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Application Of Optocoupler In Telephone Security Device
- Oct 16, 2017 -

Optocoupler to input, output electrical signal isolation, with a signal one-way transmission, input and output completely realize the electrical isolation, output signal to the input without impact, anti-interference ability, work stability, no contact point, long service life, high transmission efficiency characteristics.

Using Optocoupler as solid relay has the advantages of small size, close coupling, low driving power, fast motion and wide operating temperature range. Figure 1 shows the actual circuit diagram of a optocoupler used as a solid relay, Optocoupler the left half of the circuit can be used to transform the input signal VI into a luminous signal of the light coupling inner light-emitting diode, while the right half circuit converts the optical signal into an electrical signal by a photosensitive transistor in the optocoupler. So this is a very good combination of electro-optic and optoelectronic devices. The optical coupling current transmission ratio is 20%, the withstand voltage is 150V, Optocoupler the driving current is between 8~20ma. In actual use, because it does not have general electromagnetic relay common actual contact, therefore does not have the contact bad and burns the arc ignition and so on phenomenon, also does not suffer from the external force or the mechanical impact to cause the erroneous movement. Therefore, Optocoupler its performance is more reliable, the work is very stable.

Application of Optocoupler in telephone security device

In order to prevent the telephone line from being stolen or stolen by the telephone, a simple and practical telephone security circuit can be designed by using Optocoupler, which is composed of a vd1~vd4 polarity conversion circuit. Since the security device is connected to the telephone line, Optocoupler it is not necessary to distinguish the polarity of the feedback voltage of the telephone line, therefore, the use of the security device can bring great convenience to the installation.

circuit diagram of replacing audio transformer with Optocoupler

In the linear circuit, the two-stage amplifier is commonly used for coupling the audio transformer. The disadvantage of this coupling is that it loses part of the power in the transformer's iron chip and may cause some distortion. These drawbacks can be overcome by using Optocoupler instead of audio transformers. Optocoupler When the input signal VI by transistor BG1, BG2 front-level amplification, drive Optocoupler left led light-emitting, and by the right side of the photosensitive tube all absorbed and converted to electrical signals, the signal by the back-level circuit BG3 amplification, and by the tube emitter through the capacitor C3 output a undistorted amplification signal V0. Optocoupler Because the circuit will be completely isolated between the front and rear two amplifiers, thus eliminating the potential disturbance caused by the ground loop. At the same time, because the circuit also has the function of denoising, Optocoupler it avoids the distortion of the signal. The total gain of the whole circuit is expected to reach more than 20dB and the bandwidth is about 120kHz.

Optocoupler is a semiconductor optoelectronic device that encapsulates a light-emitting element and a photosensitive element in the same shell and transmits electrical signals in the middle by the conversion of electricity → light → electricity. According to different requirements, Optocoupler can synthesize many series of optical coupler by different kinds of light-emitting elements and photosensitive elements. At present, the most widely used is light-emitting diode and photosensitive transistor combination of optocoupler.

Optocoupler takes the optical signal as the medium to realize the coupling and transmission of the electrical signal, and the input and output are completely isolated on the electric circuit, Optocoupler which has the characteristics of strong anti-interference ability. For the industrial application measurement and control system which includes both the weak control part and the strong electric control part, the optical coupling isolation can be used to realize the isolation of weak and strong electricity, and to achieve anti-jamming. However, Optocoupler the following issues need to be considered to isolate Optocoupler: When the ① Optocoupler is directly used to isolate the transmission analog, the nonlinear problem of the optocoupler is considered, and the response speed of the optical coupling is considered when the ② of the optical coupling is isolated to transmit the digital quantity, and the Power interface design of the optical coupling must be considered when the ③ output has the power requirement.

The main characteristics of Optocoupler are as follows:

1. Input and output between the insulation, its insulation resistance is generally greater than 10000mω, withstand pressure can be more than 1kV, and some can even reach more than 10kV.

2. Because the optical receiver can only accept the information of the light source, the other can not, so the signal from the source to the optical receiver will not appear feedback phenomenon, its output signal will not affect the input.

3. Because the light-emitting device (gallium arsenide infrared diode) is a resistive current driving device, and noise is a high internal resistance of micro-current voltage signal. Therefore, Optocoupler the common-mode rejection ratio of optocoupler is very large, so the optical coupler can restrain the interference and eliminate the noise well.

4. Easy to cooperate with logic circuit.

5. Fast response speed. The time constants of optocoupler devices are usually in milliseconds or even microseconds.

6. No contact point, long life, small size, impact resistance.