## Overview of the VIPER22A The **VIPER22A** is a popular low-power offline switched-mode power supply (SMPS) controller chip. It integrates a dedicated current mode PWM controller with a high-voltage Power MOSFET on the same silicon chip. It is widely used in battery chargers, adapters, and power supplies for household appliances because it minimizes external component count. --- ### 1. Key Internal Components The VIPER22A is essentially a "system-on-a-chip" for power conversion. Its internal architecture consists of: | Component | Function | | :--- | :--- | | **Power MOSFET** | Handles high voltage (up to 730V) and switches the current through the transformer primary. | | **PWM Controller** | Regulates the output voltage by adjusting the duty cycle of the MOSFET. | | **High Voltage Start-up** | Allows the chip to power itself directly from the rectified AC line initially. | | **Control Logic** | Manages thermal shutdown, overcurrent protection, and undervoltage lockout (UVLO). | --- ### 2. Pin Configuration (DIP-8 / SO-8) Most VIPER22A chips come in an 8-pin package. Below is the functional breakdown of the pins: | Pin Number | Name | Description | | :--- | :--- | :--- | | **1 - 2** | **SOURCE** | Ground reference for the internal MOSFET and the control circuit. | | **3** | **FB (Feedback)** | Input for the feedback loop (usually connected to an optocoupler). | | **4** | **VDD** | Supply voltage for the control logic (typically 9V to 38V). | | **5 - 8** | **DRAIN** | High voltage pins connected to the primary winding of the transformer. | --- ### 3. Technical Specifications | Parameter | Value / Range | | :--- | :--- | | **Drain-Source Voltage ($V_{ds}$)** | 730V (Max) | | **Switching Frequency** | Fixed at 60 kHz | | **Output Power (Wide Range)** | 7W (85–265 VAC) | | **Output Power (European Range)** | 12W (195–265 VAC) | | **Supply Voltage ($V_{DD}$)** | 9V to 38V | --- ### 4. Basic Application Circuit In a typical circuit, the AC input is rectified into DC. The VIPER22A then "chops" this DC at 60 kHz through a high-frequency transformer. ```mermaid graph LR AC_In --> Bridge_Rectifier Bridge_Rectifier --> Bulk_Capacitor Bulk_Capacitor --> Transformer_Primary Transformer_Primary --> VIPER22A_Drain VIPER22A_FB --> Optocoupler Optocoupler --> Output_Voltage_Sense ``` ### 5. Protection Features * **Hiccup Mode:** If a short circuit occurs, the device enters a "hiccup" phase to prevent overheating. * **Thermal Shutdown:** If the internal junction temperature exceeds 170°C, the chip shuts down. * **Overvoltage Protection:** Monitors the $V_{DD}$ pin to ensure it doesn't exceed safe limits. ---