WO2013146570A1 - カスコード回路 - Google Patents
カスコード回路 Download PDFInfo
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- WO2013146570A1 WO2013146570A1 PCT/JP2013/058241 JP2013058241W WO2013146570A1 WO 2013146570 A1 WO2013146570 A1 WO 2013146570A1 JP 2013058241 W JP2013058241 W JP 2013058241W WO 2013146570 A1 WO2013146570 A1 WO 2013146570A1
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- switching element
- voltage
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- power supply
- circuit
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/22—Modifications for ensuring a predetermined initial state when the supply voltage has been applied
- H03K17/223—Modifications for ensuring a predetermined initial state when the supply voltage has been applied in field-effect transistor switches
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/08—Modifications for protecting switching circuit against overcurrent or overvoltage
- H03K17/081—Modifications for protecting switching circuit against overcurrent or overvoltage without feedback from the output circuit to the control circuit
- H03K17/0812—Modifications for protecting switching circuit against overcurrent or overvoltage without feedback from the output circuit to the control circuit by measures taken in the control circuit
- H03K17/08122—Modifications for protecting switching circuit against overcurrent or overvoltage without feedback from the output circuit to the control circuit by measures taken in the control circuit in field-effect transistor switches
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/10—Modifications for increasing the maximum permissible switched voltage
- H03K17/102—Modifications for increasing the maximum permissible switched voltage in field-effect transistor switches
Definitions
- the present invention relates to a cascode circuit, and more particularly to a cascode circuit that operates normally off.
- High voltage power transistors using SiC (silicon carbide), GaN (gallium nitride), and the like are rapidly expanding in applications such as switching power supplies.
- a gate drive circuit normally-off operation gate
- driving normally-off type switching elements generally used in switching power supplies and the like.
- Drive circuit cannot be applied.
- a cascode circuit may be configured by connecting the drain of the normally-off type switching element to the source of the normally-on type switching element.
- FIG. 7 is a circuit diagram showing a circuit configuration of a conventional cascode circuit.
- the cascode circuit shown in FIG. 7 includes a switching element Q1 and a switching element Q2.
- the switching element Q1 is a normally-off type, and the switching element Q2 is a normally-on type FET (Field Effect Transistor).
- the source of the switching element Q2 is connected to the drain of the switching element Q1.
- the source of the switching element Q1 is connected to the gate of the switching element Q2.
- a gate drive circuit 100 for normally-off operation is connected to the gate of the switching element Q1.
- the gate drive element G In the gate drive circuit 100, the gate drive element G generates a gate drive signal for normally-off operation based on the control signal supplied from the signal source S, and outputs it to the gate of the switching element Q1.
- the gate drive circuit 100 is supplied with a power supply voltage V from a power supply E via a power supply terminal P.
- the resistor R is a gate resistor and adjusts the transmission time of the gate drive signal.
- the capacitor C is a bypass capacitor of the gate drive circuit 100 and stabilizes the power supply voltage V supplied to the power supply terminal P.
- the capacitor C0 is a capacitor for stabilizing the power supply E.
- connection point P0 The connection between the source of the switching element Q1 and an external circuit (not shown) is the connection point P0, the connection between the drain of the switching element Q1 and the source of the switching element Q2 is the connection point P1, and the drain of the switching element Q2 and the external circuit ( A connection point (not shown) is defined as a connection point P2.
- the cascode circuit can turn off the normally-on switching element Q2 when the gate drive circuit 100 for normally-off operation is turned off.
- the turn-off operation of the cascode circuit shown in FIG. 7 will be described with reference to FIG.
- FIG. 8 is a waveform diagram showing temporal changes in the gate-source voltage and the drain-source voltage of each switching element during the turn-off operation in the cascode circuit shown in FIG.
- Waveform 8a is the gate-source voltage Vgs1 of switching element Q1
- waveform 8b is the drain-source voltage Vds1 of switching element Q1
- waveform 8c is the gate-source voltage Vgs2 of switching element Q2
- waveform 8d is the drain of switching element Q2.
