1.6mm Round Subminiature Infrared LED IR26-21C/L447/CT Datasheet - Dimensions 1.6mm Dia - Voltage 1.3V - Power 130mW - Water Clear Lens - English Technical Document

1. Product Overview

The IR26-21C/L447/CT is a subminiature surface-mount device (SMD) infrared emitting diode. It is housed in a compact, double-ended package molded from water-clear plastic with a spherical top-view lens. The primary function of this component is to emit infrared light at a peak wavelength of 940 nanometers, which is spectrally matched to silicon-based photodetectors and phototransistors, making it ideal for sensing applications.

This LED is constructed using a GaAlAs (Gallium Aluminum Arsenide) chip material. Its core advantages include a very low forward voltage, a small form factor suitable for space-constrained designs, and good reliability. The device is compliant with key environmental regulations, including being Pb-free (lead-free), RoHS compliant, EU REACH compliant, and halogen-free, meeting specific thresholds for bromine and chlorine content.

2. Technical Parameter Deep Dive

2.1 Absolute Maximum Ratings

The device is designed to operate within strict limits to ensure longevity and reliability. Exceeding these ratings may cause permanent damage.

• Continuous Forward Current (I_F): 65 mA. This is the maximum DC current that can continuously flow through the LED.
• Reverse Voltage (V_R): 5 V. Applying a reverse voltage higher than this can break down the LED's semiconductor junction.
• Operating Temperature (T_opr): -25°C to +85°C. The ambient temperature range for normal operation.
• Storage Temperature (T_stg): -40°C to +85°C. The temperature range for storing the device when not in use.
• Soldering Temperature (T_sol): 260°C for a maximum of 5 seconds. This defines the reflow soldering profile constraint.
• Power Dissipation (P_d): 130 mW at or below 25°C free air temperature. This is the maximum power the package can dissipate as heat.

2.2 Electro-Optical Characteristics

These parameters are measured at a standard test condition of 25°C ambient temperature and a forward current of 20 mA, which is a typical operating point.

• Radiant Intensity (I_e): 11 mW/sr (Min), 18 mW/sr (Typ). This measures the optical power emitted per unit solid angle (steradian). The typical value indicates the expected output.
• Peak Wavelength (λ_p): 940 nm (Typ). The wavelength at which the LED emits the most optical power. This is in the near-infrared spectrum, invisible to the human eye but optimal for silicon sensors.
• Spectral Bandwidth (Δλ): 55 nm (Typ). The range of wavelengths emitted, typically measured at half the peak intensity (Full Width at Half Maximum - FWHM).
• Forward Voltage (V_F): 1.3 V (Typ), 1.5 V (Max). The voltage drop across the LED when operating at 20mA. The low voltage is an efficiency advantage.
• Reverse Current (I_R): 10 µA (Max) at 5V reverse bias. A measure of the junction's leakage in the off-state.
• Viewing Angle (2θ_1/2): 25° (Typ). The angular spread where the radiant intensity is at least half of its peak value. This defines the beam pattern.

3. Performance Curve Analysis

The datasheet provides several characteristic curves that are crucial for design engineers.

3.1 Forward Current vs. Ambient Temperature

This curve shows the derating of the maximum allowable forward current as the ambient temperature increases. To prevent overheating, the current must be reduced when operating above 25°C. The curve typically shows a linear decrease, emphasizing the importance of thermal management in high-temperature environments.

3.2 Spectral Distribution

This graph plots relative radiant intensity against wavelength. It visually confirms the peak at 940nm and the approximately 55nm spectral bandwidth. The shape is characteristic of GaAlAs infrared LEDs.

3.3 Forward Current vs. Forward Voltage (I-V Curve)

This fundamental curve illustrates the exponential relationship between current and voltage for a diode. It helps in designing the current-limiting driver circuit. The curve will show a sharp turn-on around the typical V_F of 1.3V.

3.4 Relative Intensity vs. Forward Current

This curve demonstrates the linearity (or potential non-linearity at very high currents) of light output with respect to drive current. For most LEDs, the relationship is fairly linear within the recommended operating range, allowing for simple brightness control via current modulation.

