Switching device

Abstract

To provide technology which can estimate a temperature of a switching element highly accurately.SOLUTION: A control part, in a state of executing a switching control that a first transistor is turned on at a timing of turning off a second transistor and the first transistor is turned off at the timing of turning on the second transistor, when estimating a temperature of a first switching element, maintains the first transistor off without turning on the first transistor at the timing of turning off the second transistor, and may estimate the temperature of the first switching element based on forward voltage of a first diode detected by a voltage detection part while the first transistor is off and forward current of the first diode detected by a current detection part.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The technology disclosed in this specification relates to a switching device. [Background technology]

[0002] A switching device is disclosed in Patent Document 1. The switching device of Patent Document 1 includes a voltage detection means for detecting the forward voltage of the diode when a return current is generated as the voltage between the first and second terminals of the switching element, and an overheat determination means for determining whether or not the switching element is in an overheated state from the forward voltage of the diode, which has a correlation with the ambient temperature based on the terminal voltage of the switching element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-036829 A Summary of the Invention [Problem to be solved by the invention]

[0004] The switching device of Patent Document 1 has room for improvement in terms of determining the temperature of the switching element with high accuracy. This specification provides a technique that can estimate the temperature of the switching element with high accuracy. [Means for solving the problem]

[0005] In a first aspect of the present technology, a switching device may include a first switching element including a first transistor and a first diode connected in anti-parallel to the first transistor, a second switching element connected to the first switching element, the second switching element including a second transistor and a second diode connected in anti-parallel to the second transistor, a voltage detection unit detecting a forward voltage of the first diode, a current detection unit detecting a forward current of the first diode, and a control unit. When estimating a temperature of the first switching element in a state in which switching control is performed to turn on the first transistor at a timing to turn off the second transistor and to turn off the first transistor at a timing to turn on the second transistor, the control unit may maintain the first transistor off without turning on the first transistor at a timing to turn off the second transistor, and estimate the temperature of the first switching element based on the forward voltage of the first diode detected by the voltage detection unit and the forward current of the first diode detected by the current detection unit while the first transistor is off.

[0006] According to this configuration, by keeping the first transistor off without turning on the first transistor at the timing when the second transistor is turned off, a long period can be secured for detecting the forward voltage and forward current of the first diode when a return current flows through the first diode. This makes it possible to accurately detect the forward voltage and forward current of the first diode, and based on this, to accurately estimate the temperature of the switching element.

[0007] In a second aspect, in the first aspect, when estimating the temperature of the first switching element, if a forward voltage and a forward current of the first diode are detected during a period from when the first transistor is kept off without turning on the first transistor until the second transistor is turned on, the control unit may turn on the first transistor before turning on the second transistor. When estimating the temperature of the first switching element, if a forward voltage and a forward current of the first diode are not detected during a period from when the first transistor is kept off without turning on the first transistor until the second transistor is turned on, the control unit may turn on the first transistor at the timing when the second transistor is next turned off.

[0008] Since the forward resistance of the first diode is greater than the resistance of the first transistor when the first transistor is on, if the period during which the first transistor is kept off is long and the period during which the return current flows through the first diode is long, the amount of heat generated by the resistance of the first diode may increase. However, with the above configuration, when the forward voltage and forward current of the first diode for estimating the temperature of the first switching element are detected, the first transistor is turned on at an early stage, thereby shortening the period during which the return current flows through the first diode. This makes it possible to suppress heat generation due to the forward resistance of the first diode.

[0009] In a third aspect, in the first or second aspect described above, when estimating the temperature of the first switching element while the control unit is performing switching control of the first transistor at a frequency outside the audible range, the control unit may change the frequency of the switching control of the first transistor to a frequency within the audible range by maintaining the first transistor off without turning it on.

[0010] According to this configuration, an audible sound can be generated from the first transistor when estimating the temperature of the first switching element, thereby making it possible to notify those around the device of the timing for estimating the temperature of the first switching element.

