A zener diode circuit includes a semiconductor substrate having an N-doped region and a P-doped region that form a PN junction. The N-doped region and the P-doped region have areas with widths that decrease as the N-doped region and the P-doped region approach the PN junction. The zener diode circuit also includes a transistor that provides current to the zener diode, and circuitry that detects a state of the zener diode.