HSDL-4250 IR LED Datasheet - T-1 3/4 Package - Wavelength 870nm - Forward Voltage 1.6V - Power Dissipation 190mW - English Technical Documentation

1. Product Overview

The HSDL-4250 is a high-performance infrared (IR) light-emitting diode (LED) designed for applications requiring fast data transmission and reliable optical signaling. Utilizing advanced AlGaAs (Aluminum Gallium Arsenide) semiconductor technology, this component is engineered to deliver high radiant intensity with excellent speed characteristics. Its primary function is to convert electrical signals into modulated infrared light, serving as the transmitter in an optical communication link.

The core advantages of this device lie in its combination of high speed and efficient optical output. The fast rise and fall times enable it to support high data rate communication protocols. Furthermore, its low forward voltage characteristic is a significant benefit for system design, particularly in portable or battery-powered applications where power efficiency is critical. It is packaged in a industry-standard T-1 3/4 through-hole format, making it compatible with common PCB assembly processes.

The target market for this IR LED is broad, encompassing both consumer and industrial electronics. It is a key component in systems where wireless, line-of-sight data transfer is required.

2. In-Depth Technical Parameter Analysis

This section provides a detailed, objective interpretation of the key electrical, optical, and thermal parameters specified in the datasheet. Understanding these values is essential for proper circuit design and reliable operation.

2.1 Optical Characteristics

The optical performance defines the LED's effectiveness as a light source.

• Peak Wavelength (λ_pk): 870 nanometers (nm). This places the emitted light firmly in the near-infrared spectrum, which is invisible to the human eye but efficiently detected by silicon photodiodes and other common IR sensors. The 870nm wavelength offers a good balance between component availability (detectors) and atmospheric transmission.
• Radiant On-Axis Intensity (I_E): Typically 180 mW/Steradian (mW/Sr) at a forward current (I_F) of 100mA. This parameter measures the optical power emitted per unit solid angle along the central axis of the LED. A higher value indicates a more concentrated and powerful beam, which is crucial for achieving longer transmission distances or stronger signal strength.
• Viewing Angle (2θ_1/2): 15 degrees. This is the full angle at which the radiant intensity drops to half of its on-axis value. A narrow 15-degree beam is highly directional, which minimizes optical crosstalk and focuses energy on the intended receiver, improving signal-to-noise ratio but requiring more precise alignment.
• Spectral Width (Δλ): 45 nm at Full Width at Half Maximum (FWHM). This indicates the range of wavelengths the LED emits around its peak. A narrower spectral width is generally preferable for applications sensitive to specific wavelengths.
• Optical Rise/Fall Time (T_r/T_f): 40 nanoseconds (ns). This is a critical parameter for digital communication. It defines how quickly the optical output can switch from 10% to 90% of its maximum intensity (rise) and vice-versa (fall). The 40ns specification enables support for high-speed data transmission protocols.
• Temperature Coefficient of Intensity (ΔI_E/ΔT): -0.43 %/°C. This negative coefficient means the optical output power decreases as the junction temperature increases. This effect must be considered in thermal management and circuit design to ensure consistent performance over the operating temperature range.

2.2 Electrical Characteristics

These parameters govern the electrical interface and power requirements of the LED.

• Forward Voltage (V_F): Ranges from 1.4V (min) to 1.9V (max) depending on current. Typically 1.6V at 20mA and 1.9V at 100mA. This low voltage is a key feature, reducing the voltage headroom required from the power supply and enabling efficient operation, especially when multiple LEDs are connected in series.
• Series Resistance (R_S): 2.5 Ohms (typical). This internal resistance causes V_F to increase linearly with current beyond a certain point. It is important for predicting voltage drop under different drive conditions.
• Reverse Voltage (V_R): 5V maximum. Exceeding this voltage in reverse bias can permanently damage the LED. Circuit protection (like a series resistor or a parallel protection diode) is often necessary if reverse voltage conditions are possible.
• Diode Capacitance (C_O): 75 picofarads (pF) typical. This parasitic capacitance can limit the maximum achievable switching speed in very high-frequency applications by affecting the RC time constant of the drive circuit.
• Forward Voltage Temperature Coefficient (ΔV/ΔT): -1.44 mV/°C. The forward voltage decreases with increasing temperature. This characteristic can be used in some circuits for temperature sensing, but primarily it indicates that a constant-current drive is essential for stable optical output, as a constant-voltage drive would lead to increasing current (and potentially thermal runaway) as temperature rises.

2.3 Absolute Maximum Ratings and Thermal Characteristics

These are the stress limits that must not be exceeded to ensure device reliability and longevity.

