The **VIPER20B** is a high-performance, monolithic Smart Primary Switch that combines a dedicated current mode PWM (Pulse Width Modulation) controller with a high-voltage Power MOSFET on the same silicon chip. It is widely used in off-line power supplies and battery chargers. --- ## 1. Key Internal Components The VIPER20B integrates several critical electronic functional blocks into a single TO-220 or SO-20 package: | Component | Function | | :--- | :--- | | **Power MOSFET** | A high-voltage N-channel power transistor (typically rated for 700V) that handles the switching of the primary current. | | **PWM Controller** | Regulates the duty cycle of the MOSFET to maintain a constant output voltage or current. | | **Current Sense** | Monitors the source current of the MOSFET for cycle-by-cycle current limiting. | | **Start-up Circuit** | A high-voltage current source that charges the VDD capacitor during initial power-up. | | **Thermal Shutdown** | Protects the device by shutting down if the junction temperature exceeds 170°C. | --- ## 2. Technical Specifications Below are the typical electrical characteristics of the VIPER20B: * **Drain-Source Voltage ($V_{ds}$):** Up to 700V (Off-state). * **Switching Frequency:** Fixed at 100 kHz. * **Output Power:** Up to 20W (Wide range input) or 40W (Single 230V input). * **Supply Voltage ($V_{dd}$):** 8V to 15V. * **Feedback System:** Voltage regulation via an optocoupler or primary auxiliary winding. --- ## 3. Pin Configuration The device typically uses a 5-pin layout (for the TO-220 package): | Pin Name | Description | | :--- | :--- | | **SOURCE** | Ground reference for the control circuit and source of the power MOSFET. | | **DRAIN** | High voltage connection to the transformer primary winding. | | **VDD** | Supply voltage for the control logic and gate driver. | | **COMP** | Input for the error amplifier/feedback loop to control PWM. | | **OSC** | Used to set the switching frequency (external RC network can adjust this). | --- ## 4. Typical Application Circuit The VIPER20B is most commonly found in **Flyback Converter** topologies. ```c // Conceptual Block Diagram Flow [AC Input] -> [Bridge Rectifier] -> [Bulk Capacitor] -> [Transformer Primary] | [VIPER20B DRAIN] | [Feedback Loop] <- [Optocoupler] <----------------------- [Secondary Output] | [VIPER20B COMP] ``` ### Advantages 1. **Reduced Component Count:** Replaces a separate PWM IC and discrete MOSFET. 2. **Burst Mode:** Provides excellent efficiency under light-load conditions. 3. **Safety:** Includes integrated over-current and over-temperature protection. ---