Bidirectional Opto Isolator Circuit

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 coupling supports very large ground differences figure 4 shows the simplest arrangement from application note an460 ref. 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. These devices have their logic input and output buffers separated by ti s capacitive isolation technology using a silicon dioxide sio2 barrier.

Optocoupler is the perfect solution. As we discussed earlier in this article source and sensor of opto isolator are used for transferring the signals. This consists of a photovoltaic opto coupler such as the vom1271. An opto isolator also called an optocoupler photocoupler or optical isolator is an electronic component that transfers electrical signals between two isolated circuits by using light.

The max14850 can be used for isolating spi busses i 2 c busses rs 232 rs 485 rs 422 busses and general purpose isolation. 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. Due to galvanic isolation an optocoupler helps to break up ground loops. 2 illustrates the internal construction behind bidirectional ssrs.

The i2c bus also known as inter ic bus is a bidirectional two wire multi user bus as shown in fig. The isolation voltage range of this variant can be as high as 2500 volts rms. 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. The third schematic above shows an optocoupler having an ired and a mosfet photosensor featuring bi directional linear output.

Figure 1 shows the basic form of such a device. The output consists of two mosfets connected gate to gate and source to source. 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. See vom1271 photovoltaic mosfet driver circuits.

Vishay s 10 mbd high speed optocouplers are used. 2 using p82b96 and using the lowest cost 4n36 opto couplers to opto isolate the i 2c bus signal. The two bidirectional channels are open drain and each is capable of data rates from dc to 2mbps. The breakdown voltage range can be within 15 to 30 volts while the rise and fall times is around 15 microseconds each.

4 depicts an exemplary optical i2c isolator circuit. Opto electrical isolation of the i2c bus 3.