RELATED APPLICATIONS

The present application is a National Phase of International Application Number PCT/JP2018/010355, filed Mar. 16, 2018.

TECHNICAL FIELD

The present invention relates to a semiconductor switch control circuit and a switching power source device.

BACKGROUND ART

Recently, along with the progress of the development of next generation devices which use a wide band gap semiconductor made of SiC or GaN. For example, the expectation for a highly efficient and miniaturized switching power source device101shown inFIG. 29has been increased. Under such expectation, a wide band gap semiconductor which is a semiconductor switch having a considerably low ON resistance thus having a considerably high switching speed compared to a conventional semiconductor has been attracting attention.

The switching power source device101is a so-called PFC step-up chopper circuit, increases an inputted voltage to a desired voltage, and supplies the predetermined voltage to a load not shown in the drawing from a pair of output terminals. A wide band gap semiconductor (for example, silicon carbide, gallium nitride, gallium oxide, diamond or the like) is used as a semiconductor switch106of such a switching power source device101, it is possible to realize the acquisition of high efficiency and miniaturization of the device due to characteristics of the wide gap band such as low ON resistance and high speed switching.

PRIOR ART DOCUMENT

Patent Document

Patent document 1: JP 2009-22106 A

SUMMARY OF INVENTION

Problem to be Solved by the Invention

However, when a wide band gap semiconductor is used as a semiconductor switch, although high speed switching can be realized, as shown inFIG. 30, there is a concern that unexpected self-oscillation is generated due to a parasitic capacitor or a parasitic inductor during a turn-off period. Particularly, when a threshold value of a semiconductor switch of the wide band gap semiconductor is low, the semiconductor switch is erroneously operated due to self-oscillation thus giving rise to a possibility that the semiconductor switch or a circuit part around the semiconductor switch is broken.

In view of the above, in the above-mentioned switching power source device, as described in patent document 1, a technique is considered where a negative-voltage-use power source is added to the switching power source device, and a gate voltage during a turn-off period is biased to a negative voltage. However, the switching power source device which is obtained by adding the negative-voltage-use power source to the switching power source device has the complicated configuration. Further, even when such a configuration is adopted, self-oscillation is generated at the timing that a large switching current flows such as at the time of starting a power source or at the time that an overload is applied thus eventually bringing about a possibility that a semiconductor switch or a circuit part around the semiconductor switch is broken (see a gate voltage waveform in an overload region shown inFIG. 31). In a load characteristic diagram shown inFIG. 31(a load characteristic diagram having a so-called drooping characteristic), the diagram shows a load characteristic in a case where an overcurrent restricting and protecting circuit which has a fixed power drooping characteristic at a predetermined output current (power) or more and has a winding drooping characteristic generated by a burst control circuit below a predetermined output current (power) is used. As shown inFIG. 31, an operation between a point B (switching point to a burst control) and a point C (switching stop point) is subjected to a burst control and hence, a switching current is restricted whereby the above-mentioned self-oscillation is minimally generated. However, an operation between a point A (drooping start point) and the point B is subjected to a fixed power drooping control and hence, a maximum current flows as a switching current whereby the above-mentioned concern exists. This concern exists also at the time of starting a switching power source.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a semiconductor switch control circuit where self-oscillation is minimally generated even at the timing that a large switching current flows such as at the time of starting a power source or when an overload is applied.

