What the 1.2 kV blocking voltage and 30 A rating mean for your circuit
The BTW68-1200RG is a standard-recovery SCR (silicon-controlled rectifier) from STMicroelectronics, rated for a repetitive off-state voltage of 1.2 kV and a continuous on-state RMS current of 30 A. That 1.2 kV blocking voltage means it can hold off the peak of a 480 VAC line (which peaks around 678 V) with healthy margin, making it suitable for phase-control circuits in industrial power supplies, motor soft-starters, and welding equipment. The 30 A RMS rating is the continuous conduction limit at the rated case temperature — derate above 25°C per the datasheet curve. The average on-state current is 19 A, which is the thermal design limit for continuous DC-like conduction. For AC phase control, the RMS rating is the more practical number because the current waveform is sinusoidal, not flat.
Surge current and gate drive requirements
The non-repetitive surge current is 400 A at 50 Hz and 420 A at 60 Hz (one cycle). This is the peak current the die can survive during a fault or inrush event — a motor start or capacitor charging transient that lasts a few milliseconds. The gate trigger current is 50 mA max, and the gate trigger voltage is 1.5 V max, so a standard 5 V logic signal through a current-limiting resistor can drive it directly. The holding current is 75 mA max — once the SCR is latched, the load current must stay above this threshold to keep it conducting. Below that, the device turns off. The off-state leakage is only 20 µA max, which matters for standby power in battery-backed circuits.
Package and mounting: TOP-3 through-hole
The BTW68-1200RG comes in a TOP-3 through-hole package (also called TOP3), which is the standard isolated-tab power package for high-current thyristors. The three leads are formed for PCB mounting, and the package is delivered in tubes. The storage range is wider, but the junction temperature must stay within this window during operation.