The invention disclosed herein relates to a switch driving circuit.
Conventionally, various types of switch driving circuits have been devised which turn on and off a switching element.
An example of known technology related to what has just been mentioned is seen in Patent Document 1 identified below.
Inconveniently, conventional switch driving circuits may cause gate oscillation during low-speed switching.
In view of the above-mentioned problem encountered by the present inventor, an object of the invention disclosed herein is to provide a switch driving circuit that can suppress gate oscillation during low-speed switching.
According to one aspect of what is disclosed herein, a switch driving circuit includes a signal source configured to pulse-drive a gate signal for a switching element connected in series with a load, a gate resistor connected between the signal source and the gate of the switching element, a gate capacitor of which the first terminal is connected to the gate of the switching element, and a dumping resistor connected between the second terminal of the gate capacitor and the emitter or source of the switching element (a first configuration).
In the switch driving circuit of the first configuration described above, the resistance value of the dumping resistor may be equal to 1/100 to 1/1000 of the resistance value of the gate resistor (a second configuration).
In the switch driving circuit of the first or second configuration described above, the turning-on transition period and the turning-off transition period of the switching element may be each 80 μs to 1 s (a third configuration).
According to another aspect of what is disclosed herein, a load device includes a load, a switching element connected in series with the load, and the switch driving circuit of any one of the first to third configurations described above (a fourth configuration).
In the load device of the fourth configuration described above, the switching element may be an IGBT (insulated-gate bipolar transistor), or may be an SiC-MOSFET (metal-oxide-semiconductor field-effect transistor) or an Si-MOSFET (a fifth configuration).
In the load device of the fourth or fifth configuration described above, the load may be a resistive load (a sixth configuration).
According to yet another aspect of what is disclosed herein, a vehicle includes a battery, and a load device of any one of the fourth to sixth configurations described above configured to be fed with electric power from the battery (a seventh configuration).
In the vehicle of the seventh configuration described above, the load device may be a heater (an eighth configuration).
The vehicle of the eighth configuration described above may be one that has no internal combustion engine to serve as a heat source (a ninth configuration).
In the vehicle of any one of the seventh to ninth configurations described above, the battery may be a driving battery configured to output a voltage of 100 to 800 V (a tenth configuration).
According to the invention disclosed herein, it is possible to provide a switch driving circuit that can suppress gate oscillation during low-speed switching.
<Load Device>
The load RL is a resistive load. The first terminal of the load RL is connected to a positive terminal (an application terminal for the supply voltage VDD).
The collector of the switching element SW is connected to the second terminal of the load RL. The emitter of the switching element SW is connected to a negative terminal of the power supply 20 (i.e., a grounded terminal). The gate of the switching element SW is connected to an output terminal of the switch driving circuit 1 (i.e., an application terminal for a gate signal G). The switching element SW is accompanied by conductor inductances L1 and L2 at its collector and emitter respectively. The switching element SW is also accompanied by a body diode BD between its collector and emitter, with these acting as the cathode and anode, respectively, of the body diode BD.
Thus connected in series between the second terminal of the load RL and the negative terminal of the power supply 20, the switching element SW is on when the gate signal G is at high level and is off when the gate signal G is at low level.
<Switch Driving Circuit (Comparative Example)>
With reference still to
The switch driving circuit 1 of this comparative example plays the main role in turning the switching element SW on and off and includes a signal source SG, a gate resistor Rg, and a gate capacitor Cge.
The signal source SG pulse-drives the gate signal G for the switching element SW, for example, such that the collector current Ic that passes through the switching element SW equals a target value, or such that the amount of heat generated by the load RL (i.e., the sensing value of a temperature sensor) equals the target value.
The first terminal of the gate resistor Rg is connected to the output terminal for the signal source SG. The second terminal of the gate resistor Rg is connected to the gate of the switching element SW. The first terminal of the gate capacitor Cge is connected to the gate of the switching element SW. The second terminal of the gate capacitor Cge is connected to the emitter of the switching element SW.
As the gate-to-emitter voltage Vge increases while turning on the switching element SW, the collector-to-emitter voltage Vce decreases, and the collector current Ic increases (see
Incidentally, to suppress switching noise that accompanies the turning on/off of the switching element SW, it is preferable that the switching element SW be turned on and off at a low speed (at a low slew rate).
