JP2015216420A - Switch device, step-down device and step-up device - Google Patents

Abstract

A switch device with low power loss, and a step-down device and a step-up device including the switch device are provided. A switch device 2 includes two semiconductor switches A1 and A2 connected in parallel. When switching the two semiconductor switches A1 and A2 from OFF to ON, the switching circuit 20 switches the semiconductor switch A1 having a short transition period from OFF to ON, and then switches the semiconductor switch A1 having a long transition period from OFF to ON. Switch A2 on. When switching the two semiconductor switches A1 and A2 from on to off, the switching circuit 20 switches the semiconductor switch A2 having a long transition period from on to off and then switches off the semiconductor switch A2 and then has a short transition period from on to off. Switch A1 off. [Selection] Figure 1

Description

  The present invention relates to a switch device for energizing and interrupting a current path, and a step-down device and a step-up device including the switch device.

  The vehicle is mounted with a step-down device that steps down the output voltage of the battery or a step-up device that steps up the output voltage of the battery in order to convert the output voltage of the battery into a voltage to be applied to the load. As a step-down device or a step-up device mounted on a vehicle, there is a step-down device or a step-up device that includes a coil and a switch device that energizes / cuts off a current path.

  For example, the switch device has one semiconductor switch, one end of the coil is connected to one end of the semiconductor switch and the anode of the diode, and the other end of the semiconductor switch is grounded. The switch device repeats ON / OFF of the semiconductor switch to boost the voltage applied to the other end of the coil with reference to the ground potential, and outputs the boosted voltage from one end of the coil via the diode.

  Currently, in a vehicle, a large number of electric devices (loads) are supplied with power from a battery via a step-down device or a step-up device. For this reason, when the step-down device or the switch device provided in the step-up device passes a current through the current path, specifically, when the semiconductor switch is on, a large amount of current flows through the semiconductor switch, and a large amount of current flows. The loss of power caused by flowing through the semiconductor switch is so large that it cannot be ignored.

  Patent Document 1 discloses a switch device in which two semiconductor switches are connected in parallel. This switch device is mounted on the booster device in the same manner as the switch device having one semiconductor switch. In the switch device described in Patent Document 1, two semiconductor switches are turned on / off simultaneously. Boosting is performed by repeatedly turning on and off the two semiconductor switches.

For a switch device having one semiconductor switch, the loss of power that occurs when the semiconductor switch is on is calculated as Is ² × Rs × Ts. Here, Is is a current flowing through the semiconductor switch, Rs is an on-resistance of the semiconductor switch, and Ts is a period during which the semiconductor switch is on.

In the switch device described in Patent Document 1, when both of the on-resistances of two semiconductor switches are Rs, the current flowing through each of the two semiconductor switches that are on is Is / 2. At this time, in the switch device described in Patent Document 1, the loss of power that occurs when two semiconductor switches are on is (Is / 2) ² × Rs × Ts × 2 = Is ² × Rs × Ts / 2. It is small.
In addition, as the number of semiconductor switches connected in parallel increases, the current flowing through one semiconductor switch decreases, so that the power loss that occurs during the period in which a plurality of semiconductor switches connected in parallel is on is small.

JP 2013-13323 A

  However, the power loss in the switch device described in Patent Document 1 is not only the power loss that occurs when two semiconductor switches are on, but the two semiconductor switches are switched from on to off or from off to on. The loss of power generated during the transition period, so-called switching loss is also included.

  The switching loss in one semiconductor switch is calculated by integrating the product of the voltage between both ends of the semiconductor switch and the current flowing through the semiconductor switch over a transition period in which ON / OFF is switched. Therefore, the switching loss of the semiconductor switch having a short on / off transition period is small.

  Here, in general, an on / off transition period in a semiconductor switch having a small on-resistance is long, and an on / off transition period in a semiconductor switch having a large on-resistance is short.

  Therefore, in the switch device described in Patent Document 1, when two semiconductor switches having a short transition period are used, the loss of power generated in the period in which the two semiconductor switches are on although the switching loss generated in the two semiconductor switches is small. Is big.

On the other hand, when two semiconductor switches with low on-resistance are used, power loss that occurs while the two semiconductor switches are on is small, but switching loss that occurs between the two semiconductor switches is large.
For this reason, the switch device described in Patent Document 1 has a problem that power loss is large.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a switch device with low power loss, and a step-down device and a step-up device including the switch device.

  The switch device according to the present invention includes a plurality of semiconductor switches connected in parallel, and the transition period from OFF to ON in each of the plurality of semiconductor switches is at least one of the transition periods of other semiconductor switches. When switching the plurality of semiconductor switches from OFF to ON, after switching at least one of the semiconductor switches having the shortest transition period among the plurality of semiconductor switches to another semiconductor switch The switch is configured to be turned on.

  In the present invention, the transition period from OFF to ON in each of the plurality of semiconductor switches connected in parallel is different from at least one of the transition periods of the other semiconductor switches. When switching a plurality of semiconductor switches from off to on, at least one of the semiconductor switches having the shortest transition period is turned on. Thereafter, the other semiconductor switches are turned on. At this time, since at least one semiconductor switch is on, the voltage between both ends of the plurality of semiconductor switches is substantially zero volts, and the switching loss in the other semiconductor switches is substantially zero. Therefore, the switching loss that occurs when a plurality of semiconductor switches are switched from off to on is small because the semiconductor switch that has the shortest transition period is switched from off to on.

