HSDL-4251 IR Emitter Datasheet - 870nm Wavelength - 100mA Forward Current - 190mW Power Dissipation - English Technical Document

1. Product Overview

The HSDL-4251 is a discrete infrared emitter component designed for high-speed applications. It utilizes AlGaAs (Aluminum Gallium Arsenide) LED technology to produce infrared light at a peak wavelength of 870 nanometers (nm). This device is characterized by its fast switching capability, with a typical rise and fall time of 40 nanoseconds (ns), making it suitable for data transmission and communication systems. The package is clear and transparent, allowing for efficient light emission. It is a lead-free product compliant with RoHS (Restriction of Hazardous Substances) directives.

1.1 Core Advantages and Target Market

The primary advantages of the HSDL-4251 include its high-speed performance, reliable AlGaAs construction, and clear package design. Its core features position it for use in markets requiring precise and rapid infrared signaling. The target applications are diverse, spanning both consumer and industrial electronics where infrared functionality is critical.

2. In-Depth Technical Parameter Analysis

This section provides a detailed, objective interpretation of the key electrical, optical, and thermal parameters specified for the HSDL-4251 infrared emitter.

2.1 Absolute Maximum Ratings

The Absolute Maximum Ratings define the stress limits beyond which permanent damage to the device may occur. These ratings are specified at an ambient temperature (TA) of 25°C.

• Continuous Forward Current (IFDC): 100 mA maximum. This is the highest DC current that can be continuously applied.
• Peak Forward Current (IFPK): 500 mA maximum. This higher current is permissible only under pulsed conditions with a duty cycle of 20% and a pulse width of 100 microseconds (µs).
• Power Dissipation (PDISS): 190 mW maximum. This is the total power the device can dissipate, calculated as forward voltage multiplied by forward current, plus any additional losses.
• Reverse Voltage (VR): 5 V maximum. Applying a reverse voltage higher than this can break down the LED junction.
• Operating Temperature (TO): -40°C to +85°C. The device is guaranteed to operate within this ambient temperature range.
• Storage Temperature (TS): -40°C to +100°C.
• Junction Temperature (TJ): 110°C maximum. The temperature of the semiconductor die itself must not exceed this limit.
• Lead Soldering Temperature: 260°C for 5 seconds, measured 1.6mm from the package body.

2.2 Electrical and Optical Characteristics

The Electrical and Optical Characteristics are typical or guaranteed performance parameters measured at TA=25°C under the specified test conditions.

• Radiant On-Axis Intensity (IE): 56 to 168 mW/sr, with a typical value of 100 mW/sr when driven at IF=100mA. This measures the optical power emitted per unit solid angle along the central axis of the beam.
• Peak Emission Wavelength (λPeak): 870 nm typical when IF=50mA. This is the wavelength at which the emitted optical power is greatest.
• Spectral Line Half-Width (Δλ): 45 nm typical. This indicates the spectral bandwidth, specifically the width of the emission spectrum at half its maximum power.
• Forward Voltage (Vf): Ranges from 1.4V to 1.9V depending on the forward current. At IF=20mA, Vf is 1.4V to 1.6V. At IF=100mA, Vf is 1.5V to 1.9V.
• Forward Voltage Temperature Coefficient (△V/△T): -1.44 mV/°C typical. The forward voltage decreases as temperature increases.
• Viewing Angle (2θ1/2): 30 degrees typical. This is the full angle at which the radiant intensity drops to half of its on-axis value.
• Radiant Intensity Temperature Coefficient (△IE/△T): -0.43 %/°C typical. The optical output power decreases as temperature increases.
• Peak Wavelength Temperature Coefficient (△λ/△T): +0.22 nm/°C typical. The peak emission wavelength increases slightly with temperature.
• Optical Rise/Fall Time (Tr/Tf): 40 ns typical. Measured from 10% to 90% of the optical output under pulsed conditions (IFDC=500mA, Duty=20%, Pulse Width=125ns).
• Series Resistance (RS): 2.5 Ohms typical. The inherent resistance of the LED chip and bond wires.
• Diode Capacitance (CO): 75 pF typical. Measured at 0V reverse bias and 1 MHz frequency.
• Thermal Resistance (RθJA): 300 °C/W typical. This is the junction-to-ambient thermal resistance, indicating how effectively heat is transferred from the semiconductor junction to the surrounding environment.

3. Performance Curve Analysis

The datasheet references typical characteristic curves which are essential for design. While the specific graphs are not reproduced in text, their implications are analyzed below.

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

The I-V curve for an infrared emitter like the HSDL-4251 is non-linear, similar to a standard diode. The forward voltage exhibits a logarithmic relationship with current at low levels and becomes more linear at higher currents due to the series resistance (RS). Designers use this curve to select appropriate current-limiting resistors to ensure stable operation and prevent thermal runaway.

3.2 Radiant Intensity vs. Forward Current

This curve shows that the optical output (radiant intensity) is approximately proportional to the forward current in the typical operating range. However, at very high currents, efficiency may drop due to increased heat generation. The derating graph referenced in the Absolute Maximum Ratings section is crucial for determining the maximum allowable current at elevated ambient temperatures to keep the junction temperature below 110°C.

3.3 Temperature Dependence

The specified temperature coefficients (for Vf, IE, and λPeak) allow designers to predict and compensate for performance shifts over the operating temperature range. For instance, the decrease in radiant intensity with temperature must be accounted for in systems designed to operate in hot environments.