- the drain-source voltage Vds1 of the switching element Q1 and the drain-source voltage Vds2 of the switching element Q2 are both zero.
- the drain-source voltage Vds1 of the switching element Q1 starts increasing.
- the voltage applied to the source of the normally-on type switching element Q2 increases, so that the gate-source voltage Vgs2 of the switching element Q2 becomes a negative voltage.
- the magnitudes of the drain-source voltage Vds1 of the switching element Q1 and the gate-source voltage Vgs2 of the switching element Q2 are potential differences between the connection point P0 and the connection point P1, but the direction of each voltage is The sign is opposite. Therefore, the negative voltage applied to the gate-source voltage Vgs2 of the switching element Q2 increases.
- the switching element Q2 starts a turn-off operation.
- the switching element Q2 starts to turn off, but immediately starts switching from the on state to the off state. Not to do.
- Switching element Q2 starts switching from the on state to the off state after a delay time ⁇ t2 from the start of the turn-off operation. Since the switching element Q2 remains on from time (t1 + ⁇ t1) to time (t2 + ⁇ t2), the potential at the connection point P1 is the same as the potential at the connection point P2. Therefore, the increase in the drain-source voltage Vds1 of the switching element Q1 directly increases the potential at the connection point P2.
- the switching element Q2 starts switching from the on state to the off state, so that the drain-source voltage Vds2 of the switching element Q2 starts increasing.
- the potential at the connection point P2 continues to rise.
- the drain-source voltage Vds1 of the switching element Q1 and the drain-source voltage Vds2 of the switching element Q2 indicate the potential difference between the connection point P0 and the connection point P2, and the drain-source voltage of the switching element Q1.
- the voltage is divided according to the parasitic capacitance of the source-to-source voltage and the ratio of the parasitic capacitance between the drain and source of the switching element Q2. Therefore, the drain-source voltage Vds1 of the switching element Q1 continues to increase.
- the switching element Q1 and the switching element Q2 complete the turn-off operation, and both are in the off state.
- the drain-source voltage Vds1 of the switching element Q1 and the drain-source voltage Vds2 of the switching element Q2 indicate the potential difference between the connection point P0 and the connection point P2, and the parasitic between the drain-source of the switching element Q1.
- the voltage is divided according to the capacitance and the ratio of the parasitic capacitance between the drain and source of the switching element Q2.
- the withstand voltage required for the switching element Q1 is about the same as the power supply voltage V, a switching element with a low withstand voltage is used as the switching element Q1. This is because, in a switching element such as an FET, it is known that the lower the breakdown voltage, the smaller the on-resistance, so that power loss during conduction can be reduced. When an external circuit that requires a high voltage is connected to the cascode circuit, it is necessary to use a high breakdown voltage switching element as the normally-on type switching element Q2.
- drain-source voltage Vds1 of the switching element Q1 and the drain-source voltage Vds2 of the switching element Q2 are voltages obtained by dividing the potential difference between the connection point P0 and the connection point P2 as described above. Depending on the ratio of the parasitic capacitance, a high voltage may be applied between the drain and source of the switching element Q1. Therefore, in the low breakdown voltage switching element Q1, the drain-source voltage Vds1 of the switching element Q1 may exceed the breakdown voltage and be damaged.
- Patent Document 1 specifically discloses the following two circuit configurations.
- a Zener diode for clamping a voltage is connected in parallel to the switching element between the drain and the source of the normally-off type switching element so that the cathode is connected to the drain of the switching element. It is.
- the switching element can be prevented from being damaged.
- the drain-source voltage exceeds the breakdown voltage, the energy that would normally increase the voltage becomes a power loss as a Zener breakdown. Therefore, the power conversion efficiency is lowered, and there is a concern about an adverse effect on the long-term reliability of the Zener diode.
- a capacitor is connected in parallel between the drain and source of the normally-off type switching element to moderate the increase in drain-source voltage.
- the present invention has been made to solve the above-mentioned problems, and prevents a normally-off type switching element from being damaged during a turn-off operation, and reduces a power loss.
- the purpose is to provide.
