Infrared LED 940nm Datasheet - Technical Documentation

1. Product Overview

This document provides a comprehensive technical overview of an infrared (IR) light-emitting diode (LED) component. The primary function of this device is to emit light in the near-infrared spectrum, specifically at a peak wavelength (λp) of 940 nanometers (nm). This wavelength is invisible to the human eye but is highly effective for various sensing and remote control applications. The component is designed for integration into electronic assemblies requiring a reliable and consistent IR light source.

The core advantage of this IR LED lies in its specified 940nm emission, which is a common standard for consumer electronics like TV remote controls and proximity sensors. This wavelength offers a good balance between silicon photodetector sensitivity and ambient light rejection. The target market includes consumer electronics, industrial automation, security systems, and any application requiring non-visible light for signaling, detection, or data transmission.

2. In-Depth Technical Parameter Analysis

The provided PDF fragment highlights a single, critical photometric parameter: the peak wavelength.

2.1 Photometric Characteristics

Peak Wavelength (λp): 940nm

This is the most prominent wavelength emitted by the LED, where the radiant intensity is at its maximum. A 940nm peak is significant for several reasons:

• Silicon Detector Compatibility: Silicon photodiodes and phototransistors, the most common IR detectors, have peak sensitivity typically in the range of 800nm to 950nm. A 940nm source aligns well with this, ensuring efficient detection and strong signal strength.
• Low Visible Light Emission: While some near-IR LEDs emit a faint red glow, 940nm LEDs are virtually invisible, making them ideal for covert applications or where visible light leakage is undesirable.
• Sunlight Immunity: The solar irradiance spectrum has a local minimum around 940nm, which helps sensors using this wavelength to be less susceptible to interference from ambient sunlight compared to, for example, 850nm LEDs.

While the PDF excerpt only shows the peak wavelength, a complete datasheet would typically include additional photometric parameters such as radiant intensity (in milliwatts per steradian, mW/sr), viewing angle (half-intensity angle in degrees), and spectral bandwidth (full width at half maximum, FWHM, in nm).

2.2 Electrical Parameters

Although not explicitly listed in the provided text, understanding the electrical characteristics is fundamental for design.

• Forward Voltage (Vf): The voltage drop across the LED when operating at its specified current. For typical IR LEDs, this often ranges from 1.2V to 1.6V, but the exact value depends on the semiconductor material and chip design. This parameter is crucial for selecting an appropriate current-limiting resistor or driver circuit.
• Forward Current (If): The recommended continuous operating current, typically between 20mA and 100mA for standard packages. Exceeding the maximum forward current can lead to rapid degradation or catastrophic failure.
• Reverse Voltage (Vr): The maximum voltage the LED can withstand when reverse-biased without damage, usually around 5V. Exceeding this can break down the PN junction.
• Power Dissipation: Calculated as Vf * If, this determines the thermal load on the component and influences the need for heat sinking.

2.3 Thermal Characteristics

LED performance and lifespan are heavily dependent on junction temperature.

• Thermal Resistance (Rθj-a): The resistance to heat flow from the semiconductor junction to the ambient air, expressed in degrees Celsius per watt (°C/W). A lower value indicates better heat dissipation capability.
• Maximum Junction Temperature (Tj max): The highest allowable temperature at the semiconductor junction. Operating above this limit drastically shortens the LED's lifetime. Proper PCB layout (thermal vias, copper area) is essential to keep Tj within limits.
• Derating Curve: A graph showing how the maximum allowable forward current decreases as the ambient temperature increases. This is a critical design tool for ensuring reliability under all operating conditions.

3. Binning System Explanation

Manufacturing variations mean LEDs are not identical. A binning system categorizes components based on key parameters to ensure consistency within a production batch.

• Wavelength/Peak Wavelength Binning: LEDs are sorted into bins based on their actual peak wavelength, e.g., 935-945nm, 940-950nm. This ensures color consistency for the application.
• Radiant Intensity/Flux Binning: Components are grouped by their measured light output power. For example, bins might be defined as Min/ Typ/ Max radiant intensity values at a specific test current.
• Forward Voltage Binning: LEDs are sorted by their Vf at a test current. This helps in designing more uniform circuits, especially when multiple LEDs are connected in series.

Designers must specify the required bins when ordering to guarantee the performance needed for their application.

4. Performance Curve Analysis

Graphical data provides deeper insight than single-point specifications.

