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Also known as a coupler adapter optocoupler is an electric light as a medium to transmit electrical signals of a light one electric conversion device. It consists of two parts, a light source and a light composition. The light source and the light assembly in the same sealed housing, isolated from each other by a transparent insulator. Hair pin as an input source, the light pin as an output, a common light source is a light emitting diode, the optical receiver is a photodiode, phototransistor, and so on. Kind optocoupler more common type photodiode, phototransistor type photoresistor type, light control thyristor type, photoelectric Darlington type, integrated type. Figure 1 below (round shape metal shell packaging, plastic dual in-line, etc.). Works on signal at the input of the optocoupler so that light source light, the intensity of light depends on the excitation current size, this light shines after packaged together on the light, a result of the photoelectric effect and the photocurrent generated by the light the output leads, thus achieving an electro-optical power conversion. ⒈ operating characteristic (with phototransistor for example) a high common-mode rejection ratio coupler optocoupler inside, due to the coupling capacitance is very small and the light-emitting tube between (2pF less) common mode input voltage between the electrodes by coupling Effect of capacitance on the output current is very small, and thus a high common-mode rejection ratio. ⒉ output characteristics of the output characteristics of the optocoupler means that under certain light emitting current IF, the photodiode bias voltage VCE-Canada relations and the output current IC between when IF = 0, the light emitting diode does not emit light at this time phototransistor collector output current is called the dark current, generally very small. When the IF> 0, the IF under certain role, the corresponding IC substantially independent of VCE. Changes between IC and IF a linear relationship with the semiconductor curve tracers measured optocoupler output characteristics and output characteristics similar to ordinary transistor. ⒊ optocouplers can be used as a linear coupling provided on the light emitting diode using a bias current, then the signal voltage is coupled to the light emitting diode through a resistor, so the phototransistor received is to increase the bias current, reducing the change of light signal, the output current with the input signal voltage changes linearly. Optocouplers can work in the off state, the transmission pulse signal. When the transmission pulse signal between the input signal and the output signal a delay time, optocouplers different structure of input and output delay time vary greatly. Optoelectronic Test ⒈ bad judgment with a multimeter, 3 and disconnect the input power supply, R × 1k file measuring 1,2 coupler pin resistance, resistance of hundreds of Europe forward, reverse resistance tens of kilohms, 3 , 4-foot resistance should be infinite. Between 1,2 and 3,4 feet feet to any one group, the resistance is infinite, after the input power, resistance 3,4 feet small. Adjusting RP, 3,4 feet between resistance to change, indicating the device is good. Note: You can not use R × 10k file, otherwise lead to the launch tube breakdown. ⒉ simple test circuit, when the power is turned on, LED does not light, pressing the SB, LED will be light, adjust the RP, LED luminous intensity will change, indicating the test optocoupler is good. Applications ⒈ composition ui switch circuit when the input signal is low, transistor V1 is off, optocouplers B1 light emitting diode current is approximately zero, the output of Q11, Q12 resistance between the large, equivalent to switch "off "; When ui is high, resistance v1 conduction, B1 of the light emitting diode, Q11, Q12 becomes smaller, the equivalent switch" on. " The circuit because Ui is low, the switch fails, it is high conductive state. Similarly, when there is no signal (Ui low) because the switch is turned on, it is low conductive state. 2. Composition logic circuit is "and gate" logic. Its logical expression is P = A. B. figure two photodiodes in series, only when the input logic level A = 1, B = 1, the output P = 1. Similarly, it can also compose "or gate", "NAND gate", "NOR" and other logic circuits. 3. Composition isolated coupling circuit circuit shown in Figure 4. It is a typical AC-coupled amplifier. Select the appropriate light-emitting circuit current limiting resistor Rl, so B4 current transfer ratio is a constant, you can ensure that the linear amplification of the circuit.