CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-124340, filed on Jul. 3, 2019, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a drive circuit for use in switching power supplies.

BACKGROUND

In the related art, a switching power supply (a so-called DC/DC converter) that generates a desired output voltage from an input voltage has been used as a power supply means for various applications.

However, in the related art, there has been room for further study on eliminating a trade-off between noise characteristics and efficiency in the switching power supply.

SUMMARY

Some embodiments of the present disclosure provide a drive circuit capable of eliminating the trade-off between noise characteristics and efficiency in a switching power supply.

According to one embodiment of the present disclosure, there is provided a drive circuit including: a current capability switch configured to switch a current capability of driving an output transistor of a switching power supply according to whether a switch current flowing through the output transistor is in a continuous mode or in a discontinuous mode.

In some embodiments, the current capability switch may be further configured to lower the current capability when the switch current is in the continuous mode, and raise the current capability when the switch current is in the discontinuous mode.

In some embodiments, the drive circuit may further includes: a first transistor connected between a first power supply terminal and a control terminal of the output transistor; and a second transistor connected between a second power supply terminal and the control terminal of the output transistor, wherein the output transistor is driven by complementarily turning on/off the first transistor and the second transistor.

In some embodiments, the current capability switch may include a third transistor connected in parallel to the first transistor or the second transistor, and be configured to turn off the third transistor when the switch current is in the continuous mode, and turn on or off the third transistor in synchronization with the first transistor or the second transistor when the switch current is in the discontinuous mode.

In some embodiments, the current capability switch may include a third transistor connected in series with the first transistor or the second transistor, and be further configured to set the third transistor in a half-on state when the switch current is in the continuous mode, and set the third transistor in a full-on state when the switch current is in the discontinuous mode.

In some embodiments, the current capability switch may include a clamper configured to limit a voltage applied to the first transistor or the second transistor, and be further configured to lower the current capability of the clamper when the switch current is in the continuous mode, and raise the current capability of the clamper when the switch current is in the discontinuous mode.

In some embodiments, the current capability switch may include a current limiting element connected in series with the first transistor or the second transistor, and a third transistor connected in parallel with the current limiting element, and be further configured to turn off the third transistor when the switch current is in the continuous mode, and turn on the third transistor when the switch current is in the discontinuous mode.

In another embodiment of the present disclosure, there is provided a switching power supply including: a switch output circuit configured to use an output transistor to generate an output voltage from an input voltage; the drive circuit described above, which is configured to drive the output transistor; and a mode detection circuit configured to detect whether the switch current flowing through the output transistor is in the continuous mode or in the discontinuous mode.

In some embodiments, the mode detection circuit may be further configured to detect an edge of the switch current at a timing when the output transistor is turned on.

In some embodiments, the mode detection circuit may be further configured to determine that the switch current is in the continuous mode when the edge of the switch current is detected once or a plurality of times in succession, and determine that the switch current is in the discontinuous mode when the edge of the switch current is not detected for a predetermined time.

