JP6658575B2 - Gate drive circuit - Google Patents

Description

  The technology disclosed in this specification relates to a gate drive circuit that controls a gate voltage of a voltage-driven switching element.

  A gate drive circuit of a voltage-driven switching element may include a circuit that supplies a stable off-voltage instead of simply connecting the gate to the ground end of the circuit in order to hold the gate at an off-voltage ( For example, Patent Document 1). This is to prevent the switching element from malfunctioning due to noise applied to the gate through the ground end. Further, the off voltage may be set to a voltage lower than the voltage at the ground end. In that case, the circuit that supplies the off-voltage needs to generate a voltage lower than the voltage at the ground end. Hereinafter, the voltage at the ground end of the circuit is referred to as a reference voltage.

JP-A-2006-158478

  Generally, if a circuit for generating an off-state voltage lower than the reference voltage is provided, a corresponding circuit is required. The technology disclosed in this specification provides a gate drive circuit that can realize an off-state voltage lower than a reference voltage with a relatively simple circuit configuration.

  The gate drive circuit disclosed in this specification includes an on-voltage supply circuit, an inductor, a switch, a rectifier, and a controller. The on-voltage supply circuit is connected to a gate of the switching element to be driven, and supplies an on-voltage to the gate. The on-voltage supply circuit may be a known circuit. The inductor, the switch, and the rectifier correspond to an off-voltage generation circuit that supplies an off-voltage to the gate. One end of the inductor is connected to the gate. The switch is connected between a low voltage terminal held at a predetermined reference voltage lower than the ON voltage and the other end of the inductor. The switch connects or disconnects the low voltage end and the other end of the inductor. The rectifier is connected between the high-voltage end, which is maintained at a voltage equal to or higher than the on-voltage, and the other end of the inductor, and allows current flowing from the inductor to the high-voltage end to pass, but not current in the opposite direction. . The controller controls the ON voltage supply circuit and the OFF voltage supply circuit. When switching the switching element from on to off, the controller stops the on-voltage supply circuit and repeats the opening and closing of the switch until the gate voltage falls to a predetermined off-voltage lower than the reference voltage. When the switch is closed, current flows from the gate to the low voltage end through the inductor. At this time, magnetic energy is stored in the inductor. When the switch is opened, an induced current flows due to the magnetic energy stored in the inductor. This induced current forces the charge on the gate to move to the high voltage end. That is, the inductor acts as a pump to push up the gate charge to the high voltage end. As a result, the gate voltage is forcibly reduced. The controller repeats opening and closing of the switch until the gate voltage drops to a predetermined off-voltage lower than the reference voltage. The controller keeps the switch open when the gate voltage reaches the off-state voltage. The gate is disconnected from the low voltage end and is kept at an off voltage lower than the reference voltage. This gate drive circuit can realize an off-state voltage lower than the reference voltage using only the inductor, the switch, and the rectifying element.

  The details and further improvements of the technology disclosed in this specification will be described in the following “Detailed description of the invention”.

It is a circuit diagram of a gate drive circuit of an example. 5 is an example of an operation time chart of a gate drive circuit when a gate voltage is switched from an ON voltage to an OFF voltage. 9 is another example of a time chart of the gate drive circuit when the gate voltage is switched from the ON voltage to the OFF voltage.

  FIG. 1 shows a circuit diagram of the gate drive circuit 2 of the embodiment. The gate drive circuit 2 is a device that switches the gate voltage of the voltage-driven switching element 12 between an ON voltage and an OFF voltage. In the present embodiment, the switching element 12 is an n-channel transistor. More specifically, the switching element 12 is an n-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). In the switching element 12, when the gate G is set to a predetermined ON voltage, a current flows from the drain D to the source S. When the gate G is set to a predetermined off voltage (<on voltage), no current flows. Hereinafter, the voltage of the gate G may be referred to as a symbol LVG (gate voltage LVG). Note that the ON voltage of the switching element 12 may be indicated by a symbol Von (ON voltage Von), and the OFF voltage may be indicated by a symbol Voff (OFF voltage Voff).

  The gate drive circuit 2 includes an on-voltage supply circuit 8, an inductor 3, a diode 5, a switch 4, a high voltage terminal 6, a ground terminal 7, and a controller 9. The controller 9 receives a command from the host controller 14 and controls the gate voltage of the switching element 12. In FIG. 1, dotted lines indicate signal lines. In FIG. 1, illustration of a circuit connected to the drain D of the switching element 12 is omitted. The source S of the switching element 12 is connected to the ground terminal 7.

