TLP291 consists of photo transistor, optically coupled to a gallium arsenide infrared emitting diode. TLP291 is housed in the SO4 package, very small and thin coupler. Since TLP291 is guaranteed wide operating temperature (Ta=-55 to 110 ̊C) and high isolation voltage (3750Vrms), it’s suitable for high-density surface mounting applications such as small switching power supplies and programmable controllers