## Overview of the VIPER22A The **VIPER22A** is a popular low-power offline switched-mode power supply (SMPS) primary switcher. It combines a dedicated current mode PWM controller with a high-voltage Power MOSFET on the same silicon chip. --- ### 1. Key Internal Components The VIPER22A integrates several electronic stages into a single 8-pin package (typically DIP-8 or SO-8): | Component | Function | | :--- | :--- | | **Power MOSFET** | Handles high voltage (up to 730V) and switches the current through the transformer primary. | | **PWM Controller** | Regulates the duty cycle based on feedback to maintain a constant output voltage. | | **SenseFET** | Monitors the current flowing through the MOSFET for cycle-by-cycle current limiting. | | **Startup Circuit** | High voltage current source that charges the VDD capacitor directly from the drain. | | **Error Amplifier** | Compares feedback signals to an internal reference. | --- ### 2. Technical Specifications Below are the critical electronic parameters for the VIPER22A: | Parameter | Value / Range | | :--- | :--- | | **Drain-Source Voltage ($V_{dss}$)** | 730V Max | | **Switching Frequency** | Fixed at 60 kHz | | **Supply Voltage ($V_{DD}$)** | 9V to 38V | | **Feedback Current ($I_{FB}$)** | 3 mA | | **Output Power (Wide Range)** | 7W (85-265 VAC) | | **Output Power (Single Range)** | 12W (230 VAC) | --- ### 3. Pin Configuration The VIPER22A usually uses a **DIP-8** footprint with the following layout: 1. **SOURCE (Pins 1, 2):** Connected to the source of the internal MOSFET and the circuit ground. 2. **FB (Pin 3):** Feedback input. Usually connected to an optocoupler to regulate output. 3. **VDD (Pin 4):** Supply voltage for the control logic. 4. **DRAIN (Pins 5, 6, 7, 8):** Connected to the drain of the internal MOSFET and the primary winding of the transformer. --- ### 4. Typical Application Circuit In a standard Flyback converter, the VIPER22A operates as follows: ```mermaid graph LR AC_In --> Rectifier Rectifier --> Transformer_Primary Transformer_Primary --> VIPER22_Drain VIPER22_Source --> Ground Optocoupler --> VIPER22_FB ``` #### Key Features: * **Burst Mode Operation:** Reduces power consumption during "no-load" conditions (Green mode). * **Protection:** Includes over-temperature, over-voltage, and short-circuit protection. * **Simplified Design:** Because the MOSFET and startup high-voltage source are internal, it requires very few external components. ---