Nxp 4000 series logic devices nxp hef4046bt 652 the hef4046b is a phase locked loop circuit that consists of a linear voltage controlled oscillator vco and two different phase comparators with a common signal input amplifier and a common comparator input a 7 v regulator zener diode is provided for supply voltage regulation if necessaryit operates over a recommended vdd power supply range of 3 v to 15 v referenced to vss usually ground unused inputs must be connected to vdd vss or a