Introduction to the classification of optocouplers?

Optocoupler, also known as optocoupler, is a semiconductor device that achieves electrical isolation through optical signals. Its core structure consists of light-emitting diodes (LEDs) and photosensitive devices (such as phototransistors, photosensitive Darlington transistors, photosensitive thyristors, etc.), which achieve electrical isolation between input and output through optical signal transmission. Optocouplers are widely used in industrial control, communication equipment, medical electronics, consumer electronics, and other fields. Their main functions include:
Electrical isolation: Isolate high and low voltage circuits to protect low voltage devices from high voltage impacts.
Signal transmission: Transmit digital or analog signals in an isolated state to avoid ground loop interference.
Anti interference: Block the transmission path of noise and improve the electromagnetic compatibility (EMC) of the system.
1、 Classified by the number of channels
1. Single channel optocoupler
Structural features: Composed of an LED and a photosensitive device (such as a phototransistor), it achieves isolated transmission of a single signal channel.
Typical applications:
Industrial control: PLC input/output module isolation.
Power management: Switching power supply feedback loop isolation.
Representative models: PC817 (universal type), EL817 (high-speed type).
2. Dual channel optocoupler
Structural features: Contains two independent LED photosensitive device pairs to achieve parallel transmission of two signals.
Typical applications:
Communication interface: RS-485/RS-232 isolated.
Motor drive: Dual PWM signal isolation.
Representative models: TLP281-4 (four channel), ACPL-227 (dual channel).
3. Four channel and above optocouplers
Structural features: Integrated with multiple LED photosensitive device pairs, supporting multi-channel signal isolation.
Typical applications:
Industrial bus: CAN/Profibus isolation.
Data collection: multi-channel analog signal isolation.
Representative models: TLP290-4 (four channel), ISO7221 (eight channel digital isolator).
4. Darlington type optocoupler
Structural features: The photosensitive device adopts a Darlington transistor structure, with extremely high current gain (up to thousands of times).
Typical applications:
Relay drive: Control high current loads with low current.
Motor control: Drive DC motor or stepper motor.
Representative models: 4N35 (universal type), LTV-817 (high-speed type).
2、 Classified by packaging form
1. DIP package (Dual Inline Package)
Structural features: Direct insertion packaging, pin spacing of 2.54mm, easy to manually solder.
Typical applications:
Prototype development: Laboratory circuit board debugging.
Industrial equipment: scenarios that are insensitive to volume.
Representative models: PC817 (DIP-4), 4N35 (DIP-6).
2. SOP packaging (Small Outline Package)
Structural features: Surface mount packaging, small size, pin spacing of 1.27mm.
Typical applications:
Consumer electronics: portable devices such as mobile phones and tablets.
High density PCB: reduces footprint.
Representative models: EL817 (SOP-4), TLP291 (SOP-4).
3. Surface mount packaging (such as DFN, QFN)
Structural features: Ultra miniature packaging, no pin design, low thermal resistance.
Typical applications:
Wearable devices: smartwatches, health monitoring devices.
Miniature Design: Scenarios that are sensitive to volume and weight.
Representative model: AVAGO HCPL-063L (DFN-4).
3、 Classified by speed
1. Low speed optocoupler
Technical parameters: Transmission delay time (tpLH/tpHL)>10 μ s, stable current transfer ratio (CTR).
Typical applications:
Industrial control: switch signal isolation.
Power management: overvoltage/overcurrent protection circuit.
Representative models: PC817 (tpLH=18 μ s), 4N35 (tpLH=15 μ s).
2. High speed optocoupler
Technical parameters: Transmission delay time<1 μ s, supporting MHz level signal transmission.
Typical applications:
Communication equipment: fiber optic communication, Ethernet isolation.
Motor drive: high-speed PWM signal isolation.
Representative models: 6N137 (tpLH=75ns), EL817 (tpLH=2 μ s).
