Patent ID: 8373404
Filing Date: 2013-02-12
Classification: H02M

Abstract:
1. A negative lock loop for a flyback voltage converter including a transformer having a primary winding and a secondary winding and a power switch serially connected to the primary winding, the negative lock loop comprising: a current source for providing a charging current which determines a peak value of a current in the secondary winding; a capacitor; a first switch connected between the current source and capacitor, for being controlled by a first clock to charge the capacitor by the charging current; a second switch parallel connected with the capacitor, for being controlled by a second clock to reset the capacitor; a comparator coupled to the capacitor for generating a comparison signal by comparing a voltage of the capacitor with a voltage threshold; and a logic circuit coupled to the comparator for adjusting the charging current according to the comparison signal and the first and second clocks; wherein the first clock turns on the first switch when the current in the secondary winding is greater than a current threshold, to thereby allow the charging current to charge the capacitor, and the second clock turns on the second switch when the power switch is on, to thereby reset the capacitor.