[0011] In a fourth aspect, in any one of the first to third aspects, the first switching element and the second switching element may be switching elements in a voltage conversion device that converts an input voltage into an output voltage.

[0012] According to this configuration, it is possible to estimate the temperature of the switching element of the voltage conversion device without impeding the operation of the voltage conversion device. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a diagram showing a switching device according to an embodiment; [Diagram 2] FIG. 4 is a diagram showing an example of temperature characteristics of a diode according to an embodiment of the present invention. [Diagram 3] 4 is a timing chart showing switching control according to the embodiment. [Figure 4] 4 is a flowchart of a temperature estimation process according to the embodiment. [Diagram 5] 4 is a timing chart showing switching control according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] A switching device of an embodiment will be described with reference to the drawings. As shown in Fig. 1, a switching device 2 of the embodiment includes a DC / DC converter (hereinafter referred to as "converter") 20 and a control device 100. For example, the switching device 2 of the embodiment is mounted on an electric vehicle or a hybrid vehicle.

[0015] The converter 20 (an example of a voltage conversion device) will be described. The input side (primary side) of the converter 20 is connected to a DC power supply 40. The voltage of the DC power supply 40 is applied to the converter 20. The output side (secondary side) of the converter 20 is connected to, for example, a secondary battery 90. In a modified example, the output side (secondary side) of the converter 20 may be connected to a load (not shown) of an electric product. The converter 20 boosts the voltage of the power supply 40 and inputs it to the secondary battery 90 or the electric product. The secondary battery 90 stores the power supplied from the power supply 40 via the converter 20. The electric product operates on the power supplied from the power supply 40 via the converter 20.

[0016] The converter 20 includes a primary side circuit 50, a secondary side circuit 60, and a transformer 70 configured between the primary side circuit 50 and the secondary side circuit 60. The converter 20 of the embodiment is an isolated type converter in which the primary side circuit 50 and the secondary side circuit 60 are insulated from each other. The converter 20 of the embodiment is a phase-shift full-bridge type converter. The type of the converter 20 is not particularly limited. An example of the phase-shift full-bridge type converter 20 will be described below.

[0017] The primary circuit 50 of the converter 20 includes a plurality of switching elements 51 - 54 , a primary coil 55 , a primary inductor 56 , and a primary capacitor 58 .

[0018] The multiple switching elements 51-54 include a first switching element 51, a second switching element 52, a third switching element 53, and a fourth switching element 54. In the converter 20, the multiple switching elements 51-54 are periodically switched on and off to convert a DC voltage on the input side (primary side) to a DC voltage on the output side (secondary side). In the following, of the multiple switching elements 51-54 of the primary side circuit 50, the first switching element 51 will be mainly described. The second switching element 52, the third switching element 53, and the fourth switching element 54 have the same configuration as the first switching element 51, so detailed description thereof will be omitted.

[0019] The first switching element 51 includes a first transistor 51a and a first diode 51b. The first diode 51b may be a parasitic diode that is inevitably created when the first transistor 51a is created on a semiconductor substrate. The first transistor 51a and the first diode 51b are connected in anti-parallel. The first switching element 51 is turned on / off when a PWM (Pulse Width Modulation) signal is input to the first transistor 51a, and the first transistor 51a is turned on / off by the PWM signal. The first switching element 51 may generate heat when the first transistor 51a is turned on / off. When the first transistor 51a is turned on / off, switching loss occurs, and the first switching element 51 generates heat. The second switching element 52, the third switching element 53, and the fourth switching element 54 have the same configuration as the first switching element 51. For example, the second switching element 52 includes a second transistor 52a and a second diode 52b.

[0020] The multiple switching elements 51-54 are connected in series with a primary coil 55. The primary coil 55 is, for example, wound around a metal core (not shown) and constitutes a transformer 70 together with a secondary coil 65. Power of the primary circuit 50 is transmitted to the secondary circuit 60 via the transformer 70.