• Continuous Forward Current (I_FDC): 100 mA maximum.
• Peak Forward Current (I_FPK): 500 mA, but only under pulsed conditions (20% duty cycle, 100µs pulse width). Pulsing allows for higher instantaneous optical output without overheating the junction.
• Power Dissipation (P_DISS): 190 mW. This is the maximum amount of electrical power that can be converted into heat (and light) without exceeding the maximum junction temperature.
• Junction Temperature (T_J): 110 °C maximum. The temperature of the semiconductor chip itself must stay below this limit.
• Thermal Resistance, Junction to Ambient (R_θJA): 300 °C/W. This parameter defines how effectively heat travels from the semiconductor junction to the surrounding air. A lower value is better. With 300°C/W, for every watt of power dissipated, the junction temperature will rise 300°C above the ambient temperature. This highlights the importance of derating the operating current at higher ambient temperatures, as indicated in the derating curve (Figure 6 in the original datasheet).
• Storage Temperature: -40 to +100 °C.
• Operating Temperature: -40 to +85 °C.

3. Binning System Explanation

The provided datasheet for the HSDL-4250 does not explicitly detail a commercial binning structure for parameters like wavelength or intensity. In high-volume LED manufacturing, components are often sorted (binned) based on measured performance to ensure consistency within a specific order. While not specified here, designers should be aware that key parameters such as Radiant Intensity (I_E) and Forward Voltage (V_F) will have a min/typ/max spread. For critical applications, it is advisable to consult the manufacturer for available sorting options or to design circuits that are tolerant of the specified parameter ranges.

4. Performance Curve Analysis

The datasheet references several figures that graphically represent device behavior. While the exact curves are not reproduced here, their significance is explained.

• Forward Current vs. Forward Voltage (I-V Curve): This curve (referenced as Fig. 2, Fig. 3) shows the exponential relationship between current and voltage. It is used to determine the necessary drive voltage for a desired operating current and to understand the effect of the series resistance (R_S).
• Derating Curve (Power/Temperature): Figure 6 is crucial for reliable design. It shows how the maximum allowable power dissipation (or forward current) must be reduced as the ambient operating temperature increases. Ignoring this curve risks overheating the LED and premature failure.
• Relative Intensity vs. Temperature: This illustrates the -0.43%/°C coefficient, showing a linear decrease in light output as temperature rises.
• Spectral Distribution: Figure 1 would show the shape of the emitted light spectrum, centered at 870nm with a 45nm FWHM width.
• Viewing Angle Pattern: Figure 7 would depict the angular distribution of the emitted light, defining the 15-degree half-angle beam profile.

5. Mechanical and Package Information

The HSDL-4250 uses a T-1 3/4 (5mm) radial leaded package. Key dimensional notes from the datasheet include:

• All dimensions are in millimeters with a general tolerance of ±0.25mm 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 includes a flat side or other feature to indicate the cathode (negative) lead, which is typically the shorter lead or the lead adjacent to the flat spot on the lens flange. Correct polarity identification is essential during assembly.

The through-hole design requires appropriate PCB drill hole sizes and pad geometries to ensure proper fit and soldering.

6. Soldering and Assembly Guidelines

The datasheet provides specific instructions for soldering to prevent thermal damage:

• Lead Soldering Temperature: The leads can withstand a temperature of 260°C for a maximum of 5 seconds. This measurement is taken 1.6mm (0.063 inches) from the package body.
• Process Consideration: For wave soldering or hand soldering, it is vital to adhere to this time-temperature profile. Excessive heat or prolonged contact can melt the internal epoxy, damage the wire bonds, or degrade the semiconductor material.
• Storage Conditions: While not explicitly stated beyond the storage temperature range, LEDs should generally be stored in a dry, anti-static environment to prevent moisture absorption (which can cause \"popcorning\" during reflow) and electrostatic discharge damage.

7. Application Recommendations

7.1 Typical Application Scenarios

The datasheet lists several key applications, which leverage the LED's high speed and infrared output:

• High-Speed Infrared Data Links: Infrared Local Area Networks (IR LANs), wireless data transfer between computers and peripherals (e.g., IR dongles), and modern infrared communication modules. The 40ns rise time supports protocols like IrDA (Infrared Data Association) for serial data transfer.
• Portable Infrared Instruments: Devices such as non-contact thermometers, gas analyzers, and distance sensors that use active infrared sensing.
• Consumer Electronics: A very common use is as the transmitter in infrared remote controls for televisions, audio systems, and other appliances. It is also suitable for components in optical computer mice, where it illuminates the surface for tracking.

