Wait, optocouplers have isolation voltages. For example, a high-voltage optocoupler like the H11F1, but again, not matching.

Another possibility is a high-voltage transistor, such as a BJT. Companies like Fairchild (now ON Semiconductor) have parts like the 2N3904, but high-voltage models might be something else.

Another angle: sometimes users combine a manufacturer's prefix with their product line. For example, ON Semiconductor or STMicroelectronics. If "hv490fhb" is a part of a series, and "n80" is a suffix related to rating or option.