[0021] The primary side inductance 56 of the primary side circuit 50 is connected in series with the primary side coil 55. The primary side inductance 56 stores the energy of the current flowing through the primary side circuit 50 and releases the stored energy. The primary side capacitor 58 is connected in parallel with the primary side inductance 56. The primary side capacitor 58 stores the charge of the primary side circuit 50 and releases the stored charge.

[0022] The secondary circuit 60 of the converter 20 includes a plurality of switching elements 61-62, a secondary coil 65 (65a, 65b), a secondary inductor 66, and a secondary capacitor 68.

[0023] The multiple switching elements 61-62 include a fifth switching element 61 and a sixth switching element 62. In the converter 20, the multiple switching elements 51-54 of the primary side circuit 50 are periodically switched on / off, and the multiple switching elements 61-62 of the secondary side circuit 60 are periodically switched on / off, thereby converting a DC voltage on the input side (primary side) into a DC voltage on the output side (secondary side). In the following, of the multiple switching elements 61-62 of the secondary side circuit 60, the fifth switching element 61 will be mainly described. The sixth switching element 62 has the same configuration as the fifth switching element 61, so a detailed description thereof will be omitted.

[0024] The fifth switching element 61 includes a fifth transistor 61a and a fifth diode 61b. The fifth diode 61b may be a parasitic diode that is inevitably created when the fifth transistor 61a is created on a semiconductor substrate. The fifth transistor 61a and the fifth diode 61b are connected in anti-parallel. The fifth switching element 61 is turned on / off when a PWM (Pulse Width Modulation) signal is input to the fifth transistor 61a, and the fifth transistor 61a is turned on / off by the PWM signal. The fifth switching element 61 may generate heat by the fifth transistor 61a being turned on / off. When the fifth transistor 61a is turned on / off, a switching loss occurs, and the fifth switching element 61 generates heat. The sixth switching element 62 is similar to the fifth switching element 61. For example, the sixth switching element 62 includes a sixth transistor 62a and a sixth diode 62b.

[0025] The multiple switching elements 61-62 are connected in series with the secondary coil 65. The fifth switching element 61 is connected in series with the secondary coil 65a, and the sixth switching element 62 is connected in series with the secondary coil 65b. Each of the secondary coils 65a, 65b is wound around, for example, a metal core (not shown), and together with the primary coil 55 constitutes a transformer 70.

[0026] The secondary inductance 66 of the secondary circuit 60 is connected in series with each of the secondary coils 65a and 65b. The secondary inductance 66 stores the energy of the current flowing through the secondary circuit 60 and releases the stored energy. The secondary capacitor 68 is connected in parallel with the secondary inductance 66. The secondary capacitor 68 stores the charge of the secondary circuit 60 and releases the stored charge.

[0027] The converter 20 further includes a voltage detector 12 that detects a forward voltage of the first diode 51b of the first switching element 51, and a current detector 14 that detects a forward current of the first diode 51b.

[0028] The voltage detection unit 12 detects a forward voltage applied to the first diode 51b. The voltage detection unit 12 includes, for example, an internal resistor for detecting the forward voltage. The voltage detection unit 12 is connected in parallel with the first diode 51b, for example. Information on the forward voltage of the first diode 51b detected by the voltage detection unit 12 is transmitted to the control device 100.

[0029] The current detection unit 14 detects a forward current flowing through the first diode 51b. The current detection unit 14 includes, for example, an internal resistor for detecting the forward current. The current detection unit 14 is, for example, connected in series with the first diode 51b. Information on the forward current of the first diode 51b detected by the current detection unit 14 is transmitted to the control device 100.

