Photointerrupter LTH-306-01 Datasheet - English Technical Document

1. Product Overview

The LTH-306-01 is a compact, non-contact optical switch designed for reliable object detection and position sensing. Its core function is based on an infrared (IR) light-emitting diode (LED) paired with a phototransistor, housed in a single package. When an object passes through the gap between the emitter and detector, it interrupts the IR light beam, causing a change in the phototransistor's output state. This principle enables precise, wear-free switching without physical contact.

The device is engineered for direct mounting onto printed circuit boards (PCBs) or into standard dual-in-line sockets, offering significant design flexibility. Its primary advantages include fast switching speed, which is critical for high-speed counting and timing applications, and its non-contact nature, which eliminates mechanical wear and ensures long-term reliability. Typical target markets include industrial automation, consumer electronics (e.g., printers, copiers), security systems, and vending machines where object detection, paper jam sensing, or slot sensing is required.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under these conditions is not guaranteed. Key limits include:

• IR Diode Continuous Forward Current (I_F): 60 mA. This is the maximum DC current that can be continuously applied to the LED.
• IR Diode Peak Forward Current: 1 A for a pulse width of 10 μs at 300 pulses per second. This allows for brief, high-intensity pulses for enhanced signal detection.
• Phototransistor Collector-Emitter Voltage (V_CEO): 30 V. The maximum voltage that can be applied across the collector and emitter pins.
• Operating Temperature Range: -25°C to +85°C. Specifies the ambient temperature range for reliable operation.
• Lead Soldering Temperature: 260°C for 5 seconds at a distance of 1.6mm from the case. This is crucial for PCB assembly processes.

2.2 Electrical & Optical Characteristics

These parameters are specified at an ambient temperature (T_A) of 25°C and define the device's typical performance under normal operating conditions.

2.2.1 Input (IR LED) Characteristics

• Forward Voltage (V_F): Typically 1.2V to 1.6V at a forward current (I_F) of 20 mA. This is used to calculate the current-limiting resistor value for the LED driver circuit.
• Reverse Current (I_R): Maximum 100 μA at a reverse voltage (V_R) of 5V. This indicates the LED's leakage current when reverse-biased.

2.2.2 Output (Phototransistor) Characteristics

• Collector-Emitter Breakdown Voltage (V_(BR)CEO): Minimum 30V. Ensures the transistor can withstand the specified collector-emitter voltage.
• Collector-Emitter Dark Current (I_CEO): Maximum 100 nA at V_CE=10V. This is the leakage current when the LED is off (no light), which affects the "off-state" signal level.

2.2.3 Coupler (Combined) Characteristics

• On-State Collector Current (I_C(ON)): Minimum 5.0 mA at V_CE=5V and I_F=20mA. This is the phototransistor's output current when the LED is fully illuminated and unobstructed, indicating its sensitivity.
• Collector-Emitter Saturation Voltage (V_CE(SAT)): Maximum 0.4V at I_C=2.5mA and I_F=20mA. A low saturation voltage is desirable when the phototransistor is used as a switch in saturation mode, minimizing voltage drop.
• Response Time: Rise time (t_r) is typically 3-15 μs, and fall time (t_f) is typically 4-20 μs under specified test conditions (V_CE=5V, I_C=2mA, R_L=100Ω). These parameters define the device's switching speed and bandwidth, critical for detecting fast-moving objects.

3. Performance Curve Analysis

The datasheet references typical electrical/optical characteristic curves. While the specific graphs are not provided in the text, standard curves for such devices typically include:

• Forward Current vs. Forward Voltage (I_F-V_F) for the IR LED: Shows the non-linear relationship, helping to determine the operating point.
• Collector Current vs. Collector-Emitter Voltage (I_C-V_CE) for the Phototransistor: At different levels of irradiance (LED current), this shows the output transistor's behavior, similar to a bipolar transistor's output characteristics.
• Current Transfer Ratio (CTR) vs. Forward Current: CTR is the ratio of phototransistor collector current (I_C) to LED forward current (I_F). This curve shows how efficiency changes with drive current.
• Temperature Dependence of Dark Current (I_CEO) and On-State Current (I_C(ON)): Illustrates how performance degrades or varies with changes in ambient temperature, which is vital for designing stable systems across the specified operating range.

These curves are essential for designers to optimize the operating point, ensure signal integrity over temperature, and understand the device's limitations.

4. Mechanical & Package Information

The LTH-306-01 is designed for PCB or socket mounting. The package dimensions are provided in the datasheet with all measurements in millimeters (and inches). Key mechanical notes include:

• A standard tolerance of ±0.25mm (±0.010") applies unless otherwise specified on the dimensioned drawing.
• The package features a molded body with a precise gap between the IR emitter and phototransistor. The exact dimensions of this gap, the overall height, width, and length, and the lead spacing are critical for mechanical integration into the end product.
• The leads are typically made of a solderable material and are formed for through-hole mounting.

Polarity identification is crucial. The device will have markings (such as a dot, notch, or different lead lengths) to identify the anode and cathode of the IR LED and the collector and emitter of the phototransistor. Incorrect polarity connection can damage the components.

5. Soldering & Assembly Guidelines

The absolute maximum ratings specify a lead soldering temperature of 260°C for a maximum duration of 5 seconds, measured 1.6mm (0.063") from the plastic case. This is a critical parameter for wave soldering or hand-soldering processes.