  The high voltage terminal 6 is a power supply terminal of the gate drive circuit 2 and is kept at the voltage Vcc. The ground terminal 7 is held at the ground voltage Vss of the gate drive circuit 2. The output terminal 8 a of the on-voltage supply circuit 8 is connected to the gate G of the switching element 12. The ON voltage supply circuit 8 receives power supply from the high voltage terminal 6 and supplies an ON voltage Von to the gate G from the output terminal 8a or stops supplying the ON voltage Von according to a command from the controller 9. . In this embodiment, the ON voltage Von of the switching element 12 is equal to the voltage Vcc of the high voltage terminal 6. The output terminal 8a of the on-voltage supply circuit 8 has a high impedance, so that no current flows in and out. When the on-voltage supply circuit 8 stops, its output terminal 8 a is disconnected from the high voltage terminal 6. As a result, the voltage LVG of the gate G changes depending on the operation of the switch 4 described later. Since the on-voltage supply circuit 8 may be an existing circuit, a description of a specific circuit configuration will be omitted.

  One end 3a of the inductor 3 is connected to the gate G, and the other end 3b is connected to the switch 4. The inductor 3 may be, for example, a simple coil. The other end 3b of the switch 4 is connected to the ground end 7. In other words, the switch 4 connects or disconnects between the other end 3b of the inductor 3 and the ground end 7. The switch 4 is opened and closed by a controller 9. The switch 4 may be any device that switches between conduction and cutoff at both ends, but is preferably an element (for example, a transistor) that can switch at high speed.

  The other end 3b of the inductor 3 is also connected to a high voltage end 6 via a diode 5. The diode 5 has an anode connected to the inductor 3 and a cathode connected to the high voltage terminal 6. That is, the diode 5 allows the current flowing from the inductor 3 to the high voltage end 6 to pass, but does not allow the current in the reverse direction to pass.

  When the controller 9 receives a command to turn on the switching element 12 from the host controller 14, the controller 9 operates the on-voltage supply circuit 8. At this time, the switch 4 is kept “open” (that is, the switch between the ground terminal 7 and the inductor 3 is cut off). Then, the voltage of the gate G is maintained at the ON voltage Von. As described above, since the ON voltage Von is equal to the voltage Vcc at the high voltage terminal 6, no current flows from the gate G to the high voltage terminal 6 through the inductor 3 and the diode 5.

  When the controller 9 receives a command to switch the switching element 12 from on to off from the host controller 14, the controller 9 stops the on-voltage supply circuit 8, and the predetermined off voltage Voff in which the voltage of the gate G is lower than the ground voltage Vss. The opening and closing of the switch 4 is repeated until it falls to.

  The principle of the change of the gate voltage LVG accompanying opening and closing of the switch 4 will be described. As described above, the output terminal 8 a of the on-voltage supply circuit 8 has a high impedance, and no current flows into or from the on-voltage supply circuit 8. When the on-voltage supply circuit 8 is stopped while the gate voltage LVG is maintained at the on-voltage Von, the charge corresponding to the on-voltage Von remains in the gate G. Here, when the switch 4 is closed (when the inductor 3 and the ground terminal 7 are connected), current flows from the gate G to the ground terminal 7 at a stretch. At this time, the current of the current is suppressed by the inductance of the inductor 3 and magnetic energy is stored in the inductor 3. As the charge is released from the gate G, the gate voltage LVG decreases. If the switch 4 is opened before the gate voltage LVG drops to the ground voltage Vss (by cutting off between the inductor 3 and the ground terminal 7), the current does not flow from the gate G to the ground terminal 7, but at the same time, the inductor 3 Induced electromotive force is generated by the magnetic energy stored in the. The induced electromotive force at this time acts to force a current to flow from the one end 3a side of the inductor 3 to the other end 3b side. The other end 3 b of the inductor 3 is connected to a high voltage terminal 6 via a diode 5 in addition to the switch 4. Due to the induced electromotive force of the inductor 3, a current flows from the gate G to the high voltage terminal 6 via the inductor 3 and the diode 5. As a result, the gate voltage LVG further decreases. Each time the switch 4 is opened and closed, the gate voltage LVG decreases. Here, when the gate voltage LVG immediately before the switch 4 is opened is close to the ground voltage Vss, charge is forcibly transferred from the gate G to the high voltage terminal 6 by the induced electromotive force of the inductor 3 after the switch 4 is opened. As a result, the gate voltage LVG becomes lower than the ground voltage Vss. Since the diode 5 is connected between the high voltage terminal 6 and the inductor 3, no current flows from the high voltage terminal 6 to the inductor 3 (to the gate G). Thus, by repeatedly opening and closing the switch 4, the gate voltage LVG can be made lower than the ground voltage Vss.