Further, the plurality of semiconductor switches include a semiconductor switch having a long transition period, in other words, a semiconductor switch having a low on-resistance. For this reason, the loss of electric power that occurs when a plurality of semiconductor switches are on is also small.
From the above, the power loss of the device is small.

  The switch device according to the present invention includes a plurality of semiconductor switches connected in parallel, and the transition period from on to off in each of the plurality of semiconductor switches is at least one of the transition periods of the other semiconductor switches. When switching the plurality of semiconductor switches from on to off, the other semiconductor switches except for at least one of the semiconductor switches with the shortest transition period are switched off. Thereafter, the semiconductor switch having the shortest transition period is switched off.

  In the present invention, the transition period from on to off in each of the plurality of semiconductor switches connected in parallel is different from at least one of the transition periods of the other semiconductor switches. When switching a plurality of semiconductor switches from on to off, among the plurality of semiconductor switches, other semiconductor switches are turned off except at least one of the semiconductor switches having the shortest transition period. At this time, since at least one semiconductor switch is on, the voltage between both ends of the plurality of semiconductor switches is substantially zero volts, and the switching loss that occurs when the other semiconductor switches are turned off is almost zero. Thereafter, the semiconductor switch with the shortest transition period is switched off. Accordingly, the switching loss that occurs when a plurality of semiconductor switches are switched from on to off is small because the semiconductor switch that has the shortest transition period is switched from on to off.

Further, the plurality of semiconductor switches include a semiconductor switch having a long transition period, in other words, a semiconductor switch having a low on-resistance. For this reason, the loss of electric power that occurs when a plurality of semiconductor switches are on is also small.
From the above, the power loss of the device is small.

  A step-down device according to the present invention includes the above-described switch device and a coil having one end connected to one end of each of the plurality of semiconductor switches, and by repeating ON / OFF switching in the plurality of semiconductor switches, The voltage input to the other end of the plurality of semiconductor switches is stepped down, and the stepped down voltage is output from the other end of the coil.

  In the present invention, one end of the plurality of semiconductor switches included in the aforementioned switch device is connected to one end of the coil. For example, when a diode cathode is further connected to one end of a plurality of semiconductor switches, the other end of the plurality of semiconductor switches is based on the potential of the anode of the diode by repeatedly switching on / off the plurality of semiconductor switches. The voltage applied to is stepped down. The stepped down voltage is output from the other end of the coil. Since the voltage is stepped down by the switch device described above, power loss is small.

  The booster according to the present invention includes the above-described switch device and a coil having one end connected to one end of each of the plurality of semiconductor switches, and by repeatedly switching on / off in the plurality of semiconductor switches, The voltage input to the other end of the coil is boosted, and the boosted voltage is output from one end of the coil.

  In the present invention, one end of the plurality of semiconductor switches included in the aforementioned switch device is connected to one end of the coil. For example, when the anode of a diode is further connected to one end of the coil, the potential at the other end of the plurality of semiconductor switches is applied to the other end of the coil by repeatedly switching on / off the plurality of semiconductor switches. The voltage being boosted is boosted. The boosted voltage is output from one end of the coil via a diode. Since boosting is performed by the switch device described above, power loss is small.

  According to the present invention, it is possible to realize a switch device, a step-down device, and a step-up device that have low power loss.

1 is a circuit diagram showing a configuration of a main part of a power supply system according to Embodiment 1. FIG. 5 is a timing chart for explaining the operation of the step-down device. It is a timing chart for explaining detailed operation of a switch device. FIG. 6 is a circuit diagram illustrating a configuration of a main part of a power supply system according to Embodiment 2. FIG. 10 is a circuit diagram illustrating a configuration of a main part of a power supply system according to Embodiment 3.

Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.
(Embodiment 1)
FIG. 1 is a circuit diagram showing a main configuration of the power supply system according to the first embodiment. The power supply system 1 is suitably mounted on a vehicle and includes a step-down device 10, a battery 11, and a load 12. The step-down device 10 is connected to the positive electrode of the battery 11 and one end of the load 12, and the negative electrode of the battery 11 and the other end of the load 12 are grounded. The step-down device 10 steps down the output voltage of the battery 11 to a target voltage and applies the target voltage to the load 12.
The load 12 is an in-vehicle device such as a light or a wiper, and is supplied with a target voltage by the step-down device 10 and is supplied with power by applying the target voltage.

  The step-down device 10 includes a switch device 2, a capacitor C1, a diode D1, and a coil L1. The switch device 2 has a first end, a second end, and a third end. The first end is connected to the positive electrode of the battery 11, and the second end is connected to the cathode of the diode D1 and one end of the coil L1. The other end of the coil L1 is connected to one end of each of the load 12 and the capacitor C1 and the third end of the switch device 2. The anode of the diode D1 and the other end of the capacitor C1 are grounded.

  The switch device 2 energizes / cuts off the current path from the positive electrode of the battery 11 to the coil L1. The switch device 2 includes a switching circuit 20 and two semiconductor switches A1 and A2. Each of the semiconductor switches A1 and A2 is an N-channel FET (Field Effect Transistor), the drains of the semiconductor switches A1 and A2 are connected to the positive electrode of the battery 11, and the sources of the semiconductor switches A1 and A2 are the cathodes of the diode D1. And one end of the coil L1. Thus, the two semiconductor switches A1 and A2 are connected in parallel. The gates of the two semiconductor switches A1 and A2 and one end of the capacitor C1 are connected to the switching circuit 20 separately.

