Many people may ask why optocouplers are needed? In optocouplers, the primary side (LED side) and the secondary side (light receiving device side) are electrically insulated. Therefore, even if the potentials (even GND potential) of the primary and secondary sides are different, the primary side electrical signal can still be transmitted to the secondary side. Due to its small size, fast response speed, good isolation effect, and strong anti-interference ability, optocoupler devices are widely used in level conversion, signal isolation, inter stage isolation, switch circuits, long-distance signal transmission, pulse amplification, solid-state relays (SSRs), instruments and meters, communication equipment, and microcomputer interfaces. In the inverter application shown in Figure 1, the control unit (such as a microcontroller) typically operates at low DC voltage. On the other hand, IPM and IGBT will drive high-voltage loads (such as requiring 200V AC power). High voltage system components can be directly controlled by a microcontroller through a coupler.
In optocouplers, LEDs are used as inputs for optocouplers. On the other hand, there are various devices available for output. There will be different application distinctions based on the type of output.
Transistor output: Phototransistors are a type of detector and can also be of the Darlington type.
IC output: Toshiba has products such as photodiodes as light receiving devices, logic output products, high current output products for IGBT and MOSFET gate drivers, and high-performance products such as isolation amplifiers.
Controllable silicon/thyristor output: Optoelectronic thyristors or thyristors are used for output. They are mainly used for controlling communication lines.
Relay (MOSFET output): Photovoltaic array (photodiode array) drives the gate of MOSFET to turn on/off the output. Through this operation, it can be used as a relay switch for MOSFET output.
In addition to different output types, there are also many different types of optocouplers according to their packaging. Optocouplers must have packaging shapes and dielectric strength that comply with safety standards. When designing according to safety standards, the following items need to be checked. The main parameters that need to be checked are:
Insulation creepage distance - the shortest distance (primary and secondary) between two conductors along the surface of the insulator;
Gap - the shortest distance between two conductors measured by air;
Insulation thickness - the minimum distance of insulation between two conductors;
Isolation voltage - an AC voltage between two conductors that, according to UL regulations, will not damage insulation even if applied for 1 minute.
On the other hand, due to limitations such as required insulation performance, packaging size, and internal chip size, optocouplers have different types of internal packaging structures.
Single mode transmission type: Frame type LEDs and frame type photodetectors are packaged in face-to-face molding. The transparent component between LED and photodetector is made of silicone resin material.
Single mode transmission type with film: In order to improve the isolation voltage, a polyimide film can be inserted between the LED and the photodetector.
Safety standards for optocouplers
When installing optocouplers in electrical equipment to protect the human body from electric shock, optocouplers may need to comply with different safety standards. There are various regulations and standards currently in place to ensure safety. From the perspective of design and manufacturing, safety standards can be divided into "set standards" and "part standards". Setting standards is the foundation for designing and manufacturing equipment such as televisions, video recorders, and power supply devices. The "whole machine standard" varies depending on the type of equipment, isolation method and its level, driving voltage, etc. In addition, the items that the insulation part must maintain (dielectric strength (insulation voltage), creepage distance, gap, etc.) are designated as "part standards".
Advanced Optical Semiconductor was jointly established by Southern Advanced and a team led by Dr. Yang Zhenlin, a returned overseas Chinese from Japan. With Southern Advanced as the main investor and Dr. Yang's team as the technical core, it is a high-tech enterprise specializing in optoelectronic integrated circuits such as optoelectronic devices, optocouplers, optocoupler relays, and optoelectronic drives. The R&D team covers design, manufacturing, sales, and service. Advanced Optical Semiconductor has an advanced fully automatic production line for optoelectronic devices and has an annual production capacity of 80 million optoelectronic optocoupler devices. At present, the main products of advanced optoelectronic semiconductors, such as optocouplers, relays, and optocouplers, are used in power storage systems, smart meters, automatic detection equipment, telecommunications equipment, measuring instruments, medical equipment, communication equipment, PC terminals, security monitoring, O/A equipment, PLC controllers, I/O control boards, etc. Based on the comprehensive design technology and chip manufacturing technology advantages of optoelectronic semiconductors, advanced optoelectronic semiconductors expect to deeply cultivate in the field of optoelectronic control with broad development prospects, gradually improve the technical added value of products, and expand product lines with higher technological content.