Duty cycle balance module for switch mode power converter

A switch mode power converter having a half bridge, full bridge or push-pull topology in which a transformer is driven to conduct current in a first direction during a first half-cycle by a first pulse-width modulated (PWM) signal and in a second direction during a second half-cycle by a second PWM signal to achieve a desired result, comprising:

• a current limiting mechanism which senses a current in said converter and adjusts the duty cycles of at least one of said first and second PWM signals when said sensed current exceeds a predetermined limit threshold;
• and
• a duty cycle balance module comprising:
• an input block which receives first signals Dnor—1 and Dnor—2 representative of the duty cycles which would be used for said first and second PWM signals to achieve said desired result if said duty cycles were not modified by said current limiting mechanism, and second signals Dact—1 and Dact—2 representative of the duty cycles that are actually used for said first and second PWM signals;
• and
• an output block which provides signals Dbl—1 and Dbl—2, said duty cycle balance module arranged such that Dbl—1 and Dbl—2 modify said second PWM signals Dact—1 and Dact—2 as needed in response to said received first and second PWM signals so as to dynamically balance the duty cycles used for said first and second PWM signals and thereby reduce the magnetic flux imbalance in said transformer that might otherwise arise.

A duty cycle balance module for a switch mode power converter which includes an electromagnetic component that is driven to conduct current in a first direction by a first signal having an associated on- and off-time during a switching cycle and a second signal having an associated on- and off-time during said switching cycle and in a second direction by a third signal having an associated on- and off-time during said switching cycle and a fourth signal having an associated on- and off-time during said switching cycle to achieve a desired result, said first, second, third and fourth signals having associated duty cycles respectively defined as the ratio of their respective ON times to the period of said switching cycle, and which further includes a current limiting mechanism which senses a current in said converter and adjusts the ON time or duty cycle of at least one of said first, second, third and fourth signals when said sensed current exceeds a predetermined limit threshold, said duty cycle balance module comprising:

• an input block which receives signals Dnor—1, Dnor—2 representative of the duty cycles or ON times which would be used for said first and second signals, respectively, or for said second and first signals, respectively, and signals Dnor—3, Dnor—4 representative of the duty cycles or ON times which would be used for said third and fourth signals, respectively, or for said fourth and third signals, respectively, to achieve said desired result if said duty cycles or ON times were not modified by said current limiting mechanism, and which receives signals Dact—1, Dact—2 representative of the duty cycles or ON times that are actually used for said first and second signals, respectively, or used for said second and first signals, respectively, and signals Dact—3, Dact—4 representative of the duty cycles or ON times that are actually used for said third and fourth signals, respectively, or used for said fourth and third signals, respectively;
• and
• an output block which provides output signals Dbl—1, Dbl—2, Dbl—3 and Dbl—4, said duty cycle balance module arranged such that Dbl—1, Dbl—2, Dbl—3, Dbl—4 modify said signals Dact—1, Dact—2, Dact—3, Dact—4 as needed in response to said received first, second third and fourth signals so as to dynamically balance the duty cycles used for said first, second, third and fourth signals and thereby reduce the magnetic flux imbalance in said electromagnetic component that might otherwise arise.