LTR-209 Phototransistor Datasheet - Clear Package - Vce 30V - Power 100mW - Technical Documentation

1. Product Overview

LTR-209 is a silicon NPN phototransistor specifically designed for infrared detection applications. It features a transparent plastic package and offers high sensitivity to incident light, particularly in the infrared spectrum. Characterized by a wide operating range, high reliability, and cost-effectiveness, this device is suitable for various sensing and detection systems.

1.1 Core Advantages

• Wide Collector Current Range:This device supports a wide range of collector current levels, providing flexibility for circuit design and sensitivity adjustment.
• High Sensitivity Lens:Integrated lens enhances the device's sensitivity to incident infrared radiation and improves the signal-to-noise ratio.
• Low-cost plastic packaging:The use of economical plastic packaging reduces the overall system cost.
• Transparent packaging:The transparent housing maximizes the amount of light reaching the active semiconductor area, optimizing performance.

2. In-depth Technical Parameter Analysis

The following section provides a detailed and objective interpretation of the key electrical and optical parameters of the LTR-209 phototransistor.

2.1 Absolute Maximum Ratings

These ratings define the limits that may cause permanent damage to the device. Operation under or beyond these conditions is not guaranteed.

• Power consumption (P_D):100 mW. This is the maximum power that the device can dissipate as heat when the ambient temperature (T_A) is 25°C. Exceeding this limit risks thermal runaway and failure.
• Collector-emitter voltage (V_CEO):30 V. The maximum voltage that can be applied between the collector and emitter terminals with the base open (only photocurrent).
• Emitter-collector voltage (V_ECO):5 V. Maximum reverse voltage that can be applied between the emitter and collector.
• Operating temperature range:-40°C to +85°C. The device is designed to operate normally within this ambient temperature range.
• Temperature Range for Storage:-55°C to +100°C. The temperature range for storage under non-operating conditions that does not lead to performance degradation.
• Pin Soldering Temperature:At a distance of 1.6mm from the package body, maintain 260°C for 5 seconds. This defines the acceptable thermal profile for hand or wave soldering processes.

2.2 Electrical and Optical Characteristics

These parameters were measured under specific test conditions at T_A=25°C, defining the typical performance of the device.

• Collector-Emitter Breakdown Voltage (V_(BR)CEO):30 V (min). At zero irradiance (E_C= 0 mW/cm²) and I_eMeasured under the condition of = 1mA. This confirms the absolute maximum ratings.
• Emitter-collector breakdown voltage (V_(BR)ECO):5 V (minimum). At zero irradiance and I_E= 100µA condition measurement.
• Collector-emitter saturation voltage (V_CE(SAT)):0.4 V (maximum). The voltage drop across the device when it is fully "on" (conducting), at I_C= 100µA and measured under E_e= 1 mW/cm² conditions. A lower V_CE(SAT)is beneficial for reducing power loss.
• Rise time (T_r) and fall time (T_f):are 10 µs (typical) and 15 µs (typical), respectively. These parameters define the switching speed of the phototransistor. At V_CC=5V, I_C=1mA, R_L=1kΩ condition measurement. This asymmetry is common in phototransistors.
• Collector dark current (I_CEO):100 nA (maximum). This is when the device is in complete darkness (E_e= 0 mW/cm²) and V_CEWhen = 10V, the leakage current flowing from the collector to the emitter. Low dark current is crucial for high-sensitivity applications to minimize noise.

3. Explanation of the Grading System

LTR-209 has implemented a binning system for its key parameter --On-state collector current (I_C(ON))--. Binning is a quality control process that categorizes components into specific groups or "bins" based on measured performance. This allows designers to select devices with guaranteed performance ranges suitable for their applications.

