LTL-E7939Q2K Infrared LED Lamp Datasheet - Through Hole Package - Wavelength 850nm - Radiant Intensity 20mW/sr - English Technical Document

1. Product Overview

This document provides the complete technical specifications for a high-performance, through-hole mounted infrared (IR) light-emitting diode (LED). The device is designed for applications requiring a reliable and powerful source of infrared light at a typical wavelength of 850 nanometers. It features a water-clear lens and is constructed using AlGaAs (Aluminum Gallium Arsenide) semiconductor technology, which is well-suited for efficient infrared emission. The product is compliant with RoHS directives, indicating it is free from hazardous substances like lead (Pb). Its core advantages include high-speed operation, high radiant power output, and compatibility with standard integrated circuits due to its low current requirements. It is intended for versatile mounting on printed circuit boards (PCBs) or panels in various electronic equipment sectors.

2. Technical Parameter Deep-Dive

2.1 Absolute Maximum Ratings

The device's operational limits are defined under an ambient temperature (Ta) of 25°C. Exceeding these ratings may cause permanent damage.

• Power Dissipation: 120 mW maximum.
• Peak Forward Current: 1 A maximum under pulsed conditions (300 pulses per second, 10 μs pulse width).
• DC Forward Current: 60 mA maximum for continuous operation.
• Reverse Voltage: 5 V maximum. Applying a higher reverse voltage can break down the LED junction.
• Operating Temperature Range: -30°C to +85°C.
• Storage Temperature Range: -40°C to +100°C.
• Lead Soldering Temperature: 260°C for a maximum of 5 seconds, measured 2.0mm from the LED body.

2.2 Electrical & Optical Characteristics

These parameters are specified at an ambient temperature (Ta) of 25°C and represent the device's typical performance.

• Radiant Intensity (Ie): Minimum 20.0 mW/sr when driven at a forward current (IF) of 20mA. The actual value should be considered with a ±15% tolerance. The specific classification code is marked on the product's packing bag.
• Viewing Angle (2θ1/2): Typically 25 degrees, with a minimum of 18 degrees. This is the full angle at which the radiant intensity drops to half of its peak axial value.
• Peak Wavelength (λP): Typically 850 nm, placing it in the near-infrared spectrum.
• Spectral Line Half-Width (Δλ): Typically 40 nm. This defines the spectral bandwidth of the emitted light.
• Forward Voltage (VF): Typically 1.3V, with a maximum of 1.65V at IF = 20mA.
• Reverse Current (IR): Maximum 10 μA when a reverse voltage (VR) of 5V is applied.

3. Performance Curve Analysis

The datasheet includes several typical characteristic curves that provide deeper insight into the device's behavior under various conditions. These are invaluable for circuit design and thermal management.

3.1 Spectrum

The spectral distribution curve shows the intensity of light emitted across different wavelengths, centered around the 850nm peak. The 40nm half-width indicates the spread of the emission.

3.2 Forward Voltage vs. Forward Current

This IV curve illustrates the relationship between the voltage across the LED and the current flowing through it. It is non-linear, typical of a diode. Designers use this to determine the necessary drive voltage for a target operating current.

3.3 Relative Radiant Power vs. Forward DC Current

This curve shows how the light output power increases with increasing DC drive current. It helps in selecting the appropriate operating point to achieve desired brightness while managing power dissipation.

3.4 Relative Radiant Power vs. Peak Current

For pulsed operation, this curve demonstrates the relationship between peak current in a pulse and the resulting radiant power output, which is crucial for applications like infrared data transmission.

3.5 Relative Radiant Power vs. Temperature

This is a critical thermal performance curve. It shows how the light output decreases as the ambient (or junction) temperature increases. Understanding this derating is essential for designing systems that maintain consistent performance over the specified temperature range.

3.6 Directivity

The directivity or radiation pattern curve visually represents the viewing angle, showing how the intensity is distributed spatially around the central axis of the LED.

4. Mechanical & Packaging Information

4.1 Package Dimensions

The device is a standard through-hole LED package. Key dimensional notes include:

• All dimensions are in millimeters (inches provided in parentheses).
• A general tolerance of ±0.25mm (±0.010") applies unless otherwise specified.
• The maximum protrusion of resin under the flange is 1.0mm (0.04").
• Lead spacing is measured at the point where the leads emerge from the package body.

The specific dimensional drawing is referenced in the datasheet, detailing the body diameter, lead length, and spacing.

4.2 Polarity Identification

For through-hole LEDs, polarity is typically indicated by the length of the leads (the longer lead is usually the anode) or by a flat spot on the LED lens rim. The datasheet's mechanical drawing will specify the exact identification method.

5. Soldering & Assembly Guidelines

Proper handling is crucial to ensure reliability and prevent damage.

