Controller and isolated power converter

A controller, comprising:

• a bypass terminal coupled to a bypass capacitor, wherein the bypass capacitor is coupled to a secondary side of an isolated power converter;
• a first power circuit coupled to the bypass terminal and a first terminal, the first terminal coupled to a node of the secondary side of the isolated power converter, the first power circuit coupled to transfer electric charge from the first terminal to the bypass terminal so that the electric charge is stored in the bypass capacitor;
• a second power circuit coupled to the first terminal, a second terminal and a third terminal, the second terminal and the third terminal respectively coupled two terminals of a flying capacitor, the second power circuit coupled to transfer the electric charge from the first terminal to the flying capacitor and from the flying capacitor to the bypass terminal so that the electric charge is stored in the bypass capacitor;
• and
• a charging control circuit, which is coupled to control the first or second power circuit to transfer the electric charge to the bypass terminal in response to at least one of a bypass voltage at the bypass terminal and a voltage at the first terminal.