3.1 On-state Collector Current Grading

I_C(ON)Measured under standardized conditions: V_CE= 5V, E_e= 1 mW/cm², the wavelength (λ) of the infrared light source is 940nm. Based on the measured current, the device is categorized into the following bins:

• BIN C:0.8 mA (minimum) to 2.4 mA (maximum)
• BIN D:1.6 mA (minimum) to 4.8 mA (maximum)
• BIN E:3.2 mA (minimum) to 9.6 mA (maximum)
• BIN F:6.4 mA (minimum) — An upper limit is not specified in this excerpt of the datasheet.

Design Impact:A circuit designed for BIN C devices (lower current) may not function correctly if BIN F devices (higher current) are used without recalibration, and vice versa. Specifying the bin code is crucial for ensuring consistent system performance.

4. Performance curve analysis

The datasheet provides several characteristic curves illustrating how key parameters vary with operating conditions. This is essential for understanding the actual behavior beyond single-point specifications.

4.1 Collector dark current vs. ambient temperature (Figure 1)

The figure shows I_CEO(Dark current) increases exponentially with ambient temperature (T_A) rise. For example, at 100°C, the dark current may be several orders of magnitude higher than at 25°C. This is due to the fundamental semiconductor behavior caused by increased thermally generated carriers.Design considerations:In high-temperature applications, the increased dark current can become a significant noise source, potentially masking weak optical signals. Thermal management or signal conditioning may be required.

4.2 Relationship between Collector Power Dissipation and Ambient Temperature (Figure 2)

This derating curve shows the maximum allowable power dissipation (P_C) as a function of T_A. The absolute maximum rating of 100 mW is valid only at 25°C or below. As T_AAs the temperature increases, the device's heat dissipation capability decreases, so the maximum allowable power must be linearly reduced. At 85°C (the maximum operating temperature), the allowable power dissipation is significantly reduced.Design considerations:The circuit design must ensure that the actual power consumption (V_CE* I_C) does not exceed the derated value at the highest expected operating temperature.

4.3 Rise/Fall Time vs. Load Resistance (Figure 3)

This curve illustrates the trade-off between switching speed and signal amplitude. The rise time (T_r) and fall time (T_f) both increase with the load resistance (R_L). A larger R_LProvides a larger output voltage swing (ΔV = I_C* R_L), but it slows down the circuit's response time because the transistor's junction capacitance takes longer to charge/discharge through the larger resistor.Design considerations:R_LThe value of R must be chosen based on whether the application prioritizes high-speed response (lower R_L) or high output voltage gain (higher R)._L) to select.

4.4 Relative Collector Current vs. Irradiance (Figure 4)

This graph plots the normalized collector current against the incident optical power density (irradiance, E_e). A linear relationship is observed within the plotted range (0 to approximately 5 mW/cm²). This linearity is a key characteristic of phototransistors used for analog sensing applications, as the output current is proportional to the input light intensity. The curve was measured at V_CE= Drawn under 5V conditions.

4.5 Sensitivity Schematic (Figure 5)

Although the axes are abbreviated, the "Sensitivity Diagram" typically illustrates the spectral response of the detector. Silicon phototransistors like the LTR-209 are most sensitive to light in the near-infrared region, peaking around 800-950 nm. This makes them well-suited for use with common infrared emitters (such as LEDs with λ=940nm, as mentioned in the binning test conditions) and for filtering out visible light interference.

5. Mechanical and Packaging Information

5.1 Package Dimensions

This device uses a standard through-hole plastic package. Key dimensional specifications in the datasheet include:

• All dimensions are in millimeters (inches in parentheses).
• Unless otherwise specified, standard tolerances of ±0.25mm (±.010") apply.
• The maximum protrusion of resin under the flange is 1.5mm (.059").
• Pin pitch is measured where the pins extend from the package body, which is crucial for PCB pad design.

Polarity identification:The longer pin is typically the collector, and the shorter pin is the emitter. The flat side on the edge of the package may also indicate the emitter side. Always refer to the package drawing for verification.

