IC OUTPUT OPTOCOUPLER

Different sections of a circuit operate at their own voltage levels. Optocouplers are used to isolate these lines. If there is any transient voltage or noise in one of the lines, the optocoupler stops it from interfering with the other lines. It is mainly used for signal and electrical isolation. They can be considered similar to transformers or relays.

How does it work?

The input part has an infrared LED chip and the output has a silicon diode chip. A thin, transparent, Mylar plate embedded in clear silicone separates these. Resistors are also placed in the circuit. The assembly is sealed in plastic. When a forward bias voltage is applied to the input terminals of the LED an input current flows in the LED circuit. This current produces an infrared light that hits the silicon chip. The infrared light varies with the input voltage.

Selection of an IC output optocoupler:

The following parameters need to be considered for selection:

Isolation voltage: maximum voltage differential the device can tolerate between its input and output sections
Data delay and setup time: the setup and delay time of the output data, relative to the clock signal edge
Propagation delay time: defines how quickly a logic signal propagates through the optical system
Pulse-width distortion parameter: defined as the maximum data rate capability of a transmission system
Propagation delay skew: defined as the difference between the minimum and maximum propagation delays for any given group of optocouplers that are operating under the same conditions

Other important parameters are: peak inverse voltage, reverse DC current, continuous DC forward current, peak forward current, DC power dissipation and forward voltage

Applications of an IC output optocoupler:

They are used in gasoline pumps to measure the flow of gas, punch-card readers, parts counters, and end-of-tape sensors on printers or tape recorders. They are used in applications for digital logic interface/level shifting, data communication, telecommunications, motor control, power supply and industrial. They are also used in circuits for adjustable electronic loads for low voltage DC applications, high-speed BiCMOS current-mode PWM controllers, and for generating a negative voltage bias supply from a positive input voltage.