Insulation-type synchronous DC/DC converter

An insulation-type synchronous DC/DC converter comprising:

• a transformer having its primary winding and its secondary winding;
• a switching transistor coupled to the primary winding of the transformer;
• a synchronous rectifier transistor coupled to the secondary winding of the transformer;
• an output capacitor;
• a photo coupler;
• a synchronous rectifier controller provided on a secondary side of the insulation-type synchronous DC/DC converter;
• a primary controller coupled to an output of the photo coupler, and configured to control the switching transistor according to a feedback signal from the photo coupler, and
• wherein the synchronous rectifier controller comprises:
• a driver circuit for switching the synchronous rectifier transistor;
• a photo coupler connection terminal coupled to an input side of the photo coupler;
• and
• an error amplifier structured to amplify an error between a voltage detection signal according to an output voltage of the DC/DC converter and its target voltage, and to draw a current according to the error from an input side of the photo coupler via the photo coupler connection terminal, wherein the synchronous rectifier controller is packaged in a single module;
• wherein a power supply plane for the error amplifier and a power supply plane for the driver circuit are isolated from each other, and a ground plane for the error amplifier and a ground plane for the driver circuit are isolated from each other;
• and
• the power supply plane for the error amplifier is supplied with an internal power supply voltage which is generated from a voltage at the photo coupler connection terminal, and the ground plane of the error amplifier is supplied with a ground voltage at the secondary side of the DC/DC converter
• wherein the synchronous rectifier controller is structured to switch the synchronous rectifier transistor, and to supply a current according to an error between an output voltage at the output capacitor and its target voltage to an input side of the photo coupler.

A synchronous rectifier controller provided on a secondary side of an insulation-type synchronous DC/DC converter, wherein the DC/DC converter comprises:

• a transformer having its primary winding and its secondary winding;
• a switching transistor coupled to the primary winding of the transformer;
• a synchronous rectifier transistor coupled to the secondary winding of the transformer;
• a photo coupler;
• and
• a primary controller coupled to an output of the photo coupler, and configured to control the switching transistor according to a feedback signal from the photo coupler, and wherein the synchronous rectifier controller comprises:
• a driver circuit for switching the synchronous rectifier transistor;
• a photo coupler connection terminal coupled to an input side of the photo coupler;
• and
• an error amplifier structured to amplify an error between a voltage detection signal according to an output voltage of the DC/DC converter and its target voltage, and to draw a current according to the error from an input side of the photo coupler via the photo coupler connection terminal, wherein the synchronous rectifier controller is packaged in a single module;
• wherein the driver circuit comprises:
• a pulse generator that generates a pulse signal, wherein a level of the pulse signal changes according to at least a voltage across the synchronous rectifier transistor;
• and
• a driver that drives the synchronous rectifier transistor according to the pulse signal;
• wherein (i) the pulse generator sets the pulse signal at an on-level when the voltage across the synchronous rectifier transistor becomes lower than a predetermined negative first threshold voltage, and (ii) the pulse generator sets the pulse signal at an off-level when the voltage across the synchronous rectifier transistor becomes higher than a predetermined negative second threshold voltage, the second threshold voltage being higher than the first threshold voltage;
• and
• wherein the pulse generator comprises:
• a set comparator structured to compare the voltage across the synchronous rectifier transistor and the first threshold voltage so as to generate a set pulse;
• a reset comparator structured to compare the voltage across the synchronous rectifier transistor and the second threshold voltage so as to generate a reset pulse;
• and
• a flip-flop structured to change its output according to the set pulse and the reset pulse.

An insulation-type synchronous DC/DC converter comprising:

• a transformer having its primary winding and its secondary winding;
• a switching transistor coupled to the primary winding of the transformer;
• a synchronous rectifier transistor coupled to the secondary winding of the transformer;
• an output capacitor;
• a photo coupler;
• a synchronous rectifier controller provided on a secondary side of the insulation-type synchronous DC/DC converter;
• a primary controller coupled to an output of the photo coupler, and configured to control the switching transistor according to a feedback signal from the photo coupler, and
• wherein the synchronous rectifier controller comprises:
• a driver circuit for switching the synchronous rectifier transistor;
• a photo coupler connection terminal coupled to an input side of the photo coupler;
• and
• an error amplifier structured to amplify an error between a voltage detection signal according to an output voltage of the DC/DC converter and its target voltage, and to draw a current according to the error from an input side of the photo coupler via the photo coupler connection terminal, wherein the synchronous rectifier controller is packaged in a single module;
• wherein the driver circuit comprises:
• a pulse generator that generates a pulse signal, wherein a level of the pulse signal changes according to at least a voltage across the synchronous rectifier transistor;
• and
• a driver that drives the synchronous rectifier transistor according to the pulse signal;
• wherein (i) the pulse generator sets the pulse signal at an on-level when the voltage across the synchronous rectifier transistor becomes lower than a predetermined negative first threshold voltage, and (ii) the pulse generator sets the pulse signal at an off-level when the voltage across the synchronous rectifier transistor becomes higher than a predetermined negative second threshold voltage, the second threshold voltage being higher than the first threshold voltage;
• and
• wherein the pulse generator comprises:
• a set comparator structured to compare the voltage across the synchronous rectifier transistor and the first threshold voltage so as to generate a set pulse;
• a reset comparator structured to compare the voltage across the synchronous rectifier transistor and the second threshold voltage so as to generate a reset pulse;
• and
• a flip-flop structured to change its output according to the set pulse and the reset pulse
• wherein the synchronous rectifier controller is structured to switch the synchronous rectifier transistor, and to supply a current according to an error between an output voltage at the output capacitor and its target voltage to an input side of the photo coupler.