IR Emitter LED 5mm Clear Package - Dimensions 5mm Dia - Forward Voltage 1.8V - Radiant Intensity 4.81mW/sr - English Technical Datasheet

1. Product Overview

This document details the specifications for a high-power, miniature infrared (IR) light emitting diode (LED) housed in a clear transparent plastic package. The device is an end-looking emitter designed for applications requiring reliable infrared illumination. Its primary function is to convert electrical current into infrared radiation, typically for use in sensing, detection, and communication systems where it is often paired with a compatible photodetector.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

The device is designed to operate reliably within specified environmental and electrical limits. Exceeding these ratings may cause permanent damage.

• Power Dissipation: 150 mW. This is the maximum amount of power the device can safely dissipate as heat under any operating condition.
• Peak Forward Current: 2 A. This is the maximum allowable pulsed current, specified under conditions of 300 pulses per second with a 10 microsecond pulse width. It is significantly higher than the continuous rating, allowing for brief, high-intensity bursts of light.
• Continuous Forward Current: 100 mA. This is the maximum DC current that can be applied to the LED indefinitely without risk of damage.
• Reverse Voltage: 5 V. Applying a reverse bias voltage greater than this value can break down the semiconductor junction.
• Operating Temperature Range: -40°C to +85°C. The device is guaranteed to function within this ambient temperature range.
• Storage Temperature Range: -55°C to +100°C. The device can be stored without operation within this wider temperature range.
• Lead Soldering Temperature: 260°C for 5 seconds, measured 1.6mm from the package body. This defines the thermal profile tolerance for assembly processes.

2.2 Electrical & Optical Characteristics

These parameters are measured at a standard ambient temperature of 25°C and define the device's performance under normal operating conditions. The test condition for most optical parameters is a forward current (I_F) of 20 mA.

• Aperture Radiant Incidence (E_e): 0.64 mW/cm² (Min). This measures the radiant power per unit area at the emitter's aperture. It is a key parameter for applications where the emitter is placed close to a detector.
• Radiant Intensity (I_E): 4.81 mW/sr (Min). This is the radiant power emitted per unit solid angle (steradian). It is the primary measure of the LED's output "brightness" in the infrared spectrum and is crucial for calculating illumination at a distance.
• Peak Emission Wavelength (λ_Peak): 880 nm (Typ). The device emits infrared light centered around this wavelength. This is in the near-infrared (NIR) region, which is invisible to the human eye but easily detected by silicon photodetectors.
• Spectral Line Half-Width (Δλ): 50 nm (Max). This specifies the wavelength range over which the emitted optical power is at least half of its peak value. A value of 50 nm indicates a moderately broad spectral output, which is typical for standard IR LEDs.
• Forward Voltage (V_F): 1.3 V (Min), 1.8 V (Max) at I_F=20mA. This is the voltage drop across the LED when operating. It is essential for designing the current-limiting circuitry.
• Reverse Current (I_R): 100 µA (Max) at V_R=5V. This is the small leakage current that flows when the device is reverse-biased.
• Viewing Angle (2θ_1/2): 40° (Typ). This is the full angle at which the radiant intensity drops to half of its maximum value (on-axis). A 40° angle provides a wide beam, suitable for applications requiring broad area coverage.

3. Performance Curve Analysis

The datasheet provides several graphical representations of device behavior under varying conditions.

3.1 Spectral Distribution

The spectral output curve (Fig. 1) shows the relative radiant intensity as a function of wavelength. It confirms the peak emission at approximately 880 nm with a characteristic bell-shaped curve, tapering off on either side. The half-width can be visually estimated from this graph.

3.2 Forward Current vs. Forward Voltage

The I-V curve (Fig. 3) illustrates the non-linear relationship between the applied forward voltage and the resulting current. It shows the typical exponential turn-on characteristic of a diode. The specified V_F range at 20mA can be cross-referenced on this curve.

3.3 Relative Radiant Intensity vs. Forward Current

This curve (Fig. 5) demonstrates how the optical output power increases with drive current. It is generally linear over a significant range but may exhibit saturation or efficiency droop at very high currents. This graph is critical for determining the required drive current to achieve a desired output level.

3.4 Relative Radiant Intensity vs. Ambient Temperature

The temperature dependence curve (Fig. 4) shows that the output power of an LED decreases as the junction temperature increases. This is a fundamental characteristic of semiconductor light sources. The graph allows designers to derate the expected output for high-temperature operating environments.

3.5 Radiation Diagram

The polar radiation pattern (Fig. 6) provides a visual representation of the viewing angle. It plots relative intensity against the angle from the central axis, clearly showing the 40° half-angle where intensity falls to 50%.