- a cascode circuit includes a first switching element that is a normally-off type, and a second switching element in which a source is connected to the drain of the first switching element. And a normally-off operation is performed by a gate driving circuit connected to the gate of the first switching element.
- a clamp circuit that clamps a voltage between the drain and source of one switching element to a power supply voltage supplied from a power supply is further provided.
- the second switching element is normally on, and the source of the first switching element is connected to the gate.
- the clamp circuit includes a first diode connected in series between the drain of the first switching element and the power supply terminal so that the anode is connected to the drain of the first switching element.
- the second switching element is a normally-off type, and a power supply voltage supplied from a power supply is input to the gate.
- the clamp circuit includes a first diode connected in series between the drain of the first switching element and the power supply terminal so that the anode is connected to the drain of the first switching element.
- the clamp circuit includes a capacitor connected between the cathode of the first diode and the source of the first switching element, and a resistor connected between the cathode of the first diode and the power supply terminal of the gate drive circuit. And further including.
- the clamp circuit includes a capacitor connected between the cathode of the first diode and the source of the first switching element, and an inductor connected between the cathode of the first diode and the power supply terminal of the gate drive circuit. And a second diode connected in series between the power supply and the power supply terminal so as to connect the cathode to the power supply terminal.
- the cascode circuit according to the present invention includes a clamp circuit, and suppresses the drain-source voltage of the first switching element to be equal to or lower than the power supply voltage supplied to the power supply terminal of the gate drive circuit. Since the power supply voltage of the gate driving circuit is a voltage supplied to the gate for driving the first switching element, it is set to be less than the gate-source breakdown voltage of the first switching element. Therefore, the power supply voltage of the gate drive circuit is less than the drain-source breakdown voltage. Therefore, the drain-source voltage of the first switching element is suppressed to be less than the drain-source breakdown voltage, and the first switching element can be prevented from being damaged.
- the power loss of the cascode circuit is only energy consumed when the drain voltage of the first switching element exceeds the power supply voltage of the gate drive circuit in the clamp circuit. Power loss can be reduced. As described above, it is possible to realize a cascode circuit that prevents the first switching element from being damaged during the turn-off operation and that reduces power loss.
- FIG. 2 is a waveform diagram showing temporal changes in the gate-source voltage and the drain-source voltage of each switching element during the turn-off operation in the cascode circuit shown in FIG. It is a circuit diagram which shows the circuit structure of the cascode circuit which concerns on Embodiment 2 of this invention. It is a circuit diagram which shows the circuit structure of the cascode circuit which concerns on Embodiment 3 of this invention.
- FIG. 5 is a waveform diagram showing temporal changes of the gate-source voltage and the drain-source voltage of each switching element during the turn-off operation in the cascode circuit shown in FIG.
- FIG. 8 is a waveform diagram showing temporal changes in the gate-source voltage and the drain-source voltage of each switching element during the turn-off operation in the cascode circuit shown in FIG.
- FIG. 1 is a circuit diagram showing a circuit configuration of a cascode circuit according to Embodiment 1 of the present invention.
- the cascode circuit 1 shown in FIG. 1 includes a switching element Q1, a switching element Q2, and a clamp circuit 10.
- the switching element Q1 (first switching element) is a normally-off type FET, and the switching element Q2 (second switching element) is a normally-on type power transistor.
- the source of the switching element Q2 is connected to the drain of the switching element Q1.
- the source of the switching element Q1 is connected to the gate of the switching element Q2.
- a gate drive circuit 100 for normally-off operation is connected to the gate of the switching element Q1.
- the gate drive element G In the gate drive circuit 100, the gate drive element G generates a gate drive signal for normally-off operation based on the control signal supplied from the signal source S, and outputs it to the gate of the switching element Q1.
- the gate drive circuit 100 is supplied with a power supply voltage V from a power supply E via a power supply terminal P.
- the resistor R is a gate resistor and adjusts the transmission time of the gate drive signal.
- the capacitor C is a bypass capacitor of the gate drive circuit 100 and stabilizes the power supply voltage V supplied to the power supply terminal P.
