## Overview of the VIPER26 The **VIPER26** is a high-performance, high-voltage offline converter produced by STMicroelectronics. It belongs to the *ViperPlus* family and integrates an 800V avalanche-rugged power MOSFET with a Pulse Width Modulation (PWM) controller. It is specifically designed for SMPS (Switched-Mode Power Supplies) in home appliances and industrial equipment. --- ### 1. Key Internal Components The VIPER26 is an Integrated Circuit (IC) that combines several electronic functions into a single package: | Component | Function | | :--- | :--- | | **Power MOSFET** | An 800V rated N-channel MOSFET that handles high voltage switching. | | **PWM Controller** | Manages the duty cycle of the MOSFET to maintain a stable output voltage. | | **High Voltage Startup** | Allows the device to start directly from the rectified mains without an external resistor. | | **SenseFET** | A specialized structure to measure the drain current accurately for protection. | --- ### 2. Technical Specifications | Parameter | Value / Range | | :--- | :--- | | **Drain-Source Voltage ($V_{DSS}$)** | 800 V (minimum) | | **Switching Frequency** | Fixed at 60 kHz (L version) or 115 kHz (H version) | | **Supply Voltage ($V_{CC}$)** | 11.5 V to 23.5 V | | **Current Limit ($I_{DLIM}$)** | 500 mA to 700 mA (depending on version) | | **Typical Output Power** | Up to 20W (Wide range input) | --- ### 3. Pin Configuration (SO16 or DIP-7) The VIPER26 typically utilizes the following pins to interface with external electronic parts: 1. **GND:** Ground and source of the internal MOSFET. 2. **VCC:** Supply voltage for the internal control logic. 3. **CONT:** Control pin to adjust the current limit or set the switching frequency. 4. **FB:** Feedback pin used to regulate the output voltage via an optocoupler. 5. **DRAIN:** The drain of the internal high-voltage MOSFET, connected to the primary winding of the transformer. --- ### 4. Embedded Protection Features The VIPER26 includes several safety mechanisms to prevent the electronic circuit from failing: * **Hysteretic Over-Temperature Protection:** Shuts down the IC if it gets too hot. * **Overload Protection (OLP):** Detects if the output is drawing too much power. * **Overvoltage Protection (OVP):** Monitors the $V_{CC}$ to ensure it doesn't exceed safe limits. * **Frequency Jittering:** Slightly varies the switching frequency to reduce Electromagnetic Interference (EMI), simplifying the input filter requirements. --- ### 5. Application Circuit Example To build a power supply using the VIPER26, you generally need these external parts: * **Input Bridge Rectifier:** To convert AC to DC. * **Bulk Capacitor:** To smooth the DC voltage. * **Transformer:** To step down the voltage and provide isolation. * **Snubber Circuit (RCD):** To protect the DRAIN pin from voltage spikes. * **Optocoupler & TL431:** For isolated voltage feedback.