Input voltage sense circuit in a line powered network element

Abstract

Methods and systems of monitoring voltage input to network elements are provided. One method includes receiving an input voltage for a line-powered network element, applying the input voltage across a primary winding of a flyback power converter during an on-time of a primary switch, and transferring the input voltage from the primary winding to a secondary winding of the flyback power converter during an off-time of the primary switch. The method further includes sensing the voltage of the secondary winding during the on-time of the primary switch; and drawing minimal current from the flyback power converter.

1 . A voltage sensing circuit, comprising; 
 a diode adapted to couple to the secondary side of a flyback power converter;    a first capacitor adapted to couple to the diode and filter voltage spikes that occur during switch transitions on the primary; and    an output filter adapted to peak charge the output voltage, wherein the output voltage is proportional to an input voltage of the flyback power converter.    
   
   
       2 . The circuit of  claim 1 , wherein the output filter comprises a resistance-capacitance filter.  
   
   
       3 . A monitoring circuit, comprising: 
 a discontinuous flyback power converter;    a diode coupled to a secondary winding of the flyback power converter;    a filter coupled to the diode;    a capacitor coupled to the filter; and    a voltage output coupled to the capacitor, wherein the output is proportional to an input voltage on a primary side of the flyback power converter.