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Home > Technology List > The introduction of optocoupler and how to test optocoupler

The introduction of optocoupler and how to test optocoupler

Published time: 2018-07-11

The main content of this article is:

1.The description of the optocoupler

2.How does the optocoupler work

3.What are the functions of the optocoupler

4.What are the  methods to test optocoupler

5.The development of Optocoupler

The description of the optocoupler

Photovoltaic products are an indispensable device in our modern life. It brings many conveniences to our lives. Photovoltaic products can not be used normally without optoelectronic devices.

Optocouplers are quite important optoelectronic device. Jotrin Electronics will tell you that what is the optocoupler

Optocouplers (abbreviated as OC) are also known as opto-isolators or optocouplers. It is a device that transmits electrical signals through the medium of light. Usually, the light emitter (infrared light emitting diode LED) and the photoreceptor (photosensitive semiconductor tube) are packaged in the same package.When an electric signal is added to the input end, the light-emitting device emits light. After receiving the light, the light-receiving device generates light current, which flows out from the output end, thus realizing the "electro - opto - electric" conversion.

It can effectively protect the circuit and the wire, so that the optical signal and the electrical signal do not interfere with each other, and each performs work. This ensures the normal and orderly operation of the power supply and the light source, Optocouplers has good electrical insulation and anti-interference ability. There are many types of optocouplers that are common in daily life, such as photodiodes, triodes, photoresistors, and light-controlled thyristors. These are very good optocouplers.

the optocoupler 

How does the optocoupler work?

Optocoupler use light as the medium for transmitting electrical signals. It has a good isolation effect on the input and output electrical signals, so it is widely used in various circuits.At present, it has become one of the most versatile and versatile optoelectronic devices. Optocouplers generally consist of three parts: light emission, light reception, and signal amplification.

In the emission (light source) part of the light, driven by a direct current, alternating current or pulsed power supply, the light emitting diode converts the electrical energy to light energy to emit a certain wavelength of light under the forward voltage condition, and the signal amplification part and the light source .

The emitted light is received by the photodetector and it generates a photocurrent. After further amplification, the output completes the electro-optical-electrical conversion, thereby acting as an input, an output, and an isolation. Among the photodetectors, the photosensor is used. 

The reverse voltage is applied to the PN junction, and the conversion of light energy to electrical energy which is performed by the principle of large reversed resistance under light irradiation. Because the optocoupler input and output are isolated from each other and the electrical signal transmission is unidirectional, it has good electrical insulation and anti-jamming capability. Therefore, it can greatly improve the signal-to-noise ratio as a terminal isolation element in long-term transmission information. In the computer digital communication and real-time control as a signal isolation interface device, can greatly improve the reliability of computer work. Since the input of the optocoupler is a low-resistance element that operates in the current mode, it has a strong common-mode rejection capability.

How does the optocoupler work 

What are the functions of the optocoupler?

The application of optocoupler is very extensive. Jotrin Electronics Limited thinks that the role of optocoupler can be summarized in six aspects:

(1) Application on logic circuits

The optocoupler can constitute a variety of logic circuits, because the optocoupler's anti-interference performance and isolation performance is better than the transistor, so the logic circuit formed ,which it is more reliable.

(2) Application as a solid switch

In the switching circuit, it is often required that the control circuit and the switch have a good electrical isolation, which is difficult to achieve for a general electronic switch, but it is easy to realize with an optocoupler.

(3) Application on Trigger Circuit

The optocoupler is used in the bistable output circuit. Since the light emitting diodes can be respectively connected in series to the two emitter circuits, the problems of output and load isolation can be effectively solved.

(4) Application in Pulse Amplifier Circuits

Optocouplers are used in digital circuits to amplify pulse signals.

(5) Applications on Linear Circuits

Linear optocouplers are used in linear circuits with high linearity and excellent electrical isolation.

(6) Applications for special occasions

Optocouplers can also be used for high voltage control, replacing transformers, contact relays, A/D circuits and many other applications.

What are the methods to test optocoupler?

The quality of the optocoupler can be determined by measuring the forward and reverse resistance of its internal diode and triode. Jotrin Electronics Limited will tell you that the reliable detection methods ,as follows:

1. Comparison method

Remove the suspect optocoupler, use a multimeter to measure the forward and reverse resistance values of its internal diode and transistor.Comparing it with the measured value of a good optocoupler counterpart. If the resistance difference is large, the optocoupler will be damaged.

2. Digital multimeter detection method

The following takes the PC111 optocoupler detection as an example to illustrate the detection method of the digital multimeter.The detection circuit is shown in the figure below. When testing, connect the anode 1 and the cathode 2 of the optocoupler diode to the c and e jacks of the digital multimeter's hFE.

At this time, the digital multimeter should be placed in the NPN block; then the optocoupler should be connected to the phototransistor collector. c 5 feet connected pointer multimeter black table pen, emitter e 4 foot red table pen, and pointer type multimeter dial in R & TImes; 1k gear.In this way, the condition of the optocoupler can be determined by the deflection angle of the pointer of the multimeter, which is actually the change of the photocurrent. The greater the deflection angle of the pointer to the right, the higher the photoelectric conversion efficiency of the optocoupler, ie, the higher the transmission ratio, and vice versa. If the hands are not moving, the optocoupler is damaged.

the PC111 optocoupler detection  

3. The photoelectric effect judgment method

We still taking the detection of the PC111 optocoupler as an example, the detection circuit is shown in the figure below.

Putting the multimeter in 1k electric block position, the two table pens are respectively connected to the output terminals 4 and 3 of the optocoupler; then use a 1.5V battery and a 50-100Ω resistor in series, the positive terminal of the battery Connect pin 1 of PC111, and connect the negative terminal to pin 2 or the positive terminal to pin 1. Observing the deflection of the pointer connected to the output multimeter. If the pointer swings, the optocoupler is good. If it does not swing, the optocoupler is damaged. The larger the swing angle of the pointer of the multimeter, the higher the photoelectric conversion sensitivity.

The photoelectric effect judgment method 

The development of Optocoupler

Optocouplers have the advantages of small size, long life, strong anti-interference ability, insulation between the output and input, one-way transmission of signals, etc.,they are widely used in digital circuits. In addition, the use rate of optocouplers is still increasing dramatically every year. Besides the optocoupler itself, another important reason is that 20 to 30 or more optocouplers are used in each program controller. Optocouplers have a wide market space. The quality of optocoupler is a problem that all users are most concerned about. Jotrin Electronics Limited has advanced programmable power supplies, digital multimeters, and oscilloscopes. It can accurately measure the input-output relationship of optocouplers, providing you with more High quality optocoupler products.


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