[0030] The first diode 51b of the first switching element 51 has a characteristic that the relationship between the forward voltage and the forward current changes depending on the temperature. Therefore, if the forward voltage and the forward current of the first diode 51b can be specified, the temperature of the first diode 51b can be specified. FIG. 2 is a diagram showing an example of the temperature characteristic of a diode (for example, the first diode 51b). Information on the temperature characteristic shown in FIG. 2 is stored, for example, in the storage unit of the control device 100. In the temperature characteristic shown in FIG. 2, the temperature of the first diode 51b is 25° C. when the forward voltage is 0.9 V and the forward current is 1.0×10−1. The temperature characteristic shown in FIG. 2 allows the temperature of the first diode 51b to be obtained based on the forward voltage and the forward current of the first diode 51b.

[0031] The control device 100 (see FIG. 1) includes, for example, a CPU, a ROM, and a RAM, and executes predetermined control and processing related to the switching device 2 based on a program stored in a storage unit. For example, the control device 100 executes switching control for periodically switching on and off a plurality of switching elements 51-54, 61-62 of the converter 20. The following description focuses mainly on the first switching element 51 and the second switching element 52 among the plurality of switching elements 51-54, 61-62.

[0032] (Switching control) As shown in FIG. 3, the control device 100 controls the first transistor 51a of the first switching element 51 and the second transistor 52a of the second switching element 52 in a synchronized manner. The control device 100 normally synchronizes the on / off of the first transistor 51a with the off / on of the second transistor 52a as shown at T1. The control device 100 turns on the first transistor 51a at the timing when the second transistor 52a is turned off, and turns off the first transistor 51a at the timing when the second transistor 52a is turned on. Such switching control is sometimes called synchronous rectification. The control device 100 normally turns on / off the first transistor 51a and the second transistor 52a at a frequency outside the audible range (for example, a frequency less than 20 Hz or more than 20,000 Hz).

[0033] In the first switching element 51, when the first transistor 51a is turned off, a return current flows through the first diode 51b. In the second switching element 52, when the second transistor 52a is turned off, a return current flows through the second diode 52b.

[0034] When estimating the temperature of the first transistor 51a, the control device 100 does not turn on the first transistor 51a but keeps it temporarily off at the timing when the second transistor 52a is turned off (i.e., the timing when the first transistor 51a is turned on). The switching control during temperature estimation will be described in detail later.

[0035] (Temperature estimation process; Figure 4) Next, a temperature estimation process according to the embodiment will be described. In the following, a case where the temperature of the first switching element 51 of the converter 20 is estimated will be described. When estimating the temperature of the first switching element 51, the control device 100 executes switching control by the temperature estimation process. The temperature estimation process is started, for example, when a predetermined time has elapsed since the converter 20 was started. The temperature estimation process may be executed periodically at a predetermined time interval.

[0036] As shown in FIG. 4, in S12 of the temperature estimation process, the control device 100 monitors whether or not the timing P1 of temperature estimation arrives while performing normal switching control (see T1 in FIG. 3). The timing P1 of temperature estimation arrives when a predetermined time has elapsed since the start of the temperature estimation process. The timing P1 of temperature estimation may arrive periodically at a predetermined time interval. The timing P1 of temperature estimation can be set appropriately. The timing P1 of temperature estimation coincides with the timing P12 of turning off the second transistor 52a of the second switching element 52 (i.e., the timing P11 of turning on the first transistor 51a of the first switching element 51). If the timing of temperature estimation arrives (YES in S12), the process proceeds to S14. If the timing of temperature estimation has not arrived (NO in S12), the process of S12 continues.

[0037] In the next step S14, as shown at T2 in FIG. 3, the control device 100 does not turn on the first transistor 51a but keeps it off at timing P12 when the second transistor 52a is turned off (i.e., timing P11 when the first transistor 51a is turned on). This makes the off period of the first transistor 51a longer than usual. By keeping the first transistor 51a off without turning it on, the control device 100 changes the frequency of the switching control of the first transistor 51a to a frequency within the audible range (for example, a frequency not less than 20 Hz and not more than 20,000 Hz). Note that the on / off timing of the second transistor 52a is not changed.

