## Overview of the VIPER53 The **VIPER53** is an offline switched-mode power supply (SMPS) controller manufactured by STMicroelectronics. It integrates a high-voltage Power MOSFET with a dedicated Current Mode PWM controller on a single monolithic chip. It is specifically designed for applications requiring high performance and low standby power consumption, such as battery chargers and adapters for laptops or set-top boxes. --- ### 1. Key Internal Components The VIPER53 combines several electronic blocks into a single 8-pin package (typically DIP-8 or PowerSO-10): | Component | Function | | :--- | :--- | | **Power MOSFET** | A rugged 620V vertical power transistor that handles the switching of the primary current. | | **PWM Controller** | Regulates the output by adjusting the duty cycle based on feedback. | | **Startup High Voltage Source** | Internal high-voltage current source that charges the $V_{DD}$ capacitor during startup, eliminating the need for a bleed resistor. | | **Error Amplifier** | An internal op-amp used to compare the feedback signal against a reference. | | **Logic/Protection Control** | Manages thermal shutdown, overcurrent protection, and undervoltage lockout (UVLO). | --- ### 2. Technical Specifications Below are the critical electrical parameters for the VIPER53: | Parameter | Value | | :--- | :--- | | **Drain-Source Voltage ($V_{DS}$)** | 620V (Maximum) | | **Switching Frequency** | Up to 300 kHz (Adjustable) | | **Output Power** | Up to 30W (Wide range), 50W (Single range) | | **Supply Voltage ($V_{DD}$)** | 9V to 18V | | **Standby Power** | < 0.5W in no-load conditions | --- ### 3. Pinout Description (DIP-8) To use the VIPER53 in a circuit, understanding the pin functions is essential: 1. **SOURCE**: Ground reference for the internal MOSFET and control circuits. 2. **SOURCE**: Secondary ground connection. 3. **COMP**: Input for the error amplifier (Feedback loop). 4. **OSC**: Allows setting the switching frequency via an external RC network. 5. **Vdd**: Power supply for the control logic; usually supplied by an auxiliary transformer winding. 6. **DRAIN**: High voltage pin connected to the primary winding of the transformer. 7. **DRAIN**: Parallel drain connection. 8. **DRAIN**: Parallel drain connection. --- ### 4. Protection Features The VIPER53 is highly "self-protecting," which reduces the total number of external components needed: * **Overvoltage Protection (OVP):** Monitors the $V_{DD}$ pin and shuts down if the voltage exceeds safety limits. * **Hiccup Mode:** If a short circuit occurs, the device enters a low-frequency restart cycle to prevent overheating. * **Thermal Shutdown:** If the junction temperature exceeds 170°C, the power MOSFET is turned off. * **Current Limiting:** Limits the peak current through the MOSFET cycle-by-cycle. --- ### 5. Application Example: Basic Flyback Converter In a typical application, the VIPER53 is configured in a **Flyback topology**. ```text AC Input -> Bridge Rectifier -> Bulk Cap -> Transformer Primary -> VIPER53 DRAIN | VIPER53 SOURCE -> GND ``` The feedback is usually provided via an **Optocoupler** connected to the **COMP** pin, ensuring galvanic isolation between the high-voltage input and the low-voltage output.