Systems and methods for reducing switching loss in power conversion systems

A controller for a power converter, the controller comprising:

• a sampled-voltage generator configured to sample a first voltage before a first switch becomes closed and generate a sampled voltage based at least in part on the first voltage, the first voltage being proportional to a voltage difference if the first switch is not closed, the first switch including a first switch terminal, a second switch terminal, and a third switch terminal and configured to affect a first current associated with a primary winding of the power converter, the first switch terminal corresponding to a second voltage, the second switch terminal corresponding to a third voltage, the voltage difference being equal to the second voltage minus the third voltage;
• and
• an error amplifier configured to receive the sampled voltage and a reference voltage, generate an amplified voltage based at least in part on the sampled voltage and the reference voltage, and output the amplified voltage in order for a threshold voltage generator to generate a threshold voltage;
• wherein the threshold voltage generator is configured to:
• generate the threshold voltage based on at least information associated with the amplified voltage;
• and
• output the threshold voltage to a drive signal generator;
• wherein the drive signal generator is configured to:
• receive the threshold voltage and a fourth voltage;
• generate a drive signal based at least in part on the threshold voltage and the fourth voltage, the fourth voltage representing a second current associated with a secondary winding of the power converter, the secondary winding coupled to the primary winding;
• and
• output the drive signal to a second switch, the second switch including a fourth switch terminal, a fifth switch terminal, and a sixth switch terminal and configured to affect the second current;
• wherein the drive signal generator is further configured to, in response to the fourth voltage becoming larger than the threshold voltage, generate the drive signal to open the second switch;
• wherein the controller is configured to, in response to the sampled voltage and the reference voltage not being equal, generate the amplified voltage to change the threshold voltage with time.

A controller for a power converter, the controller comprising:

• a threshold voltage generator configured to generate a threshold voltage based on at least information associated with an amplified voltage generated by an error amplifier;
• and
• a drive signal generator configured to receive the threshold voltage and a first voltage, generate a drive signal based at least in part on the threshold voltage and the first voltage, and output the drive signal to a first switch, the first voltage representing a first current, the first switch including a first switch terminal, a second switch terminal, and a third switch terminal and configured to affect the first current associated with a secondary winding coupled to a primary winding of the power converter;
• wherein the error amplifier is configured to:
• receive a sampled voltage from a sampled-voltage generator and a reference voltage;
• and
• generate the amplified voltage based at least in part on the sampled voltage and the reference voltage;
• wherein the sampled-voltage generator is configured to:
• sample a second voltage before a second switch becomes closed;
• and
• generate the sampled voltage based at least in part on the second voltage, the second voltage being proportional to a voltage difference if the second switch is not closed;
• wherein the second switch including a fourth switch terminal, a fifth switch terminal, and a sixth switch terminal, the second switch being configured to affect a second current associated with the primary winding, the fourth switch terminal corresponding to a third voltage, the fifth switch terminal corresponding to a fourth voltage, the third voltage minus the fourth voltage being equal to the voltage difference;
• wherein the drive signal generator is further configured to, in response to the first voltage becoming larger than the threshold voltage, generate the drive signal to open the first switch;
• wherein the threshold voltage generator is further configured to, in response to the sampled voltage and the reference voltage not being equal, change the threshold voltage with time.

A method for a power converter, the method comprising:

• sampling a first voltage before a first switch becomes closed, the first switch including a first switch terminal, a second switch terminal, and a third switch terminal, the first switch being configured to affect a first current associated with a primary winding of the power converter;
• generating a sampled voltage based at least in part on the first voltage, the first voltage being proportional to a voltage difference if the first switch is not closed, the first switch terminal corresponding to a second voltage, the second switch terminal corresponding to a third voltage, the second voltage minus the third voltage being equal to the voltage difference;
• receiving the sampled voltage and a reference voltage;
• generating an amplified voltage based at least in part on the sampled voltage and the reference voltage;
• generating a threshold voltage based on at least information associated with the amplified voltage;
• receiving the threshold voltage and a fourth voltage;
• generating a drive signal based at least in part on the threshold voltage and the fourth voltage;
• and
• outputting the drive signal to a second switch, the fourth voltage representing a second current, the second switch including a fourth switch terminal, a fifth switch terminal, and a sixth switch terminal and configured to affect the second current associated with a secondary winding coupled to the primary winding;
• wherein the generating a drive signal based at least in part on the threshold voltage and the fourth voltage includes, in response to the fourth voltage becoming larger than the threshold voltage, generating the drive signal to open the second switch;
• wherein the generating a threshold voltage based on at least information associated with the amplified voltage includes, in response to the sampled voltage and the reference voltage not being equal, changing the threshold voltage with time.