5.0mm Infrared LED SIR323-5 Datasheet - 5mm Package - 1.3V Forward Voltage - 875nm Wavelength - 150mW Power Dissipation - English Technical Document

1. Product Overview

The SIR323-5 is a high-intensity infrared (IR) emitting diode housed in a standard T-1 3/4 (5mm) water-clear plastic package. It is designed to emit light at a peak wavelength of 875 nanometers (nm), which falls within the near-infrared spectrum. This device is engineered for applications requiring reliable and powerful infrared light sources, with its spectral output specifically matched to be compatible with common silicon phototransistors, photodiodes, and infrared receiver modules. The package features a standard 2.54mm lead spacing for easy integration into through-hole printed circuit board (PCB) designs.

1.1 Core Advantages and Target Market

The primary advantages of this component include its high radiant intensity, which ensures strong signal transmission, and its low forward voltage, contributing to energy-efficient operation. It is constructed using lead-free materials and is compliant with RoHS (Restriction of Hazardous Substances), EU REACH regulations, and halogen-free standards (Br < 900ppm, Cl < 900ppm, Br+Cl < 1500ppm), making it suitable for global markets with strict environmental requirements. The device is characterized by high reliability, a critical factor for consumer and industrial electronics. Its target applications are primarily in wireless, non-contact signaling systems.

2. In-Depth Technical Parameter Analysis

This section provides a detailed, objective interpretation of the key electrical, optical, and thermal parameters defined in the datasheet.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed.

• Continuous Forward Current (I_F): 100 mA. This is the maximum DC current that can be applied continuously to the LED without risk of degradation.
• Peak Forward Current (I_FP): 1.0 A. This high current is permissible only under pulsed conditions with a pulse width ≤ 100μs and a duty cycle ≤ 1%. This allows for very bright, short bursts of light, useful for long-range transmission.
• Reverse Voltage (V_R): 5 V. Applying a reverse bias voltage exceeding this value can cause junction breakdown.
• Power Dissipation (P_d): 150 mW at or below 25°C ambient temperature. This is the maximum power the package can dissipate as heat. Exceeding this limit raises the junction temperature, reducing lifespan and output.
• Operating & Storage Temperature: The device can function from -40°C to +85°C and be stored from -40°C to +100°C.
• Soldering Temperature: 260°C for a duration not exceeding 5 seconds, which is compatible with standard lead-free reflow soldering profiles.

2.2 Electro-Optical Characteristics

These parameters are measured under standard test conditions (Ta=25°C) and define the device's performance.

• Radiant Intensity (I_e): This is the optical power emitted per unit solid angle (steradian). At a forward current of 20mA, the typical value is 7.8 mW/sr, with a minimum of 4.0 mW/sr. Under pulsed conditions (I_F=100mA, pulse ≤100μs, duty ≤1%), the typical radiant intensity reaches 40 mW/sr, showcasing its capability for high-power bursts.
• Peak Wavelength (λ_p): 875 nm (typical). This is the wavelength at which the emitted optical power is maximum. The spectral bandwidth (Δλ) is typically 45 nm, indicating the range of wavelengths emitted around the peak.
• Forward Voltage (V_F): At 20mA, the typical forward voltage is 1.3V, with a maximum of 1.65V. At the 100mA pulsed condition, it rises to a typical 1.4V (max 1.8V). This low V_F is beneficial for low-voltage circuit design.
• Reverse Current (I_R): Maximum 10 μA at a reverse voltage of 5V, indicating good junction isolation.
• Viewing Angle (2θ_1/2): 35 degrees (typical). This is the full angle at which the radiant intensity drops to half of its maximum value (on-axis). A 35-degree angle provides a moderately focused beam, suitable for directed applications.

Note on Measurement Uncertainty: The datasheet specifies tolerances for key measurements: V_F (±0.1V), I_e (±10%), and λ_p (±1.0nm). These must be considered in precision design calculations.

3. Performance Curve Analysis

The datasheet includes several characteristic curves that illustrate device behavior under varying conditions.

3.1 Forward Current vs. Ambient Temperature

This curve (Fig.1) typically shows the derating of the maximum allowable forward current as the ambient temperature increases. To prevent exceeding the maximum junction temperature and the 150mW power dissipation limit, the continuous forward current must be reduced when operating above 25°C. Designers must consult this graph for high-temperature applications.

3.2 Spectral Distribution

The spectral distribution graph (Fig.2) plots relative intensity against wavelength. It visually confirms the peak wavelength at 875nm and the approximately 45nm spectral bandwidth. This curve is essential for ensuring compatibility with the spectral sensitivity of the intended receiver (phototransistor, photodiode, or IC).