- the capacitor C0 is a capacitor for stabilizing the power supply E.
- the clamp circuit 10 includes a diode D1, a capacitor C1, and a resistor R1.
- the diode D1 (first diode) is connected in series between the drain of the switching element Q1 and the power supply terminal P so that the anode is connected to the drain of the switching element Q1.
- the capacitor C1 is connected between the cathode of the diode D1 and the source of the switching element Q1.
- the resistor R1 is a discharge resistor, and is connected in series between the cathode of the diode D1 and the power supply terminal P in order to discharge the excess charge of the capacitor C1.
- connection point P0 The connection between the source of the switching element Q1 and an external circuit (not shown) is the connection point P0, the connection between the drain of the switching element Q1 and the source of the switching element Q2 is the connection point P1, and the drain of the switching element Q2 and the external circuit ( A connection point (not shown) is defined as a connection point P2.
- FIG. 2 is a waveform diagram showing temporal changes in the gate-source voltage and the drain-source voltage of each switching element during the turn-off operation in the cascode circuit 1 shown in FIG.
- Waveform 2a is a gate-source voltage Vgs1 of switching element Q1
- waveform 2b is a drain-source voltage Vds1 of switching element Q1
- waveform 2c is a voltage Vc1 between terminals of capacitor C1
- waveform 2d is a gate-source voltage of switching element Q2.
- a voltage Vgs2 and a waveform 2e indicate the drain-source voltage Vds2 of the switching element Q2.
- the drain-source voltage Vds1 of the switching element Q1 and the drain-source voltage Vds2 of the switching element Q2 are both zero.
- the capacitor C1 is charged with the power supply voltage V.
- the drain-source voltage Vds1 of the switching element Q1 starts increasing.
- the voltage applied to the source of the normally-on type switching element Q2 increases, so that the gate-source voltage Vgs2 of the switching element Q2 becomes a negative voltage.
- the magnitudes of the drain-source voltage Vds1 of the switching element Q1 and the gate-source voltage Vgs2 of the switching element Q2 are potential differences between the connection point P0 and the connection point P1, but the direction of each voltage is The sign is opposite. Therefore, the negative voltage applied to the gate-source voltage Vgs2 of the switching element Q2 increases.
- the switching element Q2 starts a turn-off operation.
- the switching element Q2 starts to turn off, but immediately starts switching from the on state to the off state. Not to do.
- Switching element Q2 starts switching from the on state to the off state after a delay time ⁇ t2 from the start of the turn-off operation. Since the switching element Q2 remains on from time (t1 + ⁇ t1) to time (t2 + ⁇ t2), the potential at the connection point P1 is the same as the potential at the connection point P2. Therefore, the increase in the drain-source voltage Vds1 of the switching element Q1 directly increases the potential at the connection point P2.
- the drain-source voltage Vds1 of the switching element Q1 reaches the power supply voltage V supplied to the power supply terminal P of the gate drive circuit 100.
- the current flowed through the path of connection point P2-connection point P1-connection point P0 due to the rectifying action of diode D1.
- time t3 clamps the potential at the connection point P1 to the power supply voltage V by the clamp circuit 10, a current flows through another path of the connection point P2-connection point P1-diode D1-capacitor C1.
- the switching element Q2 starts switching from the on state to the off state, so that the drain-source voltage Vds2 of the switching element Q2 starts increasing.
- the drain-source voltage Vds1 of the switching element Q1 and the terminal-to-terminal voltage Vc1 of the capacitor C1 exceed the power supply voltage V by a voltage ⁇ V due to the current flowing through another path. Since the capacitor C1 has a capacitance several orders of magnitude larger than the parasitic capacitance between the drain and source of the switching element Q1, the voltage ⁇ V is smaller than the power supply voltage V. Therefore, the drain-source voltage Vds1 of the switching element Q1 does not greatly exceed the power supply voltage V.