4、 Classified by isolation voltage
1. Standard isolation voltage optocoupler
Technical parameters: Isolation voltage (Viso) ≤ 5kVrms, meeting conventional industrial isolation requirements.
Typical applications:
Industrial automation: PLC module isolation.
Consumer electronics: charger isolation.
Representative models: PC817 (Viso=5kVrms), TLP291 (Viso=5kVrms).
2. High isolation voltage optocoupler
Technical parameters: Isolation voltage>5kVrms, suitable for high-voltage isolation scenarios.
Typical applications:
Medical equipment: ECG monitor isolation.
Industrial power supply: isolation of high-voltage frequency converter.
Representative model: AVAGO ACPL-M61L (Viso=10kVrms).
5、 Classify by output type
1. Transistor output optocoupler
Structural features: The photosensitive device is a photosensitive transistor with moderate output current capability.
Typical applications:
Digital signal isolation: TTL/CMOS level conversion.
Low power drive: LED indicator light control.
Representative models: PC817, 4N35.
2. Thyristor output optocoupler
Structural features: The photosensitive device is a photosensitive thyristor that can control AC loads.
Typical applications:
AC motor control: governor isolation.
Solid state relay: contactless switch.
Representative models: MOC3023 (random phase), MOC3043 (zero crossing trigger).
3. Light controlled thyristor (PhotoSCR)
Structural features: Integrated bidirectional thyristor, can directly drive AC loads.
Typical applications:
Home appliance control: air conditioning, washing machine motor drive.
Lighting control: Dimmer isolation.
Representative model: BTA16 (optocoupler+thyristor module).
6、 Special function optocoupler
1. Linear optocoupler
Structural features: Adopting feedback design to achieve linear transmission of analog signals.
Technical parameters: Non linearity<0.01%, bandwidth up to MHz level.
Typical applications:
Power management: feedback loop isolation.
Data collection: Analog signal isolation transmission.
Representative models: IL300, HCNR201.
2. Intelligent optocoupler (I2C/SPI isolator)
Structural features: Integrated I2C/SPI interface, supporting bidirectional data isolation.
Technical parameters: Data rate up to 1Mbps, isolation voltage>5kVrms.
Typical applications:
Industrial bus: CAN/Profibus isolation.
Energy storage system: BMS (Battery Management System) isolation.
Representative models: ADUM1250 (I2C isolation), ADUM1400 (SPI isolation).
7、 Selection Decision Framework
Signal type:
Digital signal: Select transistor output optocoupler (such as PC817).
Analog signal: Choose a linear optocoupler (such as IL300).
Communication load: Select thyristor output optocoupler (such as MOC3023).
Speed requirement:
Low speed (<10kHz): Choose PC817.
High speed (>1MHz): Choose 6N137.
Isolation voltage:
Conventional isolation (≤ 5kVrms): Select TLP291.
High voltage isolation (>5kVrms): Choose ACPL-M61L.
Packaging form:
Prototype development: Choose DIP packaging (such as PC817).
High density PCB: Choose SOP packaging (such as EL817).
Miniature design: Choose DFN packaging (such as AVAGO HCPL-063L).
Special Features:
Linear transmission: Choose HCNR201.
Intelligent interface: Select ADUM1250.
8、 Technology Trends
Miniaturization: The packaging size has evolved from DIP to SOP and DFN, with a volume reduction of over 50%.
High speed: The transmission delay time has evolved from μ s level to ns level, supporting 10Gbps communication.
Integration: Integrating I2C/SPI interfaces, LDO regulators, and other functions to simplify system design.
Intelligence: Built in self diagnosis, temperature compensation and other functions to enhance reliability.
Through the above classification and technical analysis, optocouplers can be systematically selected to balance performance, cost, and reliability requirements. In practical applications, it is recommended to conduct signal integrity simulation (such as HyperLynx) and reliability testing based on specific scenarios to ensure accurate selection.