An optocoupler device can be simply described as a sealed self contained unit that houses independently powered optical light tx and rx units that can be coupled together optically.
Bidirectional opto isolator circuit.
Opto electrical isolation of the i2c bus 3.
These devices have their logic input and output buffers separated by ti s capacitive isolation technology using a silicon dioxide sio2 barrier.
The i2c bus also known as inter ic bus is a bidirectional two wire multi user bus as shown in fig.
The output consists of two mosfets connected gate to gate and source to source.
2 using p82b96 and using the lowest cost 4n36 opto couplers to opto isolate the i 2c bus signal.
These couplers allow saturation of the photo transistor in the opto coupler.
The breakdown voltage range can be within 15 to 30 volts while the rise and fall times is around 15 microseconds each.
2 illustrates the internal construction behind bidirectional ssrs.
See vom1271 photovoltaic mosfet driver circuits.
Here the tx unit is a led but the rx unit may take the form of a phototransistor a photo.
Independent 3 0v to 5 5v supplies on each side of the isolator also make it suitable for use as a level translator.
Opto isolators prevent high voltages from affecting the system receiving the signal.
Due to galvanic isolation an optocoupler helps to break up ground loops.
The two bidirectional channels are open drain and each is capable of data rates from dc to 2mbps.
The third schematic above shows an optocoupler having an ired and a mosfet photosensor featuring bi directional linear output.
Texas instruments low power bi directional isolators are compatible with i c interfaces texas instruments iso1541 is a low power bi directional isolator that is compatible with i 2 c interfaces.
Opto coupling supports very large ground differences figure 4 shows the simplest arrangement from application note an460 ref.
Optocouplers and opto isolators can be used on their own or to switch a range of other larger electronic devices such as transistors and triacs providing the required electrical isolation between a lower voltage control signal for example one from an arduino or micro controller and a much higher voltage or mains current output signal.
This consists of a photovoltaic opto coupler such as the vom1271.
There are various types of opto isolators which are classified based on various criteria such as number of channels isolation voltage type of packing output voltage capacity current transfer ration ctr and so on.
As we discussed earlier in this article source and sensor of opto isolator are used for transferring the signals.
The isolation voltage range of this variant can be as high as 2500 volts rms.
Figure 1 shows the basic form of such a device.
Commercially available opto isolators withstand input to output voltages up to 10 kv and voltage transients with speeds up.
4 depicts an exemplary optical i2c isolator circuit.
Vishay s 10 mbd high speed optocouplers are used.
