800 V blocking, 40 A conducting — the TO-220 SCR for line-voltage switching
The STMicroelectronics TYN840RG is a standard-recovery SCR in a TO-220-3 through-hole package, rated to block 800 V off-state and conduct 40 A RMS continuous. The 480 A non-repetitive surge capacity (60 Hz) handles motor inrush and capacitor charging events without exceeding the junction's thermal limit.
Gate drive and on-state drop — the numbers that set the driver budget
Gate trigger current is 35 mA maximum, with a maximum trigger voltage of 1.3 V — the driver stage must source at least this into the gate-cathode loop, plus margin for cold-temperature operation where Igt rises. On-state voltage is 1.6 V maximum at rated current; at 25 A average this puts conduction loss near 40 W, so the TO-220 tab needs a heatsink sized for the duty cycle. The 75 mA holding current means the load current must stay above this threshold to keep the SCR latched; below it the device will commutate off.