  With reference to FIG. 2, the above-described operation of the gate drive circuit 2 will be described again. FIG. 2 shows an example of a time chart of the operation of the gate drive circuit 2 when the gate voltage LVG is switched from the ON voltage Von to the OFF voltage Voff. FIG. 2A is a time chart of the output of the on-voltage supply circuit 8. FIG. 2B is a time chart of an open / close command signal S1 that the controller 9 commands the switch 4. In FIG. 2B, “ON” means “closed”, that is, the connection between the other end 3b of the inductor 3 and the ground end 7. “OFF” means “open”, that is, the connection between the other end 3 b of the inductor 3 and the ground end 7 is cut off. The switch 4 opens and closes based on the command in FIG. FIG. 2C is a time chart of the voltage VL of the inductor 3 at the left end 3b in FIG. FIG. 2D is a time chart of the current IL flowing through the inductor 3. The direction flowing from right to left in FIG. 1 (see the arrow in FIG. 1) is defined as the positive direction in the graph in FIG. FIG. 2E is a time chart of the gate voltage LVG. The horizontal axis of the graph is all time. In the following description, the voltage drop of the diode 5 is neglected to facilitate understanding.

  At time t1, a command to switch the switching element 12 from on to off is transmitted from the host controller 14 to the controller 9. The controller 9 stops the on-voltage supply circuit 8 at time t1. Then, the controller 9 repeats the opening and closing of the switch 4 until the gate voltage LVG decreases from the ON voltage Von to the OFF voltage Voff. As described above, the ON voltage Von is equal to the voltage Vcc at the high voltage terminal 6. Further, the off voltage Voff of the switching element 12 is set to a value lower than the ground voltage Vss.

  The controller 9 closes the switch 4 from time t1 to time t2, and opens the switch 4 again at time t2. Between the time t1 and the time t2, the left end 3b of the inductor 3 is connected to the ground end 7, so that the voltage VL at the left end 3b of the inductor 3 matches the ground voltage Vss. Since the gate voltage LVG is higher than the ground voltage Vss, a current flows from the gate G to the ground terminal 7 through the inductor 3 and the switch 4. As a result, the gate voltage LVG decreases. While a current flows from the gate G to the ground terminal 7 through the inductor 3, magnetic energy is stored in the inductor 3.

  When the switch 4 is opened at time t2, the flow of current from the gate G to the ground terminal 7 stops. When the flow of current from one end 3a of inductor 3 to the other end 3b stops, magnetic energy is released and an induced electromotive force is generated. This induced electromotive force acts to force a current to flow from one end 3a to the other end 3b. While the induced electromotive force is generated (from time t2 to time t3), a current flows forcibly from the gate G to the high voltage terminal 6 through the inductor 3. At this time, the left end voltage VL of the inductor 3 rises to the voltage Vcc of the high voltage end 6. During this time, the right end voltage of the inductor 3, that is, the gate voltage LVG continues to decrease because the charge is discharged. When the magnetic energy disappears at time t3, the voltage across the inductor 3 (the left end voltage VL and the gate voltage LVG) becomes equal, and the current flowing through the inductor 3 stops. The controller 9 closes the switch 4 again from time t4 to time t5. Between time t4 and time t5, the left end 3b of the inductor 3 is connected to the ground end 7, so that the left end voltage VL drops to the ground voltage Vss, current flows from the gate G to the ground end 7, and the gate voltage LVG drops. . During this time, magnetic energy is stored again in the inductor 3.

  The controller 9 opens the switch 4 at time t5. At time t5, the gate voltage LVG has dropped to a value slightly higher than the ground voltage Vss. When the switch 4 is opened at time t5, magnetic energy is released and an induced electromotive force is generated. As in the period from the time t2 to the time t3, a current flows forcibly from the gate G to the high voltage terminal 6 by the induced electromotive force. As a result, the gate voltage LVG drops to the off voltage Voff lower than the ground voltage Vss. When the magnetic energy is released at time t6, the flow of the current stops. At this time, the voltage across the inductor 3 becomes equal to the off voltage Voff. Since the diode 5 is connected between the left end 3b of the inductor 3 and the high voltage terminal 6, even if the gate voltage LVG falls below the voltage Vss at the high voltage terminal 6, the current flows from the high voltage terminal 6 toward the gate G. Does not flow. After time t6, the gate voltage LVG is kept at the off voltage Voff.

  An example of another operation of the gate drive circuit 2 will be described with reference to FIG. The meaning of each of FIGS. 3A to 3E is the same as each of FIGS. 2A to 2E. In the example of FIG. 3, the controller 9 repeats opening and closing of the switch 4 four times. At time T1, the controller 9 starts switching the gate voltage LVG from the ON voltage Von to the OFF voltage Voff. The controller 9 switches the switch 4 on (closed) from time T1 to time T2, from time T3 to time T4, and from time T6 to time T7. While the switch 4 is on (closed), a current flows from the gate G to the ground terminal 7, and the gate voltage LVG decreases. During that time, magnetic energy is stored in the inductor 3. Immediately after the switch 4 is switched from on (closed) to off (open), an induced electromotive force is generated by magnetic energy, and a current flows forcibly from the gate G to the high voltage terminal 6. As a result, the gate voltage LVG further decreases. The period from time T5 to time T6 is a period during which the magnetic energy has disappeared, and the voltages (gate voltage LVG and left end voltage VL) across the inductor 3 become equal, and no current flows. The same applies between time T8 and time T9. The controller 9 closes the switch 4 at the same time intervals from time T1 to time T2, from time T3 to time T4, and from time T6 to time T7, and gradually lowers the gate voltage LVG.

