Synchronous rectifier and method of operation

A synchronous rectification circuit coupled to maintain a substantially constant output signal at a predetermined level in response to an input signal operating at first and second polarities, the synchronous rectification circuit comprising:

• a charging circuit including,
• (a) a first comparator having a first input coupled to receive a reference signal indicative of the predetermined level, a second input coupled to receive the output signal, a power supply input coupled to receive the output signal and an output coupled to provide a control signal;
• and
• (b) a current switch having a control terminal coupled to receive the control signal, a first conduction terminal coupled to receive the input signal and a second conduction terminal coupled to provide a charging signal when the input signal is at the first polarity;
• and
• a polarity detection circuit coupled to receive the input signal and coupled to provide a signal indicative of the polarity of the input signal.

In an integrated circuit, a synchronous rectifier receiving an input signal at first and second pins of the integrated circuit and providing a charging signal at a third pin of the integrated circuit to maintain an output signal at a predetermined level, the synchronous rectifier comprising:

• a bias supply circuit including,
• (a) a first comparator coupled to receive the output signal and a reference signal indicative of the predetermined level having a power supply input coupled to receive the output signal and having an output coupled to provide a charging control signal when the output signal is below the predetermined level;
• and
• (b) a current switch having a control terminal coupled to receive the charging control signal, a first conduction terminal coupled to receive the input signal and a second conduction terminal coupled to provide the charging signal;
• and
• a conduction control circuit coupled to the first and second pins receiving the input signal at a first polarity and blocking the input signal at a second polarity.

A method of operating a synchronous rectification circuit to maintain a predetermined output signal level in response to an alternating input signal at first and second polarities, the method comprising:

• using a current switch to provide a charging signal in response to the first polarity;
• using a comparator to regulate the charging signal to maintain the predetermined output signal level substantially independent of an input signal level, wherein the comparator is coupled to receive the predetermined output signal at a power supply input;
• and
• providing a control signal to limit the alternating input signal to a first level in response to the second polarity.

A method of operating a synchronous rectifier to maintain a substantially constant output signal substantially independent of an alternating input signal, comprising:

• receiving the alternating input signal at first and second polarities;
• using a comparator to provide a control signal when the output signal is less than a predetermined level, wherein the comparator is coupled to receive the output signal at a power supply input;
• using a current switch to provide a charging signal in response to the control signal during the first polarity of the input signal;
• and
• clamping the second polarity of the input signal to a first level.