800 V blocking, 200 µA trigger — a sensitive-gate SCR for low-power drive
The STMicroelectronics X0202NUF is a sensitive-gate silicon controlled rectifier (SCR) rated for 800 V off-state voltage and 1.25 A RMS on-state current. Its gate trigger current is just 200 µA max, making it directly drivable from a microcontroller GPIO, a comparator output, or a low-power sensor circuit without a separate driver transistor. The 800 V blocking rating suits it for mains-rectified DC buses (e.g., 240 VAC rectified to ~340 VDC) or offline flyback snubber circuits where voltage transients can spike well above the rail. The SMBflat-3L package is a low-profile, surface-mount form factor with flat leads, designed for automated assembly on dense PCBs where height clearance is tight — think LED lighting ballasts, appliance control boards, or compact power supplies.
With a maximum on-state voltage of 1.45 V at rated current, the X0202NUF dissipates about 1.2 W at 800 mA average — manageable in the SMBflat-3L package if the PCB has adequate copper area for heat sinking. The 25 A non-repetitive surge rating (60 Hz half-cycle) covers inrush from capacitive loads like a switched-mode power supply input or a motor start. Hold current is 5 mA max, so the SCR will stay latched once triggered as long as the load current stays above that threshold; below it the device will commutate off, which matters for phase-control or pulse-skipping applications.