7.2 Design Considerations

• Drive Circuit: Always use a series current-limiting resistor. For optimal stability and to prevent thermal runaway, consider using a constant-current driver circuit instead of a simple resistor with a constant voltage source, especially for operation near the maximum current or over temperature extremes.
• Heat Management: Due to the relatively high thermal resistance (300°C/W), ensure adequate airflow or consider heat sinking if operating at high ambient temperatures or high duty cycles. Adhere strictly to the derating curve.
• Optical Design: The narrow 15-degree beam requires careful mechanical alignment with the receiver (photodiode or sensor). Lenses or reflectors can be used to further collimate or shape the beam for specific applications. For remote controls, a wider, diffused pattern is often created by the plastic housing of the remote itself.
• Modulation: For data transmission, the LED is typically driven with a modulated signal (e.g., PWM) at a carrier frequency (like 38kHz for many remotes) to distinguish it from ambient IR light and improve noise immunity.

8. Technical Comparison and Differentiation

Compared to standard, lower-speed IR LEDs, the HSDL-4250's primary differentiation is its high-speed capability (40ns). This makes it unsuitable for simple on/off indicators but ideal for digital communication. Its low forward voltage is another advantage, reducing power consumption and simplifying power supply design in battery-operated devices like remote controls. The 870nm wavelength is a common standard, ensuring wide compatibility with off-the-shelf IR photodetectors that are typically most sensitive around 850-950nm.

9. Frequently Asked Questions (Based on Technical Parameters)

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

A: No. You must always use a series resistor (or active current driver) to limit the current. The forward voltage is only ~1.6V, so connecting it directly to 3.3V without a resistor would cause excessive current, destroying the LED and potentially damaging the microcontroller pin.

Q: What resistor value should I use for a 20mA drive current from a 5V supply?

A: Using Ohm's Law: R = (V_supply - V_F) / I_F. With V_F ~ 1.6V, R = (5V - 1.6V) / 0.020A = 170 Ohms. A standard 180 Ohm resistor would be a safe choice, yielding a current slightly below 20mA.

Q: Why is the peak current (500mA) so much higher than the continuous current (100mA)?

A> The peak current rating is for very short pulses. The semiconductor junction can handle a high instantaneous power burst without the heat having time to build up and exceed T_Jmax. This is exploited in communication systems to send bright, short optical pulses for better signal integrity.

Q: How does temperature affect performance?

A> Increasing temperature reduces both the forward voltage (by -1.44mV/°C) and the optical output power (by -0.43%/°C). Therefore, a constant-current drive is essential to maintain stable light output. The maximum allowable current must also be derated as ambient temperature rises.

10. Practical Design and Usage Examples

Example 1: Simple IR Remote Control Transmitter. In a basic remote, a microcontroller generates a modulated data stream (e.g., 38kHz carrier). This signal drives a transistor switch (like a BJT or MOSFET) connected in series with the HSDL-4250 LED and a current-limiting resistor. The resistor value is calculated based on the supply voltage (often 3V from two AA batteries) and the desired pulse current (e.g., 100mA for strong signal). The transistor allows the low-power microcontroller to control the higher LED current.

Example 2: High-Speed Serial Data Link (IrDA). For a bidirectional IrDA port, the HSDL-4250 would be part of the transmitter circuit. It would be driven by a dedicated IrDA encoder/transmitter IC that shapes the electrical pulses to meet the IrDA physical layer specifications (like pulse width). The fast rise/fall time of the LED is critical to achieving the required data rates (e.g., 115.2 kbps for IrDA 1.0). Careful PCB layout is needed to minimize parasitic capacitance that could slow down the edges.

11. Operating Principle Introduction

An Infrared Light Emitting Diode (IR LED) is a semiconductor p-n junction diode. When forward biased (positive voltage applied to the anode relative to the 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 the specific AlGaAs material used in the HSDL-4250, this energy is released primarily in the form of photons (light) with an energy corresponding to the infrared spectrum (around 870nm wavelength). The intensity of the emitted light is directly proportional to the rate of carrier recombination, which is controlled by the forward current flowing through the diode. The T-1 3/4 package includes an epoxy lens that shapes the emitted light beam.

12. Technology Trends and Developments

While the fundamental principle of IR LEDs remains stable, trends focus on increased efficiency, higher speed, and greater integration. Modern devices may feature:

• Higher Power and Efficiency: New semiconductor materials and chip designs aim to convert more electrical input into optical output (higher wall-plug efficiency), reducing heat generation and power consumption.
• Surface-Mount Device (SMD) Packages: While the HSDL-4250 is a through-hole component, the industry has largely moved towards SMD packages (e.g., 0805, 1206, or chip-on-board) for automated assembly and smaller form factors. Equivalent high-speed IR LEDs are available in these packages.
• Integrated Solutions: For consumer applications like remote controls, it is common to find the LED and its drive transistor integrated into a single, miniature module. For advanced sensing, LEDs are being integrated with drivers, modulators, and sometimes even detectors on a single substrate or in a multi-chip module.
• Application-Specific Optimization: LEDs are being tailored for specific uses, such as very narrow beam angles for distance sensing or specific wavelength peaks for gas sensing applications.