Invention Grant
US08385087B2 Extending achievable duty cycle range in DC/DC forward converter with active clamp reset 有权
在有源钳位复位的DC / DC正激转换器中扩展可实现的占空比范围

Extending achievable duty cycle range in DC/DC forward converter with active clamp reset
Abstract:
Novel system and methodology are provided for controlling a DC/DC forward converter having a transformer with primary and secondary windings, a reset switch, and a first switch coupled to the primary winding of the transformer. The control system involves a PWM control circuit responsive to an output signal of the converter for producing a PWM signal to control switching of the reset switch, and the first switch. A period of the PWM signal includes an on-time interval for enabling transfer of power via the transformer when the first switch is on, and a reset time interval for enabling reset of the transformer when the reset switch is on. A maximum value of the on-time interval is pre-set to provide sufficient time for the reset. The reset switch is turned off when the PWM signal goes from a first level to a second level. A first delay period is set between time when the reset switch turns off and time when the first switch turns on. A first delay control circuit is provided for reducing the first delay time when the on-time interval approaches the maximum value. Further, the converter may include a second switch coupled to the secondary winding of the transformer. A second delay period shorter than the first delay period may be set between time when the reset switch turns off and time when the second switch turns on. A second delay control circuit may be provided for reducing the second delay period when the on-time interval approaches the maximum value.
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