- the switching element Q1 and the switching element Q2 complete the turn-off operation, and both are in the off state. Since the resistor R1 consumes energy corresponding to the voltage ⁇ V stored in the capacitor C1 according to the time constant (R1 ⁇ C1), the drain-source voltage Vds1 of the switching element Q1 converges to the power supply voltage V, and the capacitor C1 The inter-terminal voltage Vc1 returns to the power supply voltage V again.
- the gate-source breakdown voltage of the switching element Q1 is set higher than the power supply voltage V. Since the drain-source breakdown voltage of the switching element Q1 is theoretically higher than the gate-source breakdown voltage, it is higher than the power supply voltage V. Therefore, if the drain voltage of the switching element Q1 is clamped to be equal to or lower than the power supply voltage V, the drain-source voltage Vds1 of the switching element Q1 can be suppressed to be less than the drain-source breakdown voltage. It can be prevented from being damaged.
- the cascode circuit 1 only energy consumed when the drain voltage of the switching element Q1 exceeds the power supply voltage V (energy corresponding to the voltage ⁇ V) is consumed as heat by the resistor R1, resulting in power loss.
- the conventional cascode circuit described in Patent Document 1 all the energy corresponding to the voltage exceeding the breakdown voltage of the Zener diode or all the energy stored in the capacitor becomes power loss. Therefore, the cascode circuit 1 can reduce power loss as compared with the conventional cascode circuit.
- the first embodiment it is possible to realize a cascode circuit that prevents the switching element Q1 from being damaged during the turn-off operation and reduces the power loss.
- FIG. 3 is a circuit diagram showing a circuit configuration of the cascode circuit according to the second embodiment of the present invention.
- the cascode circuit 2 shown in FIG. 3 is different from the cascode circuit 1 according to the first embodiment in that a clamp circuit 20 is provided. Note that the same components as those of the cascode circuit 1 are denoted by the same reference numerals and detailed description thereof will not be repeated.
- the clamp circuit 20 includes a diode D1, a capacitor C1, and a diode D2.
- the diode D1 (first diode) is connected in series between the drain of the switching element Q1 and the power supply terminal P so that the anode is connected to the drain of the switching element Q1.
- the capacitor C1 is connected between the cathode of the diode D1 and the source of the switching element Q1.
- the inductor L1 is connected in series between the cathode of the diode D1 and the power supply terminal P.
- the diode D2 (second diode) is connected in series between the power supply E and the power supply terminal P so that the cathode is connected to the power supply terminal P.
- the drain-source voltage Vds1 of the switching element Q1 and the terminal-to-terminal voltage Vc1 of the capacitor C1 exceed the power supply voltage V by a voltage ⁇ V due to the current flowing through another path. Since the capacitor C1 has a capacitance several orders of magnitude larger than the parasitic capacitance between the drain and source of the switching element Q1, the voltage ⁇ V is smaller than the power supply voltage V. The energy corresponding to the voltage ⁇ V is temporarily stored in the inductor L1, and then supplied to the gate drive circuit 100. The diode D2 prevents the energy corresponding to the voltage ⁇ V from flowing back to the power source E.
- the drain-source voltage Vds1 of the switching element Q1 and the terminal-to-terminal voltage Vc1 of the capacitor C1 are clamped and become equal to or lower than the voltage (V + ⁇ V). Therefore, the drain-source voltage Vds1 of the switching element Q1 does not greatly exceed the power supply voltage V of the gate drive circuit 100.
- the switching element Q1 and the switching element Q2 complete the turn-off operation, and both are in the off state.
- the drain-source voltage Vds1 of the switching element Q1 converges to the power supply voltage V, and the inter-terminal voltage Vc1 of the capacitor C1 also returns to the power supply voltage V.
- the switching element Q1 can be prevented from being damaged during the turn-off operation.
- energy corresponding to the voltage ⁇ V is supplied to the gate drive circuit 100 and used for its operation, it is not consumed as heat by the resistor R1 as in the first embodiment and does not cause power loss. Therefore, power loss can be further reduced.
- FIG. 4 is a circuit diagram showing a circuit configuration of a cascode circuit according to Embodiment 3 of the present invention.
