Synchronous rectifier circuit

A synchronous rectifier circuit, comprising:

• an output terminal for providing an output;
• a first switch, having a ratio of conduction period to cut-off period controlled in accordance with the output at the output terminal;
• an inducing element, connected to said first switch for storing an energy of a first current flowing therethrough;
• a rectifier element, connected to said inducing element;
• a second switch, connected in parallel with said rectifier element, said second switch being conductive so as not to overlap with the conduction period of said first switch;
• and
• control means for cutting off said second switch just before an energy stored in said inducing element is completely released, regardless of whether said first switch is conductive or cut-off, the energy being stored in said inducing element while said first switch is conductive,
• said inducing element is provided between an input terminal and the output terminal, said rectifier element is provided between said inducing element and the output terminal and has a polarity for maintaining the first current, and said first switch has a terminal which is connected between said inducing element and said rectifier element,
• said control means controlling said second switch so as to satisfy
• T2off<=Ton.multidot.Vin/(Vout-Vin),
• where Vin is a voltage of the input terminal, Vout is a voltage of the output terminal, Ton is a conduction time of said first switch, and T2off is a period between cut-off of said first switch and cut-off of said second switch.

A synchronous rectifier circuit, comprising:

• an output terminal for providing an output;
• a first switch, having a ratio of conduction period to cut-off period controlled in accordance with the output at the output terminal;
• an inducing element, connected to said first switch, for storing an energy of a first current flowing therethrough;
• a rectifier element, connected to said inducing element;
• a second switch, connected in parallel with said rectifier element, said second switch being conductive so as not to overlap with the conduction period of said first switch;
• and
• control means for cutting off said second switch just before an energy stored in said inducing element is completely released, regardless of whether said first switch is conductive or cut-off, the energy being stored in said inducing element while said first switch is conductive,
• said first switch is provided between an input terminal and the output terminal, said rectifier element is provided between said first switch and the output terminal and has a polarity in a direction from the output terminal to the input terminal, and said inducing element has a terminal which is connected between said rectifier element and said first switch,
• said control means controlling said second switch so as to satisfy
• T2off<=Ton.multidot.Vin/(-Vout),
• where Vin is a voltage of the input terminal, Vout is a voltage of the output terminal, Ton is a conduction time of said first switch, and T2off is a period between cut-off of said first switch and cut-off of said second switch.

A synchronous rectifier circuit, comprising:

• an output terminal for providing an output;
• a first switch, having a ratio of conduction period to cut-off period controlled in accordance with the output at the output terminal;
• an inducing element, connected to said first switch, for storing an energy of a first current flowing therethrough;
• a rectifier element, connected to said inducing element;
• a second switch, connected in parallel with said rectifier element, said second switch being conductive so as not to overlap with the conduction period of said first switch;
• and
• control means for cutting off said second switch just before an energy stored in said inducing element is completely released, regardless of whether said first switch is conductive or cut-off, the energy being stored in said inducing element while said first switch is conductive,
• said inducing element is provided between an input terminal and the output terminal, said rectifier element is provided between said inducing element and the output terminal and has a polarity for maintaining the first current, and said first switch has a terminal which is connected between said inducing element and said rectifier element,
• the synchronous rectifier circuit further comprising
• a capacitor provided between (i) a junction of said first switch and said inducing element and (ii) said rectifier element;
• and
• a short-circuiting inducing element or a short-circuiting resistance, having a terminal which is connected between said capacitor and said rectifier element,
• said control means controlling said second switch so as to satisfy
• T2off<=Ton.multidot.Vin/Vout,
• where Vin is a voltage of the input terminal, Vout is a voltage of the output terminal, Ton is a conduction time of said first switch, and T2off is a period between cut-off of said first switch and cut-off of said second switch.