Alpha and Omega Semiconductor International LP

Hung-Ta Hsu

Jung-Pei Cheng

Yueh-Ping Yu

Hsiang-Chung Chang

Yu-Ming Chen

Tien-Chi Lin

A flyback converter to control conduction time in AC/DC conversion technology. The flyback converter includes a primary side and a secondary side. The primary side includes a main switch connecting a primary coil to the input of the flyback converter in series. The secondary side includes a secondary coil coupling with the output terminal of the flyback converter. When a switching frequency of the main switch is at a preset first on time in the range between the off frequency and the second switching frequency, the on-time of the main switch continuously changes corresponding to output load changes. When the switching frequency of the main switch is higher than the first switching frequency, the on time of the main switch is constant. The on time is controlled to change linearly, so as to avoid excessive changes in the output voltage ripples, thereby improving circuit efficiency.

Flyback converter for controlling on time variation

A signal transmission circuit is configured for transmitting control information from a secondary side of a power converter to a primary side of the power converter. The signal transmission circuit includes a transmitter circuit, a signal transformer and a detection circuit. The transmitter circuit is configured to generate a ramp signal at least according to a first control signal outputted from the secondary side. The first control signal indicates the control information provided for a switch in the primary side. The signal transformer, coupled to the transmitter circuit, is configured to convert the ramp signal to generate an output signal. The output signal includes a positive-going component and a negative-going component to indicate the control information. The detection circuit, coupled to the signal transformer, is configured to detect the positive-going component and the negative-going component to provide the control information for the switch.

Signal transmission circuit for providing control information from secondary side to primary side of power converter, and control circuit for power converter

When a constant on-time flyback converter is in the switch-on stage, the gate voltage of the switch and the input voltage of the flyback converter adopt the primary side of the transformer to control. The gate voltage is controlled by the second control signal generated by the controller. The flyback converter is then turn off to enter the switch off stage. When the flyback converter is in the switch off stage, the secondary side controller on the secondary side of the transformer, based on the output voltage and output current of the secondary side, sends a first control signal to the primary side controller to control the main switch to turn on. Thus, the flyback converter enters the switch-on stage. Therefore, the calculation complexity is reduced, and there is no need to set a blanking time, such that the flyback converter can be used in high switching frequency applications.

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Zhudong, Taiwan

Hung-Ta Hsu