The **STR3** series (specifically the STR-W, STR-A, or STR-L families manufactured by Sanken Electric) refers to a specialized line of **Power ICs** used in switching mode power supplies (SMPS). These are known as "Power ICs" because they integrate both the control circuitry and a high-voltage power MOSFET into a single package. --- ### 1. Key Internal Components An STR3-series chip typically contains the following electronic blocks: | Component | Function | | :--- | :--- | | **Power MOSFET** | The switching element that handles high voltage (often 650V to 800V). | | **PWM Controller** | Pulse Width Modulation circuit that regulates the output voltage. | | **Startup Circuit** | High-voltage internal circuitry to start the device without external resistors. | | **Protection Logic** | Circuits for Overvoltage (OVP), Overcurrent (OCP), and Thermal Shutdown (TSD). | --- ### 2. Functional Characteristics The STR3 series is designed for efficiency and space-saving in power adapters. * **Integrated Design:** By combining the controller and the power transistor, it reduces the "bill of materials" (BOM) and saves PCB space. * **Green Mode:** Many STR3 variants feature a "Burst Mode" or "Frequency Skipping" to reduce power consumption during standby or light loads. * **Current Mode Control:** Most use peak current mode control for stable operation and fast response to load changes. --- ### 3. Common Pin Configuration (Example: STR-W6000 Series) While specific pinouts vary by model, a typical STR-series 3-pin or 5-pin TO-220/TO-3P package includes: | Pin Name | Description | | :--- | :--- | | **D/ST** | Drain / Startup. Connected to the rectified high-voltage DC bus. | | **S/OCP** | Source / Overcurrent Protection. Connected to ground via a sensing resistor. | | **VCC** | Power supply for the internal control circuit. | | **FB** | Feedback. Receives signals from the optocoupler to regulate output. | | **GND** | Ground reference for the control section. | --- ### 4. Applications These parts are ubiquitous in consumer electronics due to their reliability: 1. **TV Power Supplies:** Main or standby power blocks. 2. **Home Appliances:** Washing machines and air conditioner control boards. 3. **AC Adapters:** Laptop chargers and peripheral power bricks. 4. **Office Automation:** Printers and scanners. --- ### 5. Troubleshooting Tips If you are repairing a board with an STR3 series IC, check the following: * **VCC Voltage:** If the IC isn't starting, check the electrolytic capacitor on the VCC pin. * **Source Resistor:** A blown STR3 often kills the low-ohm sensing resistor connected to the Source pin. * **Startup Resistors:** In older STR models, external high-value resistors can go open-circuit, preventing the IC from waking up.