## Overview of the VIPER20ASP The **VIPER20ASP** is a high-performance Off-Line Switched Mode Power Supply (SMPS) Primary IC. It belongs to the VIPer (Vertical Integrated Power) family developed by STMicroelectronics. This specific part integrates a dedicated current mode PWM controller with a high-voltage Power MOSFET on the same silicon chip. --- ### 1. Key Internal Components The VIPER20ASP is essentially a "system-on-chip" for power conversion. Its internal architecture consists of: | Component | Function | | :--- | :--- | | **Power MOSFET** | Handles high voltage (typically up to 700V) and switches current through the transformer. | | **PWM Controller** | Regulates the duty cycle based on feedback to maintain a constant output voltage. | | **Current Sense** | Monitors the drain current to provide protection and cycle-by-cycle current limiting. | | **Start-up High Voltage Source** | Internal circuitry that allows the IC to power itself directly from the rectified mains. | | **Protection Logic** | Includes Thermal Shutdown, Overcurrent Protection (OCP), and Undervoltage Lockout (UVLO). | --- ### 2. Technical Specifications Below are the typical electrical characteristics for the VIPER20ASP: | Parameter | Value / Range | | :--- | :--- | | **Drain-Source Voltage ($V_{DSS}$)** | 700V | | **Switching Frequency** | Up to 200 kHz (Adjustable) | | **Output Power** | ~20W (Wide range) / ~40W (Single 230V range) | | **Package Type** | PowerSO-10 (Surface Mount) | | **Supply Voltage ($V_{DD}$)** | 8V to 15V | --- ### 3. Pin Configuration (PowerSO-10) The VIPER20ASP uses the PowerSO-10 package, which is designed for efficient heat dissipation. 1. **Source:** Connected to the internal MOSFET source and circuit ground. 2. **Drain:** High voltage connection to the transformer primary winding. 3. **$V_{DD}$:** Supply voltage for the control logic. 4. **Feedback (FB):** Input for the error amplifier (usually via an optocoupler). 5. **Compensation (COMP):** Used for loop stability and frequency compensation. 6. **Oscillator (OSC):** An external RC network is connected here to set the switching frequency. --- ### 4. Application Circuit Diagram (Concept) In a typical Flyback converter setup, the VIPER20ASP is used as follows: ```text AC Input -> Rectifier Bridge -> Bulk Capacitor -> [VIPER20ASP + Transformer] -> Output Rectifier -> DC Output ^ | | feedback | +----------+ ``` --- ### 5. Benefits of Using VIPER20ASP * **Reduced Component Count:** Because the MOSFET and PWM controller are integrated, you need fewer external parts. * **Burst Mode Operation:** Provides high efficiency during "Stand-by" or light-load conditions. * **Robustness:** Integrated thermal and electrical protections make it very reliable against mains surges or short circuits. ---