The optical coupler is also known as an opto-isolator or optocoupler, or optocoupler for short. It is a device that transmits electrical signals with light as a medium. Usually, the light emitter (infrared light emitting diode LED) and the light receiver (photosensitive semiconductor tube) are packaged in the same package. When an electric signal is applied to the input end, the light emitter emits light, and after the light receiver receives the light, it generates a photocurrent, which flows out from the output end, thus realizing the "electricity-optical-electricity" conversion. The photoelectric coupler that uses light as the medium to couple the input signal to the output end has the advantages of small size, long life, no contact, strong anti-interference ability, insulation between output and input, and unidirectional signal transmission. It is widely used in the circuit.

Optocoupler 817c pin diagram

Application of Optocoupler 817c

Optocoupler 817c is widely used, mainly used in power supply equipment to isolate high and low voltage. Related terminal product applications include home appliances, temperature control, air-conditioning (HVAC), vending machines, lighting control devices, chargers and switching power supplies. The signal transmission between the circuits completely isolates the front end from the load. The purpose is to increase safety, reduce circuit interference, and reduce circuit design.

Increase the switching speed of the optocoupler by increasing the positive feedback of the photosensitive base

How to measure the quality of 817c optocoupler

Method: Use the PN junction measurement terminal of the digital multimeter, the red test lead "battery + pole" is connected to the "1" end of the optocoupler, and the black test lead "battery-pole" is connected to the "2" end of the optocoupler (even if the light-emitting diode of the optocoupler is positive Use another electric meter to measure the resistance of terminals “3” and “4”, disconnect or connect the input terminal (light-emitting diode terminal), the output terminal resistance should have a large change, indicating that it is good to change the optocoupler. In addition, the multimeter at the LED end can be replaced by a battery string current-limiting resistor.

The role of 817c optocoupler

817c is an optocoupler, which isolates the input and output electrical signals. The optocoupler generally consists of three parts: light emission, light reception and signal amplification. The input electrical signal drives the light-emitting diode (LED) to emit light of a certain wavelength, which is received by the photodetector to generate a photocurrent, which is then further amplified and output. This completes the electrical-optical-electrical conversion, thereby playing the role of input, output, and isolation. Since the input and output of the optocoupler are isolated from each other, and the electrical signal transmission is unidirectional, it has good electrical insulation and anti-interference capabilities. In addition, since the input end of the optocoupler is a low-resistance element that works in current mode, it has a strong common mode rejection capability.

Main technical parameters of PC817C

Control terminal: maximum voltage 5V, maximum current 50mA. The maximum reverse voltage is 6V.

Controlled terminal: maximum voltage 35V, maximum current 50mA.

Isolation voltage: 5000V.

Working temperature: -30℃ ~ +100℃.

CRT (current ratio): 200% to 400%.

［Best voltage and current range］

The best voltage of the control terminal is 0.3V~1.4V, and the best current does not exceed 20mA.

The optimal voltage of the controlled terminal does not exceed 30V, and the optimal current does not exceed 30mA.