DESCRIPTION
Supply Block (see fig. 2): A precise bandgap reference is internally built to ensure a good regulation. The undervoltage comparator with hysteresis and the very-low supply current, before the turn-on threshold is reached, allows to minimize the startup and supply circuitry. Figure 2: Supply Block Diagram +Vi lows the feedback for the boosted output DC voltage regulation. The E/A output will be connected to the compensation capacitor (see biasing of I.C.) to filter the twice rectified mains frequency (2f) so that the circuit doesn’t attempt to regulate the output ripple. The device is provided with an effective overvoltage protection (OVP), realized using the same input pin used for the DC voltage regulation. Since the compensation capacitor slows the E/A response, an internal fast OVP detector is implemented. In steady state condition, the current through R1 is equal to the current in R2 because the comp. capacitor does not allow DC current (nor of course the inverting input of the E/A).