[0038] In the next step S16, the control device 100 acquires information on the forward voltage of the first diode 51b detected by the voltage detection unit 12 of the converter 20 and information on the forward current of the first diode 51b detected by the current detection unit 14. In the next step S18, the control device 100 determines whether acquisition of the information on the forward voltage and forward current of the first diode 51b has been completed. If the control device 100 has acquired the information on the forward voltage and forward current of the first diode 51b (YES in S18), the process proceeds to S20, and if the information cannot be acquired (NO in S18), the process proceeds to S42.

[0039] In S20 after YES in S18, the control device 100 estimates the temperature of the first diode 51b based on information acquired from the voltage detection unit 12 and the current detection unit 14. That is, the control device 100 estimates the temperature of the first diode 51b based on the forward voltage of the first diode 51b detected by the voltage detection unit 12 and the forward current of the first diode 51b detected by the current detection unit 14. The control device 100 estimates the temperature of the first diode 51b based on information of the temperature characteristics shown in FIG. 2. For example, when the forward voltage of the first diode 51b is 0.9V and the forward current is 1.0×10−1, the temperature of the first diode 51b is estimated to be 25° C. The control device 100 also estimates the temperatures of the first switching element 51 and the first transistor 51a from the temperature of the first diode 51b. The control device 100 considers the temperatures of the first switching element 51 and the first transistor 51a to be the same as the temperature of the first diode 51b.

[0040] In the following S22, the control device 100 determines whether or not the second transistor 52a of the second switching element 52 is off. If the second transistor 52a is off (YES in S22), the process proceeds to S24, and if the second transistor 52a is on (NO in S22), the process proceeds to S32.

[0041] In S24 after YES in S22, the control device 100 turns on the first transistor 51a as shown in T2 of FIG. 5. When the first transistor 51a is turned on, a current flows through the first transistor 51a. In the following S26, the control device 100 returns the switching control of the first transistor 51a to the normal switching control. That is, as shown in T3 of FIG. 5, the control device 100 turns off the first transistor 51a at the timing when the second transistor 52a is turned on, and turns on the first transistor 51a at the timing when the second transistor 52a is turned off. After S26, the process returns to S12.

[0042] On the other hand, in S32 after NO in S22, the control device 100 monitors whether or not the next timing P22 for turning off the second transistor 52a from the on state (i.e., timing P21 for turning on the first transistor 51a) has arrived. If the timing P22 for turning off the second transistor 52a has arrived (YES in S32), the control device 100 proceeds to S34, turns off the second transistor 52a, and turns on the first transistor 51a. On the other hand, if the next timing P22 for turning off the second transistor 52a from the on state has not arrived (NO in S32), the control device 100 continues the process of S32.

[0043] In S26 following S34, the control device 100 returns the switching control of the first transistor 51a to normal switching control. That is, as shown by T3 in Fig. 3, the control device 100 turns off the first transistor 51a at the timing when the second transistor 52a is turned on, and turns on the first transistor 51a at the timing when the second transistor 52a is turned off. After S26, the process returns to S12.

[0044] In S42 after NO in S18, the control device 100 monitors whether or not the next timing P22 at which the second transistor 52a is turned off from the on state (i.e., the timing P21 at which the first transistor 51a is turned on) has arrived. If the timing P22 at which the second transistor 52a is turned off has arrived (YES in S42), the control device 100 advances the process to S44, turns off the second transistor 52a, and turns on the first transistor 51a. On the other hand, if the timing P22 at which the second transistor 52a is turned off from the on state has not arrived (NO in S42), the control device 100 returns the process to S16.

