Οπτοσυζεύκτες Optocoupler
Optical couplers
6.4 Other Photovoltaics
There are other photodiodes other than those mentioned that are used either as sensors, for remote control, or for electrical circuit isolation where there is optical connection.
Such optoelectronic devices or photovoltaic devices are the photocurrent, photodiac, phottriac, Laser diode, photocell, optical sensor, optical switch and finally optocoupler.
The optocoupler is commercially available in a format similar to that of integrated circuits, ie with 6 or 8 pins, and consists of an infrared LED and a photoconductor. The phototransistor may have a base terminal for bias application or may not have.
Such optocouplers are marketed by various companies such as CNY13, 4N25 -28, 6N135-136 and others.
Figure 6.4.1 shows the 4N25 with its terminals and photodetectors.
Figure 6.4.1 4N 25 Coupler (a) Internal circuit, (b) Figure
By using an optocoupler circuit, the input and output of the circuit are electrically isolated and there is only optical connection. Its function is as follows:
The light emitting diode (LED) is polarized correctly (terminals 1,2) and the direct current IF is converted to infrared radiation by the LED emitted and received by the phototransistor (terminals 4,5,6). This radiation is converted into electricity and leaves the collector as IC (terminal 5).
This output current is amplified relative to the input current, and the Ic / IF ratio (also called CTR) can reach values up to 1000.
Optical couplers, which are widely used in modern microelectronics, will be described and analyzed later.
Example:
Here in this example, the 270kΩ externally coupled resistor is used to control the sensitivity of the base region of the phototransistor. The resistance value can be selected to match the selected photodetector and the required amount of switching sensitivity. The capacitor stops any unwanted spikes or transiently from the false activation of the opto-transistor base.
