TOSHIBA Photocoupler IRED & Photo-Transistor TLP181 Office Machine Programmable Controllers AC Adapter I/O Interface Board TLP181 Unit: mm The TOSHIBA mini flat coupler TLP181 is a small outline coupler, suitable for surface mount assembly. TLP181 consist of a photo transistor optically coupled to an infrared emitting diode. Since TLP181 is smaller than DIP package, it’s suitable for highdensity surface mounting applications such as programmable controllers. Collector-emitter voltage.