  Controller 9 closes switch 4 again at time T9. At this time, the gate voltage LVG is higher than the ground voltage Vss. The controller 9 holds the switch 4 "closed" for a longer period from time T9 to time T11. From time T9 to time T11, the left end 3b of the inductor 3 is directly connected to the ground end 7, and the left end voltage VL is maintained at the ground voltage Vss. On the other hand, the gate voltage LVG keeps decreasing, reaches the ground voltage Vss at the time T10, and thereafter becomes lower than the ground voltage Vss. Gate voltage LVG reaches OFF voltage Voff lower than ground voltage Vss at time T11.

  After time T10, the voltage at the right end of the inductor 3 (that is, the gate voltage LVG) becomes lower than the ground voltage Vss with the left end 3b of the inductor 3 connected to the ground end 7. This is because while the magnetic energy remains in the inductor 3, the inductor 3 continues to flow a current from the right end 3a to the left end 3b in the figure. In other words, the magnetic energy causes the inductor 3 to function as if it were a pump, so that the charge of the gate G is absorbed and sent to the ground terminal 7.

  At time T11 when the gate voltage LVG reaches the off voltage Voff, the controller 9 switches the switch 4 from on (closed) to off (open). From time T11 to time T12, the left end voltage VL of the inductor 3 rises to the voltage Vcc at the high voltage end 6 due to the induced electromotive force. (Gate voltage LVG), and the current stops flowing. Thereafter, the gate voltage LVG is kept at the off voltage Voff lower than the ground voltage Vss.

  As described above, the gate drive circuit 2 can realize the off-voltage Voff lower than the ground voltage Vss by the inductor 3, the switch 4, the diode 5, the high voltage terminal 6, and the controller 9. The switching of the gate voltage LVG from the off-voltage Voff to the on-voltage Von may be performed by operating the on-voltage supply circuit 8 with the switch 4 opened.

  Points to keep in mind regarding the technology described in the embodiment will be described. The gate voltage LVG can be adjusted by adjusting the timing and the number of times the controller 9 switches the switch 4. More specifically, the gate voltage LVG can be adjusted by the number of times that the switch 4 is kept “closed” and the length thereof.

  The ground voltage Vss in the embodiment corresponds to an example of a “reference voltage”. The ground end 7 in the embodiment corresponds to an example of a “reference voltage end”. In the embodiment, the voltage Vcc at the high voltage terminal 6 is equal to the ON voltage Von. The voltage Vcc at the high voltage end 6 is desirably equal to the ON voltage Von, but may be equal to or higher than the ON voltage Von. The ground voltage Vss is lower than the ON voltage Von. Further, the gate drive circuit 2 disclosed in the present specification exerts its effect when the set off voltage Voff is lower than the ground voltage Vss, but also when the off voltage Voff is higher than the ground voltage Vss. Can be applied.

  As described above, the specific examples of the present invention have been described in detail, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples illustrated above. The technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Further, the technology illustrated in the present specification or the drawings can simultaneously achieve a plurality of objects, and has technical utility by achieving one of the objects.

2: Gate drive circuit 3: Inductor 4: Switch 5: Diode 6: High voltage terminal 7: Ground terminal 8: ON voltage supply circuit 8a: Output terminal 9: Controller 12: Switching element 14: Host controller D: Drain G : Gate S: Source LVG: Gate voltage VL: Left end voltage Vcc: High voltage end voltage Voff: Off voltage Von: On voltage Vss: Ground voltage

Claims (1)

A gate drive circuit that controls the voltage of the gate of the voltage-driven switching element,
An on-voltage supply circuit that is connected to the gate and supplies an on-voltage;
An inductor having one end connected to the gate;
A switch for connecting or disconnecting the reference voltage end held at a predetermined reference voltage lower than the ON voltage and the other end of the inductor,
It is connected between a high voltage end held at a voltage equal to or higher than the ON voltage and the other end of the inductor, and allows a current flowing from the inductor to the high voltage end to pass, but does not allow a current in a reverse direction to pass. A rectifying element,
When switching the switching element from ON to OFF, while stopping the ON voltage supply circuit, a controller that repeats the opening and closing of the switch until the voltage of the gate drops to a predetermined OFF voltage lower than the reference voltage,
A gate drive circuit comprising:

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