[0045] In S46 following S44, the control device 100 stores in the storage unit that information on the forward voltage and forward current of the first diode 51b has not been acquired. In S26 following S46, the control device 100 returns the switching control of the first transistor 51a to normal switching control. That is, as shown by T3 in FIG. 3, the control device 100 turns off the first transistor 51a at the timing when the second transistor 52a is turned on, and turns on the first transistor 51a at the timing when the second transistor 52a is turned off. After S26, the process returns to S12. The above temperature estimation process ends, for example, when the normal switching control of the converter 20 ends.

[0046] (effect) The switching device 2 of the embodiment has been described above. As is clear from the above description, in the switching device 2 of the embodiment, when the control device 100 estimates the temperature of the first switching element 51 in a state in which the control device 100 executes switching control to turn on the first transistor 51a at the timing to turn off the second transistor 52a and to turn off the first transistor 51a at the timing to turn on the second transistor 52a (see T1 in FIG. 3), the first transistor 51a is not turned on at the timing P12 to turn off the second transistor 52a but is kept off (see T2 in FIG. 3), and the temperature of the first switching element 51 is estimated based on the forward voltage of the first diode 51b detected by the voltage detection unit 12 and the forward current of the first diode 51b detected by the current detection unit 14 while the first transistor 51a is off (see S12-S20 in FIG. 4).

[0047] According to this configuration, by keeping the first transistor 51a off without turning it on at the timing P12 when the second transistor 52a is turned off, a long period can be secured for detecting the forward voltage and forward current of the first diode 51b when a return current flows through the first diode 51b. This allows the forward voltage and forward current of the first diode 51b to be detected with high accuracy, and based on this, the temperature of the first switching element 51 can be estimated with high accuracy. In addition, the temperature of the first switching element 51 can be estimated without impeding the operation of the converter 20.

[0048] When estimating the temperature of the first switching element 51, if the forward voltage and forward current of the first diode 51b are detected during the period from when the first transistor 51a is not turned on and the first transistor 51a is kept off until the second transistor 52a is turned on, the control device 100 turns on the first transistor 51a before turning on the second transistor 52a (see S14-S24 in FIG. 4 and T2 in FIG. 5). Also, when estimating the temperature of the first switching element 51, if the forward voltage and forward current of the first diode 51b are not detected during the period from when the first transistor 51a is not turned on and the first transistor 51a is kept off until the second transistor 52a is turned on, the control device 100 turns on the first transistor 51a at the timing P22 at which the second transistor 52a is next turned off (see NO in S18 in FIG. 4, S42, S44, FIG. 3).

[0049] Since the forward resistance of the first diode 51b is greater than the resistance of the first transistor 51a when the first transistor 51a is on, if the period during which the first transistor 51a is kept off is long and the period during which the return current flows through the first diode 51b is long, the amount of heat generated by the resistance of the first diode 51b may increase. However, according to the above configuration, when the forward voltage and forward current of the first diode 51b for estimating the temperature of the first switching element 51 are detected, the first transistor 51a is turned on at an early stage, thereby shortening the period during which the return current flows through the first diode 51b. This makes it possible to suppress heat generation due to the forward resistance of the first diode 51b.

[0050] When estimating the temperature of the first switching element 51 while the control device 100 is performing switching control of the first transistor 51a at a frequency outside the audible range, the control device 100 changes the frequency of the switching control of the first transistor 51a to a frequency within the audible range by keeping the first transistor 51a off rather than turning it on. With this configuration, an audible sound can be generated from the first transistor 51a when estimating the temperature of the first switching element 51. This makes it possible to notify the surroundings of the timing to estimate the temperature of the first switching element 51.

