LTR-1650D Phototransistor Datasheet - Package Size 5.0x4.0x3.2mm - Voltage 30V - Power 100mW - Dark Transparent Package - Technical Documentation

1. Product Overview

LTR-1650D is a silicon NPN phototransistor specifically designed for infrared detection applications. It utilizes a low-cost, dark transparent plastic package that effectively filters out visible light while transmitting infrared wavelengths (primarily around 940nm). The integrated lens focuses incident infrared radiation onto the transistor's active area, thereby enhancing the device's sensitivity. This component is designed to deliver reliable performance across a wide operating temperature range, making it suitable for various sensing and control systems.

2. Key Features and Core Advantages

• Wide Range Collector Current:This device offers multiple performance grades (A through F), with a wide selection range for on-state collector current (IC(ON)), from a minimum of 0.2mA to over 9.6mA, allowing designers to choose the appropriate model based on specific sensitivity requirements.
• High Sensitivity Lens:Integrated epoxy lens increases the effective collection area of infrared light, improving signal-to-noise ratio and overall responsivity.
• Cost-effective plastic packaging:Uses standard, economical plastic housing, suitable for mass production and broad market applications.
• Special dark transparent packaging:The encapsulation material is color-treated to attenuate visible light, reduce interference from ambient light sources, and enhance performance in environments with fluctuating light conditions.

3. In-depth Technical Parameter Analysis

3.1 Absolute Maximum Ratings

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

• Power Dissipation (P_D):At T_A=25°C, it is 100 mW. This is the maximum power the device can safely dissipate as heat.
• Collector-Emitter Voltage (V_CEO):30 V. The maximum voltage that can be applied between the collector and emitter terminals with the base open.
• Emitter-collector voltage (V_ECO):5 V. The maximum reverse voltage that can be applied between the emitter and collector.
• Operating Temperature Range (T_opr):-40°C to +85°C. The specified ambient temperature range over which the device is designed to operate.
• Storage Temperature Range (T_stg):-55°C to +100°C.
• Pin soldering temperature:At a distance of 1.6mm from the package body, maintain at 260°C for 5 seconds. This is critical for wave soldering or reflow soldering processes.

3.2 Electrical and Optical Characteristics (T_A=25°C)

The following parameters, tested under specific conditions, define the device's performance.

• Collector-Emitter Breakdown Voltage (V_(BR)CEO):30 V (min). At zero irradiance (E_C= 0 mW/cm²) and I_e= Test under the condition of 1mA.
• Emitter-Collector Breakdown Voltage (V_(BR)ECO):5 V (minimum). Under no irradiance and I_ETested under the condition of = 100µA.
• Collector-Emitter Saturation Voltage (V_CE(SAT)):0.4 V (max). The voltage drop across the transistor when it is fully "on", tested under the condition of I_C= 100µA and E_e= 1 mW/cm². Low V_CE(SAT)is desirable for efficient switching operation.
• Rise time (T_r) and fall time (T_f):10 µs (typical). These switching speed parameters are at V_CC=5V, I_C=1mA, R_L=1kΩ condition measurement. They determine the phototransistor's response speed to changes in light intensity.
• Collector dark current (I_CEO):100 nA (maximum). This is the device's current under complete darkness (E_e= 0 mW/cm²) and V_CE= 10V. Low dark current is crucial for achieving a good signal-to-noise ratio in low-light detection.

3.3 On-state Collector Current (I_C(ON)) Grading System

LTR-1650D is classified into different grades based on its sensitivity, which is determined under standardized conditions (V_CE= 5V, E_e= 1 mW/cm², λ = 940nm) measured on-state collector current definition. This allows for precise selection based on application gain requirements.

• Grade A:0.2 - 0.6 mA
• Grade B:0.4 - 1.2 mA
• Level C:0.8 - 2.4 mA
• Level D:1.6 - 4.8 mA
• Level E:3.2 - 9.6 mA
• Grade F:6.4 mA (min)

Designers should consult the specific grade code when ordering to ensure the phototransistor meets the circuit's sensitivity and output current requirements.

4. Performance Curve Analysis

The datasheet provides several characteristic curves illustrating how key parameters vary with environmental and electrical conditions.

4.1 Collector Dark Current vs. Ambient Temperature (Figure 1)

The curve shows that the collector dark current (I_CEO) increases exponentially with rising ambient temperature. This is a fundamental semiconductor property, where thermally generated carriers become more prevalent. In high-temperature applications, this increased leakage current can become a significant noise source and must be considered in the design of the sensing amplifier's threshold.

4.2 Collector Power Dissipation vs. Ambient Temperature (Figure 2)

This graph depicts the derating of maximum allowable power dissipation with increasing ambient temperature. At 25°C, the device can withstand 100mW. As temperature rises, this rating decreases linearly. For reliable operation above 25°C, the actual dissipated power (V_CE* I_C) must remain below the derating curve. This is crucial to prevent thermal runaway and ensure long-term reliability.