3.5 Relative Radiant Intensity vs. Angular Displacement

This polar plot defines the spatial radiation pattern. For this LED with a spherical lens, the pattern is expected to be roughly Lambertian (cosine distribution) or slightly narrower, centered on the axis perpendicular to the emitting surface. The 25-degree viewing angle is derived from this curve.

4. Mechanical and Packaging Information

4.1 Package Dimensions

The device is a round, subminiature SMD package with a 1.6mm body diameter. Detailed mechanical drawings in the datasheet provide all critical dimensions including overall height, lead spacing, and lens geometry. All dimensions are in millimeters with a standard tolerance of ±0.1mm unless otherwise specified.

4.2 Pad Layout and Solder Paste Recommendation

A suggested land pattern (pad layout) for PCB design is provided for reference. Designers are advised to modify this based on their specific manufacturing process and reliability requirements. The datasheet recommends a solder paste composition of Sn/Ag3.0/Cu0.5 and a stencil thickness of 0.10mm for optimal solder joint formation.

4.3 Polarity Identification

The package features a double-ended design. Polarity is typically indicated by a marking on the cathode side or by a specific shape feature in the package or tape. The exact marking should be verified against the package dimension drawing.

4.4 Carrier Taping Dimensions

The LEDs are supplied in embossed carrier tape on 7-inch diameter reels for automated pick-and-place assembly. The tape dimensions (pocket size, pitch, etc.) are specified to ensure compatibility with standard SMD assembly equipment. Each reel contains 1500 pieces.

5. Soldering and Assembly Guidelines

5.1 Reflow Soldering Profile

A lead solder temperature profile is recommended. Key parameters include a preheat stage, a peak temperature not exceeding 260°C, and a time above liquidus (TAL) controlled to prevent thermal damage. Reflow soldering should not be performed more than two times on the same device.

5.2 Hand Soldering Precautions

If hand soldering is necessary, extreme care must be taken. The soldering iron tip temperature should be below 350°C, and contact time per terminal should not exceed 3 seconds. A low-power iron (≤25W) is recommended, with an interval of at least 2 seconds between soldering each terminal to allow cooling.

5.3 Storage and Moisture Sensitivity

The LEDs are packaged in a moisture-proof bag. Do not open the bag until ready for use. After opening, unused devices should be stored at ≤30°C and ≤60% Relative Humidity (RH). The "floor life" after opening is 168 hours (7 days). If this time is exceeded or if the moisture indicator (silica gel) shows saturation, a baking treatment at 60±5°C for 24 hours is required before use to remove absorbed moisture and prevent "popcorning" during reflow.

5.4 Repair and Rework

Repair after soldering is strongly discouraged. If unavoidable, a specialized double-head soldering iron must be used to simultaneously heat both terminals, minimizing thermal stress on the plastic package. The potential for damaging the LED's characteristics during repair must be evaluated beforehand.

6. Application Suggestions

6.1 Typical Application Circuits

The most critical design consideration is current limiting. An external series resistor is mandatory. Due to the diode's exponential I-V characteristic, a small increase in voltage can cause a large, destructive increase in current. The resistor value (R) is calculated using: R = (V_supply - V_F) / I_F. For a 5V supply and a target I_F of 20mA with V_F~1.3V, R ≈ (5 - 1.3) / 0.02 = 185 Ω. A standard 180Ω or 200Ω resistor would be suitable.

6.2 Design Considerations

• Heat Sinking: While small, power dissipation (up to 130mW) must be considered, especially in high ambient temperatures or at higher drive currents. Adequate PCB copper area around the pads can act as a simple heat sink.
• Optical Alignment: The 25-degree viewing angle requires careful alignment with the paired photodetector in barrier or reflective sensor designs to ensure sufficient signal strength.
• Electrical Noise: In sensitive analog sensing circuits, the LED driver should be decoupled from sensitive detector amplifiers to prevent electrical crosstalk.