4.1 Current vs. Voltage (I-V) Curve

This curve shows the relationship between forward voltage and forward current. It is non-linear, exhibiting a "knee" voltage (typically ~1.2V for IR LEDs) above which current increases rapidly with small increases in voltage. This underscores the importance of current control, not voltage control, for driving LEDs.

4.2 Temperature Characteristics

Key graphs include:

• Forward Voltage vs. Junction Temperature: Vf has a negative temperature coefficient, meaning it decreases as temperature increases. This can be used for temperature sensing.
• Radiant Intensity vs. Junction Temperature: Light output typically decreases as temperature rises. The slope of this curve indicates the thermal stability of the output.
• Relative Intensity vs. Forward Current: Shows how light output scales with drive current, usually in a linear or slightly sub-linear relationship until thermal effects dominate.

4.3 Spectral Distribution

A graph plotting relative intensity against wavelength. For a 940nm LED, this curve would be centered around 940nm with a typical FWHM of 40-50nm. The shape and width of this curve affect how the light interacts with filters and detectors.

5. Mechanical and Package Information

The PDF mentions packaging terms but lacks a dimensional drawing.

• Package Type: Common packages for IR LEDs include 3mm, 5mm radial leads, and surface-mount device (SMD) packages like 0805, 1206, or specialized IR packages.
• Dimensions: A detailed mechanical drawing would specify length, width, height, lead diameter/spacing (for through-hole), or pad dimensions (for SMD).
• Pad Design/Land Pattern: For SMD parts, the recommended PCB footprint (pad size, shape, and spacing) is critical for reliable soldering and mechanical strength.
• Polarity Identification: LEDs are diodes and must be connected with correct polarity. Identification is typically via a flat edge on the lens, a longer anode lead, or a marked cathode on the SMD package body.

6. Soldering and Assembly Guidelines

Proper handling ensures reliability.

• Reflow Soldering Profile: For SMD components, a time-temperature profile specifying preheat, soak, reflow peak temperature (typically 260°C max for a few seconds), and cooling rates must be followed.
• Hand Soldering: If applicable, guidelines for iron temperature (<350°C) and maximum soldering time per lead (e.g., 3 seconds) are provided to prevent thermal damage to the epoxy lens or semiconductor.
• ESD Precautions: LEDs are sensitive to electrostatic discharge. Handling should occur at ESD-protected workstations using grounded equipment. The mention of an "electrostatic bag" in the PDF highlights this requirement.
• Storage Conditions: Components should be stored in a dry, controlled environment (e.g., <40°C/40% RH) to prevent moisture absorption, which can cause "popcorning" during reflow.

7. Packaging and Ordering Information

The PDF fragment lists several packaging levels.

• Electrostatic Bag: The primary moisture and ESD barrier for the bulk components or reels.
• Inner Carton: Contains multiple electrostatic bags or reels.
• Outside Carton: The master shipping carton containing multiple inner cartons.
• Packing Quantity: The standard quantity per reel (e.g., 1000pcs), per bag, or per carton.
• Labeling: Labels should include part number, quantity, date code, lot/batch number, and ESD/moisture sensitivity level (MSL).
• Model Numbering Rule: A complete part number typically encodes key attributes like package type, wavelength bin, intensity bin, and forward voltage bin.

8. Application Recommendations

8.1 Typical Application Scenarios

• Infrared Remote Controls: For TVs, set-top boxes, audio systems. The 940nm wavelength is the industry standard.
• Proximity and Presence Sensors: Used in smartphones (to disable touchscreens during calls), automatic faucets, soap dispensers.
• Object Detection and Counting: In industrial automation, vending machines, and security beams.
• Optical Data Transmission: For short-range, low-speed data links (IrDA was a common standard).
• Night Vision Illumination: Paired with IR-sensitive cameras for surveillance in low-light conditions.

8.2 Design Considerations

• Drive Circuit: Always use a series current-limiting resistor or a constant-current driver. Calculate resistor value using R = (Supply Voltage - Vf) / If.
• PCB Layout: Provide adequate copper area or thermal vias under the LED's thermal pad (if SMD) to dissipate heat.
• Optical Design: Consider lensing or apertures to shape the beam. The LED's viewing angle must match the detector's field of view.
• Filtering: Use an IR-pass filter on the detector to block visible light and improve signal-to-noise ratio.
• Modulation: For sensing applications, modulating the IR signal (e.g., at 38kHz) and using a synchronized detector can effectively reject ambient light interference.