Solution to Problem

[1] According to an aspect of the present invention, there is provided a semiconductor switch control circuit configured to perform an ON/OFF control of a semiconductor switch having a source electrode, a drain electrode and a gate electrode by supplying a drive current to the gate electrode, the semiconductor switch control circuit including: a pulse signal generating part configured to generate a pulse signal which becomes a time reference for performing the ON/OFF control of the semiconductor switch; a drive current generating part configured to generate the drive current based on the pulse signal which the pulse signal generating part generates and to supply the drive current to the gate electrode of the semiconductor switch; a current detecting part configured to detect a drain current or a source current of the semiconductor switch, or a current which flows through a predetermined current path of a peripheral circuit of the semiconductor switch; and a drive current control part configured to have a function of controlling the drive current which the drive current generating part generates based on the pulse signal which the pulse signal generating part generates and the current which the current detecting part detects.[2] According to the semiconductor switch control circuit of the present invention, it is preferable that the drive current generating part include: a source part configured to charge a current to the gate electrode of the semiconductor switch; and a sink part configured to discharge a current from the gate electrode of the semiconductor switch, and the drive current control part be configured to control the drive current by controlling a charge current to be charged to the gate electrode of the semiconductor switch, or a discharge current to be discharged from the gate electrode of the semiconductor switch.[3] According to the semiconductor switch control circuit of the present invention, it is preferable that the drive current control part be configured, when a current which the current detecting part detects exceeds a predetermined first set current, to control the drive current such that a falling speed of a gate voltage during a turn-off period of the semiconductor switch becomes lower than the falling speed of the gate voltage before detection of the current by the current detecting part which exceeds the predetermined first set current.[4] According to the semiconductor switch control circuit of the present invention, it is preferable that the drive current control part be capable of setting a plurality of current levels as the first set current, and be configured to control the drive current such that the falling speed of the gate voltage is lowered in a stepwise manner in accordance with a detection of a current which exceeds a higher current level among the plurality of current levels by the current detection part.[5] According to the semiconductor switch control circuit of the present invention, it is preferable that the semiconductor switch control circuit further include a second pulse signal generating part configured to generate a second pulse signal when a current which the current detecting part detects exceeds the first set current, wherein the drive current control part be configured to control the drive current based on the second pulse signal which the second pulse signal generating part generates.[6] According to the semiconductor switch control circuit of the present invention, it is preferable that the sink part include a plurality of discharge current paths which are connected to each other in parallel, and the drive current control part include: an R terminal into which the pulse signal from the pulse signal generating part is inputted; an S terminal into which the second pulse signal from the second pulse signal generating part is inputted; and a Q terminal from which a control signal for controlling the discharge current is outputted, and the drive current control part also include an RS flip-flop which is configured, when the second pulse signal is inputted from the second pulse signal generating part during an ON period, to stop a discharge operation on at least one discharge current path out of the plurality of discharge current paths at the time of turning off the semiconductor switch following the ON period.[7] According to the semiconductor switch control circuit of the present invention, it is preferable that the sink part include a plurality of discharge current paths which are connected to each other in parallel, and the drive current control part includes a charge/discharge control part which is configured, when the second pulse signal is inputted from the second pulse signal generating part during an ON period, to stop a discharge operation on at least one discharge current path out of the plurality of discharge current paths at the time of turning off the semiconductor switch following the ON period.[8] According to the semiconductor switch control circuit of the present invention, it is preferable that the plurality of discharge current paths respectively have different discharge abilities.[9] According to the semiconductor switch control circuit of the present invention, it is preferable that the drive current control part include a charge/discharge control part which is configured, when the second pulse signal is inputted from the second pulse signal generating part during an ON period, to decrease, in an analogue manner, a current amount of a current which flows through the sink part at the time of turning off the semiconductor switch following the ON period.[10] According to the semiconductor switch control circuit of the present invention, it is preferable that the drive current control part be configured, when a current which the current detecting part detects exceeds a predetermined second set current, to control the drive current such that a rising speed of the gate voltage during a turn-on period of the semiconductor switch becomes lower than the rising speed of the gate voltage before detection of the current by the current detecting part which exceeds the predetermined second set current.