The BZT52C4V3S with Zener Diodes SOD-323 RoHS is a device manufactured by the company Bourne that is used effectively as a low-cost voltage regulator. Essentially, it acts as a reverse biased diode between two power sources, providing a typical VZ breakdown voltage of 4.3 Volts. In addition, this device boasts a low capacitance and a low-power voltage regulator, making it ideal for a wide range of applications like power supply circuits, RC oscillators, miniature switching, etc. It is also RoHS compliant, meaning that it meets all requirements for hazardous materials. Furthermore, this component comes with an SOD-323 package, a very common and popular type for these kinds of applications.