9. Technical Comparison

Compared to other IR sources:

• vs. 850nm IR LEDs: 850nm LEDs often have a faint red glow and are more susceptible to sunlight interference but may offer slightly higher radiant intensity for the same drive current due to material efficiency. 940nm is preferred for covert operation and better sunlight rejection.
• vs. Laser Diodes: Lasers provide a coherent, narrow beam ideal for long-range or precision sensing but are more expensive, require more complex drive and safety measures, and have a narrower emission spectrum.
• vs. Incandescent IR Sources: Filament-based sources emit broad-spectrum IR but are inefficient, slow, fragile, and generate significant heat.

The 940nm LED offers an optimal balance of cost, efficiency, reliability, and performance for mainstream consumer and industrial applications.

10. Frequently Asked Questions (FAQs)

Q: Why is my 940nm LED not visible?
A: The human eye's sensitivity drops sharply beyond about 750nm. 940nm is far into the infrared spectrum and is essentially invisible, which is a key feature for many applications.

Q: Can I drive this LED directly from a 5V or 3.3V microcontroller pin?
A: No. You must always use a current-limiting resistor in series. A microcontroller's GPIO pin cannot supply a stable current and may be damaged by the LED's low forward voltage, which could create a near-short circuit condition.

Q: How do I determine the optimal resistor value?
A: Use Ohm's Law: R = (Vs - Vf) / If. For example, with Vs=5V, Vf=1.4V (typical), and If=20mA: R = (5 - 1.4) / 0.02 = 180 Ohms. Use the next standard value (e.g., 180Ω or 220Ω).

Q: What is the purpose of the "electrostatic bag" mentioned?
A> It protects the LED from electrostatic discharge (ESD) during storage and transport, which can damage the sensitive semiconductor junction even if the damage is not immediately visible.

Q: Does ambient temperature affect performance?
A> Yes, significantly. Radiant intensity decreases as temperature increases, and forward voltage decreases. For critical applications, consult the derating curves and design thermal management accordingly.

11. Practical Use Cases

Case Study 1: Smartphone Proximity Sensor
A 940nm LED is placed near the earpiece. When a call is active, the LED emits a brief pulse. A nearby photodetector measures the reflected light. If an object (like the user's ear) is close, the reflected signal is strong, and the touchscreen is disabled to prevent accidental inputs. The 940nm wavelength ensures no visible glow is seen during the call.

Case Study 2: Industrial Conveyor Object Counter
An IR LED and detector are mounted on opposite sides of a conveyor belt, creating a beam. When an object passes through, it breaks the beam, triggering a counter. Using a modulated 940nm signal helps the system ignore the constant IR radiation from hot objects or machinery on the factory floor.

12. Operating Principle

An infrared LED is a semiconductor p-n junction diode. When forward-biased (positive voltage applied to the p-side, anode), electrons from the n-region are injected across the junction into the p-region, and holes from the p-region are injected into the n-region. These minority carriers recombine with majority carriers in the opposing regions. In a direct bandgap semiconductor material like Gallium Arsenide (GaAs) or Aluminum Gallium Arsenide (AlGaAs), commonly used for IR LEDs, this recombination event releases energy in the form of a photon (light particle). The wavelength (color) of the emitted photon is determined by the bandgap energy (Eg) of the semiconductor material, according to the equation λ ≈ 1240 / Eg (eV), where λ is in nanometers. For a 940nm wavelength, the bandgap energy is approximately 1.32 eV. The specific material composition (e.g., AlGaAs) is engineered to achieve this precise bandgap.

13. Technology Trends

The development of IR LEDs follows several key trends driven by application demands:

• Increased Power and Efficiency: Ongoing material science and chip design improvements yield higher radiant intensity and wall-plug efficiency (optical power out / electrical power in), enabling longer range or lower power consumption.
• Miniaturization: Package sizes continue to shrink (e.g., chip-scale packages) to fit into ever-smaller consumer devices like wearables and ultra-thin smartphones.
• Integrated Solutions: There is a move towards modules that combine the LED, driver, photodetector, and sometimes even a microcontroller into a single package, simplifying design for end-users (e.g., complete proximity sensor modules).
• Expansion into New Spectra: While 850nm and 940nm dominate, there is growing interest in other IR wavelengths for specialized applications, such as gas sensing (using specific absorption lines) or enhanced biological tissue imaging.
• Improved Thermal Management: New package designs with lower thermal resistance allow higher drive currents and sustained output in demanding environments.

These trends aim to make IR sensing more reliable, compact, energy-efficient, and accessible for a broader range of applications, from automotive LiDAR and biometric authentication to advanced environmental monitoring.