  The parallel connection means that the drains of the semiconductor switches A1 and A2 are directly or indirectly connected to each other and the sources of the semiconductor switches A1 and A2 are directly or indirectly connected. To do. For example, when the drain of the semiconductor switch A1 is connected to the drain of the semiconductor switch A2 through a resistor (not shown), and the sources of the semiconductor switches A1 and A2 are connected to the cathode of the diode D1 and one end of the coil L1. Even if it exists, semiconductor switch A1, A2 is connected in parallel.

  Each of the semiconductor switches A1 and A2 is turned on when a high level voltage is applied to the gate, and a current can flow between the drain and the source of each of the semiconductor switches A1 and A2. Further, each of the semiconductor switches A1 and A2 is turned off when a low level voltage is applied to the gate, and no current flows between the drain and the source of each of the semiconductor switches A1 and A2.

  The switching circuit 20 turns on or off each of the semiconductor switches A1 and A2 by outputting a high level or low level voltage to the gate of each of the semiconductor switches A1 and A2. The switching circuit 20 switches the semiconductor switches A1 and A2 from OFF to ON by changing the voltage output to the gates of the semiconductor switches A1 and A2 from the low level voltage to the high level voltage. The switching circuit 20 switches the semiconductor switches A1 and A2 from on to off by changing the voltage output to the gates of the semiconductor switches A1 and A2 from a high level voltage to a low level voltage.

FIG. 2 is a timing chart for explaining the operation of the step-down device 10. FIG. 2 shows ON / OFF transitions in each of the semiconductor switches A1 and A2.
In the step-down device 10, the switching circuit 20 of the switch device 2 repeats on / off switching in the two semiconductor switches A1 and A2, as shown in FIG. 2, so that the drains of the two semiconductor switches A1 and A2 are respectively connected. The output voltage of the input battery 11 is stepped down. The switching circuit 20 switches on / off of the semiconductor switches A1 and A2 simultaneously. On / off of the semiconductor switches A1 and A2 is repeated at a constant cycle.

  When the switching circuit 20 switches the semiconductor switches A <b> 1 and A <b> 2 from off to on, current flows from the positive electrode of the battery 11 to the coil L <b> 1 through the switch device 2. Since the coil L1 tries to maintain the current flowing through the coil L1, the current flowing through the coil L1 gradually increases with a certain slope. At this time, a first voltage obtained by subtracting a voltage determined to be high / low according to the magnitude of the increasing current slope from the output voltage of the battery 11 is applied across the capacitor C1. The first voltage is lower than the output voltage of the battery 11.

  When the switching circuit 20 switches the semiconductor switches A1 and A2 from on to off, the current from the battery 11 to the coil L1 is interrupted. For this reason, the coil L1 is discharged in order to maintain the current flowing through it. At this time, current flows in the order of the diode D1 and the coil L1. The current flowing through the coil L1 decreases with a constant slope. A second voltage determined to be high / low according to the magnitude of the decreasing current slope is applied across the capacitor C1. The second voltage is lower than the first voltage.

The capacitor C1 smoothes the voltage output from the other end of the coil L1, and applies the smoothed voltage to the load 12. The voltage applied to the load 12 is less than the output voltage of the battery 11.
As described above, the step-down device 10 steps down the output voltage of the battery 11 and outputs the stepped-down voltage to the load 12 from the other end of the coil L1.

  The capacitor C1 applies a higher voltage to the load 12 as the period during which the first voltage is applied is longer, that is, as the duty is larger. The duty is a ratio of the ON period of the semiconductor switches A1 and A2 to one cycle. The switching circuit 20 reduces the duty when the voltage across the capacitor C1 is high, and increases the duty when the voltage across the capacitor C1 is low, thereby setting the voltage applied to the load 12 to the target voltage. adjust.

  As can be seen from FIG. 2, the timing at which the switching circuit 20 switches on / off of the semiconductor switches A1 and A2 does not completely match.

  FIG. 3 is a timing chart for explaining the detailed operation of the switch device 2. FIG. 3 shows the transition of the voltages Vg1 and Vg2 applied to the gates of the semiconductor switches A1 and A2, the transition of the voltage Vds between the drain and the source in the semiconductor switches A1 and A2, and the transitions of the semiconductor switches A1 and A2. The transition of currents I1 and I2 flowing between the drain and the source is shown. In FIG. 3, the high level voltage is indicated by “H”, and the low level voltage is indicated by “L”.

  There is a stray capacitance between the gate and the source of each of the semiconductor switches A1 and A2. Therefore, for each of the semiconductor switches A1 and A2, the voltage output from the switching circuit 20 to the gate is changed from the low level voltage to the high level voltage until the voltages Vg1 and Vg2 become the high level voltage. A transition period occurs. Similarly, for each of the semiconductor switches A1 and A2, the voltage output from the switching circuit 20 to the gate is changed from a high level voltage to a low level voltage until the voltages Vg1 and Vg2 become a low level voltage. A transition period occurs.

  As can be seen from FIG. 3, the transition period in which the voltage Vg1 transitions from the low level voltage to the high level voltage is shorter than the period in which the voltage Vg2 transitions from the low level voltage to the high level voltage. Furthermore, the period in which the voltage Vg1 transitions from the high level voltage to the low level voltage is shorter than the period in which the voltage Vg2 transitions from the high level voltage to the low level voltage. In other words, the transition period from off to on in the semiconductor switch A1 is shorter than the transition period from off to on in the semiconductor switch A2, and the transition period from on to off in the semiconductor switch A1 is from on to off in the semiconductor switch A2. Shorter than the transition period.