6.3 Common Application Scenarios

• PCB-Mounted Infrared Sensors: Used as the light source in proximity sensors, object detection, and tachometers.
• Miniature Light Barriers / Slotted Opto-interrupters: Paired with a phototransistor to detect objects breaking a light beam, used in printers, encoders, and vending machines.
• Floppy Disk Drive: Historically used for track-zero detection and write-protect sensing.
• Optoelectronic Switches: In reflective sensors for detecting surface presence or contrast (e.g., line-following robots).
• Smoke Detectors: Employed in obscuration-type smoke detectors where smoke particles scatter or block an internal infrared beam between an LED and a photodiode.

7. Technical Comparison and Differentiation

The IR26-21C/L447/CT occupies a specific niche in the infrared LED market. Its primary differentiators are its extremely small 1.6mm round package and low forward voltage. Compared to larger 3mm or 5mm through-hole infrared LEDs, it enables miniaturization of end products. Compared to other SMD infrared LEDs, its water-clear lens (as opposed to tinted or diffused) and specific 940nm wavelength with good Si matching make it optimized for maximum energy transfer to a silicon receiver, improving system signal-to-noise ratio and range in sensing applications. The halogen-free and RoHS compliance ensures it meets modern environmental standards for global electronics manufacturing.

8. Frequently Asked Questions (FAQ)

8.1 Why is a current-limiting resistor absolutely necessary?

An LED is a current-operated device, not a voltage-operated one. Its forward voltage remains relatively constant over a wide current range. Without a series resistor, connecting it directly to a voltage source would attempt to draw current limited only by the source's internal resistance and the LED's dynamic resistance, which is very low. This would almost certainly exceed the maximum forward current (65mA) and destroy the LED instantly.

8.2 Can I drive this LED with a PWM signal for brightness control?

Yes, pulse-width modulation (PWM) is an excellent method for controlling the average radiant intensity. You drive the LED at its nominal current (e.g., 20mA) during the "on" pulses. The frequency should be high enough to avoid visible flicker in the sensing system (typically >100Hz). The driver circuit (transistor/MOSFET) must be able to handle the peak current.

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

Luminous intensity (measured in candela) is weighted by the sensitivity of the human eye (photopic response). Since this is an infrared LED emitting at 940nm, where the human eye has zero sensitivity, its luminous intensity is effectively zero. Radiant intensity measures the actual optical power emitted per solid angle, which is the relevant metric for machine sensors.

8.4 How do I interpret the "View Angle" of 25 degrees?

The viewing angle (2θ_1/2 = 25°) means the total angular spread where the intensity is at least half of the peak value. The half-angle (θ_1/2) is 12.5 degrees from the center axis. This defines a relatively narrow beam, concentrating the infrared energy for longer range or more directed sensing compared to LEDs with wider angles (e.g., 60° or 120°).

9. Operating Principle

An infrared 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 and holes from the p-region are injected across the junction. When these charge carriers recombine in the active region of the semiconductor (made of GaAlAs), energy is released. In this specific material composition, the energy corresponds to photons in the infrared spectrum with a peak wavelength of 940nm. The water-clear epoxy package acts as both a protective enclosure and a lens to shape the emitted light's radiation pattern.

10. Industry Trends and Context

The demand for miniaturized, high-reliability infrared components continues to grow, driven by the proliferation of the Internet of Things (IoT), smart home sensors, industrial automation, and wearable devices. Key trends influencing components like the IR26-21C/L447/CT include:

• Increased Integration: Movement towards modules that combine the IR LED, photodetector, and signal conditioning circuitry in a single package.
• Higher Efficiency: Ongoing development of semiconductor materials and chip designs to achieve higher radiant output for a given input current, improving battery life in portable devices.
• Enhanced Reliability: Focus on robust packaging to withstand higher reflow temperatures and harsher environmental conditions required by automotive and industrial applications.
• Standardization: Adherence to global environmental (RoHS, REACH, Halogen-Free) and manufacturing (MSL, tape-and-reel) standards is now a baseline requirement for global market access.

Components such as this subminiature infrared LED are fundamental building blocks enabling non-contact sensing, which is a critical technology across these evolving sectors.