5.1 Lead Forming

• Bending must be performed at a point at least 3mm from the base of the LED lens.
• The base of the leadframe must not be used as a fulcrum during bending.
• Lead forming should be done at normal room temperature and before the soldering process.
• During PCB insertion, use the minimum clinch force necessary to avoid imposing excessive mechanical stress on the LED body.

5.2 Soldering Process

• Maintain a minimum clearance of 2mm from the base of the lens to the soldering point.
• Avoid immersing the lens into solder.
• Do not apply external stress to the leads while the LED is at high temperature from soldering.

Recommended Soldering Conditions:

• Soldering Iron: Maximum temperature 350°C, for a maximum time of 3 seconds (one-time soldering only).
• Wave Soldering:
  • Pre-heat: Maximum 100°C for up to 60 seconds.
  • Solder Wave: Maximum 260°C for up to 5 seconds.

Important Note: Excessive soldering temperature or time can deform the lens or cause catastrophic LED failure. Infrared (IR) reflow soldering is not suitable for this through-hole type LED.

5.3 Cleaning

If cleaning is necessary, use alcohol-based solvents such as isopropyl alcohol.

5.4 Storage

For optimal shelf life:

• Storage environment should not exceed 30°C and 70% relative humidity.
• LEDs removed from their original, protective packaging should be used within three months.
• For extended storage outside the original packaging, store in a sealed container with desiccant or in a nitrogen-purged desiccator.

6. Drive Method & Circuit Design

LEDs are current-operated devices. To ensure consistent light output, especially when driving multiple LEDs, proper current regulation is essential.

• Recommended Circuit (Circuit A): Incorporate a current-limiting resistor in series with each LED. This is the preferred method as it compensates for minor variations in the forward voltage (Vf) characteristic between individual LEDs, ensuring uniform brightness across all devices in an array.
• Non-Recommended Circuit (Circuit B): Connecting multiple LEDs directly in parallel with a single shared current-limiting resistor is discouraged. Due to natural variances in the I-V curve of each LED, the current (and thus brightness) will not be distributed evenly, leading to some LEDs being brighter than others.

7. Electrostatic Discharge (ESD) Protection

This component is sensitive to electrostatic discharge. ESD can cause immediate or latent damage, manifesting as high reverse leakage current, abnormally low forward voltage, or failure to illuminate at low currents.

Prevention Measures:

• Personnel should wear conductive wrist straps or anti-static gloves when handling the LEDs.
• All equipment, workstations, and machinery must be properly grounded.
• Use ionizers to neutralize static charge that may accumulate on the plastic lens surface due to handling friction.

Verification for ESD Damage: Check suspect LEDs by testing for illumination and measuring the forward voltage (Vf) at a low test current.

8. Packaging & Ordering Information

8.1 Packaging Specification

The product is supplied in a multi-level packaging system:

• Basic Unit: 1,000 pieces per anti-static packing bag.
• Inner Carton: Contains 6 packing bags, totaling 6,000 pieces.
• Outer Carton: Contains 8 inner cartons, totaling 48,000 pieces.

8.2 Part Number Structure

The part number LTL-E7939Q2K encodes key attributes:

• LTL: Product family identifier.
• E7939: Specific device model/series.
• Q2K: Likely denotes specific binning for radiant intensity and/or viewing angle as per the classification code marked on the bag (e.g., intensity in the 18-21.5 mW/sr min range, viewing angle 20-29 deg typ).

9. Application Suggestions & Design Considerations

9.1 Typical Application Scenarios

This high-power 850nm IR LED is suitable for a wide range of applications including, but not limited to:

• Infrared Illumination: For security cameras, night vision systems, and machine vision in low-light conditions.
• Optical Sensing: Proximity sensors, object detection, and line-following robots.
• Data Transmission: Infrared data links (IrDA), remote controls (where high power extends range), and optical encoders.
• Industrial Automation: Position sensing, counting, and break-beam sensors.

9.2 Design Considerations

• Heat Management: While the device can handle 120mW, operating at or near the maximum DC current (60mA) will generate heat. Ensure adequate PCB copper area or heatsinking if used in high-ambient-temperature environments to prevent performance degradation and extend lifespan.
• Optical Design: The 25-degree typical viewing angle provides a relatively focused beam. For wider coverage, secondary optics (diffusers) may be required. For longer range, a lens can be used to collimate the beam.
• Driver Circuit: Always use a constant current driver or a series resistor. Calculate the resistor value based on the supply voltage (Vs), the LED's typical forward voltage (Vf), and the desired operating current (If): R = (Vs - Vf) / If. Account for Vf tolerance and supply voltage variations.
• ESD Protection in Circuit: In ESD-prone environments, consider adding transient voltage suppression (TVS) diodes or other protection components on the lines connected to the LED.

