# SSL21081T: High Voltage LED Driver IC The **SSL21081T** is a high-efficiency controller developed by NXP Semiconductors specifically designed for driving LED lamps in non-isolated, high-voltage applications. It is part of the GreenChip family, focused on low component count and high power factor. --- ## 1. Key Technical Specifications | Parameter | Specification | | :--- | :--- | | **Topology** | Non-isolated Buck Converter | | **Input Voltage Range** | 100V to 230V AC (Mains) | | **Integrated Switch** | Power MOSFET (Internal) | | **Max Output Voltage** | Up to 300V | | **Package** | SO8 (Small Outline 8-pin) | | **Efficiency** | Up to 95% | --- ## 2. Core Electronic Components & Functions The SSL21081T integrates several critical functions into a single 8-pin package to minimize the Bill of Materials (BOM). ### Internal Architecture * **High-Voltage Power Switch:** Contains an internal MOSFET designed to handle the switching of the LED string current. * **Current Sensing:** It monitors the current through the inductor to provide accurate LED current regulation without needing an external optocoupler. * **Internal Supply:** Features an internal high-voltage start-up source, eliminating the need for an external bleeder resistor. ### Operational Modes 1. **Boundary Conduction Mode (BCM):** The IC operates by waiting for the inductor current to hit zero before starting a new cycle. This reduces switching losses and EMI. 2. **Valley Switching:** The MOSFET turns on at the lowest voltage point (the "valley"), which maximizes efficiency. --- ## 3. Pin Configuration (SO8) The table below describes the function of each pin on the electronic chip: | Pin Number | Name | Description | | :---: | :--- | :--- | | 1 | **GND** | Ground reference for the IC. | | 2 | **DVDD** | Internal supply voltage for logic. | | 3 | **NC** | No internal connection. | | 4 | **ROVP** | Overvoltage protection programming pin. | | 5 | **SENSE** | Current sense input (connected to a resistor). | | 6 | **DRAIN** | Drain connection of the internal power MOSFET. | | 7 | **DRAIN** | High-voltage drain connection (heat sink capability). | | 8 | **HV** | High voltage start-up pin. | --- ## 4. Typical Application Circuit A typical circuit using the SSL21081T includes the following external electronic parts: * **Bridge Rectifier:** To convert AC mains to DC. * **Inductor:** Stores energy during the MOSFET "On" phase; sizing this is critical for the output current. * **Freewheeling Diode:** Allows current to flow through the LEDs when the internal switch is "Off". * **Smoothing Capacitors:** Used at the input (to reduce EMI) and output (to reduce LED flicker). --- ## 5. Protective Features The IC is equipped with several safety mechanisms to prevent failure: * **Under-Voltage Lockout (UVLO):** Prevents the IC from operating at unstable voltage levels. * **Over-Temperature Protection (OTP):** Shuts down the IC if it exceeds safe thermal limits. * **Short-Winding Protection (SWP):** Protection against shorted inductors. * **Over-Voltage Protection (OVP):** Protects the output capacitors if the LED string becomes an open circuit.