How does the optocoupler 817C work?

Principle: When the input terminal is energized, the luminaire emits light and irradiates it on the light receiver, and the light receiver conducts on after receiving the light, and generates photocurrent output from the output terminal, thus realizing the conversion of "electricity-optical-electric".

Optocoupler. Full name: Optocoupler.

The main function is isolation, such as signal isolation or photoelectric isolation. Isolation can act as a protection, such as a microprocessor on one side.

The control circuit, on the other side is the high-voltage actuator end, such as mains-started motors, lights, etc., which can be isolated by optocouplers. When two different types of optocouplers differ only with load current, the optocoupler with a larger load current can be used instead of the optocoupler with a small load current.

PC817 is a commonly used linear light lotus, which is often used as a coupling device in various functional circuits that require more precision, and has the function of complete isolation of upper and lower circuits, and does not affect each other.

When the input terminal is powered by the signal, the luminaire emits light and shines on the light receiver, and the light receiver receives the light and conducts it on, generating photocurrent output from the output terminal, thus realizing the conversion of "electricity-optical-electric".

Ordinary optocouplers can only transmit digital signals.

switching signals), which are not suitable for transmitting analog signals.

Linear photocoupler is a new type of optoelectronic isolation device, which can transmit continuously changing analog voltage or current signals, so that with the change of the strength of the input signal, the corresponding optical signal will be generated, so that the conduction degree of the photosensitive transistor is also different, and the output voltage or current is also different.

The PC817 photocoupler can not only play a feedback role, but also play an isolation role.

The first question: the role of feedback circuits in switching power supply circuitsThe feedback is to keep the load of the circuit in a constant current and regulated state, if there is no feedback, the circuit will output a very high voltage V according to the frequency of the switch, and if I need the output to be less than V, the feedback circuit can play this role.

The second question is already on the first floor.

The third problem, the TL431 is a regulated output, combining it with the optocoupler, and connecting the optocoupler with its output in series, it can output a low level when there is light and a high level when there is no light.

Measure the end with the PN junction of a digital multimeter.

Use the "battery + pole" of the red pen to connect the "1" end of the optocoupler, use the "battery-pole" of the black pen to connect the "2" end of the optocoupler, and use another meter to measure the resistance of the "3" and "4" ends, disconnect or turn on the input end, when the resistance of the output end changes significantly, it means that the optocoupler is good. Otherwise, it is bad.

Summary. 3. Different applications 1. Optocoupler PC817: Optocoupler PC817 is widely used in computer terminals, thyristor system equipment, measuring instruments, photocopiers, automatic ticketing, household appliances, such as fans, heaters and other circuits.

2. Optocoupler PC817B: Optocoupler PC817B is widely used in voltage automatic gain loop and voltage stabilization circuit, as well as photoelectric test circuit and optical control circuit.

The difference between optocoupler 781 and 817.

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Hello, the difference between optocoupler PC817 and PC817B is: different peak forward current, different functions, and different applications.

1. The peak forward current is different1. Optocoupler PC817: The peak forward current (ICE Max) of optocoupler PC817 is Optocoupler PC817B: The peak forward current (ICE Max) of optocoupler PC817B is.

2. Different functions 1. Optocoupler PC817: Optocoupler PC817 is used for signal transmission, reducing circuit interference and simplifying circuit design. The aim is to increase security.

2. Optocoupler PC817B: Optocoupler PC817B is regarded as a coupling device, which has the function of complete isolation of upper and lower circuits, and does not affect each other.

3. Different applications 1. Optocoupler PC817: Optocoupler PC817 is widely used in computer terminals, thyristor system equipment, measuring instruments, photocopiers, automatic ticketing, household appliances, such as fans, heaters and other circuits. 2. Optocoupler PC817B:

Optocoupler PC817B is widely used in voltage automatic gain loops and voltage regulation circuits, as well as photoelectric test circuits and optical control circuits.

Hope it helps you <>

Optocouplers 781 and 817 are both optocouplers, but they have some key differences:

Xin Yongcheng optocoupler.

First, the 781 is a high-current, low-isolation optocoupler that is suitable for high-voltage environments. In contrast, the 817 is a low-current, high-isolation optocoupler that is suitable for low-voltage environments.

Second, the 781's optical receiver is non-self-locking, which means that the output signal does not persist when the input signal disappears. The 817's optical receiver is self-locking, and when the input signal disappears, the outgoing signal will remain until the next input signal arrives.

In addition, the transmission rate of the 781 is faster than that of the 817, but the isolation performance of the 817 is better, which can provide greater safety and noise isolation.

Finally, due to the different characteristics and application scenarios of these optocouplers, their ** and use are also different. When selecting an optocoupler, there are trade-offs and choices that need to be made based on specific circuit requirements and application environments.

In summary, 781 and 817 are two different types of optocouplers with different characteristics and applications. Proper selection and use of them can help designers achieve efficient, reliable rubber circuit designs and safe use.

It's important to note that while both the 781 and 817 are widely used optocouplers, there are other types of optocouplers available. When choosing an optocoupler, you need to consider factors such as circuit requirements, use environment, and budget, and choose the right model and brand.

In conclusion, knowing and understanding the differences between optocouplers 781 and 817 is important for electronics engineers and designers to better apply these devices for circuit design and functional optimization. At the same time, understanding other types of cavity and optocouplers can also provide designers with more options and flexibility to meet different needs and challenges.

