The SMBJ188A is a unidirectional surface mount Transient Voltage Suppressor (TVS) diode manufactured by Youtai. It is a RoHS compliant component rated at 2A, 1uA, 328V, 209V, 188V, and 231V. This diode is designed to protect sensitive equipment from voltage transients, which are brief and high voltage overshoots that can damage electronics. It typically functions by diverting the voltage surge away from the protected device, dissipating it into a ground path safely.