LTH-301-23P1 Photointerrupter Datasheet - Dimensions 7.62mm - Voltage 1.6V - Power 60mW - English Technical Document

1. Product Overview

The LTH-301-23P1 is a compact, through-hole mounted photointerrupter module. It functions as a non-contact optical switch, utilizing an infrared light-emitting diode (IR LED) paired with a phototransistor. The core principle involves the IR LED emitting light, which is detected by the phototransistor. When an object interrupts the light path between the emitter and detector, the phototransistor's output state changes, enabling precise position sensing, object detection, or limit switching without physical contact. Its primary advantages include fast switching speed, reliable non-contact operation, and a design suitable for direct PCB or dual-in-line socket mounting, making it ideal for applications in printers, copiers, vending machines, and industrial automation where durability and precision are required.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operating the device continuously at or near these limits is not recommended.

• IR Diode Continuous Forward Current (I_F): 50 mA. This is the maximum steady-state current that can be passed through the infrared LED.
• IR Diode Reverse Voltage (V_R): 5 V. Exceeding this reverse bias voltage across the LED can cause breakdown.
• Transistor Collector Current (I_C): 20 mA. The maximum continuous current the phototransistor's collector can handle.
• Transistor Power Dissipation (P_D): 75 mW at 25°C, derating linearly at 1.33 mW/°C above 25°C. This limits the heat generated in the phototransistor.
• IR Diode Peak Forward Current: 1 A (pulse width = 10 µs, 300 pps). Allows for brief, high-current pulses for applications requiring high instantaneous optical output.
• Diode Power Dissipation (P_D): 60 mW at 25°C, also derated at 1.33 mW/°C. This governs the thermal limits of the IR LED.
• Phototransistor Collector-Emitter Voltage (V_CEO): 30 V. The maximum voltage that can be applied between the collector and emitter when the transistor is off.
• Phototransistor Emitter-Collector Voltage (V_ECO): 5 V. The maximum reverse voltage across the collector-emitter junction.
• Operating Temperature Range: -25°C to +85°C. The ambient temperature range for reliable device operation.
• Storage Temperature Range: -55°C to +100°C. The temperature range for non-operational storage.
• Lead Soldering Temperature: 260°C for 5 seconds at 1.6mm from the case. Defines the reflow or hand-soldering profile to prevent package damage.

2.2 Electrical & Optical Characteristics

These parameters are measured under standard test conditions (T_A = 25°C) and define the device's typical performance.

2.2.1 Input LED Characteristics

• Forward Voltage (V_F): Typically 1.2V to 1.6V at I_F = 20 mA. This is the voltage drop across the IR LED when driven with the standard test current. A current-limiting resistor must be calculated based on this value and the supply voltage.
• Reverse Current (I_R): Maximum 100 µA at V_R = 5V. This is the small leakage current when the LED is reverse-biased.

2.2.2 Output Phototransistor Characteristics

• Collector-Emitter Breakdown Voltage (V_(BR)CEO): Minimum 30V at I_C = 1mA. This high breakdown voltage allows the use of higher supply voltages in the collector circuit.
• Emitter-Collector Breakdown Voltage (V_(BR)ECO): Minimum 5V at I_E = 100µA.
• Collector-Emitter Dark Current (I_CEO): Maximum 100 nA at V_CE = 10V. This is the leakage current when the phototransistor is in complete darkness (no IR light). A low value is critical for good signal-to-noise ratio in sensing applications.

2.2.3 Coupler (Complete Device) Characteristics

• Collector-Emitter Saturation Voltage (V_CE(SAT)): Maximum 0.4V at I_C = 0.2mA and I_F = 20mA. This is the voltage across the phototransistor when it is fully "on" (saturated). A lower value is better as it minimizes power loss.
• On-State Collector Current (I_C(ON)): Minimum 0.4 mA at V_CE = 5V and I_F = 20mA. This specifies the minimum photocurrent generated when the IR LED is driven and the light path is unobstructed. This parameter directly relates to the device's sensitivity.
• Rise Time (T_r): Typical 25 µs under test conditions (I_C=2mA, R_L=1kΩ, V_CE=5V). This is the time for the phototransistor output to transition from 10% to 90% of its final value when the IR LED is turned on.
• Fall Time (T_f): Typical 26 µs under the same conditions. This is the transition time when the IR LED is turned off. These switching times define the maximum frequency at which the device can reliably operate.