4. Mechanical & Packaging Information

4.1 Package Dimensions

The device uses a standard 5mm diameter, end-looking, clear plastic package (often referred to as a T-1 3/4 package). Key dimensional notes include:

• All dimensions are provided in millimeters with inch equivalents.
• A standard tolerance of ±0.25mm applies unless otherwise specified.
• The maximum protrusion of resin under the flange is 1.5mm.
• Lead spacing is measured at the point where the leads exit the package body.

The package is transparent, allowing the infrared light to pass through with minimal absorption. The leads are typically made of tinned copper alloy.

4.2 Polarity Identification

For this style of package, the longer lead typically denotes the anode (positive connection), and the shorter lead denotes the cathode (negative connection). Additionally, the package may have a flat spot on the rim near the cathode lead. Correct polarity must be observed for the device to emit light.

5. Soldering & Assembly Guidelines

The absolute maximum rating for lead soldering is 260°C for a duration of 5 seconds, measured 1.6mm from the package body. This rating is intended for hand soldering or wave soldering processes.

• Reflow Soldering: While not explicitly specified for reflow, the 260°C limit suggests it may tolerate some reflow profiles. However, a profile with a lower peak temperature (e.g., 245°C) and controlled ramp rates is strongly recommended to minimize thermal stress on the plastic package and internal wire bonds.
• General Precautions: Avoid excessive mechanical stress on the leads. Do not bend leads at the root of the package. Use appropriate heat sinking during soldering if necessary.
• Storage Conditions: Store in a dry, anti-static environment within the specified temperature range (-55°C to +100°C) to prevent moisture absorption and other degradation.

6. Application Suggestions

6.1 Typical Application Scenarios

This IR emitter is well-suited for a variety of optoelectronic applications, including:

• Object Detection & Sensing: Used in proximity sensors, object counters, and level detection systems, often paired with a phototransistor like the mentioned LTR-3208 series to form an optical interrupter or reflective sensor.
• Remote Control Systems: Serving as the transmitter in infrared remote controls for consumer electronics.
• Optical Data Links: Enabling short-range, wireless serial data communication.
• Security Systems: Used in infrared illumination for night-vision cameras or as part of intrusion detection beams.

6.2 Design Considerations

• Current Limiting: An LED is a current-driven device. Always use a series current-limiting resistor or a constant current driver circuit to prevent exceeding the maximum continuous forward current, especially since the forward voltage has a range (1.3V-1.8V).
• Heat Management: While power dissipation is low, operating at high continuous currents or in high ambient temperatures will reduce output and lifespan. Ensure adequate ventilation if needed.
• Optical Matching: The datasheet notes the device is mechanically and spectrally matched to specific phototransistors. Using the recommended detector ensures optimal sensitivity at the 880nm peak wavelength and physical alignment in assembled modules.
• Circuit Protection: Consider adding protection against reverse voltage spikes or electrostatic discharge (ESD), as the maximum reverse voltage is only 5V.

7. Technical Comparison & Differentiation

Key features that differentiate this IR emitter include:

• Selected Intensity Ranges: Devices are binned or selected to meet specific radiant intensity specifications, ensuring consistency in production.
• High Power Output: The minimum radiant intensity of 4.81 mW/sr at 20mA is competitive for a standard 5mm package, offering good signal strength.
• Wide Viewing Angle (40°): Provides broad coverage, which is advantageous for proximity sensing and reflective sensing where alignment is less critical.
• Clear Package: Unlike tinted or diffused packages, the clear lens maximizes forward light output and is neutral to the color of the emitted light, which is ideal for IR applications.
• Matched to Detector Series: This simplifies design and procurement for systems using the paired phototransistor, guaranteeing optical and mechanical compatibility.

8. Frequently Asked Questions (Based on Technical Parameters)

8.1 What resistor value should I use with a 5V supply?

Using Ohm's Law (R = (V_supply - V_F) / I_F) and assuming a target I_F of 20mA, the resistor value depends on the actual V_F. For a worst-case design ensuring current never exceeds 20mA, use the minimum V_F (1.3V). R = (5V - 1.3V) / 0.02A = 185 Ohms. The nearest standard value is 180 Ohms. This provides a maximum current of ~20.6mA, which is safe. Power rating: P = I²R = (0.02)² * 180 = 0.072W, so a 1/8W or 1/4W resistor is sufficient.

8.2 Can I drive it with a microcontroller pin directly?

Typically, no. Most microcontroller GPIO pins have a current sourcing/sinking limit of 20-40mA, which is at the edge of this LED's operating point. Even if within limit, the pin's output voltage will drop under load, making current control imprecise. It is always recommended to use a transistor (e.g., NPN BJT or N-channel MOSFET) as a switch driven by the microcontroller pin to control the LED current independently.