  When the switching circuit 20 outputs a low level voltage to the gates of the semiconductor switches A1 and A2, the output voltage of the battery 11 is applied to the drains of the semiconductor switches A1 and A2, so the voltage Vds is a constant voltage. That's it. Furthermore, since the semiconductor switches A1 and A2 are off, the currents I1 and I2 are both zero amperes.

  When switching the semiconductor switches A1 and A2 from OFF to ON, the switching circuit 20 first outputs a high level voltage to the gate of the semiconductor switch A1 that has a short transition period from OFF to ON, and sets the voltage Vg1 to a low level voltage. To a high level voltage. Thereby, the switching circuit 20 switches on the semiconductor switch A1.

  As the voltage Vg1 increases, the voltage Vds decreases and the current I1 increases. Switching loss occurs while the voltage Vg1 is transitioning from a low level voltage to a high level voltage. The switching loss is calculated by integrating the product of the voltage Vds and the current I1 over the transition period of the voltage Vg1.

  The switching circuit 20 outputs the high-level voltage to the gate of the semiconductor switch A2 after the voltage Vg1 transitions to the high-level voltage and switches on the semiconductor switch A1, and changes the voltage Vg2 from the low-level voltage to the high-level. Transition to the voltage of. Thereby, the switching circuit 20 switches on the semiconductor switch A2.

  As the voltage Vg2 rises, a part of the current that has flowed to the semiconductor switch A1 starts to flow to the semiconductor switch A2, so that the current I1 decreases and the current I2 increases. The voltage Vg2 rises from a low level voltage to a high level voltage in a state where the semiconductor switch A1 is on, that is, in a state where the voltage Vds is approximately zero volts. For this reason, the switching loss generated while the voltage Vg2 is increasing is substantially zero.

Accordingly, the switching loss that occurs when the two semiconductor switches A1 and A2 are switched from OFF to ON is small because the semiconductor switch A1 that has a short transition period from OFF to ON is switched from OFF to ON.
This switching loss is the same as the switching loss that occurs when two semiconductor switches A1 and A1 are simultaneously switched from OFF to ON in a switch device in which the semiconductor switch A1 is used instead of the semiconductor switch A2.

  For example, the switching circuit 20 outputs a high level voltage to the gate of the semiconductor switch A2 after a predetermined time has elapsed since the high level voltage was output to the gate of the semiconductor switch A1. Thus, a configuration in which the semiconductor switch A2 is turned on after the semiconductor switch A1 is turned on may be realized. Further, for example, the switching circuit 20 may be configured to output a high level voltage to the gate of the semiconductor switch A2 when the voltage Vg1 becomes a high level voltage.

  When the voltages Vg1 and Vg2 are both high level voltages, the semiconductor switches A1 and A2 are both turned on, and a current flows through each of the semiconductor switches A1 and A2.

When the on-resistances of the semiconductor switches A1 and A2 are R1 and R2, and the on-periods of the semiconductor switches A1 and A2 are T1 and T2, the power generated by the on-resistance of the semiconductor switch A1 while the semiconductor switch A1 is on. Loss is I1 ² × R1 × T1. Further, while the semiconductor switch A2 is on, the power loss caused by the on-resistance of the semiconductor switch A2 is I2 ² × R2 × T2.

  Here, the on-resistance R1 of the semiconductor switch A1 having a short on / off transition period is larger than the on-resistance R2 of the semiconductor switch A2 having a long on / off transition period. Since the switch device 2 includes the semiconductor switch A2 having a low on-resistance, power loss that occurs when the two semiconductor switches A1 and A2 are on is small.

  This can also be explained as follows. In the switch device 2, when the two semiconductor switches A1 and A2 are both on, the combined resistance of the on-resistance is (R1 × R2) / (R1 + R2). In the switch device using the semiconductor switch A1 instead of the semiconductor switch A2, the combined resistance of the on-resistance when the two semiconductor switches A1 and A1 are both on is R1 / 2. Since the on-resistance R1 is larger than the on-resistance R2, (R1 × R2) / (R1 + R2) is smaller than R1 / 2. Therefore, the power loss that occurs when the two semiconductor switches A1 and A2 are both on is smaller than the power loss that occurs when the two semiconductor switches A1 and A1 are both on.

  When switching the semiconductor switches A1 and A2 from on to off, the switching circuit 20 first outputs a low level voltage to the gate of the semiconductor switch A2 having a long transition period from on to off, and converts the voltage Vg2 to a high level voltage. To a low level voltage. Thereby, the switching circuit 20 switches the semiconductor switch A2 off.

  As the voltage Vg2 decreases, a part of the current flowing through the semiconductor switch A2 flows into the semiconductor switch A1, so that the current I1 increases and the current I2 decreases. Since the semiconductor switch A1 is kept on while the switching circuit 20 switches the semiconductor switch A2 from on to off, the voltage Vds is substantially zero volts. For this reason, the switching loss generated while the switching circuit 20 switches the semiconductor switch A2 from on to off is substantially zero.

  The switching circuit 20 outputs a low level voltage to the gate of the semiconductor switch A1 after the voltage Vg2 transitions to a low level voltage and the semiconductor switch A2 is turned off, and changes the voltage Vg1 from the high level voltage to the low level. Transition to the voltage of. Thereby, the switching circuit 20 switches the semiconductor switch A1 off.

  As the voltage Vg1 decreases, the voltage Vds increases and the current I1 decreases. Switching loss occurs while the voltage Vg1 is transitioning from a high level voltage to a low level voltage. The switching loss is calculated by integrating the product of the voltage Vds and the current I1 over the transition period of the voltage Vg1.

