## Overview of VIPER22AS-E The **VIPER22AS-E** is a high-performance, low-power offline switcher IC manufactured by STMicroelectronics. It combines a dedicated current mode PWM controller with a high-voltage Power MOSFET on the same silicon chip. It is widely used in SMPS (Switched Mode Power Supplies) for applications requiring power outputs typically between 5W and 20W, such as battery chargers, adapters, and standby power supplies for white goods. --- ### 1. Key Internal Components The VIPER22AS-E is an integrated solution containing several critical electronic blocks: | Component | Function | | :--- | :--- | | **Power MOSFET** | Handles high voltage (up to 730V breakdown) and switches the primary current. | | **PWM Controller** | Regulates the duty cycle based on feedback to maintain output voltage. | | **High Voltage Start-up** | Allows the IC to power itself directly from the rectified mains initially. | | **Current Sense** | Monitors the drain current for protection and control. | | **Thermal Shutdown** | Protects the IC from overheating by shutting down at ~170°C. | --- ### 2. Pin Configuration (SO-8 Package) The device is typically housed in an **SO-8** surface-mount package. Note that several pins are tied together for heat dissipation. | Pin Number | Name | Description | | :--- | :--- | :--- | | **1-2** | SOURCE | Connected to the source of the internal MOSFET and circuit ground. | | **3** | FB | Feedback input. Controls the PWM operation. | | **4** | VDD | Supply voltage for the control logic (usually 9V to 38V). | | **5-8** | DRAIN | High voltage drain pin of the MOSFET; also used for start-up current. | --- ### 3. Technical Specifications | Parameter | Value | | :--- | :--- | | **Drain-Source Voltage ($V_{dss}$)** | 730 V | | **Switching Frequency** | Fixed at 60 kHz | | **Max Supply Voltage ($V_{DD}$)** | 42 V | | **Feedback Current ($I_{fb}$)** | 0.5 mA to 1 mA | | **Typical Output Power** | 7W (85-265 VAC) / 12W (230 VAC) | --- ### 4. Circuit Protection Features The VIPER22AS-E is designed to be "robust," meaning it includes several failsafe mechanisms: * **Hiccup Mode:** If a short circuit occurs, the device enters a "hiccup" phase where it repeatedly tries to restart safely until the fault is removed. * **Overvoltage Protection:** The VDD pin has a Zener clamp to protect the internal circuitry from voltage spikes. * **Undervoltage Lockout (UVLO):** Ensures the device only operates when the supply voltage is high enough to drive the MOSFET gate effectively. --- ### 5. Application Example: Basic Flyback Converter In a typical circuit, the VIPER22AS-E acts as the primary switcher: 1. **Rectification:** AC mains are rectified to DC. 2. **Start-up:** The internal high-voltage current source charges a capacitor on the **VDD** pin. 3. **Switching:** Once VDD reaches ~14.5V, the internal **PWM** starts toggling the **MOSFET**. 4. **Feedback:** An optocoupler sends a signal to the **FB** pin to adjust the pulse width, keeping the output voltage stable.