3.3 Relative Intensity vs. Forward Current

This graph (Fig.3) demonstrates the relationship between the drive current and the light output. For LEDs, the optical output is generally proportional to the forward current in the normal operating range. However, efficiency may drop at very high currents due to thermal effects and other non-linearities. The curve helps designers select the appropriate drive current to achieve the desired radiant intensity.

3.4 Relative Radiant Intensity vs. Angular Displacement

This polar plot (Fig.4) maps the emission pattern of the LED. It shows how the intensity decreases as the observation angle moves away from the central axis (0°). The 35-degree viewing angle (where intensity is 50% of peak) is derived from this curve. This information is critical for optical system design, determining beam coverage and alignment tolerances.

4. Mechanical and Packaging Information

4.1 Package Dimensions

The device uses a standard 5mm (T-1 3/4) round LED package. The detailed mechanical drawing in the datasheet provides all critical dimensions, including body diameter, lens shape, lead length, and lead spacing. The lead spacing is confirmed as 2.54mm (0.1 inches), which is the standard for through-hole components. All dimensions have a tolerance of ±0.25mm unless otherwise specified. The lens material is water-clear plastic, optimized for infrared transmission with minimal absorption.

4.2 Polarity Identification

For through-hole LEDs, polarity is typically indicated by two features: lead length and internal structure. The longer lead is the anode (positive), and the shorter lead is the cathode (negative). Additionally, many packages have a flat spot on the rim of the lens base near the cathode lead. Always verify polarity before soldering to prevent reverse bias damage.

5. Soldering and Assembly Guidelines

The device is rated for wave or hand soldering. The key parameter is the maximum soldering temperature of 260°C for a duration not exceeding 5 seconds. This aligns with IPC/JEDEC J-STD-020 standards for lead-free reflow profiles. Prolonged exposure to high temperature can damage the plastic package and the internal wire bonds. When hand soldering, use a temperature-controlled iron and minimize contact time. Ensure the device is stored in a dry environment as per the storage temperature range (-40 to +100°C) to prevent moisture absorption, which can cause "popcorning" during reflow.

6. Packaging and Ordering Information

6.1 Packing Specification

The components are packed in anti-static bags for protection. The standard packing quantity is 200 to 500 pieces per bag. Five bags are then placed into one box. Finally, ten boxes are packed into one shipping carton.

6.2 Label Specification

The packaging label contains several key identifiers:

• CPN: Customer's Production Number (customer-specific part number).
• P/N: Production Number (the manufacturer's part number, e.g., SIR323-5).
• QTY: Packing Quantity.
• CAT: Ranks (may indicate performance bins).
• HUE: Peak Wavelength (e.g., 875nm).
• REF: Reference.
• LOT No: Lot Number for traceability.

7. Application Suggestions

7.1 Typical Application Scenarios

• Infrared Remote Control Units: The high radiant intensity, especially in pulsed mode (40 mW/sr typ.), makes it ideal for long-range remote controls for TVs, audio systems, and other consumer electronics.
• Free-Air Transmission Systems: Used in short-range wireless data links, intrusion alarms, and object detection systems where an IR beam is transmitted through air to a receiver.
• Smoke Detectors: Often employed in optical (photoelectric) smoke detectors. An IR LED beam is scattered by smoke particles onto a photodiode, triggering the alarm.
• General Infrared Applied Systems: Includes industrial automation (object counting, position sensing), touchscreens, and optical encoders.

7.2 Design Considerations and Circuit Protection

• Current Limiting: An LED is a current-driven device. Always use a series current-limiting resistor (or a constant current driver) to prevent exceeding the maximum continuous forward current (100mA). The resistor value is calculated using Ohm's Law: R = (V_supply - V_F) / I_F.
• Pulsed Operation: For high-intensity bursts, ensure the driver circuit can deliver the 1A peak current while strictly adhering to the pulse width (≤100μs) and duty cycle (≤1%) limits. A simple microcontroller GPIO pin often cannot source this much current directly and may require a transistor switch (e.g., MOSFET).
• Reverse Voltage Protection: Although the device can tolerate up to 5V in reverse, it is good practice to avoid reverse bias. In AC-coupled circuits or where reverse voltage is possible, consider adding a protection diode in parallel with the LED (cathode to anode).
• Heat Management: While the package is small, at higher currents and ambient temperatures, power dissipation becomes important. Ensure adequate ventilation and consider the derating curve if operating above 25°C.
• Optical Design: Consider the 35-degree viewing angle. For focused beams, external lenses or reflectors may be needed. For wide-area illumination, the native angle may be sufficient. Ensure the receiver is spectrally matched to the 875nm peak.

