## Overview of the VIPER20SP The **VIPER20SP** is a high-performance SMPS (Switched Mode Power Supply) primary switcher IC produced by STMicroelectronics. It integrates a dedicated current-mode PWM controller with a high-voltage Power MOSFET on the same silicon chip. It is specifically designed for off-line applications such as battery chargers and power supplies for consumer electronics. --- ### 1. Key Internal Components The device is sophisticated because it combines low-voltage control logic with high-voltage power components: | Component | Function | | :--- | :--- | | **Power MOSFET** | Handles high voltage (up to 700V) and switching currents. | | **PWM Controller** | Regulates the duty cycle based on feedback to maintain output voltage. | | **Current Sense** | Monitors the drain current for cycle-by-cycle protection. | | **Error Amplifier** | Compares the feedback signal against an internal reference. | | **Start-up High Voltage Source** | Allows the chip to self-start directly from the rectified mains. | --- ### 2. Technical Specifications Below are the primary electrical characteristics of the VIPER20SP: | Parameter | Value | | :--- | :--- | | **Drain-Source Voltage ($V_{DS}$)** | 700 V (Maximum) | | **Output Current ($I_D$)** | 0.5 A | | **Switching Frequency** | Up to 200 kHz (Adjustable) | | **Package Type** | PowerSO-10 (Surface Mount) | | **Supply Voltage ($V_{DD}$)** | 8V to 15V | --- ### 3. Pin Configuration (PowerSO-10) The VIPER20SP uses a specialized surface-mount package to handle heat dissipation. 1. **Source:** Ground reference for the high voltage section. 2. **Drain:** High voltage connection to the transformer primary winding. 3. **VDD:** Supply voltage for the control logic. 4. **Feedback (FB):** Input for the control loop (usually from an optocoupler). 5. **Comp:** Connection for external compensation network. 6. **Oscillator (OSC):** Pin to set the switching frequency using an external RC network. --- ### 4. Functional Features * **Automatic Burst Mode:** In low-load conditions, the device enters a "burst mode" to reduce power consumption and meet energy-saving standards. * **Integrated Start-up:** You don't need a high-wattage external resistor to start the IC; it draws initial power internally from the Drain pin. * **Protections:** * **Over-temperature:** Thermal shutdown if the die gets too hot. * **Over-current:** Limits the maximum peak current in the MOSFET. * **Under-voltage Lockout (UVLO):** Ensures the chip only operates when the supply voltage is stable. --- ### 5. Application Example The most common use case is a **Flyback Converter**. ```c // Typical Operation Sequence 1. Rectified AC Mains enters the Drain pin. 2. Internal High-Voltage current source charges the VDD capacitor. 3. Once VDD reaches the threshold, the PWM starts switching the MOSFET. 4. Energy is transferred through the transformer to the secondary side. 5. Feedback pin adjusts the pulse width to keep the output steady. ```