The **VIPer12A** (specifically the **VIPer12AS** in SMD packaging) is a popular "Off-line Primary Switcher" manufactured by STMicroelectronics. It is widely used in low-power AC-DC converters (wall adapters, appliances, and standby power supplies). --- ## 1. Internal Components The VIPer12A is an Integrated Circuit (IC) that combines two major functional blocks into a single monolithic chip: | Component | Description | | :--- | :--- | | **Power MOSFET** | A high-voltage Power MOSFET with a typical breakdown voltage of **730V**. | | **PWM Controller** | A sophisticated pulse-width modulation circuit that controls the switching frequency and duty cycle. | ### Key Internal Features: * **Fixed Switching Frequency:** Internally set to **60 kHz**. * **Current Mode Control:** Provides stable operation and cycle-by-cycle current limiting. * **Startup High Voltage Source:** It can draw power directly from the high-voltage DC bus to start up, eliminating the need for a startup resistor. --- ## 2. Pin Configuration (SO-8 Package) The "S" in VIPer12AS refers to the **SO-8** surface-mount package. | Pin Number | Name | Function | | :--- | :---: | :--- | | 1, 2 | **SOURCE** | Connected to the internal MOSFET source; typically connected to the primary ground. | | 3 | **FB** | **Feedback:** Used to regulate the output voltage via an optocoupler. | | 4 | **VDD** | Supply voltage for the internal control logic (typically 9V to 38V). | | 5, 6, 7, 8 | **DRAIN** | Connected to the internal MOSFET drain; connects to the primary winding of the transformer. | --- ## 3. Technical Specifications Below are the critical operating parameters for the VIPer12AS: | Parameter | Value | | :--- | :--- | | **Drain-Source Voltage ($V_{dss}$)** | 730 V | | **Switching Frequency** | 60 kHz | | **Max Output Power (85-265 VAC)** | ~5W (Wide Range) | | **Max Output Power (230 VAC)** | ~8W (European Range) | | **Supply Voltage Range ($V_{dd}$)** | 9V to 38V | | **Feedback Current ($I_{fb}$)** | ~3 mA | --- ## 4. Typical Application Circuit In a standard **Flyback Converter** topology, the VIPer12AS operates as follows: 1. **Rectification:** AC mains are rectified into High-Voltage DC. 2. **Startup:** The internal high-voltage current source charges a capacitor on the **VDD** pin. 3. **Switching:** Once $V_{dd}$ reaches the threshold, the PWM controller starts switching the internal MOSFET. 4. **Regulation:** An optocoupler sends a signal to the **FB** pin to adjust the duty cycle, maintaining a constant output voltage. 5. **Protection:** The IC includes built-in thermal shutdown and short-circuit protection. ---