6. Welding and Assembly Guide

The primary guidelines provided are applicable for hand or wave soldering: the pins can withstand a temperature of 260°C for a maximum duration of 5 seconds, measured at a point 1.6mm (.063") from the package body. This prevents thermal damage to the internal semiconductor die and the plastic package.

For reflow soldering:Although not explicitly stated in this datasheet, similar plastic packages typically require a profile compliant with JEDEC standards (e.g., J-STD-020), with a peak temperature generally not exceeding 260°C. Specific Moisture Sensitivity Level (MSL) and baking requirements are not provided here and should be confirmed with the manufacturer.

Storage conditions:The device should be stored within the specified temperature range of -55°C to +100°C, in a dry, non-corrosive environment. For long-term storage, anti-static measures are recommended.

7. Application Recommendations

7.1 Typical Application Scenarios

• Object Detection and Proximity Sensing:Used in conjunction with infrared LEDs to detect the presence, absence, or proximity of objects (e.g., in vending machines, printers, industrial automation).
• Slot-Type Sensors and Encoders:Detects the interruption of infrared beams to count objects or measure rotational speed.
• Remote control receiver:Although slower than dedicated photodiodes, they can be used in simple, low-cost infrared receiving circuits.
• Grating and Security System:Creating invisible beams for intrusion detection.

7.2 Design Considerations and Circuit Configuration

The most common circuit configuration isCommon emittermode. The collector of the phototransistor is connected through a load resistor (R_CC) Connect to the positive power supply (V_L), emitter grounded. Incident light causes photocurrent (I_C) to flow, generating an output voltage (V_OUT): V_OUT= V_CC- (I_C* R_L). When there is no light, V_OUTis at a high level (~V_CC). When there is light, V_OUT drops.

Key design steps:

1. Select R_L:Based on the required output swing (V_CC/I_C(ON)) and the desired speed (see Figure 3). Values between 1kΩ and 10kΩ are common.
2. Consider bandwidth:R_LThe value, combined with the junction capacitance of the device, forms a low-pass filter. For pulse operation, ensure the circuit's RC time constant is much smaller than the pulse width.
3. Manage ambient light:Use optical filtering (cover the sensor with a dark or infrared pass filter) to block unwanted visible light and reduce noise.
4. Temperature compensation:For precision analog sensing, consider the temperature dependence of dark current (Figure 1). Techniques include using matched dark reference sensors in a differential configuration or implementing software compensation.

8. Technical Comparison and Differentiation

Compared with other optical detectors:

• Compared with photodiodes:Phototransistors provide inherent current gain (β or h_FE), resulting in higher output current at the same light level. This simplifies circuit design as less subsequent amplification is required. However, phototransistors are generally slower than photodiodes (longer rise/fall times) and have a more limited linear range.
• Compared to photodarlingtons:Photodarlingtons offer higher gain than standard phototransistors, but have significantly slower response times and a higher saturation voltage (V_CE(SAT)). The LTR-209 provides a good balance between gain, speed, and voltage drop.
• Differentiating features of the LTR-209:其Transparent Encapsulation和Integrated LensIt is a key differentiating factor. Many competing phototransistors use black epoxy encapsulation that attenuates light. The transparent encapsulation of the LTR-209 maximizes sensitivity, while the lens helps focus incident light onto the active area, improving directionality and signal strength.

9. Frequently Asked Questions (Based on Technical Specifications)

9.1 What does the "BIN" code mean? Why is it important?

BIN codes (C, D, E, F) are based on the measured collector on-state current (I_C(ON)) Classify the device. It is crucial because it ensures a specific performance range. Using a device with the wrong grade may cause insufficient or excessive sensitivity in your circuit, leading to malfunction. Please be sure to specify the required grade when ordering.

9.2 Can I use this sensor with a visible light source?

Although silicon material does respond to visible light, its peak sensitivity is in the near-infrared region (see implied Figure 5). For optimal performance and to avoid interference from ambient visible light, it is strongly recommended to pair it with an infrared emitter (typically 850nm, 880nm, or 940nm) and use an infrared pass filter on the detector.