[11] According to the semiconductor switch control circuit of the present invention, it is preferable that the drive current control part be capable of setting a plurality of current levels as the second set current, and be configured to control the drive current such that the rising speed of the gate voltage is lowered in a stepwise manner in accordance with a detection of a current which exceeds a higher current level among the plurality of current levels by the current detection part.[12] According to the semiconductor switch control circuit of the present invention, it is preferable that the semiconductor switch control circuit further include a third pulse signal generating part configured to generate a third pulse signal when a current which the current detecting part detects exceeds the second set current, wherein the drive current control part is configured to have a function of controlling the drive current based on the third pulse signal which the third pulse signal generating part generates.[13] According to the semiconductor switch control circuit of the present invention, it is preferable that the source part include a plurality of charge current paths which are connected to each other in parallel, and the drive current control part include: an R terminal into which the pulse signal from the pulse signal generating part is inputted; an S terminal into which the third pulse signal from the third pulse signal generating part is inputted; and a Q terminal from which a control signal for controlling the charge current is outputted, and the drive current control part also include an RS flip-flop which is configured, when the third pulse signal is inputted from the third pulse signal generating part during an ON period, to stop a charge operation on at least one charge current path out of the plurality of charge current paths at the time of turning on the semiconductor switch during an ON period next to the ON period.[14] According to the semiconductor switch control circuit of the present invention, it is preferable that the source part include a plurality of charge current paths which are connected to each other in parallel, and the drive current control part be configured, when the third pulse signal is inputted from the third pulse signal generating part during an ON period, to stop a charge operation on at least one charge current path out of the plurality of charge current paths at the time of turning on the semiconductor switch during an ON period next to the ON period.[15] According to the semiconductor switch control circuit of the present invention, it is preferable that the plurality of charge current paths respectively have different charge abilities.[16] According to the semiconductor switch control circuit of the present invention, it is preferable that the drive current control part include a charge/discharge control part which is configured, when the third pulse signal is inputted from the third pulse signal generating part during an ON period, to decrease, in an analogue manner, a current amount of a current which flows through the source part at the time of turning on the semiconductor switch during an ON period next to the ON period.[17] According to the semiconductor switch control circuit of the present invention, it is preferable that the semiconductor switch control circuit further include a gate voltage detecting part configured to detect a gate voltage of the semiconductor switch, wherein the drive current control part is configured to have a function of controlling the drive current which the drive current generating part generates based on the pulse signal which the pulse signal generating part generates and the gate voltage which the gate voltage detecting part detects.[18] According to the semiconductor switch control circuit of the present invention, it is preferable that the first set current or the second set current be set to a value which exceeds a current range of the drain current or the source current in a rated load region of the semiconductor switch or a current which flows through a predetermined current path of a peripheral circuit of the semiconductor switch.[19] According to the semiconductor switch control circuit of the present invention, it is preferable that the semiconductor switch be formed of a wide gap semiconductor.[20] According to the semiconductor switch control circuit of the present invention, it is preferable that the wide gap semiconductor be formed of silicon carbide, gallium nitride, gallium oxide or diamond.[21] According to another aspect of the present invention, there is provided a switching power source device including: a semiconductor switch having a source electrode, a drain electrode and a gate electrode; and a semiconductor switch control circuit configured to perform an ON/OFF control of the semiconductor switch by supplying a drive current to the gate electrode of the semiconductor switch, wherein the switching power source device includes the semiconductor switch control circuit according to the present invention as the semiconductor switch control circuit.

Advantageous Effects of Invention

The semiconductor switch control circuit and the switching power source device according to the present invention include the drive current control part which controls a drive current which the drive current generating part generates based on a pulse signal which the pulse signal generating part generates and a current which the current detecting part detects. Accordingly, by controlling a drive current such that a falling speed of a gate voltage or a rising speed of the gate voltage is lowered (becomes slow) at the timing that a large switching current flows such as at the time of starting the power source or at the time that an overload is applied (seeFIG. 4,FIG. 7,FIG. 13andFIG. 16), it is possible to provide the semiconductor switch control circuit and the switching power source device which minimally cause a phenomenon that a semiconductor switch or a circuit part around the semiconductor switch is broken due to self-oscillation and an erroneous operation of the semiconductor switch caused by the self-oscillation even at the timing that the large switching current flows such as at the time of starting the power source or at the time that an overload is applied (seeFIG. 5andFIG. 14).