Therefore, the switching loss that occurs when the two semiconductor switches A1 and A2 are switched from on to off occurs when the semiconductor switch A1 that has a short transition period from on to off is switched from on to off.
This switching loss is the same as the switching loss that occurs when two semiconductor switches A1 and A1 are simultaneously switched from on to off in a switch device in which the semiconductor switch A1 is used instead of the semiconductor switch A2.

As described above, in the switch device 2, the switching loss and the power loss that occurs when the two semiconductor switches A1 and A2 are both on are small, so the power loss in the switch device 2 is small.
Further, since the step-down is performed by the switch device 2, the power loss of the step-down device 10 is small.

  Note that the step-down device 10 may use the switch device 2 in which the first end is connected to one end of the coil L1 and the second end is grounded instead of the diode D1. In this case, the switching circuit 20 of the switching device 2 used in place of the diode D1 is connected to itself when the switching circuit 20 of the other switching device 2 switches the semiconductor switches A1 and A2 on (or off). The switched semiconductor switches A1 and A2 are switched off (or on). Thereby, the output voltage of the battery 11 is stepped down.

(Embodiment 2)
FIG. 4 is a circuit diagram showing a main configuration of the power supply system according to the second embodiment. The power supply system 3 is different from the power supply system 1 in the first embodiment in that a step-down device 30 is provided instead of the step-down device 10. The step-down device 30 is different from the step-down device 10 in the first embodiment in that the switch device 4 is provided instead of the switch device 2. The switch device 4 is different from the switch device 2 in the first embodiment in that m (m is an integer of 3 or more) semiconductor switches A1, A2,.
In the following, the differences between the second embodiment and the first embodiment will be described. Since the other configuration except the configuration to be described later is the same as that of the first embodiment, the same reference numerals are given and the description thereof is omitted.

The power supply system 3 in the second embodiment is suitably mounted on a vehicle, and includes a battery 11 and a load 12 as in the power supply system 1 in the first embodiment. As described above, the power supply system 3 further includes the step-down device 30, and the battery 11, the load 12, and the step-down device 30 are connected in the same manner as in the first embodiment. Here, the step-down device 10 in the first embodiment corresponds to the step-down device 30.
The step-down device 30 steps down the output voltage of the battery 11 to a target voltage and applies the target voltage to the load 12. The load 12 is supplied with power by applying the target voltage.

  The step-down device 30 according to the second embodiment includes a capacitor C1, a diode D1, and a coil L1, similarly to the step-down device 10 according to the first embodiment. The step-down device 30 further includes the switch device 4 as described above. The switch device 4 has a first end, a second end, and a third end similarly to the switch device 2 in the first embodiment, and the switch device 4, the capacitor C1, the diode D1, and the coil L1 are the same as those in the first embodiment. It is connected to the. Here, the switch device 2 in the first embodiment corresponds to the switch device 4.

  The switch device 4 energizes / cuts off the current path from the positive electrode of the battery 11 to the coil L1. The switch device 4 includes a switching circuit 20 and m semiconductor switches A1, A2,. Each of the semiconductor switches A1, A2,... Am is an N-channel type FET. The drains of the semiconductor switches A1, A2,..., Am are connected to the positive electrode of the battery 11, and the sources of the semiconductor switches A1, A2, ..., Am are connected to the cathode of the diode D1 and one end of the coil L1, respectively. It is connected. In this way, the m semiconductor switches A1, A2,... Am are connected in parallel. The gates of the m semiconductor switches A1, A2,..., Am and one end of the capacitor C1 are connected to the switching circuit 20 separately as in the first embodiment. In FIG. 4, currents flowing between the drain and the source in each of the semiconductor switches A1, A2,..., Am are denoted by I1, I2,.

  As in the first embodiment, being connected in parallel means that the drains of the semiconductor switches A1, A2,..., Am are directly or indirectly connected to each other, and the semiconductor switches A1, A2,. .., means that Am sources are connected directly or indirectly.

Each of the semiconductor switches A3, A4,..., Am is configured similarly to the semiconductor switch A1 or A2. The switching circuit 20 turns on / off the semiconductor switches A3, A4,..., Am, similarly to the semiconductor switches A1 and A2.
In the step-down device 30 as well, as in the step-down device 10 in the first embodiment, the switching circuit 20 repeats on / off switching in the m semiconductor switches A1, A2,. The output voltage of the battery 11 input to the drains of the switches A1, A2,. The switching circuit 20 switches on / off of each of the semiconductor switches A1, A2,. On / off of each of the semiconductor switches A1, A2,..., Am is repeated at a constant cycle like the on / off transition of the semiconductor switch A1 shown in FIG.

  When the switching circuit 20 repeats on / off switching in the semiconductor switches A1, A2,... Am, the current flows in the same manner as in the first embodiment, the output voltage of the battery 11 is stepped down, and the stepped down voltage is applied. Is output to the load 12 from the other end of the coil L1. Here, in the description of the first embodiment, the switch device 2 corresponds to the switch device 4, and the semiconductor switches A1, A2 correspond to the semiconductor switches A1, A2,. The switching circuit 20 adjusts the voltage applied to the load 12 to the target voltage by adjusting the duty. The duty is the ratio of the ON period of the semiconductor switches A1, A2,.

  Next, a configuration in which the switching circuit 20 switches the semiconductor switches A1, A2,..., Am from OFF to ON, and a configuration in which the switching circuit 20 switches the semiconductor switches A1, A2,. Will be explained.

