JP7577620B2 - DC-DC converter with auxiliary resonant circuit - Google Patents

Description

The present invention relates to a DC-DC converter equipped with an auxiliary resonant circuit that performs DC power conversion between a low-voltage node and a high-voltage node.

Conventionally, auxiliary resonant commutated pole (ARCP) type DC-DC converters are known. This type of DC-DC converter achieves soft switching by operating an auxiliary resonant circuit, which is connected in parallel to a converter main circuit consisting of switching elements, for a short period of time prior to the converter main circuit (see, for example, Non-Patent Document 1).

In addition, for this type of DC-DC converter, it is being considered to determine whether soft switching can be maintained by comparing the duty of the switch element that constitutes the converter's main circuit with a duty limit value, and if it cannot be maintained, to stop operation of the auxiliary resonant circuit or change the switching period of the switch element that constitutes the converter's main circuit (see, for example, Patent Document 1).

It is preferable that the auxiliary inductor that constitutes the auxiliary resonant circuit does not saturate while the auxiliary resonant circuit is in operation. For this reason, an upper limit is often set for the operating time of the auxiliary resonant circuit to prevent saturation.

Naoki Koike and three others, "High-efficiency bidirectional insulated DCDC converter", [online], Pony Electric Co., Ltd., [Retrieved May 19, 2021], Internet <URL: http://pony-e.jp/High_efficiency_bi-directional_insulated_DCDCconverter.pdf>

Patent No. 5617227

However, because the characteristics of the auxiliary inductor change considerably depending on its temperature, simply limiting the operating time of the auxiliary resonant circuit uniformly according to a preset upper limit value may not be enough to prevent saturation of the auxiliary inductor, for example, when the temperature of the auxiliary inductor is relatively high.

The present invention was made in consideration of the above circumstances, and aims to provide a DC-DC converter that can reliably prevent saturation of the auxiliary inductor that constitutes the auxiliary resonant circuit.

In order to solve the above problems, the DC-DC converter of the present invention is provided with a converter main circuit section, an auxiliary resonant circuit section, and a control section for controlling these, and performs DC power conversion between a low voltage node and a high voltage node, and (1) the converter main circuit section has a main inductor provided between the low voltage node and a first intermediate node, and main switching elements provided between the first intermediate node and the high voltage node and between the first intermediate node and a reference node, respectively; (2) the auxiliary resonant circuit section has an auxiliary inductor provided between the first intermediate node and a second intermediate node, an auxiliary switching element provided at least either between the second intermediate node and the high voltage node or between the second intermediate node and the reference node, and a temperature sensor for detecting the ambient temperature of the auxiliary inductor; and (3) the control section controls the on/off switching of the main switching element. The inductor includes a duty setting unit that sets a duty, a storage unit that stores rules regarding the on-time of the auxiliary switch element in a predetermined switching period and an upper limit value of the on-time, a first on-time setting unit that sets a first on-time that is a temporary value of the on-time based on the rules, a temperature correction unit that obtains a corrected upper limit value by correcting the upper limit value based on the ambient temperature of the auxiliary inductor, a second on-time setting unit that determines whether the first on-time is equal to or less than the corrected upper limit value, sets the second on-time that is the on-time to the first on-time if it is equal to or less than the corrected upper limit value, and sets the second on-time to zero if it is determined that it exceeds the corrected upper limit value, and a drive signal generation unit that generates a drive signal for the main switch element and the auxiliary switch element based on the duty and the second on-time.

In this configuration, instead of using the upper limit value stored in the memory unit as is, a corrected upper limit value (corrected upper limit value) based on the ambient temperature of the auxiliary inductor is used to determine whether to set the second on-time to zero, i.e., whether to stop the auxiliary resonant circuit unit from operating. Therefore, with this configuration, for example, if the auxiliary inductor has a tendency to be easily saturated at high temperatures, saturation can be reliably prevented by correcting the upper limit value to decrease as the temperature increases.

When the storage unit stores a first upper limit value equivalent to the upper limit value and a second upper limit value smaller than the first upper limit value, the temperature correction unit obtains the first corrected upper limit value by correcting the first upper limit value based on the ambient temperature of the auxiliary inductor, and obtains the second corrected upper limit value by correcting the second upper limit value, and it is preferable that the second on-time setting unit continues to set the second on-time to zero once the first on-time exceeds the first corrected upper limit value until the first on-time becomes equal to or less than the second corrected upper limit value, and continues to set the second on-time to the first on-time once the first on-time becomes equal to or less than the second corrected upper limit value until the first on-time exceeds the first corrected upper limit value.