Recommendations:

6. Application Suggestions

6.1 Typical Application Circuits

A basic application circuit involves:

1. LED Driver Circuit: A current-limiting resistor in series with the IR LED. The resistor value (R_limit) is calculated as (Supply Voltage - V_F) / I_F. For a 5V supply and I_F=20mA, with V_F~1.4V, R_limit ≈ (5-1.4)/0.02 = 180Ω.
2. Phototransistor Output Circuit: The phototransistor can be used in two common configurations:
   • Switch Mode (Saturation): Connect a pull-up resistor from the collector to a positive supply (e.g., 5V). The emitter is connected to ground. When light hits the transistor, it turns on hard (saturates), pulling the collector voltage low (close to V_CE(SAT)). When light is blocked, the transistor turns off, and the collector voltage is pulled high by the resistor. The output is a digital signal.
   • Linear Mode: Use the phototransistor in a common-emitter amplifier configuration with a collector resistor. The output voltage varies linearly with the intensity of received light, useful for analog sensing.

6.2 Design Considerations

• Ambient Light Immunity: The device uses modulated IR light, but strong ambient IR sources (sunlight, incandescent bulbs) can cause false triggering. Using a pulsed LED drive and synchronous detection, or adding an optical filter, can improve immunity.
• Object Characteristics: The detection reliability depends on the object's opacity to the IR wavelength. Very thin or translucent materials may not fully interrupt the beam.
• Alignment: Precise mechanical alignment of the object path with the sensor gap is necessary for consistent operation.
• Speed: Ensure the object's speed and the system's required response time are compatible with the device's rise/fall times (microseconds range).
• Electrical Noise: In noisy environments, keep signal traces short, use bypass capacitors near the device, and consider shielding.

7. Technical Comparison & Differentiation

Compared to mechanical micro-switches, the LTH-306-01 offers clear advantages: no contact bounce, no mechanical wear, faster switching speed, and higher reliability over millions of cycles. Compared to other optical sensors like reflective sensors, transmissive photointerrupters (slotted couplers) are generally more immune to variations in object surface reflectivity and color, providing a more consistent on/off signal based purely on beam interruption.

Its key differentiators within the photointerrupter category would be its specific package size (enabling compact designs), its electrical characteristics (sensitivity defined by I_C(ON), speed defined by t_r/t_f), and its robust specifications for soldering and operating temperature.

8. Frequently Asked Questions (FAQs)

Q: What is the typical lifetime of this device?
A: As a solid-state device with no moving parts, its lifetime is primarily determined by the LED's gradual output degradation. When operated within specifications, it typically far exceeds the lifespan of mechanical switches, often rated for hundreds of thousands to millions of operations.

Q: Can I drive the LED with a voltage source directly?
A: No. An LED must be driven with a current-limited source. Connecting it directly to a voltage source exceeding its forward voltage will cause excessive current flow, potentially destroying it. Always use a series current-limiting resistor or a constant current driver.

Q: How do I interpret the "On-State Collector Current" (I_C(ON)) minimum value?
A: This is a guaranteed minimum output current under the specified test conditions (V_CE=5V, I_F=20mA). In your design, you should ensure that your circuit (e.g., the value of your pull-up resistor) can work reliably with this minimum current to produce a valid logic low voltage when the beam is unblocked.

Q: The response time is in microseconds. Is this fast enough for my application?
A: For most object counting, position sensing, and paper detection applications, microsecond response is more than adequate. For example, to detect an object moving at 1 m/s through a 1mm gap, the interruption time is 1ms (1000 μs), which is much longer than the device's switching time. For extremely high-speed applications, verify the required timing.

9. Practical Use Case

Scenario: Paper Jam Detection in a Printer
The LTH-306-01 can be placed along the paper path. A paper sheet passing through the gap allows the IR beam to reach the phototransistor, keeping its output in one state (e.g., low). If a jam occurs, the paper stops in the gap, blocking the beam and changing the output state (e.g., high). This signal is fed to the printer's microcontroller, which can then halt operation and alert the user. The non-contact sensing ensures no wear on the paper or sensor, and the fast response time allows detection even if paper is moving quickly.

10. Operating Principle

The LTH-306-01 is a transmissive optical sensor. It contains two main components in opposing arms of a U-shaped package: an infrared light-emitting diode (IR LED) and a silicon NPN phototransistor. The IR LED emits invisible infrared light when forward-biased with an appropriate current. The phototransistor is designed to be sensitive to this specific IR wavelength. When no object is present in the gap between them, the IR light shines directly onto the base region of the phototransistor. This incident light generates electron-hole pairs, which act as base current, turning the transistor on and allowing a significant collector current (I_C) to flow. When an opaque object enters the gap, it blocks the light path. The phototransistor receives no (or greatly reduced) light, the effective base current drops to nearly zero, and the transistor turns off, reducing the collector current to a very low leakage level (I_CEO). This change in output current/voltage is detected by external circuitry to register an "object present" event.

11. Technology Trends

The field of optoelectronic components like photointerrupters continues to evolve. General trends observable in the industry include:

• Miniaturization: Development of even smaller package footprints and lower profiles to fit into increasingly compact consumer and industrial devices.
• Enhanced Integration: Incorporating additional circuitry on-chip, such as Schmitt triggers for hysteresis, built-in current-limiting resistors, or even digital interfaces (I2C), simplifying external design.
• Improved Performance: Higher sensitivity (allowing lower LED drive currents for power savings), faster response times for high-speed automation, and better temperature stability.
• Focus on Power Efficiency: Designs that enable pulsed operation with very low duty cycles to minimize average power consumption, crucial for battery-powered applications.
• Robustness: Improved resistance to environmental factors like dust, humidity, and mechanical shock.

These trends aim to make optical sensing solutions more reliable, easier to implement, and suitable for a broader range of applications.