  The transition period from OFF to ON in each of the m semiconductor switches A1, A2,..., Am differs from at least one of the transition periods from OFF to ON in the other (m−1) semiconductor switches. Yes. That is, not all of the transition periods from OFF to ON in each of the m semiconductor switches A1, A2,. The transition period from OFF to ON in each of the semiconductor switches A1, A2,..., Am is any one of H1, H2,..., Hk (k: an integer from 2 to m). The transition periods H1, H2,..., Hk are different from each other. Regarding the transition period from OFF to ON, H1 is the shortest and is long in the order of H1, H2,.

  The transition period from on to off in each of the m semiconductor switches A1, A2,..., Am is also different from at least one of the transition periods from on to off in the other (m−1) semiconductor switches. Yes. That is, not all the transition periods from on to off in the m semiconductor switches A1, A2,. The transition period from ON to OFF in each of the semiconductor switches A1, A2,..., Am is any one of L1, L2,..., Lk (k: an integer of 2 or more and m or less). The transition periods L1, L2,..., Lk are different from each other. Regarding the transition period from on to off, L1 is the shortest and is long in the order of L1, L2,..., Lk.

  The transition periods from on to off in the semiconductor switches whose transition periods from off to on are H1, H2,..., Hk are L1, L2,. That is, in a semiconductor switch having a short transition period from off to on, the transition period from on to off is also short.

When switching the semiconductor switches A1, A2,..., Am from OFF to ON, first, the switching circuit 20 is a semiconductor switch whose transition period is H1 among the m semiconductor switches A1, A2,. At least one of the switches from OFF to ON. For example, when the number of semiconductor switches whose transition period from off to on is H1 is two, both of the two semiconductor switches whose transition period from off to on is H1 may be switched from off to on. One of the two semiconductor switches whose transition period from off to on is H1 may be switched from off to on.
A switching loss occurs when the switching circuit 20 switches at least one of the semiconductor switches whose transition period from OFF to ON is H1 from OFF to ON.

The switching circuit 20 switches at least one of the semiconductor switches whose transition period from OFF to ON is H1 to ON, and then switches the other semiconductor switch from OFF to ON. Therefore, in the semiconductor switch in which the transition period from OFF to ON is any one of H2, H3,..., Hk, at least one of the semiconductor switches in which the transition period from OFF to ON is H1 is from OFF. After being switched on, it is switched from off to on.
Therefore, the timing at which the switching circuit 20 switches the semiconductor switches A1, A2,..., Am from OFF to ON is not completely the same.

  Since at least one of the semiconductor switches whose transition period from off to on is H1 is on while other semiconductor switches are switched from off to on, m semiconductor switches A1, A2,..., Am The voltage Vds between the drain and the source is approximately zero volts. For this reason, the switching loss that occurs while the other semiconductor switches are switched from OFF to ON is substantially zero.

Therefore, the switching loss that occurs when the m semiconductor switches A1, A2,..., Am are switched from off to on is that one or more semiconductor switches whose transition period from off to on is H1 is off. Small because it occurs when switched on.
This switching loss is such that the transition periods from the OFF state to the ON state of the m semiconductor switches A1, A2,..., Am are all H1, and the m semiconductor switches A1, A2,. This is the same switching loss that occurs when switching from off to on.

  As for the on resistance of each of the m semiconductor switches A1, A2,..., Am, the on resistance of the semiconductor switch having a short transition period from off to on or a short transition period from on to off is large. Therefore, since the switch device 4 has a semiconductor switch whose on-resistance is smaller than the on-resistance of the semiconductor switch whose transition period from off to on is H1, m semiconductor switches A1, A2,. • The loss of power that occurs when Am is on is small.

  When the on-resistance of the semiconductor switch whose transition period from off to on is H1 is Rmax, the on-resistance of each of the m semiconductor switches A1, A2,. It is smaller than the combined resistance when m semiconductor switches are connected in parallel.

  When switching the m semiconductor switches A1, A2,... Am from on to off, the switching circuit 20 switches from on to off among the m semiconductor switches A1, A2,. Other semiconductor switches except at least one of the semiconductor switches whose transition period is L1 are switched from on to off. For example, among the m semiconductor switches A1, A2,..., Am, when the number of semiconductor switches whose transition period from on to off is L1 is one, the switching circuit 20 is switched from on to off. The (m−1) semiconductor switches whose transition period to is one of L2, L3,..., Lk is turned off from on.

  A semiconductor whose on-to-off transition period is L1 while the switching circuit 20 switches other semiconductor switches excluding at least one of the semiconductor switches whose on-to-off transition period is L1. Since at least one of the switches remains on, the voltage Vds is approximately zero volts. For this reason, the switching loss that occurs while the switching circuit 20 switches other semiconductor switches excluding at least one of the semiconductor switches having a transition period from on to off of L1 from on to off is substantially zero.

The switching circuit 20 is configured to switch the m semiconductor switches A1, A2,..., Am after the other semiconductor switches except for at least one of the semiconductor switches whose transition period from on to off is L1. Among them, one or a plurality of semiconductor switches whose transition period from on to off is L1 are switched off.
Therefore, the timing at which the switching circuit 20 switches the semiconductor switches A1, A2,..., Am from on to off is not completely coincident.

  Switching loss occurs while one or more semiconductor switches whose transition period is L1 are transitioning from on to off. As described above, the switching loss that occurs while the switching circuit 20 switches the other semiconductor switches excluding at least one of the semiconductor switches having the transition period from on to off of L1 from on to off is substantially zero. is there. Therefore, the switching loss that occurs when the m semiconductor switches A1, A2,... Am are switched from on to off is one or more semiconductor switches whose transition time from on to off is L1. It occurs when switching to, so it is small.

