LTH-301-07P5 Photo Interrupter Datasheet - Slotted Optical Switch - English Technical Document

1. Product Overview

The LTH-301-07P5 is a photo interrupter, a type of optoelectronic component designed for non-contact switching applications. It integrates an infrared light-emitting diode (LED) and a phototransistor within a single, compact slotted housing. The fundamental operating principle involves the interruption of the infrared light beam between the emitter and the detector by an external object, which causes a corresponding change in the output signal of the phototransistor. This design offers a reliable and precise method for detecting the presence, absence, or position of objects without physical contact.

The core advantage of this device lies in its non-contact nature, which eliminates mechanical wear and tear, leading to high reliability and long operational life. It features fast switching speeds, making it suitable for applications requiring rapid detection. The component is designed for direct printed circuit board (PCB) mounting or for use with a dual-in-line socket, providing flexibility in system design and assembly.

Typical target markets and applications include, but are not limited to, office automation equipment such as facsimile machines, photocopiers, printers, and scanners. It is also widely used in various industrial automation, consumer electronics, and instrumentation systems where precise object detection is required.

2. Technical Parameters Deep Objective Interpretation

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 and should never be exceeded, even momentarily, under normal operating conditions.

Input LED: The continuous forward current is limited to 50 mA, with a peak forward current of 1 A allowed under pulsed conditions (300 pulses per second, 10 μs pulse width). The maximum power dissipation for the LED is 80 mW. The reverse voltage withstand capability is 5 V, which is a critical parameter for protecting the LED from accidental reverse bias.

Output Phototransistor: The collector-emitter voltage (V_CE) rating is 30 V, while the emitter-collector voltage (V_EC) is 5 V. The maximum collector current is 20 mA, and the power dissipation limit is 100 mW. Adherence to these limits is essential for ensuring the longevity and stable operation of the phototransistor.

Environmental Limits: The device is rated for an operating temperature range of -25°C to +85°C. The storage temperature range is wider, from -40°C to +100°C. The lead soldering temperature is specified as 260°C for 5 seconds, measured 1.6mm from the case, which is crucial information for assembly processes.

2.2 Electrical and Optical Characteristics

These characteristics define the expected performance of the device under normal operating conditions at 25°C. They provide the key parameters for circuit design.

Input LED Characteristics: The typical forward voltage (V_F) is 1.2 V at a forward current (I_F) of 20 mA, with a maximum of 1.6 V. This parameter is vital for designing the current-limiting resistor for the LED driver circuit. The reverse current (I_R) is a maximum of 100 μA at a reverse voltage (V_R) of 5 V, indicating the LED's leakage in the off state.

Output Phototransistor Characteristics: The collector-emitter dark current (I_CEO) is a maximum of 100 nA at V_CE=10V, representing the output leakage current when the LED is off (no light). The breakdown voltages (BV_CEO and BV_ECO) confirm the maximum ratings.

Coupler (System) Characteristics: These parameters describe the combined performance of the LED and phototransistor. The on-state collector current (I_C(ON)) is guaranteed to be at least 0.6 mA when the LED is driven with I_F=20mA and V_CE=5V. This is the key output signal level when the slot is unobstructed. The collector-emitter saturation voltage (V_CE(SAT)) is a maximum of 0.4 V under the same conditions with I_C=0.2mA, indicating a good "on" state characteristic. The response times, with a typical rise time (T_r) of 3 μs and fall time (T_f) of 4 μs (under specific test conditions), define the device's switching speed capability.

3. Mechanical and Packaging Information

3.1 Outline Dimensions

The LTH-301-07P5 features a standard through-hole package. The detailed mechanical drawing is provided in the datasheet. All dimensions are specified in millimeters. The standard tolerance for unspecified dimensions is ±0.25 mm. Key dimensions include the overall length, width, and height of the housing, the slot width and depth (which defines the gap where the interrupting object passes), and the lead spacing and diameter. The component is designed for wave soldering or hand soldering processes.

Polarity Identification: The device has a specific pinout. Typically, the longer lead or a specific marking on the housing indicates the anode of the LED. It is critical to consult the dimensional drawing for the exact pin identification (e.g., pin 1 is often the LED anode, pin 2 is the LED cathode, pin 3 is the phototransistor emitter, and pin 4 is the collector) to ensure correct orientation during PCB assembly. Incorrect polarity will prevent the device from functioning.

4. Soldering and Assembly Guidelines

Proper handling during soldering is essential to prevent damage to the plastic housing and the internal semiconductor die.

General Precautions: The housing must not be dipped into the solder. No external stress should be applied to the lead frame while the product is at high temperature during soldering, as this can cause internal cracks or misalignment.