4. Mechanical and Package Information

4.1 Outline Dimensions and Tolerances

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

• All dimensions are in millimeters (with inches in parentheses).
• A standard tolerance of ±0.25mm (±0.010\") applies unless otherwise specified.
• The maximum protrusion of resin under the flange is 1.5mm (0.059\").
• Lead spacing is measured at the point where the leads exit the package body.

Designers must refer to the detailed mechanical drawing in the original datasheet for precise placement and footprint design on a PCB.

4.2 Polarity Identification

For through-hole LEDs, the anode (positive) lead is typically longer than the cathode (negative) lead. The cathode may also be identified by a flat spot on the plastic lens or a notch on the flange of the package. Correct polarity is essential for device operation.

5. Soldering and Assembly Guidelines

Proper handling is critical to maintain reliability and prevent damage to the LED.

5.1 Storage Conditions

LEDs should be stored in an environment not exceeding 30°C and 70% relative humidity. If removed from their original moisture-barrier packaging, they should be used within three months. For longer storage outside the original bag, use a sealed container with desiccant or a nitrogen-filled desiccator.

5.2 Cleaning

If cleaning is necessary, use alcohol-based solvents like isopropyl alcohol. Harsh chemicals should be avoided.

5.3 Lead Forming

Bend leads at a point at least 3mm from the base of the LED lens. Do not use the package body as a fulcrum. Lead forming must be done at room temperature and before the soldering process. Apply minimal force during PCB assembly to avoid mechanical stress.

5.4 Soldering Process

Important: Do not immerse the lens in solder. Avoid applying stress to the leads while the LED is hot.

• Soldering Iron: Maximum temperature 350°C. Maximum soldering time 5 seconds per lead. Position the iron no closer than 1.6mm from the base of the epoxy lens.
• Wave Soldering: Maximum preheat temperature 100°C for up to 60 seconds. Maximum solder wave temperature 260°C for up to 5 seconds. The device should be dipped no lower than 1.6mm from the base of the epoxy lens.
• Reflow Soldering: The datasheet explicitly states that IR reflow is not suitable for this through-hole type LED product.

Excessive temperature or time can deform the lens or cause catastrophic failure.

6. Application Design Considerations

6.1 Drive Circuit Design

LEDs are current-operated devices. To ensure uniform brightness when driving multiple LEDs in parallel, it is strongly recommended to use a individual current-limiting resistor in series with each LED (Circuit Model A). Using a single resistor for multiple parallel LEDs (Circuit Model B) is not recommended due to variations in the forward voltage (Vf) of individual devices, which can lead to significant differences in current and, consequently, brightness.

6.2 Electrostatic Discharge (ESD) Protection

The HSDL-4251 is sensitive to electrostatic discharge. A comprehensive ESD control program is necessary during handling and assembly:

• Personnel must wear grounded wrist straps or anti-static gloves.
• All equipment, workstations, and storage racks must be properly grounded.
• Use ionizers to neutralize static charge that may build up on the plastic lens.
• Implement regular checks and training for personnel working in ESD-protected areas.

6.3 Thermal Management

With a thermal resistance (RθJA) of 300°C/W, careful thermal design is needed, especially when operating at high currents or in warm environments. The power dissipation (PD = Vf * IF) generates heat at the junction. Using the derating information, designers must ensure the junction temperature (TJ) does not exceed 110°C. Adequate spacing on the PCB and possibly airflow can help manage temperature.

7. Typical Application Scenarios

Based on its specifications, the HSDL-4251 is well-suited for:

• High-Speed Infrared Data Links: IR LANs, modems, and dongles requiring the 40ns response time.
• Industrial Equipment: Sensors, encoders, and safety curtains where reliable IR beams are needed.
• Portable Instruments: Medical devices, handheld scanners, or measurement tools.
• Consumer Electronics: Infrared remote controls and optical pointing devices (e.g., optical mice).

8. Frequently Asked Questions (FAQs)

8.1 What is the difference between peak wavelength and dominant wavelength?

Peak wavelength (λPeak) is the wavelength at the highest point of the emission spectrum. Dominant wavelength is related to the perceived color and is more relevant for visible LEDs. For infrared emitters like the HSDL-4251, peak wavelength is the standard specification.

8.2 Can I drive this LED directly from a microcontroller pin?

No. A microcontroller pin typically cannot source 100mA continuously. You must use a driver circuit (e.g., a transistor) controlled by the microcontroller, along with a series current-limiting resistor as described in the drive method section.

8.3 How do I calculate the required series resistor value?

Use Ohm's Law: R = (Vsupply - Vf_LED) / I_desired. For example, with a 5V supply, a desired current of 50mA, and a typical Vf of 1.5V at that current: R = (5V - 1.5V) / 0.05A = 70 Ohms. Always use the maximum Vf from the datasheet for a conservative design to limit current.

8.4 Why is the viewing angle important?

The viewing angle defines the beam spread. A 30-degree angle is moderately focused. This is important for aligning the emitter with a detector. A wider angle might be better for proximity sensing, while a narrower angle is better for long-range, directed communication.

9. Technical Introduction and Operating Principle

The HSDL-4251 is a semiconductor light source. When a forward voltage is applied across its terminals, electrons and holes recombine in the active region of the AlGaAs semiconductor material. This recombination process releases energy in the form of photons (light). The specific composition of the AlGaAs layers determines the bandgap energy, which directly corresponds to the wavelength of the emitted light—in this case, 870nm in the infrared spectrum. The clear epoxy package acts as a lens, shaping the output beam to the specified viewing angle and providing mechanical and environmental protection for the semiconductor chip.