  This switching loss is that the transition periods from the on-off of the m semiconductor switches A1, A2,..., Am are all L1, and the m semiconductor switches A1, A2,. This is the same switching loss that occurs when switching from on to off.

As described above, in the switch device 4, the switching loss and the power loss generated when both of the m semiconductor switches A 1, A 2,... The loss is small.
Further, since the step-down is performed by the switch device 4, the power loss of the step-down device 30 is small.

  In the second embodiment, the step-down device 30 may use the switching device 4 in which the first end is connected to one end of the coil L1 and the second end is grounded instead of the diode D1. In this case, the switching circuit 20 of the switching device 4 used in place of the diode D1 is such that the switching circuit 20 of the other switching device 4 switches the semiconductor switches A1, A2,..., Am on (or off). At this time, the semiconductor switches A1, A2,... Am connected to itself are switched off (or on). Thereby, the output voltage of the battery 11 is stepped down.

(Embodiment 3)
FIG. 5 is a circuit diagram showing a main configuration of the power supply system according to the third embodiment. This power supply system 5 is different from the first or second embodiment in that the output voltage of the battery 11 is not stepped down but the output voltage of the battery 11 is stepped up.
In the following, the differences between the third embodiment and the first or second embodiment will be described. Since the other configurations except for those described later are the same as those in the first or second embodiment, the same reference numerals are given and the description thereof is omitted.

  The power supply system 5 in the third embodiment is suitably mounted on a vehicle, and includes a battery 11 and a load 12 as in the power supply system 1 in the first embodiment. The power supply system 5 further includes a booster 50. The booster 50 is connected to the positive electrode of the battery 11 and one end of the load 12, and the negative electrode of the battery 11 and the other end of the load 12 are grounded. The booster 50 boosts the output voltage of the battery 11 to a target voltage and applies the target voltage to the load 12. The load 12 is supplied with power by applying the target voltage.

  The booster 50 in the third embodiment includes a switch device 6, a capacitor C2, a diode D2, and a coil L2. The switch device 6 has a first end, a second end, and a third end. One end of the coil L2 is connected to the positive electrode of the battery 11, and the other end of the coil L2 is connected to the anode of the diode D2 and the first end of the switch device 6. The second end of the switch device 6 is grounded. The cathode of the diode D <b> 2 is connected to one end of each of the load 12 and the capacitor C <b> 2 and the third end of the switch device 6. The other end of the capacitor C2 is grounded.

  The switch device 6 energizes / cuts off the current path from the other end of the coil L2 to the ground potential, for example, the vehicle body. The switch device 6 includes a switching circuit 20 and n (n: an integer of 2 or more) semiconductor switches A1, A2,. Each of the semiconductor switches A1, A2,..., An is an N-channel type FET. The drains of the semiconductor switches A1, A2,..., An are connected to the other end of the coil L2 and the anode of the diode D2, and the sources of the semiconductor switches A1, A2,. . In this way, the n semiconductor switches A1, A2,..., An are connected in parallel. The gates of the n semiconductor switches A1, A2,..., An and one end of the capacitor C2 are connected to the switching circuit 20 separately. 5, currents flowing between the drain and the source in the semiconductor switches A1, A2,..., An are indicated by I1, I2,.

  As in the first and second embodiments, connected in parallel means that the drains of the semiconductor switches A1, A2,..., An are connected directly or indirectly to each other, and the semiconductor switches A1, A2 are connected. ,..., An means that the respective sources are connected directly or indirectly.

Each of the semiconductor switches A3, A4,..., An is configured similarly to the semiconductor switch A1 or A2. The switching circuit 20 turns on / off each of the semiconductor switches A2, A3,..., An similarly to the semiconductor switch A1.
In the step-up device 50, as in the first embodiment, the switching circuit 20 repeats on / off switching in the n semiconductor switches A1, A2,..., An to be input to one end of the coil L2. The output voltage of the battery 11 is boosted. The switching circuit 20 switches on / off of the semiconductor switches A1, A2,. The on / off of each of the semiconductor switches A1, A2,..., An is repeated at a constant cycle like the on / off transition of the semiconductor switch A1 shown in FIG.

  When the switching circuit 20 switches the semiconductor switches A1, A2,..., An from off to on, current flows in order from the positive electrode of the battery 11 to the coil L2 and the switch device 6. A large amount of current flows through the coil L2. At this time, no voltage is applied across the capacitor C2 via the diode D2.

  When the switching circuit 20 switches the semiconductor switches A1, A2,..., An from on to off, current flows from the positive electrode of the battery 11 in the order of the coil L2 and the diode D2. At this time, since the coil L2 tries to maintain the current flowing through the coil L2, the current flowing through the coil L1 gradually decreases with a certain slope. A third voltage obtained by adding a voltage determined to be high / low according to the magnitude of the decreasing current slope to the output voltage of the battery 11 is applied to both ends of the capacitor C2. The third voltage is higher than the output voltage of the battery 11.

Capacitor C2 smoothes the voltage output from the cathode of diode D2, and applies the smoothed voltage to load 12. The voltage applied to the load 12 exceeds the output voltage of the battery 11.
As described above, the booster 50 boosts the output voltage of the battery 11 and outputs the boosted voltage from the other end of the coil L2 to the load 12 via the diode D.

  The capacitor C2 has a higher voltage because the third voltage becomes higher as the period during which the switching circuit 20 turns on the n semiconductor switches A1, A2,. Applied to load 12. The duty is the ratio of the ON period of the semiconductor switches A1, A2,. The switching circuit 20 adjusts the voltage applied to the load 12 to the target voltage by decreasing the duty when the voltage across the capacitor C2 is high and increasing the duty when the voltage across the capacitor C2 is low. .

