The structure characteristics of the photoelectric coupler
1. The input and output terminals, the insulation between the insulation resistance is usually greater than 10000 m Ω, usually can be more than 1 kv voltage, some even can reach above 10 kv.
2. Since the light receiver can only receive information from the light source and vice versa, when the signal is transmitted from the light source to the light receiver in one direction, the signal will not be fed back and its output signal will not affect the input terminal.
3. Since the light-emitting device (GaAs infrared diode) is an impedance current driving device, and the noise is a high internal resistance microcurrent voltage signal.
Therefore, the common mode suppression ratio of optocouplers is very large, so optocouplers can suppress interference and eliminate noise.
Performance characteristics of photocouplers
The main advantage of photocouplers is the one-way transmission of signals.
Input and output terminals are completely isolated, with strong anti-interference ability, long service life and high transmission efficiency.
It is widely used for level conversion, signal isolation, interstage isolation, switching circuits, long distance signal transmission, pulse amplification, solid state relays (SSR), instrumentation, communication equipment and microcomputer interfaces.
Because the input impedance of the optical coupler is smaller than that of the general interference source, the interference voltage at the input end of the optical coupler is very small, the current it can provide is not large, and it is not easy to produce semiconductor diode emitting diode;
The case of the coupler is sealed and impervious to external light.
Optical coupler isolation resistance being very high (about 1012 Ω), isolation capacitance is small (about a few pF), so it can prevent electromagnetic interference caused by coupling circuit.
A linear optocoupler works by adding a control voltage to the input end of the optocoupler, and a proportional voltage is generated at the output end for further control of the next level circuit.
A linear photocoupler consists of a light-emitting diode and a phototransistor.
When the LED is on and is emitting light, the phototransistor is on.
A photocoupler is a current-driven type.
A large enough current is needed to turn on the LED.
If it is too small, the LED will not light up and its output signal will be distorted.
In switching power supply, especially in digital switching power supply.
The main advantages of optocouplers
Unidirectional signal transmission, complete electrical isolation of input and output terminals, no influence of output signals on input terminals, strong anti-interference ability, stable operation, no contact, long service life, high transmission efficiency.
Photoelectric coupler is a new device developed in the 1970 s, is now widely used in electric insulation, level conversion, interstage coupling, drive circuit, switching circuit, chopper, multivibrator, signal isolation, isolation between level, pulse amplification circuit, digital instrument, long distance signal transmission, the pulse amplifier, solid state relay (SSR), instrumentation, communications equipment and computer interface.
A linear optocoupler can be used to form an optocoupler feedback circuit in a single-chip switching power supply.
The duty ratio can be changed by adjusting the current on the control terminal to achieve accurate voltage regulation and signal receiving and transmission.
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