SCR for phase-control and power-switching — what the ratings mean
The STMicroelectronics TYN208RG is a standard-recovery SCR (silicon-controlled rectifier) in a TO-220 through-hole package, rated for 200 V off-state blocking and 5 A average / 8 A RMS on-state conduction. It is designed for medium-current phase-control applications such as AC motor speed controllers, lighting dimmers, heater controls, and inrush current limiters where a simple gate-triggered latch is needed. The 45 mA maximum hold current (Ih) means the SCR will stay latched once triggered as long as the load current stays above that threshold — useful for inductive loads where current may ring near zero. The 25 mA maximum gate trigger current (Igt) and 1.5 V gate trigger voltage (Vgt) are compatible with standard logic-level or optocoupler gate drives, though a series resistor and snubber are typical in AC line designs.
Sourcing an obsolete SCR — lifecycle and replacement path
The TYN208RG is listed as obsolete. For a BOM that requires a TO-220 standard-recovery SCR with 200 V / 5 A average ratings, the buyer should evaluate pin-compatible alternatives from the broader TYN208 family (base product number TYN208) or from other manufacturers' 8 A RMS SCR lines in the same package.
Thermal and surge handling in the TO-220 package
The TO-220 case allows mounting to a heatsink via the metal tab — the 5 A average rating assumes adequate heatsinking; without a heatsink, derate the current significantly. The 5 µA maximum off-state leakage is typical for a standard-recovery SCR at rated voltage and 25°C; leakage doubles roughly every 10°C rise, so at 125°C it can be a factor in standby power budgets.