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

This curve illustrates the trade-off between switching speed and load resistance (R_L). Rise and fall times increase with larger load resistance. This is because a larger R_Lforms a larger RC time constant with the phototransistor's junction capacitance. For applications requiring fast pulse detection, a smaller load resistor should be used, albeit at the cost of reduced output voltage swing.

4.4 Relative Collector Current vs. Irradiance (Figure 4)

This figure shows the relationship between the incident infrared irradiance (E_e) and the generated collector current. The response is typically linear within a certain range, which is ideal for analog optical sensing applications. The slope of the line represents the responsivity of the device. Understanding this characteristic is crucial for calibrating the sensor output to specific light intensity levels.

4.5 Sensitivity Pattern (Figure 5)

This polar plot illustrates the angular dependence of the phototransistor's sensitivity. Sensitivity is typically highest when infrared light is incident perpendicularly to the lens (0°). It decreases as the angle of incidence increases. This characteristic is crucial for designing optical paths in applications, such as ensuring proper alignment in slot-type interrupters or defining the field of view for proximity sensors.

5. Mechanical and Packaging Information

5.1 Package Dimensions

The device is housed in a standard 3mm (T-1) radial leaded package. Key dimensions include:

• Package body diameter: approximately 5.0mm.
• Package height: approximately 3.2mm (excluding leads).
• Lead pitch: measured where leads extend from the package, typically 2.54mm (0.1").
• Maximum resin bulge under the flange is allowed to be 1.5mm.

Note:Unless otherwise specified, all dimensions are in millimeters with a standard tolerance of ±0.25mm. Designers must refer to the detailed mechanical drawings for precise pad layout and placement planning.

5.2 Polarity Identification

Phototransistors have two pins: the collector and the emitter. The longer pin is usually the collector. There may be a flat side or other marking on the package near the collector pin. Correct polarity is crucial for proper circuit operation and applying the correct bias voltage.

6. Welding and Assembly Guide

• Manual Welding:Use a temperature-controlled soldering iron. Limit soldering time to prevent excessive heat transfer to the semiconductor chip.
• Wave Soldering/Reflow Soldering:Strictly adhere to the maximum rating: 5 seconds at 260°C, 1.6mm from the package body. Exceeding this may damage internal wire bonds or the epoxy package.
• Cleaning:Use appropriate solvents compatible with dark transparent epoxy. Avoid ultrasonic cleaning unless verified safe for the package.
• Storage:Store in a dry, anti-static environment within the specified temperature range of -55°C to +100°C to prevent moisture absorption (which may cause the "popcorn" effect during reflow soldering) and electrostatic discharge damage.

7. Application Suggestions and Design Considerations

7.1 Typical Application Scenarios

• Object Detection and Interruption:Used for slot-type photoelectric switches (e.g., paper detection in printers, limit sensing in 3D printers).
• Proximity Sensing:Paired with an infrared LED for non-contact detection of objects.
• Encoder:Detecting patterns on rotating discs for speed or position measurement.
• Industrial Control:Used for sensing in automated equipment requiring resistance to ambient light interference.
• Consumer Electronics:Infrared Remote Control Receiver (although often used with dedicated ICs, phototransistors can form the front end).

7.2 Key Design Considerations

• Bias Circuit:Phototransistors can be used in switch (common-emitter) or follower (emitter-follower) configurations. The common-emitter configuration provides voltage gain and is often used for digital switching. A pull-up resistor (R_L) is required.
• Selecting R_L:The value of the load resistor involves a trade-off. For a given photocurrent, a larger R_LIt can provide a larger output voltage swing, but it will slow down the switching speed (see Figure 3). Choose based on the required speed and signal level.
• Ambient Light Rejection:Although dark packaging helps, strong ambient infrared light sources (sunlight, incandescent bulbs) can saturate the sensor. Consider using optical filters, modulated infrared light sources, and synchronous detection techniques.
• Temperature Compensation:For precision analog sensing, it is necessary to compensate for the variation of dark current and sensitivity with temperature in the signal conditioning circuit (Figure 1 and Figure 2).
• Electrical Noise:High-impedance nodes at the collector are susceptible to electromagnetic interference (EMI). Keep traces short, use shielding when necessary, and consider at R_LA small capacitor (e.g., 10-100pF) is connected in parallel at both ends to filter out high-frequency noise, while paying attention to its impact on speed.

8. Technical Comparison and Differentiation

Compared to basic photodiodes, phototransistors like the LTR-1650D provide internal gain, producing a larger output current for the same light input, which often eliminates the need for additional external amplifiers in simple switching applications. Compared to photodarlington transistors, they offer faster response times (microseconds vs. tens/hundreds of microseconds) but lower gain. Its design for I_C(ON)The specific grading system, compared to devices with only a broad specification, allows for more precise system design. The dark transparent package is a key distinction from the transparent package, providing built-in visible light suppression.