Hand/Lead Soldering: For manual soldering, the recommended maximum iron temperature is 350°C. The soldering time per lead should not exceed 3 seconds, and this should be performed only once per lead. The soldering point should be no closer than 2 mm from the base of the component housing to prevent heat damage.

Wave Soldering: For automated wave soldering, a specific profile is recommended. The pre-heat temperature should not exceed 100°C, with a pre-heat time up to 60 seconds. The solder wave temperature should be a maximum of 260°C, with a contact time not exceeding 5 seconds. The dipping position must be no lower than 2 mm from the base of the housing. Adhering to this profile prevents thermal shock and ensures reliable solder joints without compromising the integrity of the plastic package.

5. Storage Conditions and Cautions

To maintain solderability and prevent performance degradation, specific storage conditions must be observed.

The ideal storage environment is at a temperature below 30°C and relative humidity below 70%. Components should be assembled within 3 months of the delivery date. To extend storage life while the parts remain in their original moisture-sensitive packaging, they should be stored in a sealed container with appropriate desiccant or in a nitrogen-purged desiccator. However, storage should not exceed one year under these controlled conditions.

Once the original sealed package is opened, the components must be used within 3 months and should be kept in a controlled environment of <25°C and <60% relative humidity. Rapid transitions in ambient temperature, especially in high-humidity environments, must be avoided to prevent condensation, which can lead to oxidation of the component leads. If storage conditions do not meet the specified criteria, the solderability of the pins may be compromised. In such cases, a solderability assessment and potential re-sorting of components must be performed before use in production.

6. Application Suggestions

6.1 Typical Application Scenarios

The LTH-301-07P5 is versatile and finds use in numerous applications:

• Paper Detection in Printers/Copiers/Scanners: Detecting the presence of paper, paper jams, or the end of a paper roll.
• Position Sensing: Detecting the home position or limit of travel in moving mechanisms (e.g., printer carriages, robotic arms).
• Rotary Encoding: Used with a slotted wheel to measure speed or position of a rotating shaft.
• Object Counting: Counting items on a conveyor belt as they pass through the slot.
• Security Systems: As part of a beam-break sensor for intrusion detection.

6.2 Design Considerations

When designing a circuit with this photo interrupter, several factors must be considered:

• LED Drive Current: The recommended operating current is 20 mA. A series resistor must be calculated based on the supply voltage (V_CC) and the LED forward voltage (V_F) using Ohm's Law: R = (V_CC - V_F) / I_F. Using the typical V_F of 1.2V and a 5V supply, the resistor would be approximately (5V - 1.2V) / 0.02A = 190 Ohms. A standard 200 Ohm resistor would be suitable.
• Phototransistor Biasing: The phototransistor output can be used in a common-emitter configuration (emitter grounded, collector pulled up to V_CC via a load resistor, R_L) or as a switch. The value of R_L affects the output voltage swing and the switching speed. A smaller R_L provides faster response but a smaller output voltage change. The datasheet test condition uses R_L=100Ω.
• Signal Conditioning: The output is an analog current that varies with light intensity. For digital switching applications, a comparator or a Schmitt trigger circuit may be needed after the load resistor to provide a clean digital signal, especially if the interrupting object does not fully block the light beam.
• Ambient Light Immunity: As the device uses infrared light, it is somewhat immune to visible ambient light. However, strong sources of infrared light (e.g., sunlight, incandescent bulbs) can affect performance. Using a modulated LED drive signal and synchronous detection can greatly enhance immunity to ambient light.
• Mechanical Alignment: The interrupting object must reliably pass through the slot and fully interrupt the beam for consistent operation. The slot dimensions and the object's size and path must be carefully considered.

7. Technical Comparison and Differentiation

Photo interrupters like the LTH-301-07P5 compete with other sensing technologies such as mechanical micro-switches, Hall effect sensors, and reflective optical sensors.

vs. Mechanical Switches: The primary advantage is the complete absence of physical contact, leading to virtually infinite mechanical life, no contact bounce, silent operation, and higher reliability in dirty or dusty environments. The disadvantage can be a slightly higher cost and the need for an electronic drive circuit.

vs. Reflective Optical Sensors: Slotted photo interrupters offer higher positional accuracy and consistency because the emitter and detector are precisely aligned in a fixed geometry. They are less susceptible to variations in the reflectivity of the target object. Reflective sensors are better suited for detecting objects at a distance or where a physical slot is not feasible.

vs. Hall Effect Sensors: Hall sensors detect magnetic fields, not light interruption. They are used for sensing the position of magnets. The choice depends entirely on the application: detecting any opaque object (photo interrupter) vs. detecting a magnetic field (Hall sensor).