- the cascode circuit 3 shown in FIG. 4 is characterized in that the switching element Q2 is a normally-off power transistor and that the power supply voltage V is input to the gate of the switching element Q2 accordingly. This is different from the cascode circuit 1 according to FIG.
- the clamp circuit 10 is the same as that in the cascode circuit 1. Note that the same components as those of the cascode circuit 1 are denoted by the same reference numerals and detailed description thereof will not be repeated.
- FIG. 5 is a waveform diagram showing temporal changes in the gate-source voltage and the drain-source voltage of each switching element during the turn-off operation in the cascode circuit 3 shown in FIG.
- Waveform 5a is a gate-source voltage Vgs1 of switching element Q1
- waveform 5b is a drain-source voltage Vds1 of switching element Q1
- waveform 5c is a voltage Vc1 between terminals of capacitor C1
- waveform 5d is a gate-source voltage of switching element Q2.
- a voltage Vgs2 and a waveform 5e indicate the drain-source voltage Vds2 of the switching element Q2.
- the gate-source voltage Vgs2 of the normally-off type switching element Q2 is the power supply voltage V, and both the switching element Q1 and the switching element Q2 are in the on state.
- the drain-source voltage Vds1 of the switching element Q1 and the drain-source voltage Vds2 of the switching element Q2 are both zero.
- the switching element Q2 starts to turn off, but immediately starts switching from the on state to the off state. Not to do.
- Switching element Q2 starts switching from the on state to the off state after a delay time ⁇ t2 from the start of the turn-off operation. Since the switching element Q2 remains on from time (t1 + ⁇ t1) to time (t2 + ⁇ t2), the potential at the connection point P1 is the same as the potential at the connection point P2. Therefore, the increase in the drain-source voltage Vds1 of the switching element Q1 directly increases the potential at the connection point P2.
- the drain-source voltage Vds1 of the switching element Q1 reaches the power supply voltage V supplied to the power supply terminal P of the gate drive circuit 100.
- the current flowed through the path of connection point P2-connection point P1-connection point P0 due to the rectifying action of diode D1.
- time t3 clamps the potential at the connection point P1 to the power supply voltage V by the clamp circuit 10, a current flows through another path of the connection point P2-connection point P1-diode D1-capacitor C1.
- the switching element Q2 starts switching from the on state to the off state, so that the drain-source voltage Vds2 of the switching element Q2 starts increasing.
- the drain-source voltage Vds1 of the switching element Q1 exceeds the power supply voltage V by the voltage ⁇ V due to the current flowing through another path.
- the gate-source voltage Vgs2 of the switching element Q2 increases from zero in the negative direction by the voltage ⁇ V. Since the capacitor C1 has a capacitance several orders of magnitude larger than the parasitic capacitance between the drain and source of the switching element Q1, the voltage ⁇ V is smaller than the power supply voltage V. Therefore, the drain-source voltage Vds1 of the switching element Q1 does not greatly exceed the power supply voltage V of the gate drive circuit 100.
- the switching element Q1 and the switching element Q2 complete the turn-off operation, and both are in the off state. Since the resistor R1 consumes energy corresponding to the voltage ⁇ V stored in the capacitor C1 according to the time constant (R1 ⁇ C1), the drain-source voltage Vds1 of the switching element Q1 and the terminal voltage Vc1 of the capacitor C1 are the power supply. At the voltage V, the gate-source voltage Vgs2 of the switching element Q2 converges to zero.
- the switching element Q1 is prevented from being damaged during the turn-off operation, and A cascode circuit with reduced power loss can be realized.
- FIG. 6 is a circuit diagram showing a circuit configuration of the cascode circuit according to the fourth embodiment.
- the cascode circuit 4 shown in FIG. 6 is different from the cascode circuit 3 according to the third embodiment in that a clamp circuit 20 is provided instead of the clamp circuit 10.
- the clamp circuit 20 is the same as that in the cascode circuit 2 according to the second embodiment.
- Components equivalent to those of the cascode circuit according to Embodiments 1 to 3 are denoted by the same reference numerals and detailed description thereof will not be repeated.
