Current-direction detecting circuit and dc-dc converter

DC-DC converter comprising:

• a first switching transistor whose one end is connected to first power potential;
• a second switching transistor whose one end is connected to second power potential and the other end is connected to the other end of the first switching transistor;
• a gate controller configured to output a gate signal to turn on and off the first switching transistor and the second switching transistor;
• an inductor whose one end is connected to the other end of the first switching transistor and the other end of the second switching transistor;
• and
• a current-direction detecting circuit connected to a monitoring target transistor to be monitored and the gate controller, and configured to detect a direction of current being passed between the one end and the other end of the monitoring target transistor, the monitoring target transistor being one of the first switching transistor and the second switching transistor,
• wherein the current-direction detecting circuit comprises:
• an amplifier configured to amplify a voltage on the other end of the monitoring target transistor to output a first amplified signal and configured to amplify a voltage on the one end to output a second amplified signal;
• a first offset compensation capacitor connected to a first output terminal of the amplifier, the first amplified signal being outputted from the first output terminal;
• a second offset compensation capacitor connected to a second output terminal of the amplifier, the second amplified signal being outputted from the second output terminal;
• a switch configured to form a first loop circuit comprising the amplifier and the first offset compensation capacitor based on the gate signal when the switching transistor is turned off, configured to form a second loop circuit comprising the amplifier and the second offset compensation capacitor based on the gate signal when the switching transistor is turned off, configured to supply a common reference voltage to the first loop circuit and the second loop circuit in such a manner that a charge is stored in the first offset compensation capacitor and the second offset compensation capacitor, and configured to end the first loop circuit and the second loop circuit based on the gate signal when the switching transistor is turned on;
• and
• a monitoring comparator configured to compare a first input signal with a second input signal and configured to output a signal in accordance with a comparison result when the switching transistor is turned on, the first input signal being input through the first offset compensation capacitor, the second input signal being input through the second offset compensation capacitor.

DC-DC converter comprising:

• an inductor whose one end is connected to first power potential;
• a first switching transistor whose one end is connected to the other end of the inductor;
• a second switching transistor whose one end is connected to second power potential and the other end is connected to the other end of the first switching transistor and the other end of the inductor;
• a gate controller configured to output a gate signal to turn on and off the first switching transistor and the second switching transistor;
• and
• a current-direction detecting circuit connected to a monitoring target transistor to be monitored and the gate controller, and configured to detect a direction of current being passed between the one end and the other end of the monitoring target transistor, the monitoring target transistor being one of the first switching transistor and the second switching transistor,
• wherein the current-direction detecting circuit comprises:
• an amplifier configured to amplify a voltage on the other end of the monitoring target transistor to output a first amplified signal and configured to amplify a voltage on the one end to output a second amplified signal;
• a first offset compensation capacitor connected to a first output terminal of the amplifier, the first amplified signal being outputted from the first output terminal;
• a second offset compensation capacitor connected to a second output terminal of the amplifier, the second amplified signal being outputted from the second output terminal;
• a switch configured to form a first loop circuit comprising the amplifier and the first offset compensation capacitor based on the gate signal when the switching transistor is turned off, configured to form a second loop circuit comprising the amplifier and the second offset compensation capacitor based on the gate signal when the switching transistor is turned off, configured to supply a common reference voltage to the first loop circuit and the second loop circuit in such a manner that a charge is stored in the first offset compensation capacitor and the second offset compensation capacitor, and configured to end the first loop circuit and the second loop circuit based on the gate signal when the switching transistor is turned on;
• and
• a monitoring comparator configured to compare a first input signal with a second input signal and configured to output a signal in accordance with a comparison result when the switching transistor is turned on, the first input signal being input through the first offset compensation capacitor, the second input signal being input through the second offset compensation capacitor.