| 摘要 |
<p>A flyback power supply (10) which includes a sample and hold feedback path. A pulse width modulation circuit (23) provides control signals for a drive device (20) that determines current excitation pulses for a primary winding (17) of a transformer (16). A secondary winding (19) of the transformer is connected to a rectifier circuit (21, 22) and provides a DC voltage signal at an output terminal (12). A selective feedback path (40-49) is provided between the output terminal and a sense input terminal (24) of the pulse width modulation circuit. The selective feedback path comprises a sample and hold circuit (40) which provides for effectively coupling the output terminal to the sense input terminal at times during the storage of energy in the transformer, corresponding to an increase in transformer flux, and wherein at other times when the transformer flux is decreasing and energy is being transferred from the transformer to the rectifier circuit the feedback path effectively disconnects the output terminal from the sense input. The sample and hold circuit comprises a series pass transistor (41) and a holding capacitor (42). The series pass transistor is selectively turned on and off in accordance with the control output signal of the pulse width modulation circuit (23) that determines the primary winding current pulses. This provides a stable, continuous mode flyback power supply operable over a wide range of circuit parameters and which generates minimal RF interference.</p> |
