## Overview of the VIPER25HD The **VIPER25HD** is a high-performance, high-voltage converter belonging to the VIPerPlus family by STMicroelectronics. It is specifically designed for SMPS (Switched-Mode Power Supply) applications, integrating an 800 V avalanche-rugged power MOSFET with a PWM controller. --- ### Key Specifications | Parameter | Value / Range | | :--- | :--- | | **Drain-Source Voltage ($V_{DSS}$)** | 800 V | | **Switching Frequency ($F_{OSC}$)** | 115 kHz (High Frequency) | | **Maximum Drain Current ($I_{Dlim}$)** | 0.7 A | | **Supply Voltage ($V_{DD}$)** | 8.5 V to 23.5 V | | **Package** | SO16 Narrow | --- ### Integrated Functional Blocks The device combines several electronic sub-systems into a single chip to reduce component count and improve reliability: 1. **Power MOSFET:** An 800 V rugged power transistor that handles the high-voltage switching of the transformer primary. 2. **PWM Controller:** A current-mode controller that regulates the output voltage by modulating the pulse width. 3. **High Voltage Startup:** An internal high-voltage current source that allows the chip to start up directly from the rectified mains, eliminating the need for external startup resistors. 4. **Frequency Jittering:** The switching frequency is slightly modulated to spread the energy of the EMI (Electromagnetic Interference), making it easier to meet regulatory standards. --- ### Protection Features The VIPER25HD includes robust protection mechanisms to ensure the safety of the electronic circuit: * **Hysteresis Thermal Shutdown:** Automatically shuts down if the junction temperature exceeds 150°C to prevent silicon damage. * **Overload Protection (OLP):** Limits power if the output is shorted or heavily loaded. * **Overvoltage Protection (OVP):** Monitors the $V_{DD}$ pin to protect against feedback loop failures. * **Soft Start:** Gradually increases the current limit during startup to reduce stress on components. --- ### Typical Application Circuit The VIPER25HD is primarily used in **Flyback Converters**. Below is a conceptual representation of the pin functions: | Pin Name | Description | | :--- | :--- | | **DRAIN** | Connected to the primary winding of the transformer. | | **SOURCE** | Ground reference for the power MOSFET. | | **VDD** | Supply voltage for the internal control logic. | | **CONT** | Control pin for setting the overvoltage protection threshold. | | **FB** | Feedback input to regulate the output voltage via an optocoupler. | ---