Driver ICs play an important role in powering LEDs. The driver is normally powered by a UL approved constant voltage LED supply. Consider the variables in powering an array of LEDs. The LEDs may require an adjustable current for brightness and dimming. Also, the forward voltage drop across an LED is not exact. It is specified with a min/max spread that is typically in the range of 3.4 to 4V to account for diode variations with temperature and current. Should an LED fail short, the voltage across the string of LEDs would drop. To protect against an open failure, a zener bypass diode may be used in parallel with each diode. The zener breakdown voltage must be greater than that of the worst case LED, and thus when an LED fails open and a zener takes over, voltage across the string of LEDs increases. The driver IC provides dynamic voltage and current adjustment. Additionally, it will provide dimming using pulse width modulation or by use of an adjustable 0 ~ 10V signal, as well as performing other control and monitoring functions.