The **PBY276** (often referred to simply as the **276**) is a high-sensitivity **Hall Effect Sensor Integrated Circuit (IC)**. It is primarily used in DC brushless fan motors and magnetic proximity switches. --- ## 1. Technical Overview The PBY276 combines several functions into a single four-pin package. It is designed to detect magnetic field polarity and switch output states to drive motor coils. ### Key Internal Components | Component | Function | | :--- | :--- | | **Hall Sensor Element** | Converts magnetic flux into a millivolt signal. | | **Amplifier** | Boosts the small Hall voltage to a usable level. | | **Schmitt Trigger** | Provides hysteresis to prevent "chattering" (rapid switching) near the threshold. | | **Complementary Outputs** | Two open-collector drivers (DO and DOB) that switch alternately. | --- ## 2. Technical Specifications Typical operating parameters for the PBY276 are as follows: | Parameter | Value | | :--- | :--- | | **Operating Voltage ($V_{CC}$)** | 3.5V to 20V | | **Output Current ($I_{out}$)** | 400mA (Continuous) | | **Operating Temperature** | -20°C to +85°C | | **Package Type** | SIP-4L (Four-pin single in-line) | | **Magnetic Sensitivity** | High (typically $\pm$ 50 Gauss) | --- ## 3. Pin Configuration The device usually features four pins, arranged as follows: 1. **Vcc**: Input power supply. 2. **DO**: Output 1 (Open Collector). 3. **DOB**: Output 2 (Complementary to DO). 4. **GND**: Ground. --- ## 4. Working Principle The PBY276 operates based on the **magnetic polarity** it senses: * **South Pole Detection:** If a South magnetic pole approaches the branded side of the IC, Output 1 (DO) turns **ON** (low voltage) and Output 2 (DOB) turns **OFF** (high impedance). * **North Pole Detection:** If a North magnetic pole approaches, DO turns **OFF** and DOB turns **ON**. * **Commutation:** In a brushless DC (BLDC) fan, this alternating switching allows the current to flow through different motor coils, creating a rotating magnetic field that spins the rotor. --- ## 5. Common Applications * **Dual-coil Brushless DC Fans:** The most common use case for cooling computers and power supplies. * **Rotational Speed Sensors:** Used to count RPM by detecting passing magnets. * **Proximity Switches:** Detecting the open/closed state of a lid or door. * **Non-contact Switches:** Replacing mechanical switches in harsh environments. --- ## 6. Typical Application Circuit In a standard fan circuit, the coils are connected between $V_{CC}$ and the two output pins (DO/DOB). A protection diode is often added to the $V_{CC}$ line to prevent damage from reverse voltage. ```text Vcc (+) | [Protection Diode] | +-----+-----+ | | | [Coil1][IC] [Coil2] | | | DO GND DOB ```