## VIPER22AS13TR: Low Power Off-line Switched Mode Power Supply Primary Switcher The **VIPER22AS13TR** is a popular monolithic 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 low-power AC-DC converters (wall adapters, standby power, etc.). --- ### 1. Key Technical Specifications The following table highlights the primary electrical characteristics of the VIPER22AS13TR: | Feature | Specification | | :--- | :--- | | **Integrated MOSFET Vds** | 730 V (Minimum breakdown voltage) | | **Switching Frequency** | Fixed 60 kHz | | **Supply Voltage (Vdd)** | 9 V to 38 V | | **Drain Current (Id)** | 0.7 A (Peak) | | **Package** | SO-8 (Surface Mount) | | **Feedback Type** | Voltage or Current mode | | **Startup High Voltage Current Source** | Integrated (Self-starting) | --- ### 2. Core Functional Components The IC integrates several critical stages that typically require multiple discrete parts: 1. **High-Voltage MOSFET:** Capable of handling up to 730V, allowing it to interface directly with the rectified AC mains. 2. **PWM Controller:** Operates at a fixed 60kHz frequency to manage the duty cycle based on the load. 3. **Start-up Current Source:** When power is applied, an internal high-voltage current source charges the Vdd capacitor, eliminating the need for an external start-up resistor. 4. **Protection Circuitry:** * **Hysteretic Over-temperature Protection:** Shuts down the IC if it gets too hot. * **Overcurrent Protection (OCP):** Limits the peak current through the MOSFET. * **Undervoltage Lockout (UVLO):** Ensures the chip only operates when the supply voltage is stable. --- ### 3. Pin Configuration (SO-8 Package) The VIPER22AS13TR uses a standard 8-pin layout, though several pins are connected internally for thermal management. | Pin Number | Name | Description | | :--- | :--- | :--- | | 1-2 | **SOURCE** | Ground reference for the IC and the MOSFET source. | | 3 | **FB** | Feedback input. Controls the PWM duty cycle. | | 4 | **VDD** | Supply voltage for the control logic. | | 5-8 | **DRAIN** | High voltage drain of the MOSFET; also used for heat dissipation. | --- ### 4. Typical Application Circuit In a flyback converter configuration, the VIPER22A is used as the primary side switch. ```mermaid graph LR AC[AC Input] --> Rect[Bridge Rectifier] Rect --> Cap[Bulk Capacitor] Cap --> Trans[Transformer Primary] Trans --> VIPER[VIPER22A DRAIN] VIPER --> FB[Optocoupler Feedback] FB --> VIPER ``` ### 5. Advantages of using VIPER22AS13TR * **Reduced Component Count:** Because the MOSFET and start-up circuit are internal, the total PCB footprint is minimized. * **Low Standby Power:** The "Burst Mode" operation allows the device to meet energy-saving regulations (like Energy Star) during no-load conditions. * **Robustness:** The high breakdown voltage (730V) provides a safety margin against voltage spikes on the AC line. ---