## Overview of the VIPER27L The **VIPER27L** is a high-performance, off-line converter part of the VIPerPlus family. It integrates an 800 V avalanche-rugged power MOSFET with PWM (Pulse Width Modulation) control logic in a single package. It is primarily designed for Switch Mode Power Supplies (SMPS). --- ### 1. Key Internal Components | Component | Description | | :--- | :--- | | **800 V Power MOSFET** | High voltage power switch that handles the primary current. | | **PWM Controller** | Regulates the output by adjusting the duty cycle based on feedback. | | **High Voltage Startup** | Allows the chip to start directly from the rectified mains voltage. | | **Oscillator** | Sets the switching frequency (typically 60 kHz for the 'L' version). | | **Error Amplifier** | Compares feedback voltage to an internal reference for regulation. | --- ### 2. Technical Specifications | Parameter | Value / Characteristic | | :--- | :--- | | **Drain-Source Voltage ($V_{DSS}$)** | 800 V (Maximum) | | **Switching Frequency** | 60 kHz (Fixed) | | **Typical Power Output** | 12W - 20W (depending on input voltage range) | | **Package Types** | DIP-7, SDIP10, or SO16 | | **Standby Power** | < 30 mW at 230 $V_{AC}$ (Low consumption) | --- ### 3. Integrated Protection Features The VIPER27L is "rugged" because it includes several built-in protection mechanisms: * **Overload Protection (OLP):** Shuts down the device if the output current exceeds a safe limit. * **Hysteretic Thermal Shutdown:** Disables switching if the junction temperature exceeds $150^\circ C$. * **Overvoltage Protection (OVP):** Protects the secondary circuit from voltage spikes. * **Soft-Start:** Gradually increases the current limit during startup to reduce stress on components. * **Brown-out Protection:** Monitors the input line voltage to prevent operation under insufficient voltage conditions. --- ### 4. Basic Application Circuit A typical circuit using the VIPER27L involves the following external parts: 1. **Input Bridge Rectifier:** Converts AC to DC. 2. **Bulk Capacitor:** Smooths the rectified DC voltage. 3. **Transformer (Flyback):** Provides isolation and voltage step-down. 4. **Optocoupler:** Provides feedback from the isolated secondary side to the **FB** (Feedback) pin. 5. **Snubber Circuit:** (Resistor/Capacitor/Diode) protects the MOSFET from inductive spikes. --- ### 5. Pinout Configuration (DIP-7) ```text Pin 1: GND (Ground) Pin 2: VDD (Supply voltage for control logic) Pin 3: CONT (Control pin for OVP and Brown-out) Pin 4: FB (Feedback input) Pin 5: BR (Brown-out protection) Pin 7-8: DRAIN (Connection to the transformer primary) ```