For example, by setting the turning-on transition period τon (i.e., the time required from the start of turning-on to the completion of turning-on) and the turning-off transition period τoff (i.e., the time required from the start of turning-off to the completion of turning-off) each at 80 μs to 1 s (for example, 120 μs), it is possible to sufficiently suppress switching noise; this eliminates the need to introduce a noise filter in the switch driving circuit 1. It is thus possible to reduce the cost and size of the switch driving circuit 1 (and hence of the load device 10).
However, turning on and off the switching element SW at a low speed (at a low slew rate) may cause, as shown in
The following description discusses a novel embodiment of the switch driving circuit 1 that can suppress gate oscillation during low-speed switching.
<Switch Driving Circuit (First Embodiment)>
With the switch driving circuit 1 of the embodiment, by adjusting as necessary the resistance value of the gate resistor Rg and the capacitance values of the gate capacitor Cge and Cgc, it is possible to suppress the gate oscillation described above.
However, as a trade-off, the turning-on transition period τon′ and the turning-off transition period τoff of the switching element SW are longer than the turning-on transition period τon and the turning-off transition period τoff of the comparative example. In particular, if the turning-on transition period τon and the turning-off transition period τoff are set at large values (for example, several hundred microseconds to one second) in the first place, τon′ and τoff can be extremely large, possibly leading to a very large switching loss Psw.
<Switch Driving Circuit (Second Embodiment)>
The dumping resistor Rd is connected between the second terminal of the gate capacitor Cge and the emitter of the switching element SW. The resistance value of the dumping resistor Rd can be set to be equal to, for example, 1/100 to 1/1000 of the resistance value of the gate resistor Rg.
With the switch driving circuit 1 according to the embodiment, as a result of the dumping resistor Rd being added, it is possible to suppress gate oscillation during low-speed switching while keeping the turning-on transition period τon and the turning-off transition period τoff substantially as long as those of the comparative example (for example, 120 μs). This helps prevent an unnecessary increase in the switching loss Psw; and thus makes the thermal breakdown of the switching element SW less likely.
<A Vehicle>
The heater X10 is a kind of load device that produces heat by being fed with the supply voltage VDD (of, for example, 100 V to 800 V) from the driving battery X20. As the heater X10, for example, the load device 10 (
The driving battery X20 is an HV (high voltage) battery that feeds the supply voltage VDD to the heater X10 and the motor X40. Suitably used as the driving battery X20 is, for example, a nickel metal hydride battery or a lithium-ion battery.
The auxiliary battery 30 is a lead storage battery that outputs a voltage of 12 V, that is, the same voltage as in common engine vehicles. The auxiliary battery 30 is used as a power source for various kinds of electric components (such as a car navigation system, a car audio system, an air conditioner, and lamps).
The motor X40 is a driving power source for driving tires (the rear wheels in the diagram) of the vehicle X. The motor X40 operates by being fed with the supply voltage VDD from the driving battery X20. Suitably used as the motor X40 is, for example, a DC motor or an AC motor (for example, a water-cooled synchronous motor).
The vehicle X includes, other than the above-mentioned components X10 to X40, various components (such as an accelerator, a brake, an electric hydraulic brake pump, an ECU (electronic control unit), a CAN (controller area network), an electric power steering system, a transmission, a selector lever, a combination meter, an air conditioner, a charge connector, a vehicle-mounted battery charger, a DC/DC converter, an inverter, and various lamps), although these are omitted from illustration and detailed description.
<Further Modifications>
Although the above description deals with an example of a switch driving circuit for a heater mounted on an electric vehicle, this is not meant to limit the application of the present invention. The present invention can be widely applied to switch driving circuits in general that perform low-speed switching of a switching element.
Likewise, the various technical features disclosed herein may be implemented in any other manner than in the embodiments described above, and allow for many modifications without departing from the spirit of the present invention. That is, the above embodiments should be understood to be in every aspect illustrative and not restrictive. The scope of the present invention is defined not by the description of the embodiments given above but by the appended claims, and should be understood to encompass any modifications made in a sense and scope equivalent to those of the claims.
The switch driving circuit disclosed herein finds applications as means for driving, for example, a switching element in a heater mounted on an electric vehicle.
Number | Date | Country | Kind |
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2019-159866 | Sep 2019 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2020/025755 | 7/1/2020 | WO |