TLP3431 Photorelay Photocoupler Toshiba TLP3431 Photorelay Photocoupler is a non-leaded photo relay consisting of an infrared emitting diode optically combined with a photo MOSFET. The TLP3431 is convenient for surface-mount assembly and is housed in a VSON 4-pin package. The TLP3431 features exceptional low ON-state resistance of 0.8Ω (typ.), making it ideal for high-frequency measuring instrument applications.