[0051] (Modification) (1) In the above embodiment, the configuration for estimating the temperature of the first switching element 51 has been described, but the present invention is not limited to this configuration. In a modified example, the configuration for estimating the temperature of the second switching element 52 may be used. In this case, the above-mentioned first and second relationships are interchanged. For example, the voltage detection unit 12 detects the forward voltage of the second diode 52b of the second switching element 52. The current detection unit 14 detects the forward current of the second diode 52b of the second switching element 52. When estimating the temperature of the second switching element 52, the control device 100 does not turn on the second transistor 52a at the timing of turning off the first transistor 51a, but keeps the second transistor 52a off, and estimates the temperature of the second switching element 52 based on the forward voltage of the second diode 52b detected by the voltage detection unit 12 and the forward current of the second diode 52b detected by the current detection unit 14 while the second transistor 52a is off.

[0052] (2) In the above embodiment, the relationship between the first switching element 51 and the second switching element 52 has been described, but the present invention is not limited to this configuration. For example, the same relationship as the relationship between the first switching element 51 and the second switching element 52 is also established between the third switching element 53 and the fourth switching element 54. The same relationship as the relationship between the first switching element 51 and the second switching element 52 is also established between the fifth switching element 61 and the sixth switching element 62. The same relationship as the relationship between the first switching element 51 and the third switching element 53 is also established. The same relationship as the relationship between the second switching element 52 and the fourth switching element 54 is also established. In a modified example, the temperature of the third switching element 53, the fourth switching element 54, the fifth switching element 61, or the sixth switching element 62 may be estimated.

[0053] (3) In the above embodiment, the switching element of the DC / DC converter 20 has been described, but the technology described in this specification can also be applied to, for example, a switching element of an AC / DC converter or a switching element of an inverter. An AC / DC converter and an inverter are other examples of a voltage conversion device.

[0054] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives is itself technically useful. [Explanation of symbols]

[0055] 2: switching device, 12: voltage detection unit, 14: current detection unit, 20: DC / DC converter, 40: power supply, 50: primary side circuit, 51: first switching element, 51a: first transistor, 51b: first diode, 52: second switching element, 52a: second transistor, 52b: second diode, 53: third switching element, 54: fourth switching element, 55: primary side coil, 56: primary side inductance, 58: primary side capacitor, 60: secondary side circuit, 61: fifth switching element, 62: sixth switching element, 65: secondary side coil, 66: secondary side inductance, 68: secondary side capacitor, 70: transformer, 90: secondary battery, 100: control device

Claims

1. a first switching element including a first transistor and a first diode connected in anti-parallel to the first transistor; a second switching element connected to the first switching element, the second switching element including a second transistor and a second diode connected in anti-parallel to the second transistor; a voltage detection unit that detects a forward voltage of the first diode; a current detection unit that detects a forward current of the first diode; A control unit, a control unit that performs switching control to turn on the first transistor at the timing to turn off the second transistor and turn off the first transistor at the timing to turn on the second transistor, and when estimating the temperature of the first switching element, the control unit maintains the first transistor off without turning on the first transistor at the timing to turn off the second transistor, and estimates the temperature of the first switching element based on the forward voltage of the first diode detected by the voltage detection unit and the forward current of the first diode detected by the current detection unit while the first transistor is off.

2. 2. The switching device of claim 1, When estimating the temperature of the first switching element, the control unit: If a forward voltage and a forward current of the first diode are detected during a period from when the first transistor is not turned on and the first transistor is kept off until the second transistor is turned on, the first transistor is turned on before the second transistor is turned on; a switching device which turns on the first transistor at the timing when the second transistor is next turned off if a forward voltage and a forward current of the first diode are not detected during the period from when the first transistor is not turned on but when the first transistor is kept off until the second transistor is turned on.

3. 3. A switching device according to claim 1 or 2, a control unit that, when estimating the temperature of the first switching element while performing switching control of the first transistor at a frequency outside the audible range, changes the frequency of the switching control of the first transistor to a frequency within the audible range by maintaining the first transistor off without turning it on.

4. 3. A switching device according to claim 1 or 2, A switching device, wherein the first switching element and the second switching element are switching elements in a voltage conversion device that converts an input voltage into an output voltage.

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