9.3 How can I convert the output to a digital signal?

Hanya mafi sauki ita ce haɗa fitarwa (mahaɗar taro) zuwa shigarwar mai jujjuyawar Schmitt ko mai kwatancin da ke da hysteresis. Wannan yana canza jujjuyawar ƙarfin lantarki na analog zuwa siginar lamba mai tsabta, ba tare da tasirin hayaniya ba. Ya kamata a saita kofa na mai kwatancin a tsakanin matakan fitarwar ƙarfin lantarki na "haske" da "duhu".

9.4 Me ya sa fitarwa ta ba ta karko a cikin yanayi mai haske da zafi?

This is likely due to the combined effects of high dark current (which increases with temperature according to Figure 1) and the response to ambient light. Solutions include: 1) Adding physical shielding or tubing to limit the field of view, 2) Using a modulated infrared light source with synchronous detection, 3) Implementing temperature-stable bias or compensation circuits.

10. Practical Design Case Studies

Scene:Design a paper detection sensor for the printer.

Implementation:Place the infrared LED and LTR-209 on opposite sides of the paper path, aligned to form a light beam. When paper is present, it blocks the beam. The phototransistor is configured in common-emitter mode, with R_L= 4.7kΩ, V_CC= 5V.

Component Selection and Calculation:Select device from BIN D (I_C(ON)= 1.6-4.8mA). When no paper (beam intact), assume I_C= 3mA (typical). V_OUT= 5V - (3mA * 4.7kΩ) = 5V - 14.1V = -9.1V. This is impossible, meaning the transistor is saturated. When saturated, V_OUT≈ V_CE(SAT)≈ 0.4V (low-level signal). When the paper blocks the light beam, I_C≈ I_CEO(very small, ~nA), so V_OUT≈ 5V (high-level signal). The GPIO pin of the microcontroller can directly read this high/low-level signal to detect paper presence. It is recommended to add a decoupling capacitor (e.g., 100nF) between the sensor's power supply pins to filter out noise.

11. Working Principles

A phototransistor is a bipolar junction transistor (BJT) with its base region exposed to light. Incident photons with sufficient energy generate electron-hole pairs in the base-collector junction. These photogenerated carriers are swept out by the internal electric field, effectively acting as a base current. This "optical base current" is then amplified by the transistor's current gain (h_FE), producing a much larger collector current. The magnitude of this collector current is proportional to the intensity of the incident light, thereby providing the sensing function. The transparent package and lens of the LTR-209 maximize the number of photons reaching the sensitive semiconductor junction.

12. Technology Trends

LTR-209 gibi fototransistörler, olgun ve uygun maliyetli bir teknolojiyi temsil eder. Optoelektroniğin mevcut trendleri şunları içerir:

• Entegrasyon:Evolving towards integrated solutions, integrating photodetectors, amplifiers, and digital logic (e.g., photoelectric circuit breakers with built-in logic outputs) on a single chip reduces the number of external components and improves noise immunity.
• Surface Mount Device (SMD):While through-hole packages remain popular for prototyping and certain applications, the industry is strongly shifting towards smaller SMD packages (e.g., SMT-3) to accommodate automated assembly and space-constrained designs.
• Performance Enhancement:Develop devices with faster response times, lower dark current, and higher temperature stability to meet the more demanding application requirements in the automotive, industrial, and consumer electronics fields.
• Application-Specific Optimization:Sensors are being customized for specific wavelengths (e.g., for heart rate monitoring at specific infrared wavelengths) or with built-in daylight filters.

The fundamental operating principle of phototransistors remains valid, and devices like the LTR-209 continue to be a reliable choice for a range of sensing needs, from basic to intermediate, due to their simplicity, robustness, and low cost.