9. Frequently Asked Questions (Based on Technical Specifications)

9.1 What does the "BIN" specification mean, and how should I choose?

BIN code (A to F) specifies the guaranteed range of phototransistor sensitivity (I_C(ON)) . Select the grade based on the output current required for your specific irradiance level. For applications requiring higher sensitivity/lower light levels, choose a grade with a higher letter (e.g., E or F). For cost-sensitive applications where high gain is not critical, a lower grade (A or B) may be sufficient.

9.2 Why is dark current important?

Dark Current (I_CEO) is the output signal present when no light is incident. It sets the lower limit of detectable light and acts as a noise source. In digital switching applications, the circuit's detection threshold must be set above the maximum expected dark current, especially at high temperatures where dark current increases significantly.

9.3 How does the load resistor affect performance?

The load resistor (R_L) directly affects two key parameters:Voltage Output(V_out= I_C* R_L) andSwitching speed(See Figure 3). You must select R_Lto provide the necessary voltage swing for your logic level or ADC input, while ensuring the rise/fall time is sufficiently fast for your application data rate or response time.

9.4 Zan iya amfani da shi a cikin hasken rana mai haske?

The dark transparent package provides some suppression capability, but direct sunlight contains intense infrared radiation that can easily saturate the sensor. For outdoor use, additional measures are necessary: physical shading (a hood), an optical narrowband filter centered at your infrared source's wavelength (e.g., 940nm), and preferably, using a modulated infrared source with synchronous detection in the receiver circuit to distinguish the signal from the steady DC component of sunlight.

10. Actual Design and Usage Case Studies

Scenario: Designing a paper detection sensor for a printer.

1. Model Selection:Select a medium sensitivity level (e.g., Class C or D) to ensure reliable triggering without being overly sensitive to dust or reflections.
2. Circuit Configuration:Use a common-emitter switching configuration. Pair the LTR-1650D with an infrared LED (e.g., 940nm) and place it on the opposite side of the paper path.
3. Component Parameter Determination:Select an R_LValue (e.g., 4.7kΩ), such that when paper is present (blocking light, I_Clow) the output is logic low (close to 0V), and when no paper is present (light present, I_CChigh) the output is logic high (close to V_C). Verify voltage level compatibility with the microcontroller's input pins.
4. Noise Immunity:In R_LA 10nF capacitor is connected in parallel at both ends to suppress electrical noise from the printer motor. The resulting speed (approximately 100µs) is still much faster than the mechanical movement of the paper.
5. Alignment:Use the sensitivity polar pattern (Figure 5) to guide the mechanical design. Ensure the infrared LED and phototransistor are aligned within the high-sensitivity cone angle (e.g., ±20°) to maximize signal strength.
6. Test:Test the sensor under worst-case conditions: high temperature (check for increased dark current) and using various paper types (some may be more transparent to infrared light).

11. Working Principle

A phototransistor is essentially a bipolar junction transistor (BJT) where the base current is generated by light rather than supplied electrically. Incident photons with energy greater than the semiconductor bandgap are absorbed in the base-collector junction region, creating electron-hole pairs. The electric field in the reverse-biased collector-base junction sweeps these charge carriers, effectively generating a photocurrent that acts as the base current (I_B). This photogenerated base current is then amplified by the transistor's current gain (h_FE) Amplification, producing a much larger collector current (I_C= h_FE* I_B). This internal amplification is its key advantage over a simple photodiode. The dark transparent packaging material acts as a long-pass filter, allowing infrared wavelengths (such as 940nm) to pass while absorbing shorter visible wavelengths, thereby improving the signal-to-noise ratio in environments with visible light.

12. Industry Trends and Development

The optoelectronics industry continues to evolve. While discrete phototransistors like the LTR-1650D remain critical for cost-sensitive, high-volume, or specific performance applications, broader trends include:

• Integration:Integrating photodetectors with analog front-end amplifiers, analog-to-digital converters (ADC), and digital logic into single-chip solutions (e.g., ambient light sensors, proximity sensor modules). These offer calibrated digital outputs, smaller footprints, and simplified design, but potentially higher unit cost.
• Miniaturization:The demand for smaller package sizes (e.g., chip-scale packages) to accommodate shrinking consumer electronics.
• Performance Enhancement:Develop devices with lower dark current, faster response time (entering the nanosecond range), and higher sensitivity to meet more demanding applications such as LiDAR and high-speed communication.
• Specialization:Sensors customized for specific wavelengths (e.g., for heart rate monitoring, gas sensing) or with built-in spectral filters.

Discrete phototransistors are likely to maintain their position in applications where their simplicity, robustness, low cost, and specific performance characteristics (such as the dark package of the LTR-1650D) provide the optimal solution.