- the drain-source voltage Vds1 of the switching element Q1 exceeds the power supply voltage V by the voltage ⁇ V due to the current flowing through another path.
- the voltage ⁇ V is smaller than the power supply voltage V.
- the gate-source voltage Vgs2 of the switching element Q2 increases from zero in the negative direction by the voltage ⁇ V.
- the energy corresponding to the voltage ⁇ V is temporarily stored in the inductor L1, and then supplied to the gate drive circuit 100.
- the diode D2 prevents energy corresponding to the voltage ⁇ V from flowing back to the power source E.
- the drain-source voltage Vds1 of the switching element Q1 and the terminal-to-terminal voltage Vc1 of the capacitor C1 are clamped and become equal to or lower than the voltage (V + ⁇ V). Therefore, the drain-source voltage Vds1 of the switching element Q1 does not greatly exceed the power supply voltage V of the gate drive circuit 100.
- the switching element Q1 and the switching element Q2 complete the turn-off operation, and both are in the off state.
- the drain-source voltage Vds1 of the switching element Q1 and the terminal-to-terminal voltage Vc1 of the capacitor C1 both converge to the power supply voltage V, and the gate-source voltage Vgs2 of the switching element Q2 converges to zero.
- the clamp circuit 20 can prevent the switching element Q1 from being damaged during the turn-off operation as in the third embodiment.
- energy corresponding to the voltage ⁇ V is supplied to the gate driving circuit 100 and used for its operation, it is not consumed as heat by the resistor R1 as in the third embodiment and does not cause power loss. Therefore, power loss can be further reduced.
- the switching element Q1 is FET and the switching element Q2 is a power transistor was demonstrated, it is not limited to this. Even when the switching element Q1 and the switching element Q2 are both FETs, the same effect can be obtained if the breakdown voltage of the switching element Q2 is equal to or higher than the breakdown voltage required for the cascode circuit. Even when the switching element Q1 is a bipolar transistor, it can be handled in the same manner by making the drain correspond to the collector, the gate correspond to the base, and the source correspond to the emitter.
- the gate drive circuit 100 includes the signal source S, the gate drive element G, the resistor R, and the capacitor C
- the gate drive signal is supplied from the power supply terminal P to the gate drive signal of the switching element Q1.
- the present invention is applicable regardless of the circuit configuration as long as it is output to the gate.
- Q1, Q2 switching element, 1, 2, 3, 4 cascode circuit, 10, 20 clamp circuit 100 gate drive circuit, G gate drive element, S signal source, P power supply terminal, R, R1 resistance, C, C0, C1 Capacitor, D1, D2 diode, L1 inductor, E power supply, V power supply voltage, P0, P1, P2 connection point, ⁇ V, (V + ⁇ V) voltage, Vc1 terminal voltage, Vds1, Vds2 drain-source voltage, Vgs1, Vgs2 gate -Source voltage, Vth2 gate threshold voltage, 2a, 2b, 2c, 2d, 2e, 5a, 5b, 5c, 5d, 5e, 8a, 8b, 8c, 8d waveform, t1, t2, t3, t4, t5, ( t1 + ⁇ t1), (t2 + ⁇ t2) time, ⁇ t1, ⁇ t2 delay time.
