The ISL9V3040D3ST is an ignition IGBT (Insulated Gate Bipolar Transistor) from onsemi in TO-220, rated at 400V VCE(OFF) and 30A IC at 25C. It is specifically designed for automotive ignition coil driver applications. Unlike a standard IGBT, the ignition IGBT includes an internal Zener gate clamp and an integrated reverse diode (emitter-to-collector) for coil flyback protection. In an ignition system, the IGBT operates as a switch: when the gate is driven HIGH (5V logic level), the IGBT turns ON and current flows through the ignition coil primary winding (typically 5-10A, limited by coil resistance and dwell time). When the gate goes LOW, the IGBT turns OFF and the coil current interrupts. The collapsing magnetic field induces a high voltage (300-400V) on the primary and 20-40kV on the secondary, which fires the spark plug. The internal Zener clamp (typically 350-400V) protects the IGBT collector from exceeding its breakdown voltage during the flyback event. The integrated reverse diode protects against negative voltage transients when the spark fires. The 400V rating provides margin above the typical 350V clamp voltage. The ISL9V prefix denotes ignition-specific IGBT from onsemi. The D3ST suffix specifies TO-220 package. The device is used in electronic distributorless ignition systems (DIS) and coil-on-plug (COP) applications, typically one IGBT per cylinder.