The **VIPER25LD** is a high-performance, off-line converter belonging to the VIPerPlus family by STMicroelectronics. It integrates an 800 V avalanche-rugged power MOSFET with a Pulse Width Modulation (PWM) controller. --- ### ## Key Technical Specifications The following table summarizes the primary electrical characteristics of the VIPER25LD: | Parameter | Specification | | :--- | :--- | | **Drain-Source Voltage ($V_{DSS}$)** | 800 V | | **Switching Frequency ($F_{OSC}$)** | 60 kHz (Fixed) | | **Max Drain Current ($I_{Dlim}$)** | 0.7 A | | **Supply Voltage ($V_{DD}$)** | 8.5 V to 23.5 V | | **Package** | SO-16 (Narrow) | | **Typical Power Output** | 20W (Wide range), 25W (European range) | --- ### ## Functional Electronic Parts The internal architecture of the VIPER25LD consists of several critical stages that manage power conversion and safety: #### 1. Integrated Power MOSFET The device features an **800 V breakdown voltage** MOSFET. This high rating allows for a simplified "snubber" circuit design and provides high reliability against lightning surges or mains voltage spikes. #### 2. PWM Controller The internal controller operates in **Current Mode Control**. This ensures: * Excellent line and load regulation. * Inherent cycle-by-cycle current limiting. #### 3. High Voltage Startup The VIPER25LD includes a high-voltage current source directly connected to the Drain pin. This eliminates the need for external startup resistors, reducing standby power consumption (less than 30 mW at 265 Vac). #### 4. Protection Circuitry The chip is embedded with multiple protection layers to prevent component failure: * **Hysteresis Thermal Shutdown:** Turns off the device if the temperature exceeds 150°C. * **Overload Protection (OLP):** Limits power if the output is shorted. * **Overvoltage Protection (OVP):** Protects the secondary circuit if the feedback loop breaks. --- ### ## Pin Configuration (SO-16) | Pin Name | Function | | :--- | :--- | | **DRAIN** | High voltage drain of the MOSFET and internal startup source. | | **GND** | Ground and reference for all signals. | | **VDD** | Supply voltage for the internal control logic. | | **FB** | Feedback input for regulation. | | **CONT** | Connection for an external capacitor to set the shutdown delay. | | **LIM** | Allows adjustment of the default current limit. | --- ### ## Typical Application Diagram In a standard Flyback converter, the VIPER25LD is used as follows: ```mermaid graph LR AC_Input --> Rectifier Rectifier --> Transformer_Primary Transformer_Primary --> VIPER25_Drain VIPER25_FB --> Optocoupler Optocoupler --> Secondary_Output ```