positive terminal of the battery to the ① pin of PC111, and the negative terminal to the ② pin, or the positive terminal to the ① pin and the negative terminal to the ② pin. At this time, observe the deflection of the pointer of the multimeter connected to the output terminal. If the pointer swings, it means that the optocoupler is good. If it does not swing, it means that the optocoupler is damaged. The larger the swing deflection angle of the multimeter pointer, the higher the sensitivity of the photoelectric conversion.
2. The internal structure of various optocoupler circuits In order for readers to find the internal structure of various types of optocouplers, the circuit diagram shown in the following table is attached.