Patent ID: 8711584
Filing Date: 2014-04-29
Classification: H02M

Abstract:
1. A method for adjusting a duty cycle of switching of a switch in a flyback converter, wherein the flyback converter further includes a transformer having (i) a primary winding and (ii) a secondary winding, wherein the switch is coupled to the primary winding of the transformer, the method comprising, while applying an input voltage to the primary winding of the transformer; alternately switching the switch between a closed position and an opened position in accordance with a first duty cycle, wherein while the switch is in the open position, no current flows in the secondary winding of the transformer, and wherein while the switch is in the closed position, current flows in the secondary winding of the transformer which causes an output voltage of the flyback converter to increase; applying the output voltage to a load based on the current flowing through the secondary winding; while the switch is being alternately switched between the closed position and the opened position in accordance with the first duty cycle, monitoring the output voltage of the flyback converter to determine whether the output voltage has exceeded a voltage threshold, wherein the voltage threshold is predetermined and set to limit the output voltage supplied to the load; in response to the output voltage being determined to have exceeded the voltage threshold, alternately switching the switch between the open position and the closed position in accordance with a second duty cycle, wherein the second duty cycle is greater than the first duty cycle; generating a first control signal having the first duty cycle; generating a second control signal having the second duty cycle, wherein the second control signal is separate from the first control signal, wherein alternately switching the switch between the closed position and the opened position in accordance with the first duty cycle comprises alternately switching the switch based on the first control signal, and wherein alternately switching the switch between the closed position and the opened position in accordance with the second duty cycle comprises alternately switching the switch based on the second control signal; controlling a level of current flowing through the secondary winding according to the first control signal during a first period of time; controlling the level of current flowing through the secondary winding according to the second control signal during a second period of time, wherein the second period of time is subsequent to the first period of time; generating a first plurality of pulses during the first period of time, wherein the first plurality of pulses are output at a predetermined frequency; generating a second plurality of pulses during the second period of time, wherein the second plurality of pulses are output at the predetermined frequency; during the first period of time, outputting every predetermined number of pulses from of the first plurality of pulses as the first control signal during the first period of time; during the second period of time, outputting every pulse from each of the second plurality of pulses as the second control signal at the time subsequent to the first period of time; comparing a first threshold value to the level of the current flowing through the switch; based on a result of the comparing of the first threshold value to the level of the current flowing through the switch, generating a first pulse to be output as the first control signal; incrementing the first threshold value to provide a second threshold value; comparing the second threshold value to the level of the current flowing through the switch; and based on the comparing of the second threshold value to the level of the current flowing through the switch, generating a second pulse to be output as the first control signal.