3. Mechanical & Package Information

3.1 Package Dimensions

The device is housed in a standard 4-pin dual-in-line package. Key dimensional notes from the datasheet include:

• All dimensions are provided in millimeters, with inches in parentheses.
• The standard tolerance is ±0.25mm (±0.010") unless a specific feature note states otherwise.
• The body width is approximately 7.62mm, and the pin spacing follows a standard 0.1-inch (2.54mm) grid pattern for through-hole PCB mounting.

The package is designed for wave soldering or manual soldering processes. The dimensional drawing in the datasheet provides critical measurements for PCB footprint design, including lead diameter, pin spacing (between rows and columns), body length and width, and the slot gap width which defines the sensing aperture.

3.2 Pinout and Polarity Identification

The device has four pins. Typically, two pins are for the anode and cathode of the IR LED, and the other two are for the collector and emitter of the phototransistor. The datasheet drawing indicates pin 1, which is crucial for correct orientation. The IR LED is an anode-driven device, and the phototransistor is an NPN type where the collector should be connected to a positive supply via a load resistor, and the emitter to ground. Incorrect polarity connection to the LED will prevent it from emitting light, and incorrect connection to the phototransistor will result in no output signal.

4. Soldering & Assembly Guidelines

The datasheet specifies a critical soldering parameter: leads can be subjected to a temperature of 260°C for a maximum of 5 seconds, measured at a distance of 1.6mm (0.063") from the plastic case. This guideline is essential to prevent thermal damage to the internal semiconductor die and the plastic package material during wave soldering or hand-soldering operations. For reflow soldering, a standard profile with a peak temperature not exceeding 260°C and time above liquidus (TAL) controlled should be used. It is advisable to follow JEDEC or IPC standards for through-hole component soldering.

5. Application Suggestions

5.1 Typical Application Circuits

The most common circuit configuration involves driving the IR LED with a constant current source or, more simply, a voltage source in series with a current-limiting resistor (R_limit). R_limit = (V_CC - V_F) / I_F. For a 5V supply and a desired I_F of 20mA, with V_F = 1.4V, R_limit = (5 - 1.4) / 0.02 = 180 Ω. The phototransistor output is typically connected as a switch: the collector is connected to V_CC via a pull-up resistor (R_load), and the emitter is connected to ground. The output signal is taken from the collector node. When light falls on the transistor, it turns on, pulling the collector voltage low (near V_CE(SAT)). When the light path is blocked, the transistor turns off, and the collector voltage is pulled high to V_CC by R_load. The value of R_load affects switching speed and current consumption; a smaller resistor gives faster switching but higher power dissipation in the 'on' state.

5.2 Design Considerations

• Ambient Light Immunity: Since the device uses infrared light, it is somewhat immune to visible ambient light. However, strong sources of IR radiation (e.g., sunlight, incandescent bulbs) can cause false triggering. Using a modulated IR signal and synchronous detection can greatly improve immunity.
• Alignment: Precimechanical alignment between the emitter and detector slots is crucial for maximum signal strength. The PCB footprint and mounting should ensure this alignment.
• Object Characteristics: The object interrupting the beam should be opaque to the IR wavelength used. Reflective or translucent materials may not reliably trigger the sensor.
• Speed Requirements: The rise and fall times (~25 µs) limit the maximum switching frequency to roughly 1/(Tr+Tf) ≈ 20 kHz for a square wave, though practical limits are lower to ensure full transition.