This configuration prevents the auxiliary resonant circuit from frequently stopping and restarting operation.

A specific example of the configuration of the converter main circuit section may include a main inductor, a first main switching element provided between the first intermediate node and the high-voltage node, a second main switching element provided between the first intermediate node and the reference node, a first main diode connected in anti-parallel to the first main switching element, and a second main diode connected in anti-parallel to the second main switching element.

A specific configuration of the auxiliary resonant circuit section may include an auxiliary inductor, a temperature sensor, auxiliary capacitors provided between the first intermediate node and the high voltage node, and between the first intermediate node and a reference node, a first winding having an intermediate tap connected to a second intermediate node, a first auxiliary switch element provided between one end of the first winding and the high voltage node, a second auxiliary switch element provided between the other end of the first winding and the reference node, a first auxiliary diode connected in anti-parallel to the first auxiliary switch element, a second auxiliary diode connected in anti-parallel to the second auxiliary switch element, a second winding forming a transformer together with the first winding, and a diode bridge connected to one end and the other end of the second winding.

The ambient temperature of the auxiliary inductor is also the ambient temperature of the transformer, and it is preferable that it be affected not only by the temperature of the auxiliary inductor but also by the temperature of the transformer.

With this configuration, it is possible to determine whether or not to stop the auxiliary resonant circuit unit from operating, taking into account not only the auxiliary inductor but also the saturation of the transformer.

The present invention provides a DC-DC converter that can reliably prevent saturation of the auxiliary inductor that constitutes the auxiliary resonant circuit.

1 is a circuit diagram of a DC-DC converter according to a first embodiment of the present invention. 4 is an operational waveform diagram during boosting of the DC-DC converter according to the first embodiment; FIG. 4 is an operational waveform diagram during step-down of the DC-DC converter according to the first embodiment; FIG. 4 is a flow chart showing the operation of a control unit in the DC-DC converter according to the first embodiment; FIG. 5 is a diagram showing an example of a rule referred to in step S2 in FIG. 4. FIG. 5 is a diagram for explaining steps S4, S5a, and S5b in FIG. 4. FIG. 5 is a circuit diagram of a DC-DC converter according to a second embodiment of the present invention. FIG. 11 is a diagram illustrating the operation of a control unit (particularly, a second on-time setting unit) in the DC-DC converter according to the second embodiment.

Below, an embodiment of a DC-DC converter according to the present invention will be described with reference to the attached drawings.

[First embodiment]
A DC-DC converter 10A according to a first embodiment of the present invention is shown in Fig. 1. As shown in the figure, the DC-DC converter 10A includes a converter main circuit section 11, an auxiliary resonant circuit section 12, low-voltage side input/output terminals 13, 13, high-voltage side input/output terminals 14, 14, a control section 20A, and a capacitor C2.

The DC-DC converter 10A according to this embodiment can boost the voltage V1 output by the DC power source (e.g., a storage battery) 30 connected to the low-voltage input/output terminals 13, 13, and supply the voltage V2 obtained thereby to various load circuits from the high-voltage input/output terminals 14, 14. The DC-DC converter 10A can also step down the voltage V2 provided by various load circuits, and charge the storage battery 30 with the voltage V1 obtained thereby. In other words, the DC-DC converter 10A can perform DC power conversion in both directions between the low-voltage node NL and the high-voltage node NH.

The converter main circuit section 11 has a main inductor Lm provided between the low-voltage node NL and the first intermediate node NM1, a first main switching element Qm1 provided between the first intermediate node NM1 and the high-voltage node NH, a second main switching element Qm2 provided between the first intermediate node NM1 and the reference node NB, a first main diode Dm1 connected in anti-parallel to the first main switching element Qm1, a second main diode Dm2 connected in anti-parallel to the second main switching element Qm2, and a capacitor C1 provided between the low-voltage node NL and the reference node NB. The low-voltage node NL is connected to one of the low-voltage side input/output terminals 13, 13, the high-voltage node NH is connected to one of the high-voltage side input/output terminals 14, 14, and the reference node NB is connected to the other of the low-voltage side input/output terminals 13, 13 and the other of the high-voltage side input/output terminals 14, 14.