8. Technical Comparison and Differentiation

The SIR323-5 differentiates itself in the 5mm IR LED market through a combination of key parameters. Compared to generic 5mm IR LEDs, it offers a higher typical radiant intensity (7.8 mW/sr @20mA vs. often 5-6 mW/sr), enabling longer range or lower power consumption for the same signal strength. Its low forward voltage (1.3V typ.) is advantageous for battery-powered devices. The 875nm wavelength is a common standard, ensuring wide compatibility with silicon-based receivers. Its compliance with modern environmental standards (RoHS, REACH, Halogen-Free) is a mandatory requirement for most contemporary electronics manufacturing, which may not be the case for older or lower-cost alternatives.

9. Frequently Asked Questions (Based on Technical Parameters)

9.1 What is the difference between Radiant Intensity and Luminous Intensity?

Radiant Intensity (I_e, measured in mW/sr) is the optical power emitted per solid angle, relevant for all wavelengths. Luminous Intensity (measured in candela, cd) is weighted by the human eye's sensitivity (photopic curve) and is only meaningful for visible light. Since this is an infrared LED, Radiant Intensity is the correct and specified metric.

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

You should not connect it directly. A microcontroller GPIO pin has a current sourcing limit (often 20-40mA) and cannot handle the LED's potential current draw or the 1A pulse. More importantly, you must have a series resistor to limit the current. For example, from a 5V supply targeting I_F=20mA and V_F=1.3V: R = (5V - 1.3V) / 0.02A = 185 Ohms (use a standard 180 or 220 Ohm resistor). The GPIO pin would then drive the base/gate of a transistor that switches the LED current.

9.3 Why is the Peak Forward Current (1A) so much higher than the Continuous Current (100mA)?

This is due to thermal limits. The 1A pulse is so short (≤100μs) and infrequent (duty ≤1%) that the semiconductor junction does not have time to heat up significantly. The 100mA continuous rating considers the steady-state heat generated, which the package must dissipate to the environment to keep the junction temperature within safe limits.

9.4 How do I choose a matching receiver for this LED?

Look for a phototransistor, photodiode, or IR receiver module whose peak spectral sensitivity is around 875nm. Most silicon-based detectors have peak sensitivity between 800nm and 950nm, making them a good match. Always check the receiver's datasheet for its spectral sensitivity curve.

10. Practical Design and Usage Case

Case: Designing a Long-Range IR Remote Control
Goal: Transmit a reliable signal up to 15 meters in a typical living room.
Design Choices:

1. Drive Mode: Use pulsed operation at I_FP = 1A to maximize radiant intensity (40 mW/sr typ.) for the longest range.
2. Circuit: A microcontroller generates the coded pulse train. A GPIO pin controls an N-channel MOSFET. The LED and a small current-sense resistor are placed in series between the supply (e.g., 2xAA batteries ~3V) and the MOSFET drain. The resistor value is small, just to set the peak current: R = (V_bat - V_{F_pulse} - V_{DS_on}) / 1A. A gate resistor is used for the MOSFET.
3. Pulse Timing: Ensure each high pulse in the remote control code (e.g., NEC protocol) is ≤100μs in width. The duty cycle over the entire transmission burst must be ≤1%. This is usually easily satisfied for short remote control codes.
4. Optics: The native 35-degree beam may be sufficient. For better directionality and range, a simple plastic collimating lens could be added in front of the LED.

This approach leverages the key strengths of the SIR323-5: high pulsed output and low forward voltage, enabling a powerful remote from a small battery supply.

11. Operating Principle Introduction

An Infrared Light Emitting Diode (IR LED) is a semiconductor p-n junction diode. When a forward voltage is applied (anode positive relative to cathode), electrons from the n-type region and holes from the p-type region are injected into the junction region. When these charge carriers recombine, they release energy. In a standard silicon diode, this energy is primarily released as heat. In materials like Gallium Aluminum Arsenide (GaAlAs), used in this LED, a significant portion of this recombination energy is released as photons (light). The specific wavelength of the emitted light (875nm in this case) is determined by the bandgap energy of the semiconductor material, which is engineered during the crystal growth process. The water-clear epoxy package acts as a lens, shaping the emitted light into the characteristic beam pattern.

12. Technology Trends and Developments

Infrared LED technology continues to evolve. While the basic 5mm through-hole package remains popular for legacy designs and hobbyist use, the industry trend is strongly towards surface-mount device (SMD) packages (e.g., 0805, 1206, or chip-scale packages). SMDs offer smaller size, better suitability for automated pick-and-place assembly, and often improved thermal performance. There is also ongoing development in materials to achieve higher efficiency (more light output per electrical watt input), different peak wavelengths for specific sensing applications (e.g., 940nm for covert operation, 850nm for surveillance cameras with IR illumination), and integration of the LED with driver circuitry or even the receiver into a single module. However, the fundamental operating principle and key parameters described for the SIR323-5 remain the cornerstone for understanding and specifying any IR LED.