8.3 How does temperature affect performance?

As shown in Fig. 4, the relative radiant intensity decreases as ambient temperature increases. At +85°C, the output may be only 60-80% of its value at 25°C. Conversely, at very low temperatures, output may be higher. This must be factored into system sensitivity calculations, especially for outdoor or high-reliability applications. The forward voltage (V_F) also has a negative temperature coefficient, meaning it decreases slightly as temperature rises.

8.4 What is the difference between Radiant Incidence and Radiant Intensity?

Radiant Intensity (I_E, mW/sr) is an angular measure of power—it describes how much power is emitted into a specific direction (per steradian). It is independent of distance. Aperture Radiant Incidence (E_e, mW/cm²) is an areal measure of power density—it describes how much power is passing through a unit area at the source's aperture. E_e is more relevant for very close-range applications where the detector is essentially at the emitter's surface, while I_E is used with the inverse square law to calculate irradiance at a distance.

9. Design & Usage Case Study

Scenario: Designing a Paper Sheet Counter for a Printer.

An optical interrupter sensor is needed to count sheets of paper passing through a printer mechanism. A U-shaped bracket holds the IR emitter on one side and a matched phototransistor on the other. When no paper is present, IR light from the emitter directly strikes the detector, causing it to conduct. When a sheet of paper passes through the gap, it blocks the IR beam, causing the detector's conduction to drop.

Component Selection Rationale:

• This IR emitter is chosen for its high radiant intensity (4.81 mW/sr min), ensuring a strong signal can reach the detector even if the bracket alignment is not perfect or if dust accumulates.
• The wide 40° viewing angle is beneficial as it provides tolerance for minor mechanical misalignments between the emitter and detector housed in the separate arms of the U-bracket.
• Its spectral match to the LTR-3208 phototransistor guarantees the detector is most sensitive at the 880nm wavelength being emitted, maximizing signal-to-noise ratio.
• The clear package is ideal as it does not attenuate the IR light unnecessarily.

Circuit Implementation: The emitter is driven by a constant 20mA current source for consistent output. The phototransistor is connected in a common-emitter configuration with a pull-up resistor. A comparator or microcontroller ADC pin monitors the voltage at the collector of the phototransistor. A passing sheet of paper causes a distinct voltage transition, which is counted by the microcontroller's firmware.

10. Operating Principle Introduction

An Infrared Light Emitting Diode (IR LED) is a semiconductor p-n junction diode. When a forward voltage exceeding the junction's built-in potential is applied, 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 injected minority carriers (electrons in the p-region, holes in the n-region) recombine with the majority carriers. In a direct bandgap semiconductor material like Gallium Arsenide (GaAs) or similar compounds used for IR emission, a significant portion of these recombinations is radiative.

During radiative recombination, the energy of the recombining electron-hole pair is released in the form of a photon. The wavelength (λ) of this photon is determined by the bandgap energy (E_g) of the semiconductor material, according to the equation λ = hc / E_g, where h is Planck's constant and c is the speed of light. For an emission peak at 880 nm, the corresponding bandgap energy is approximately 1.41 eV. The clear epoxy package encapsulates the semiconductor chip, provides mechanical protection, and acts as a lens to shape the emitted light's radiation pattern.

11. Technology Trends

While the fundamental principle of IR LEDs remains stable, several trends influence their development and application:

• Increased Power & Efficiency: Ongoing material science and chip design improvements lead to devices with higher radiant intensity and wall-plug efficiency (optical power out / electrical power in), allowing for either brighter signals or lower power consumption.
• Miniaturization: There is a strong trend towards surface-mount device (SMD) packages (e.g., 0805, 0603, chip-scale) for automated assembly, reducing size and cost. The through-hole 5mm package remains popular for prototyping, educational use, and applications requiring higher single-device output or easier manual assembly.
• Wavelength Specialization: Beyond common 850-940 nm LEDs, there is growing use of specific wavelengths for specialized applications, such as 810nm for medical pulse oximetry or 1450nm for eye-safe LiDAR.
• Integration: Emitters are increasingly integrated with drivers, modulators, and sometimes even detectors into single modules or ICs, simplifying system design for data communication and sensing.
• Application Expansion: The proliferation of the Internet of Things (IoT), wearable devices, automotive LiDAR, and advanced biometric sensing (e.g., facial recognition, vein detection) continues to drive demand for reliable, low-cost IR emitters with specific performance characteristics.