The first main switching element Qm1 is switched on/off by the drive signal Sm1 output by the control unit 20A. Similarly, the second main switching element Qm2 is switched on/off by the drive signal Sm2 output by the control unit 20A.

The auxiliary resonant circuit section 12 includes an auxiliary inductor Ls provided between the first intermediate node NM1 and the second intermediate node NM2, a first auxiliary capacitor Cs1 provided between the first intermediate node NM1 and the high-voltage node NH, a second auxiliary capacitor Cs2 provided between the first intermediate node NM1 and a reference node NB, a first winding Tr1 having an intermediate tap connected to the second intermediate node NM2, and a first auxiliary switch element Qs provided between one end of the first winding Tr1 and the high-voltage node NH. The inverter circuit has a first winding Tr1 connected in anti-parallel to the first auxiliary switching element Qs1, a second auxiliary diode Ds2 connected in anti-parallel to the second auxiliary switching element Qs2, a second winding Tr2 forming a transformer Tr together with the first winding Tr1, diodes Db1, Db2, Db3, and Db4 connected to one end and the other end of the second winding Tr2, and a temperature sensor 15. The diodes Db1, Db2, Db3, and Db4 form a diode bridge.

The first auxiliary switch element Qs1 is switched on/off by the drive signal Ss1 output by the control unit 20A. Similarly, the second auxiliary switch element Qs2 is switched on/off by the drive signal Ss2 output by the control unit 20A.

When a predetermined switching period (hereinafter also simply referred to as “period”) is T [s], the duty of the main switching elements Qm1, Qm2 in the period T is D [%], and the on-time of the auxiliary switching elements Qs1, Qs2 in the period T (a second on-time described later) is Ton2 [s], the control unit 20A operates each of the switching elements Qm1, Qm2, Qs1, Qs2 as follows during voltage boost (V1 → V2) (see FIG. 2 ).

For each period T, the second main switching element Qm2 is turned on for T×D/100.
For each period T, the second auxiliary switching element Qs2 is turned on for Ton2.
The second main switching element Qm2 is turned on in the center of Ton2 (times t1 and t5).
The first main switching element Qm1 is turned on/off in a manner substantially complementary to the second main switching element Qm2.
The first auxiliary switching element Qs1 is kept off.

The above control makes it possible to realize zero voltage switching (ZVS) in which the second main switching element Qm2 is turned on at times t1 and t5 when the voltage Vm2 across the second main switching element Qm2 becomes zero. In addition, the above control turns off the second auxiliary switching element Qs2 at times t2 and t6 when the auxiliary inductor current Is, which began to decrease as a result of the second main switching element Qm2 being turned on, becomes zero, thereby preventing unnecessary excitation of the transformer Tr.

On the other hand, when stepping down (V2→V1), the control unit 20A operates the switching elements Qm1, Qm2, Qs1, and Qs2 as follows (see FIG. 3).

For each period T, the first main switching element Qm1 is turned on for T×D/100.
For each period T, the first auxiliary switching device Qs1 is turned on for Ton2.
The first main switching element Qm1 is turned on in the center of Ton2 (times t1 and t5).
The second main switching element Qm2 is turned on/off so as to be substantially complementary to the first main switching element Qm1.
The second auxiliary switching device Qs2 remains off.

The above control realizes ZVS, in which the first main switching element Qm1 turns on at times t1 and t5 when the voltage Vm1 across the first main switching element Qm1 becomes zero. In addition, the above control turns off the first auxiliary switching element Qs1 at times t2 and t6 when the auxiliary inductor current Is, which began to rise as a result of the first main switching element Qm1 being turned on, becomes zero, preventing unnecessary excitation of the transformer Tr.

As will be described in detail later, the second on-time Ton2 is typically equal to the first on-time Ton1 set by the first on-time setting unit 22 of the control unit 20A. Furthermore, when synchronous rectification is not required, the control unit 20A may keep the first main switching element Qm1 in the step-up mode and the second main switching element Qm2 in the step-down mode off.

