Why is VECO very low (0.3V) for Darlington transistors such as TLP187 and TLP387? What precautions should be taken when using such transistors?


When a transistor in a Darlington configuration with base-emitter resistance is incorporated into an Si chip, stray diode Di is put between the emitter and the collector in an equivalent manner. Owing to this, for VECO, the characteristics in the forward direction of the Di also appear; VECO  is thus specified with a very low (0.3V) value. Through this Di element, a current flows between the emitter and the collector. The circuit must be designed so that the VECO value (0.3V) will not be exceeded.