10. Technical Comparison & Differentiation

Compared to standard visible LEDs or lower-power IR LEDs, this device offers distinct advantages:

• High Radiant Intensity: A minimum of 20 mW/sr provides strong signal strength for sensing and illumination, allowing for longer operating distances or lower receiver sensitivity requirements.
• High-Speed Capability: The ability to handle 1A peak current in short pulses (10μs) makes it suitable for modulated data transmission applications.
• RoHS Compliance: Meets modern environmental regulations for lead-free manufacturing.
• Through-Hole Reliability: The through-hole package offers robust mechanical attachment and excellent thermal conduction to the PCB compared to some surface-mount alternatives, which is beneficial for high-power operation.

11. Frequently Asked Questions (FAQs)

11.1 What is the difference between radiant intensity (mW/sr) and luminous intensity (mcd)?

Radiant intensity measures the actual optical power emitted per solid angle (steradian), independent of human eye sensitivity. It is used for infrared and ultraviolet devices. Luminous intensity is weighted by the photopic (daylight-adapted) response of the human eye and is measured in candelas (cd) or millicandelas (mcd). It is only meaningful for visible light. This IR LED is correctly specified in mW/sr.

11.2 Can I drive this LED directly from a 3.3V or 5V microcontroller pin?

No. Microcontroller pins have limited current sourcing/sinking capability (typically 20-50mA max) and are not designed for constant current drive. Connecting the LED directly would likely overload the pin, damage the microcontroller, and provide uncontrolled current to the LED. Always use a driver circuit with a series resistor or a dedicated LED driver IC.

11.3 Why is there a ±15% tolerance on the radiant intensity?

This is a normal variation inherent in semiconductor manufacturing processes. The LEDs are binned (sorted) based on measured intensity. The specific "classification code" on the packing bag indicates which intensity bin the LEDs belong to, allowing designers to select parts with consistent performance for their application.

11.4 Is an IR filter needed for the receiver?

In many applications, yes. Using an 850nm bandpass filter on the receiver (photodiode or sensor) can dramatically improve the signal-to-noise ratio by blocking ambient visible light and other unwanted IR sources (like sunlight or incandescent bulbs), making the system more reliable, especially in daylight conditions.

12. Practical Application Example

Design Case: Simple IR Proximity Sensor

Objective: Detect an object within 10cm.

Design: 1. Emitter Circuit: Drive the LTL-E7939Q2K LED with a 20mA constant current. Using a 5V supply and a typical Vf of 1.3V, calculate the series resistor: R = (5V - 1.3V) / 0.020A = 185 Ohms. Use a standard 180 or 200 Ohm resistor. 2. Receiver Circuit: Place a silicon phototransistor or photodiode sensitive to 850nm light a few centimeters away from the LED, aligned on the same axis. Use a reverse-biased photodiode with a transimpedance amplifier or a phototransistor in a simple switch configuration. 3. Operation: The LED continuously emits IR light. When an object enters the detection zone, it reflects some of this light back to the receiver. The receiver's output signal increases, which can be read by a comparator or microcontroller ADC to trigger an action. 4. Considerations: Shield the receiver from direct exposure to the emitter to prevent saturation. Use modulated light (pulsing the LED) and a synchronous detection circuit in the receiver to make the system immune to ambient light fluctuations.

13. Operating Principle

This device is a light-emitting diode based on an AlGaAs semiconductor junction. When a forward voltage exceeding the junction's threshold (approximately 1.3V) is applied, electrons and holes are injected across the junction. Their recombination releases energy in the form of photons (light). The specific composition of the Aluminum Gallium Arsenide (AlGaAs) semiconductor material determines the bandgap energy, which directly corresponds to the wavelength of the emitted photons—in this case, approximately 850nm, which is in the near-infrared region of the electromagnetic spectrum, invisible to the human eye.

14. Technology Trends

Infrared LED technology continues to evolve. General trends in the industry include:

• Increased Efficiency: Development of new semiconductor materials and epitaxial structures (like multi-quantum wells) to achieve higher wall-plug efficiency (more light output per electrical watt input), reducing heat generation and power consumption.
• Higher Power Density: Advancements in packaging and thermal management allow for smaller devices to handle higher drive currents, enabling more compact and powerful IR illumination systems.
• Wavelength Diversification: While 850nm and 940nm are common, there is development for specific applications, such as 810nm for medical therapy or specific wavelengths optimized for particular sensor sensitivities.
• Integration: Trends towards integrating the LED driver circuitry, protection components, and sometimes even the sensor into more compact modules or system-in-package (SiP) solutions to simplify end-user design.

These trends aim to provide more reliable, efficient, and application-specific solutions for the growing markets in machine vision, biometric sensing, LiDAR, and optical communication.