The P781 optocoupler is optical fiber transmission, and the PC817 optocoupler is optical detection and closed power defeat and intelligent splitting transmission.

Optocoupler 817 is a model of EL817 photocoupler, which is a device that encapsulates infrared light emitting devices, infrared light receiving devices and signal processing circuits in the same tube base. PC817 is a commonly used linear optocoupler, which is widely used in signal transmission between circuits such as measuring instruments.

2. Characteristics: 1. Transmission ratio of electric Bishen (IF=5mA, VCE=5V). 2. High isolation voltage: 5000V RMS, linear optocoupler element.

Feedback circuit is widely used in various electronic circuits, feedback is to feed back part or all of the amplifier output signal (voltage or current) to the amplifier input terminal and the input signal for comparison (addition or subtraction), and use the effective input signal obtained by comparison to control the output, which is the feedback process of the amplifier.

If the feedback signal fed back to the input end of the amplifier strengthens the input original input signal, the input signal increases is called positive feedback, and vice versa. Positive feedback circuits are mostly used in electronic oscillation circuits, while negative feedback circuits are mostly used in various high and low frequency amplification circuits.

An optocoupler is a device that uses light as a medium to transmit electrical signals, usually encapsulating a light-emitting device (infrared light-emitting diode LED) and a light-receiving device (photosensitive semiconductor tube) in the same tube shell. When the signal is energized at the input end, the luminaire emits light, and the light receiver generates photocurrent after receiving the light, which flows out from the output end, thus realizing the "electricity-optical-electric" conversion.

The TL431 is a regulated output that combines it with an optocoupler, which is connected in series to output a low level when there is light and a high level when there is no light.

The withstand voltage of the output part is not the same

The withstand voltage VCE0 of the output part of the PC817 is 35V, and the withstand voltage VCE0 of the output part of the PC816 is 70V.

There is little difference between the other two.

Optocouplers are used in a wide range of electronic devices. With the rapid development of digital communication technology and the continuous expansion of the application of automatic control components such as optical isolators and solid relays in the machinery industry, especially the application and promotion of microprocessors in various fields (sometimes the amount of a microcomputer can reach more than a dozen or even hundreds of failures) and the gradual improvement of product performance.

The application market of optocouplers will be expanding day by day, and at the same time, its social and economic benefits will also be very significant. In the future, optocouplers will be developed in the direction of high speed, high performance, small size, and light weight.

Extended Closed-Mode Data:

Optocoupler 817 is widely used, mainly used in power supply equipment, to isolate high and low voltages. Related end product applications include home appliances, temperature control, HVAC, vending machines, lighting controls, chargers, and switching power supplies. The signal transmission between the circuits makes the front end completely isolated from the load, in order to increase safety, reduce circuit interference, and reduce circuit design.

The two resistors were sampled in series to the 431R terminal for comparison with the internal comparator. Then, according to the generated signal, the resistance of the 431k terminal (the end of the anode connected to the optocoupler) to the ground is controlled, and then the brightness of the light-emitting diode inside the optocoupler is controlled. (Inside the optocoupler is a light-emitting diode on one side and a phototransistor on the other) through the intensity of the luminescence.

The resistance at the CE terminal of the triode at the other end changes the current at the PWM detection pin. Depending on the magnitude of the current. PWMIC will automatically adjust the duty cycle of the output signal to achieve the purpose of voltage stabilization.

In some laboratories or high-demand occasions, for the safety of experimenters, the input power supply of the experiment is generally isolated from the mains power by a 1:1 power frequency transformer, so that the laboratory experimenters will not be at risk of electric shock no matter which line they touch, because the isolated power supply is not connected to the earth. In industrial control equipment, it is sometimes required to isolate the power ground between the two systems, such as isolating the ground noise, isolating the high common-mode voltage, etc., and a DC converter with a transformer is used to separate the two power supplies from each other so that they are independent of each other.

Opto-decoupled isolated feedback is a simple, low-cost way to use a general isolated power supply. However, there has been no in-depth study on the various connection modes and their differences for optocoupler feedback. Moreover, in many cases, due to the lack of deep understanding of the working principle of optocoupler, the optocoupler method is chaotic, which often leads to the failure of the circuit to work normally.

In this study, the working principle of optocoupler will be analyzed in detail, and several typical connection methods of optocoupler feedback will be compared.

1 Several common connection methods and how they work.

The photocoupler has small size, long service life, wide operating temperature range, and strong anti-interference performance. The absence of contacts and the complete electrical isolation of input and output make it widely used in a wide range of electronic devices. Optocouplers can be used in circuits such as isolation circuits, load interfaces, and various household appliances.

Optocoupler models commonly used for feedback include TLP521, PC817, etc. The TLP521 is used as an example to describe the characteristics of this type of optocoupler.

The primary side of TLP521 is equivalent to a light-emitting diode, the larger the primary current if, the stronger the light intensity, and the larger the current IC of the secondary triode. The ratio of the secondary triode current IC to the primary diode current if is called the current amplification coefficient of the optocoupler, which changes with temperature and is greatly affected by temperature.

TL431 is usually chosen in combination with TLP521 for feedback. In this case, the operating principle of TL431 is equivalent to a voltage error amplifier with an internal reference of V, so between its pins 1 and 3, a compensation network should be connected.

For details, see the application circuit set for optocouplers (optocouplers).

Optocoupler is a photosensitive diode plus a triode, and the diode is turned on and then triggers the triode to work, which can play the role of isolation.