6. Performance Curve Analysis

The datasheet references a section for "Typical Electrical / Optical Characteristics Curves." These graphs, typically included in such documents, provide visual representations of how key parameters vary with conditions. Expected curves include:

• Forward Current vs. Forward Voltage (I_F-V_F): Shows the exponential relationship for the IR LED, helping to determine V_F at currents other than the test condition.
• Collector Current vs. Collector-Emitter Voltage (I_C-V_CE): Family of curves for the phototransistor with incident light intensity (or LED drive current) as a parameter, showing the saturation and active regions.
• Current Transfer Ratio (CTR) vs. Forward Current: CTR = (I_C / I_F) * 100%. This graph shows the efficiency of the optical coupling, which typically decreases at very high I_F.
• On-State Collector Current vs. Temperature (I_C(ON)-T_A): Illustrates how the phototransistor's sensitivity changes with ambient temperature, usually showing a decrease at higher temperatures.
• Dark Current vs. Temperature (I_CEO-T_A): Shows the exponential increase in leakage current with temperature, which is critical for high-temperature operation.

Analyzing these curves allows designers to optimize operating points, understand performance trade-offs across temperature, and predict behavior under non-standard conditions.

7. Technical Comparison & Differentiation

Compared to mechanical micro-switches, the LTH-301-23P1 offers distinct advantages: no contact bounce, much longer operational life (millions vs. thousands of cycles), immunity to contamination from dust or oils (as it is a sealed package), and faster switching speed. Compared to reflective optical sensors, transmissive photointerrupters like this one provide more consistent and reliable detection as they are less sensitive to the color or reflectivity of the target object; they simply detect the presence or absence of an object in the slot. The key differentiator for this specific part is its balance of standard through-hole packaging, robust electrical ratings (30V V_CEO, 50mA I_F), and specified switching speed, making it a versatile general-purpose choice.

8. Frequently Asked Questions (FAQ)

Q: What is the typical sensing distance or gap width?
A: The sensing "distance" is effectively the width of the slot in the package. Objects must pass through this physical gap to interrupt the beam. The datasheet dimensional drawing provides the exact slot width.

Q: Can I drive the IR LED directly from a microcontroller pin?
A: Possibly, but you must check the pin's current sourcing capability. A typical MCU pin can source 20-25mA, which matches the test condition. However, you MUST include a series current-limiting resistor as calculated in the application notes. Driving the LED without a resistor will likely destroy both the LED and the MCU pin.

Q: How do I interface the phototransistor output to a microcontroller?
A: The simplest method is to use the phototransistor as a digital input. Connect the collector to the MCU's digital I/O pin (which typically has an internal pull-up resistor that can be enabled) and also to V_CC via an external pull-up resistor (e.g., 10kΩ). The emitter connects to ground. When the beam is unbroken, the transistor is on, pulling the pin LOW. When broken, the pin is pulled HIGH. Ensure the MCU's input voltage levels are compatible with the V_CC used.

Q: What affects the switching speed?
A> The intrinsic rise/fall times of the phototransistor (~25µs) are the primary limit. However, circuit factors can slow it down further. A large load resistor (R_L) increases the RC time constant for charging/discharging any parasitic capacitance, slowing the rise time. Similarly, driving the IR LED with excessive current can cause slower turn-off due to carrier storage effects. For maximum speed, use the recommended I_F and a moderately small R_L.

9. Operational Principle

A photointerrupter is a transmissive optoelectronic device. It contains two separate components in a single package: an infrared light source (an IR LED) and a light detector (a phototransistor), facing each other across a small air gap or slot. The IR LED is forward-biased with a suitable current, causing it to emit infrared photons. These photons travel across the gap and strike the base region of the NPN phototransistor. The photon energy generates electron-hole pairs in the base, effectively creating a base current. This photogenerated base current is amplified by the transistor's gain, resulting in a much larger collector current that can flow from the collector to the emitter, turning the transistor "on." When an opaque object is inserted into the slot, it blocks the light path. The photogeneration of base current stops, the transistor ceases to be biased on, and the collector current drops to a very low value (the dark current), turning the transistor "off." This on/off action provides a clean digital signal corresponding to the presence or absence of an object.

10. Packaging and Ordering Information

The part number is LTH-301-23P1. The datasheet does not specify bulk packaging details (e.g., tape and reel, tube quantities). For production, one should consult the manufacturer's or distributor's packaging specifications. The "Spec No." DS-55-96-0025 and document code BNS-OD-C131/A4 are internal references for the datasheet itself. The effective date of this document revision is 08/03/2000.