## Overview of the VIPER23A The **VIPER23A** is an off-line converter manufactured by STMicroelectronics. It belongs to the VIPerPlus family and integrates a high-voltage power MOSFET with a PWM controller in a single package. It is primarily used for switched-mode power supplies (SMPS). --- ### 1. Key Internal Components The VIPER23A is highly integrated, containing the following functional blocks: | Component | Function | | :--- | :--- | | **800V Power MOSFET** | Handles high voltage switching and provides ruggedness against voltage spikes. | | **PWM Controller** | Regulates the output voltage via Pulse Width Modulation. | | **Start-up High Voltage Source** | Allows the chip to start directly from the rectified mains, eliminating the need for an external start-up resistor. | | **Error Amplifier** | Features an integrated 3.3V reference for precise voltage regulation. | | **Protection Circuitry** | Includes thermal shutdown, overcurrent protection, and overvoltage protection. | --- ### 2. Pin Configuration (DIP-7 / SO-16) The device is commonly found in a DIP-7 or SO-16 package. Below are the standard pin functions: | Pin Name | Description | | :--- | :--- | | **DRAIN** | Connected to the internal MOSFET drain and the transformer primary winding. | | **SOURCE** | Ground reference for the controller and source for the MOSFET. | | **VDD** | Supply voltage for the internal control logic. | | **COMP** | Feedback input for loop compensation and output regulation. | | **CONT** | Control pin for setting the switching frequency or additional filtering. | --- ### 3. Technical Specifications Typical operating parameters for the VIPER23A: * **Fixed Switching Frequency:** 60 kHz (Standard version). * **Drain-Source Voltage ($V_{DSS}$):** 800 V. * **Max Output Power:** Up to 18W (Wide range input) or 23W (European/Fixed input). * **Standby Consumption:** Very low power consumption in "Burst Mode" (< 30mW at 230VAC). * **Jittering:** Integrated frequency jittering to reduce EMI filter costs. --- ### 4. Basic Application Circuit In a typical Flyback converter setup, the VIPER23A is used as follows: ```text AC Input -> Bridge Rectifier -> Bulk Capacitor -> [VIPER23A + Transformer] -> Output DC ^ | Optocoupler Feedback ``` The device senses the output via an optocoupler connected to the **COMP** pin, adjusting the duty cycle of the internal 800V MOSFET to maintain a stable output voltage. --- ### 5. Notable Features 1. **Hysteretic Over-temperature Protection:** Automatically shuts down if the chip gets too hot. 2. **Safe Auto-restart:** If a fault (like a short circuit) occurs, the device attempts to restart periodically rather than burning out. 3. **Frequency Jittering:** Slightly varies the switching frequency to spread energy across the spectrum, making it easier to pass electromagnetic interference (EMI) tests.