  The switching circuit 20 in the third embodiment switches the semiconductor switches A1, A2,..., An from off to on. The switching circuit 20 in the second embodiment switches the semiconductor switches A1, A2,. This is the same as the configuration for switching from off to on. Further, the configuration in which the switching circuit 20 in the third embodiment switches the semiconductor switches A1, A2,... An from on to off is the same as the switching circuit 20 in the second embodiment in which the semiconductor switches A1, A2,. The configuration is the same as switching from ON to OFF.

  In the description of the configuration in which the switching circuit 20 in the second embodiment switches the semiconductor switches A1, A2,..., Am from OFF to ON, m (m: an integer of 3 or more) is changed to n (n: an integer of 2 or more). Replace with Thus, the configuration in which the switching circuit 20 in the third embodiment switches the semiconductor switches A1, A2,..., An from off to on can be described.

  In the description of the configuration in which the switching circuit 20 in the second embodiment switches the semiconductor switches A1, A2,... Am from on to off, m (m: an integer of 3 or more) is changed to n (n: an integer of 2 or more). Replace with Thereby, the configuration in which the switching circuit 20 in the third embodiment switches the semiconductor switches A1, A2,..., An from on to off can be described.

  Therefore, the switch device 6 in the third embodiment has the same effect as the switch device 4 in the second embodiment. Further, since the boosting is performed by the switch device 6 with a small power loss, the power loss of the boosting device 50 is also small.

  In the third embodiment, the booster 50 uses a switch device 6 having a first end connected to one end of the capacitor C2 and a second end connected to the other end of the coil L2, instead of the diode D2. May be. In this case, the switching circuit 20 of the switching device 6 used in place of the diode D2 is such that the switching circuit 20 of the other switching device 6 switches the semiconductor switches A1, A2, ..., An on (or off). At this time, the semiconductor switches A1, A2,..., An connected to itself are switched off (or on). Thereby, the output voltage of the battery 11 is boosted.

  In the first to third embodiments, the configuration in which the plurality of semiconductor switches included in the switch devices 2, 4, 6 are switched from on to off excludes at least one semiconductor switch having the shortest transition period from on to off. A configuration in which one or a plurality of semiconductor switches having the shortest transition period after switching off other semiconductor switches is not necessarily required. Even in this case, the switching loss that occurs when the plurality of semiconductor switches are switched from OFF to ON is small, and furthermore, the loss of power that occurs during the period in which the plurality of semiconductor switches are both ON is also small. , 4 and 6 have small power loss. Therefore, power loss in the step-down device 10 including the switch device 2, the step-down device 30 including the switch device 4, and the step-up device 50 including the switch device 6 is also small.

  In addition, the configuration in which the plurality of semiconductor switches included in the switch devices 2, 4, and 6 are switched from OFF to ON is configured such that after switching at least one of the semiconductor switches having the shortest transition period from OFF to ON, The switch may not be switched on. Even in this case, the switching loss that occurs when the plurality of semiconductor switches are switched from on to off is small, and furthermore, the loss of power that occurs during the period in which the plurality of semiconductor switches are both on is also small. The power loss at 4 and 6 is small. Therefore, power loss in the step-down device 10 including the switch device 2, the step-down device 30 including the switch device 4, and the step-up device 50 including the switch device 6 is also small.

Further, each of the plurality of semiconductor switches provided in the switch devices 2, 4, 6 is not limited to the N-channel type FET, but may be a P-channel type FET, or may be a bipolar transistor.
Further, the device on which the switch devices 2, 4, 6 are mounted is not limited to a step-down device or a step-up device. The switch devices 2, 4, and 6 may be mounted on a device that needs to energize and shut off a current path through which a large amount of current flows, particularly a large amount of current.

  The disclosed first to third embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

2, 4, 6 Switch device 10, 30 Step-down device 20 Switching circuit 50 Step-up device A1, A2,..., Am Semiconductor switch L1, L2 Coil

Claims (4)

In a switch device comprising a plurality of semiconductor switches connected in parallel,
The transition period from OFF to ON in each of the plurality of semiconductor switches is different from at least one of the transition periods of the other semiconductor switches,
When switching the plurality of semiconductor switches from off to on, after switching on at least one of the semiconductor switches having the shortest transition period among the plurality of semiconductor switches, the other semiconductor switches are switched on. A switch device characterized by being configured as follows. In a switch device comprising a plurality of semiconductor switches connected in parallel,
The transition period from on to off in each of the plurality of semiconductor switches is different from at least one of the transition periods of the other semiconductor switches,
When switching the plurality of semiconductor switches from on to off, among the plurality of semiconductor switches, after switching off other semiconductor switches except at least one of the semiconductor switches having the shortest transition period, the transition A switch device characterized by being configured to switch off the semiconductor switch having the shortest period. The switch device according to claim 1 or 2,
A coil having one end connected to one end of each of the plurality of semiconductor switches,
By repeating ON / OFF switching in the plurality of semiconductor switches, the voltage input to the other end of the plurality of semiconductor switches is stepped down, and the stepped down voltage is output from the other end of the coil. A step-down device characterized by that. The switch device according to claim 1 or 2,
A coil having one end connected to one end of each of the plurality of semiconductor switches,
By repeating ON / OFF switching in the plurality of semiconductor switches, the voltage input to the other end of the coil is boosted, and the boosted voltage is output from one end of the coil. A step-up device characterized.

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