It appears you are referring to the **LED APFK** (Active Power Factor Correction) circuitry, which is a critical electronic subsystem in modern LED drivers and power supplies. The primary goal of an APFK circuit is to ensure that the current drawn by the LED driver is in phase with the AC line voltage, reducing harmonic distortion and improving energy efficiency. --- ## 1. Core Electronic Components of an APFK An Active Power Factor Correction circuit is essentially a specialized **Boost Converter**. Below are the primary components involved: | Component | Function | | :--- | :--- | | **Bridge Rectifier** | Converts incoming AC voltage to pulsating DC voltage. | | **PFC Controller IC** | The "brain" that monitors input voltage and output current to adjust switching timing. | | **Boost Inductor** | Stores energy in a magnetic field when the switch is ON and releases it when OFF. | | **Power MOSFET** | Acts as a high-speed electronic switch controlled by the PFC IC. | | **Ultrafast Recovery Diode** | Prevents the storage capacitor from discharging back into the inductor. | | **Bulk Capacitor** | Smooths the high-voltage DC output (usually around 400V) for the LED driver stage. | --- ## 2. Circuit Architecture The typical layout of a LED driver with APFK follows this signal path: 1. **EMI Filter:** Removes high-frequency noise from the AC line. 2. **Rectification:** The AC is turned into DC. 3. **Boost Stage (The APFK):** * The **PFC IC** senses the shape of the rectified input voltage. * It triggers the **MOSFET** to pulse at high frequencies (kHz). * This forces the input current to follow the sinusoidal shape of the input voltage. 4. **DC-DC Stage:** A secondary stage (like a Flyback or Buck converter) steps down the 400V DC to the specific voltage/current required by the LEDs. --- ## 3. Why APFK is Used in LEDs Electronic standards (such as EN61000-3-2) require high-power LED lighting to have a Power Factor (PF) close to **1.0**. ### Comparison Table: Passive vs. Active PFC | Feature | Passive PFC | Active PFC (APFK) | | :--- | :--- | :--- | | **Efficiency** | Lower (~70-80%) | Higher (>90%) | | **Power Factor** | 0.7 - 0.8 | 0.95 - 0.99 | | **Weight/Size** | Heavy/Bulky (Uses large inductors) | Small/Light (Uses ICs and MOSFETs) | | **Voltage Range** | Fixed input (e.g., 110V only) | Universal Input (90V - 265V AC) | --- ### Example PFC Controller Logic (Pseudocode Concept) While these are hardware ICs, the logic follows a specific control loop: ```c // Simplified logic within a PFC Controller IC void loop() { float V_in = read_rectified_voltage(); float I_in = read_current_draw(); // Adjust PWM to match Current Waveform to Voltage Waveform if (I_in < V_in_target) { increase_mosfet_duty_cycle(); } else { decrease_mosfet_duty_cycle(); } } ```