## Overview of the VIPER22A-E (DIP-8) The **VIPER22A** is a popular low-power off-line 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. It is widely used in battery chargers, adapters, and auxiliary power supplies for home appliances. --- ### 1. Key Internal Components The VIPER22A integrates several electronic stages into a single 8-pin DIP package: | Component | Description | | :--- | :--- | | **Power MOSFET** | A high-voltage power switch with a typical breakdown voltage of 730V. | | **PWM Controller** | Handles the pulse-width modulation to regulate output voltage. | | **Start-up High Voltage Source** | Internal high-voltage current source that charges the VDD capacitor directly from the Drain. | | **Error Amplifier** | Manages the feedback loop to maintain stable voltage. | | **Protection Circuits** | Includes Thermal shutdown, Overcurrent protection, and Undervoltage Lockout (UVLO). | --- ### 2. Pin Configuration (DIP-8) The VIPER22A uses a standard 8-pin Dual In-line Package (DIP), though several pins are connected internally for heat dissipation. | Pin Number | Name | Function | | :--- | :--- | :--- | | **1 - 2** | **SOURCE** | Ground reference for the integrated MOSFET and control circuits. | | **3** | **FB** | Feedback input. Controls the PWM duty cycle based on output voltage. | | **4** | **VDD** | Supply voltage for the control IC (typically 9V to 38V). | | **5 - 8** | **DRAIN** | High voltage drain of the MOSFET; also used for internal start-up current. | --- ### 3. Technical Specifications Typical operating parameters for the VIPER22A: * **Fixed Switching Frequency:** 60 kHz (internal oscillator). * **Supply Voltage (VDD):** 9V to 38V. * **Drain-Source Voltage ($V_{dss}$):** 730V Max. * **Feedback Current ($I_{fb}$):** ~3mA. * **Output Power:** * *Wide Range (85-265 VAC):* Up to 7W. * *Single Range (180-265 VAC):* Up to 12W. --- ### 4. Application Circuit Example In a typical Flyback converter configuration, the VIPER22A operates as follows: ```text AC Input -> Bridge Rectifier -> DC Bulk Cap -> VIPER22A (Drain) | Transformer Primary | VIPER22A (Source) ``` 1. **Start-up:** The internal high-voltage current source charges the capacitor on the **VDD** pin. 2. **Switching:** Once VDD reaches the threshold (~14.5V), the internal MOSFET starts switching at 60 kHz. 3. **Regulation:** An optocoupler (like the PC817) usually sends a signal to the **FB** pin to adjust the duty cycle, ensuring the output remains constant despite load changes. --- ### 5. Common Protections * **Hiccup Mode:** If a short circuit occurs, the device enters a "hiccup" phase, attempting to restart periodically until the fault is cleared. * **Thermal Shutdown:** If the internal junction temperature exceeds 170°C, the device shuts down to prevent permanent damage.