## Technical Overview of the OP552B The **OP552B** is a high-sensitivity NPN silicon phototransistor manufactured by OPTEK (TT Electronics). It is designed to detect infrared radiation and convert it into an electrical signal. It is commonly paired with an Infrared LED (IRED) to create sensing circuits. --- ### 1. Key Technical Specifications The following table summarizes the primary electrical and physical characteristics of the OP552B: | Parameter | Specification | Description | | :--- | :--- | :--- | | **Component Type** | Phototransistor | NPN Silicon | | **Package Type** | T-1 (3mm) | Clear Plastic Radial Package | | **Wavelength Sensitivity** | 800nm to 1100nm | Optimized for Near-Infrared | | **Collector Current ($I_{C(ON)}$)** | 2.5 mA (min) | Current flow when light is detected | | **Collector-Emitter Voltage ($V_{CEO}$)** | 30 V | Maximum voltage across collector-emitter | | **Dark Current ($I_{CEO}$)** | 100 nA (max) | Leakage current without light source | | **Acceptance Angle** | 20° | Half-power beam angle | --- ### 2. Physical Design and Pinout The OP552B uses a standard 3mm (T-1) dome package. This dome acts as a lens, focusing incoming infrared light onto the silicon die to increase sensitivity. * **Collector (C):** Usually the shorter lead (connected to the positive supply in common-emitter mode). * **Emitter (E):** Usually the longer lead (connected to ground or a load resistor). --- ### 3. Working Principle The OP552B operates based on the **Photoelectric Effect**: 1. **Detection:** Photons from an IR source strike the base region of the NPN transistor. 2. **Current Generation:** These photons create electron-hole pairs, which act as a base current ($I_B$). 3. **Amplification:** The transistor multiplies this light-induced current by its gain ($h_{FE}$), allowing a larger collector current ($I_C$) to flow. 4. **Output:** By placing a resistor in series with the collector or emitter, the changing current is converted into a measurable voltage signal. --- ### 4. Implementation Example Below is a basic wiring diagram logic for using the OP552B with a microcontroller (like an Arduino). ```cpp // Basic logic for detecting an object with OP552B int sensorPin = A0; // Collector connected to A0 and a Pull-up resistor int val = 0; void setup() { Serial.begin(9600); } void loop() { val = analogRead(sensorPin); // Higher value means less light (blocked) if (val > 500) { Serial.println("Object Detected!"); } delay(100); } ``` --- ### 5. Common Applications * **Non-contact Sensing:** Detecting the presence or absence of an object. * **Optical Encoders:** Measuring the speed or position of a rotating shaft. * **Safety Curtains:** Creating an invisible light barrier for industrial safety. * **Data Communication:** Low-speed wireless infrared data transfer.