![]() ![]() Silicon-based isolation technology is based on CMOS technology, and consists of two separate integrated circuit (IC) chips – an input circuit and an output circuit – connected through bond-wires to enable data transfer, as shown in Figure 2.įigure 2: Cross section of digital isolator constructionīoth the input and output sides of the digital isolator, as shown in Figure 3, require separate voltage supplies (VCC1, VCC2) and separate grounds (GND1, GND2) to maintain signal isolation between the input and output.Ĭommunication within a digital isolator occurs when applying a transistor-transistor logic or CMOS logic input to the digital input. Optocoupler standards have not historically included lifetime reliability performance data or high-voltage stress testing for sustained applied high voltages, and thus their sustained long-term performance and reliability can vary significantly. Standards bodies including Underwriters Laboratories (UL) and Verband der Elektrotechnik (VDE) determine optocoupler ratings, and those ratings specifically define the “distance through insulation” to accommodate molding compound variations during manufacture, along with partial discharge tests to identify molding compound defects that could compromise isolation performance under stress. Because the molding compound is a key contributor to isolation barrier strength, its quality plays a significant role in optocoupler lifetime, reliability and performance. The isolation performance of an optocoupler is determined by a combination of the LED, the molding compound used between the input and output, and the distance through the molding compound. Both the input and output of an optocoupler isolator require separate voltage supplies connected through the anode and collector pins, and separate grounds typically connected at the cathode and emitter pins, in order to maintain signal isolation between the input and output.įigure 1: Optocoupler with pinout diagramĬommunication within an optocoupler occurs when an applied CMOS logic input generates an input-side current, which then creates a proportional LED output for transmission through the molding compound barrier to the receiving photodetector and output. The driver circuit and LED circuits are typically built using complementary metal-oxide semiconductor (CMOS) technology, with the insulation or isolation barrier usually consisting of molding compound. Over the past several decades, the technology used to isolate circuits has moved from optical-based to silicon-based – but how are these technologies really different?Īn optocoupler, as shown in Figure 1, consists of an input LED, a receiving photodetector and an output driver. Isolation as a form of protection requires that communication between two circuits occurs through an insulation or isolation barrier, which prevents current from directly flowing between the circuits. Therefore they are ideal for applications which may experience variations in voltage.Galvanic isolation is a necessary form of protection for all electronics that interface with humans or other circuits against possible high-voltage events ranging from tens of volts to kilovolts. This ensures that, if there is a spike in one part of a circuit, it will not affect other parts. Optocouplers are often used in high-voltage applications to block the high voltages and variations in voltage. ![]() The light detector senses the light emitter and converts it back into an electrical signal. The light emitter receives the input and converts it into a light signal. The light emitter device can come in the form of an LED (light emitting diode) that produces IR or visible light, or a laser diode. ![]() Optocouplers work by transferring energy from one circuit to another circuit via an optical transmission path, while providing electrical isolation Optocouplers usually come in a semiconductor package, such as SOIC or PDIP. Within an optocoupler you will find a light emitter and a light sensor. An optocoupler IC, also known as an opto-isolator or photocoupler, is a semiconductor device which is used to couple isolated circuits. ![]()
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