DC-DC converter and method of controlling DC-DC converter
A DC-DC converter includes a drive circuit configured to drive a first switching element, and a second switching element coupled between a low potential power terminal of the drive circuit and a first node corresponding to the input voltage or the output voltage. A current detecting section detects a load current flowing in the output terminal. A control circuit turns on a third switching element, which is coupled between the low potential power terminal of the drive circuit and a second node having a potential lower than both the input voltage and the output voltage, in a case where a difference between the input voltage and the output voltage is lower than a threshold. The control circuit controls the second and third switching elements based on a detection result of the current detecting section in a case where the difference is equal to or greater than the threshold.
1. A DC-DC converter that converts an input voltage to an output voltage, the DC-DC converter comprising:
a first switching element;
a drive circuit coupled to the first switching element and configured to drive the first switching element so as to convert the input voltage to the output voltage;
a second switching element coupled between a low potential power terminal of the drive circuit and a first node corresponding to the input voltage or the output voltage;
a third switching element coupled between the low potential power terminal of the drive circuit and a second node having a potential lower than both the input voltage and the output voltage;
a current detecting section configured to detect a load current flowing in an output terminal of the DC-DC converter; and
a control circuit configured to turn on the third switching element in a case where a difference between the input voltage and the output voltage is lower than a threshold, and to control the second switching element and the third switching element based on a detection result of the current detecting section in a case where the difference is equal to or greater than the threshold.
2. The DC-DC converter according to claim 1 , wherein the control circuit turns on one of the second switching element and the third switching element based on the detection result of the current detecting section.
3. The DC-DC converter according to claim 1 , wherein:
the control circuit includes a comparator configured to compare a multiplied value with a certain voltage value, the multiplied value being obtained by multiplying a current value detected by the current detecting section and a certain resistance value, and
the control circuit controls the second switching element and the third switching element based on an output signal of the comparator.
4. The DC-DC converter according to claim 3 , wherein the certain voltage value is determined based on an amount of loss according to charges accumulated in a control terminal of the first switching element and a loss increase by an on-resistance of the first switching element caused by a connection with the low potential power terminal of the drive circuit and the output terminal.
5. The DC-DC converter according to claim 1 , wherein:
the first switching element includes a terminal coupled to the second node, and
during a period in which the first switching element is in an off-state, the control circuit turns on the second switching element for a predetermined time, and subsequently turns on the third switching element.
6. The DC-DC converter according to claim 1 , wherein the control circuit includes a voltage detecting circuit configured to detect the difference between the input voltage and the output voltage in accordance with a voltage change in a control terminal of the first switching element.
7. The DC-DC converter according to claim 6 , wherein the voltage detecting circuit detects the voltage change in the control terminal during a period in which the second switching element is in an on-state, and retains a detected result of the voltage change.
8. The DC-DC converter according to claim 6 , wherein:
the control circuit includes a signal generating circuit configured to generate a periodic signal of a predetermined cycle, and
the control circuit resets a detected result of the voltage change responsive to the periodic signal, and thereafter retains the detected result of the voltage change.
9. The DC-DC converter according to claim 8 , wherein:
the control circuit includes a switching element coupled between a resistive element having the certain resistance value and the second node and configured to turn on or off according to the periodic signal, and
the comparator operates and stops according to the periodic signal.
10. The DC-DC converter according to claim 8 , wherein the signal generating circuit generates the periodic signal according to a switching cycle of the first switching element.
11. A DC-DC converter that converts an input voltage to an output voltage and supplies the output voltage to an output terminal of the DC-DC converter, the DC-DC converter comprising:
a first switching element;
a drive circuit coupled to the first switching element and configured to drive the first switching element so as to convert the input voltage to the output voltage;
a second switching element coupled between a low potential power terminal of the drive circuit and a first node corresponding to the input voltage or the output voltage;
a third switching element coupled between the low potential power terminal of the drive circuit and a second node having a potential lower than both the input voltage and the output voltage;
a control circuit configured to turn on one of the second switching element and the third switching element in accordance with a difference between the input voltage and the output voltage.
12. A method of controlling a DC-DC converter, the method comprising:
converting an input voltage to an output voltage by controlling a first switching element, and outputting the output voltage to an output terminal;
detecting a load current flowing in an external load coupled to the output terminal;
determining whether a difference between the input voltage and the output voltage is lower than a threshold;
controlling a second switching element coupled between a low potential power terminal of a drive circuit configured to drive the first switching element and a first node corresponding to the input voltage or the output voltage and a third switching element based on a detection result of the load current in a case where the difference is equal to or greater than the threshold; and
turning on the third switching element coupled between the low potential power terminal of the drive circuit configured to drive the first switching element and a second node having a potential lower than the input voltage and the output voltage in a case where the difference between the input voltage and the output voltage is lower than the threshold.