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Abstract
Description
図1は、本発明の実施の形態1に係るカスコード回路の回路構成を示す回路図である。図1に示すカスコード回路1は、スイッチング素子Q1、スイッチング素子Q2、クランプ回路10を備える。
図2は、図1に示すカスコード回路1において、ターンオフ動作時のそれぞれのスイッチング素子のゲート-ソース間電圧およびドレイン-ソース間電圧の時間変化を示す波形図である。波形2aはスイッチング素子Q1のゲート-ソース間電圧Vgs1、波形2bはスイッチング素子Q1のドレイン-ソース間電圧Vds1、波形2cはコンデンサC1の端子間電圧Vc1、波形2dはスイッチング素子Q2のゲート-ソース間電圧Vgs2、波形2eはスイッチング素子Q2のドレイン-ソース間電圧Vds2を示す。
スイッチング素子Q1のドレインの電圧をクランプするクランプ回路10変更することで、電力損失を一層低減することができる。以下、実施の形態2に係るカスコード回路について、図3を参照しながら説明する。
実施の形態1および実施の形態2では、スイッチング素子Q2がノーマリーオン型である場合について説明したが、スイッチング素子Q2がノーマリーオフ型である場合にも、本発明を適用することができる。以下、実施の形態3に係るカスコード回路について、図4および図5を参照しながら説明する。
図5は、図4に示すカスコード回路3において、ターンオフ動作時のそれぞれのスイッチング素子のゲート-ソース間電圧およびドレイン-ソース間電圧の時間変化を示す波形図である。波形5aはスイッチング素子Q1のゲート-ソース間電圧Vgs1、波形5bはスイッチング素子Q1のドレイン-ソース間電圧Vds1、波形5cはコンデンサC1の端子間電圧Vc1、波形5dはスイッチング素子Q2のゲート-ソース間電圧Vgs2、波形5eはスイッチング素子Q2のドレイン-ソース間電圧Vds2を示す。
実施の形態1に対する実施の形態2と同様に、クランプ回路の回路構成を変更することで、実施の形態3の電力損失を一層低減することができる。以下、実施の形態4に係るカスコード回路について、図6を参照しながら説明する。
Claims (5)
- ノーマリーオフ型である第1のスイッチング素子と、
前記第1のスイッチング素子のドレインをソースに接続した第2のスイッチング素子とを備え、
前記第1のスイッチング素子のゲートに接続したゲート駆動回路によりノーマリーオフ動作させるカスコード回路であって、
電源が接続される前記ゲート駆動回路の電源端子と、前記第1のスイッチング素子のドレインとの間に設けられ、前記ゲート駆動回路が前記第1のスイッチング素子および前記第2のスイッチング素子をターンオフ動作したときに、前記第1のスイッチング素子のドレイン-ソース間の電圧を、前記電源から供給される電源電圧にクランプするクランプ回路をさらに備える、カスコード回路。 - 前記第2のスイッチング素子は、ノーマリーオン型であって、前記第1のスイッチング素子のソースをゲートに接続してあり、
前記クランプ回路は、アノードを前記第1のスイッチング素子のドレインに接続するように、前記第1のスイッチング素子のドレインと前記電源端子との間に直列に接続した第1のダイオードを含む、請求項1に記載のカスコード回路。 - 前記第2のスイッチング素子は、ノーマリーオフ型であって、前記電源から供給される前記電源電圧をゲートに入力してあり、
前記クランプ回路は、アノードを前記第1のスイッチング素子のドレインに接続するように、前記第1のスイッチング素子のドレインと前記電源端子との間に直列に接続した第1のダイオードを含む、請求項1に記載のカスコード回路。 - 前記クランプ回路は、
前記第1のダイオードのカソードと前記第1のスイッチング素子のソースとの間に接続したコンデンサと、
前記第1のダイオードの前記カソードと前記ゲート駆動回路の前記電源端子との間に接続した抵抗とをさらに含む、請求項2または3に記載のカスコード回路。 - 前記クランプ回路は、
前記第1のダイオードのカソードと前記第1のスイッチング素子のソースとの間に接続したコンデンサと、
前記第1のダイオードの前記カソードと前記ゲート駆動回路の前記電源端子との間に接続したインダクタと、
カソードを前記電源端子に接続するように、前記電源と前記電源端子との間に直列に接続した第2のダイオードとをさらに含む、請求項2または3に記載のカスコード回路。
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JP2016058810A (ja) * | 2014-09-08 | 2016-04-21 | 新電元工業株式会社 | カスコード素子 |
JP2016139996A (ja) * | 2015-01-28 | 2016-08-04 | 株式会社東芝 | 半導体装置 |
JP2016201693A (ja) * | 2015-04-10 | 2016-12-01 | シャープ株式会社 | 半導体装置 |
JP2018042188A (ja) * | 2016-09-09 | 2018-03-15 | 株式会社東芝 | スイッチングユニットおよび電源回路 |
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