| 摘要 |
Novel system and methodology are provided for controlling a DC/DC forward converter (200) having a transformer (PT) with primary and secondary windings, a reset switch (AG), and a first switch (PG) coupled to the primary winding of the transformer. The control system involves a PWM control circuit (202,204,206) responsive to an output signal (V out ) of the converter (200) for producing a PWM signal to control switching of the reset switch (AG), and the first switch (PG). A period of the PWM signal includes an on-time interval for enabling transfer of power via the transformer (PT) when the first switch (PG) is on, and a reset time interval for enabling reset of the transformer (PT) when the reset switch (AG) is on. A maximum value of the on-time interval is pre-set to provide sufficient time for the reset. The reset switch (AG) 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 (PG) on. A first delay control circuit (206) is provided for reducing the first delay time when the on-time interval approaches the maximum value. Further, the converter (200) may include a second switch (FG) coupled to the secondary winding of the transformer (PT). A second delay period shorter than the first delay period may be set between time when the reset switch (AG) turns off and time when the second switch (FG) turns on. A second delay control circuit (204) may be provided for reducing the second delay period when the on-time interval approaches the maximum value. |
