Stacked Chip 32M Flash Memory and 4M SRAM # Technical Documentation: LRS1337 Infrared Emitting Diode
Manufacturer: SHARP
Component Type: Infrared (IR) Emitting Diode
Document Version: 1.0
Date: October 26, 2023
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## 1. Application Scenarios
The SHARP LRS1337 is a high-efficiency GaAlAs infrared emitting diode designed for applications requiring reliable, low-power IR signal transmission. Its primary function is to convert electrical signals into modulated infrared light for remote control, data transmission, and sensing applications.
### Typical Use Cases
- Remote Control Systems: The most common application is in consumer electronics remote controls (TVs, audio systems, set-top boxes). The diode emits pulsed IR signals corresponding to command codes.
- Proximity and Object Detection: Used in automatic faucets, hand dryers, and security systems where breaking an IR beam triggers an action.
- Data Transmission Links: Short-range serial data communication in environments where RF interference is problematic or where wired connections are impractical.
- Optical Switches and Encoders: Industrial equipment uses these diodes with phototransistors to create contactless position sensing.
- Night Vision Illumination: Arrays of LRS1337 diodes provide invisible illumination for security cameras with IR-sensitive sensors.
### Industry Applications
- Consumer Electronics: Universal remotes, smart home device controllers, gaming peripherals.
- Industrial Automation: Machine safety curtains, conveyor belt object counting, equipment status signaling.
- Automotive: Garage door openers, tire pressure monitoring system (TPMS) receivers, in-car entertainment controls.
- Medical Devices: Non-contact thermometers, pulse oximetry sensors (as part of emitter pairs).
- Telecommunications: IrDA-compliant data transfer ports in legacy PDAs, printers, and laptops.
### Practical Advantages
- High Output Power: Typical radiant intensity of 9 mW/sr at 100 mA enables longer operational range (up to 10 meters in optimal conditions).
- Narrow Emission Angle: 30° half-angle provides focused beam, reducing power waste and increasing signal directionality.
- Fast Response Time: Rise/fall time < 100 ns supports high-frequency modulation (up to several hundred kHz for data transmission).
- Low Forward Voltage: Typically 1.35V at 100 mA reduces power consumption and thermal load.
- Reliability: Solid-state construction with typical lifespan exceeding 100,000 hours.
### Limitations
- Line-of-Sight Requirement: IR signals cannot penetrate solid objects and are affected by obstacles.
- Ambient Light Interference: Direct sunlight or strong incandescent light containing IR spectrum can saturate receivers.
- Limited Data Rate: Suitable for low to moderate speed data transmission (typically < 115.2 kbps for IrDA).
- Thermal Management: Continuous operation at maximum current requires heat sinking to prevent wavelength shift and accelerated degradation.
- Eye Safety: Although invisible, high-intensity IR can cause retinal damage; designs must comply with IEC 60825-1 Class 1 limits.
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## 2. Design Considerations
### Common Design Pitfalls and Solutions
1. Overdriving the Diode
- Pitfall: Applying continuous current beyond absolute maximum ratings (typically 100 mA continuous) causes rapid degradation.
- Solution: Implement current-limiting resistors or constant-current drivers. For pulsed operation, ensure duty cycle ≤ 50% for peak currents up to 1A.
2. Insufficient Modulation
- Pitfall: Using DC or low-frequency modulation makes the signal vulnerable to ambient light interference.
- Solution: Modulate at carrier frequencies between 30-56 kHz (standard for remote controls) or 1.6 MHz for IrDA. Use dedicated encoder ICs like the NEC µPD6121 or microcontrollers with hardware
