## Overview of the VIPER38HD The **VIPER38HD** is a high-performance, high-voltage converter belonging to the VIPerPlus family by STMicroelectronics. It is specifically designed for offline Switch Mode Power Supplies (SMPS). It integrates an 800 V avalanche-rugged power MOSFET with a Pulse Width Modulation (PWM) controller. --- ### Key Technical Specifications | Feature | Specification | | :--- | :--- | | **Drain-Source Voltage ($V_{DS}$)** | 800 V | | **Max Output Power** | Up to 15W (Wide Range) / 20W (European Range) | | **Switching Frequency** | 115 kHz (Fixed) | | **RDS(on)** | 4.5 $\Omega$ (Typical) | | **Supply Voltage ($V_{CC}$)** | 11.5 V to 23.5 V | --- ### Core Electronic Components & Internal Blocks The VIPER38HD consists of several critical internal stages that manage power conversion and protection: 1. **Power MOSFET:** The integrated 800 V power transistor is the primary switching element. Its high breakdown voltage provides a significant safety margin against lightning strikes or grid fluctuations. 2. **PWM Controller:** This block controls the duty cycle of the MOSFET. It uses **Current Mode Control**, which simplifies loop compensation and provides inherent pulse-by-pulse current limiting. 3. **High Voltage Startup:** The IC features an internal high-voltage current source. This allows the device to start up directly from the rectified mains voltage, eliminating the need for external "bleeder" resistors and improving standby efficiency. 4. **Frequency Jittering:** The internal oscillator incorporates a "jitter" function. This spreads the energy of the switching frequency over a wider band, significantly reducing Electro-Magnetic Interference (EMI). --- ### Main Features and Protections The device is "Hardened" (indicated by the **HD** suffix) for robust performance in industrial environments. * **Soft-Start:** Gradually increases the peak drain current during startup to prevent component stress and transformer saturation. * **Auto-Restart:** If a fault is detected (like a short circuit), the device attempts to restart automatically once the fault is removed. * **Protection Suite:** * **Overvoltage Protection (OVP):** Protects against feedback loop failures. * **Hysteretic Thermal Shutdown:** Shuts the device down if the junction temperature exceeds $150^\circ C$. * **Overload Protection (OLP):** Limits the power delivered to the load. --- ### Typical Application Circuit (Schematic View) ```mermaid graph LR AC_Input --> Rectifier_Bridge Rectifier_Bridge --> Bulk_Capacitor Bulk_Capacitor --> Transformer_Primary Transformer_Primary --> VIPER38HD_Drain VIPER38HD_Source --> GND Transformer_Auxiliary --> VIPER38HD_VCC Transformer_Secondary --> Output_DC ```