The LTH-301-07P5's specific differentiation lies in its balanced set of electrical characteristics (forward voltage, output current, speed), its robust mechanical package suitable for wave soldering, and its clearly defined storage and handling requirements, making it a reliable choice for volume manufacturing.

8. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the purpose of the "Peak Forward Current" rating for the LED?
A: This rating (1A at 300pps, 10μs) allows the LED to be pulsed with a much higher current than its continuous rating (50mA) for short durations. This can be used to achieve a brighter optical pulse, which can improve signal-to-noise ratio or allow for a lower duty cycle, reducing average power consumption and heat generation.

Q: The I_C(ON) is specified as a minimum of 0.6mA. What does this mean for my circuit design?
A: This is a guaranteed lower limit. Under the standard test conditions (I_F=20mA, V_CE=5V), the phototransistor will sink at least 0.6mA when the slot is clear. The actual current in your application may be higher. You must design your load resistor (R_L) and any following logic gates to recognize a voltage level corresponding to this minimum current. For example, with R_L=1kΩ, the output voltage would drop to at most V_CE = 5V - (0.6mA * 1kΩ) = 4.4V when the beam is unblocked.

Q: Why are the storage conditions so strict, especially after opening the bag?
A: The component leads are susceptible to oxidation when exposed to humid air. Oxidized leads have poor solderability, leading to weak or non-existent solder joints ("dewetting"). The moisture-sensitive packaging and strict storage rules are industry-standard practices (aligned with IPC/JEDEC standards) to ensure high assembly yield and long-term reliability.

Q: Can I use this sensor outdoors?
A: The operating temperature range is -25°C to +85°C, which covers many outdoor conditions. However, direct exposure to sunlight (a strong source of infrared radiation) can saturate the phototransistor, causing false triggering. The device is also not sealed against water or dust ingress. For outdoor use, it would require careful optical shielding from ambient light and environmental protection, or a different sensor technology might be more appropriate.

9. Operating Principle Introduction

The photo interrupter operates on a straightforward optoelectronic principle. It contains two main components housed opposite each other across a physical gap (the slot):

1. Infrared Emitter (LED): This is a semiconductor diode that emits infrared light (invisible to the human eye) when forward biased with an appropriate current (e.g., 20mA).
2. Phototransistor: This is a light-sensitive transistor. When photons from the infrared emitter strike its base region, they generate electron-hole pairs, which act as base current. This light-induced base current is amplified by the transistor's gain, resulting in a much larger collector current flowing from the collector to the emitter.

States of Operation:
- Unobstructed (Beam Present): The infrared light from the emitter falls directly on the phototransistor. The phototransistor turns on, allowing a significant collector current (I_C(ON)) to flow. In a common-emitter circuit with a pull-up resistor, the output voltage at the collector is pulled low (close to V_CE(SAT)).
- Obstructed (Beam Blocked): An opaque object placed in the slot blocks the infrared light. No light reaches the phototransistor base, so it turns off. Only a tiny leakage current (I_CEO, the dark current) flows. The output voltage at the collector rises to near the supply voltage (V_CC).

This transition between a high-output voltage (beam blocked) and a low-output voltage (beam clear) provides a clean digital signal for detection logic.

10. Development Trends

The field of optoelectronic sensors, including photo interrupters, continues to evolve. Objective trends observable in the industry include:

• Miniaturization: There is a constant drive towards smaller package sizes (e.g., surface-mount devices with smaller footprints and lower profiles) to enable more compact end products and higher density PCB assembly.
• Enhanced Performance: Improvements in semiconductor materials and packaging aim to provide higher sensitivity (allowing lower LED drive currents for reduced power consumption), faster response times for high-speed applications, and better temperature stability of parameters.
• Integration and Smart Features: Some modern photo interrupters integrate the driver circuitry for the LED and signal conditioning (amplifier, comparator, Schmitt trigger) for the phototransistor output into the same package. This simplifies external circuit design and can provide a direct digital logic-level output. Integration of multiple sensing elements is also a trend.
• Focus on Reliability and Manufacturing: Designs increasingly prioritize robustness for automated assembly processes like pick-and-place and reflow soldering. Materials are selected for better resistance to thermal stress and environmental factors.
• Application-Specific Variants: Development continues for sensors tailored to specific market needs, such as ultra-thin sensors for paper handling in portable devices, or sensors with very narrow slots for high-precision edge detection.

The LTH-301-07P5 represents a mature and reliable technology that meets the core requirements for a wide array of standard applications, while these broader trends shape the development of next-generation devices.