The temperature sensor 15 is disposed around the auxiliary inductor Ls and detects the ambient temperature (TMP) of the auxiliary inductor Ls. When the temperature of the auxiliary inductor Ls rises due to the flow of the auxiliary inductor current Is, the ambient temperature of the auxiliary inductor Ls also rises. The same is true in the reverse case. For this reason, it can be said that the temperature sensor 15 indirectly detects the temperature of the auxiliary inductor Ls.

Next, the characteristic configuration and operation of the control unit 20A will be explained with reference to Figures 1 and 4 to 6.

As shown in FIG. 1, the control unit 20A has a duty setting unit 21, a first on-time setting unit 22, a memory unit 23A, a temperature correction unit 24A, a second on-time setting unit 25A, and a drive signal generation unit 26.

The duty setting unit 21 sets the duty D of the main switching elements Qm1 and Qm2 in a period T. For example, the duty setting unit 21 sets the duty D during boosting based on the difference between the voltage V1 detected by a sensor (not shown) and the target voltage V2. Alternatively, the duty setting unit 21 sets the duty D during stepping down based on the difference between the voltage V2 detected by a sensor (not shown) and the target voltage V1.

This operation of the duty setting unit 21 corresponds to step S1 shown in FIG. 4.

The first on-time setting unit 22 sets the first on-time Ton1, which is a provisional value of the on-time of the auxiliary switching elements Qs1 and Qs2 in the period T, based on the voltage V2 and the main inductor current Im detected by a sensor (not shown) and the rule (the relationship between V2/Im and the first on-time Ton1) stored in the memory unit 23A. In this embodiment, the rule shown in FIG. 5 is stored in the memory unit 23A. By referring to this rule, the first on-time setting unit 22 can uniquely determine the suitable first on-time Ton1 corresponding to the current voltage V2 and the main inductor current Im. Note that this rule is determined in advance so that the step-up/step-down operation of the DC-DC converter 10A is most efficient (i.e., so that soft switching is most effectively performed).

This operation of the first on-time setting unit 22 corresponds to step S2 shown in FIG. 4.

The memory unit 23A stores the above-mentioned rules as well as an upper limit value Tth1 for the operating time of the auxiliary resonant circuit unit 12 when the temperature of the auxiliary inductor Ls is approximately room temperature. When the temperature of the auxiliary inductor Ls is approximately room temperature, if the operating time of the auxiliary resonant circuit unit 12, i.e., the time during which the auxiliary inductor current Is flows through the auxiliary inductor Ls, exceeds the upper limit value Tth1, the auxiliary inductor Ls becomes saturated. The upper limit value Tth1 can be determined experimentally or by circuit simulation.

The temperature correction unit 24A reads out the upper limit value Tth1 from the memory unit 23A and corrects the read upper limit value Tth1 based on the ambient temperature of the auxiliary inductor Ls detected by the temperature sensor 15. If there is a tendency for saturation to occur earlier at higher temperatures, the temperature correction unit 24A decreases the upper limit value Tth1 as the ambient temperature rises. Conversely, if there is a tendency for saturation to occur earlier at lower temperatures, the temperature correction unit 24A increases the upper limit value Tth1 as the ambient temperature rises. In the following description, the corrected upper limit value Tth1 will be referred to as the "corrected upper limit value Tth2."

This operation of the temperature correction unit 24A corresponds to step S3 shown in FIG. 4.

As shown in FIG. 6, the second on-time setting unit 25A determines whether the first on-time Ton1 is equal to or less than the corrected upper limit value Tth2, and if the first on-time Ton1 is equal to or less than the corrected upper limit value Tth2, the second on-time Ton2, which is the final on-time, is set to the first on-time Ton1, and if the first on-time Ton1 is greater than the corrected upper limit value Tth2, the second on-time Ton2 is set to zero.

This operation of the second on-time setting unit 25A corresponds to steps S4, S5a, and S5b shown in FIG. 4.

The drive signal generating unit 26 generates drive signals Sm1, Sm2 for the main switch elements Qm1, Qm2 based on the set duty D, and generates drive signals Ss1, Ss2 for the auxiliary switch elements Qs1, Qs2 based on the set second on-time Ton2, and outputs these to each switch element Qm1, Qm2, Qs1, Qs2.

This operation of the drive signal generating unit 26 corresponds to step S6 shown in FIG. 4.

In this way, the control unit 20A of the DC-DC converter 10A according to this embodiment is configured to determine whether or not to operate the auxiliary resonant circuit unit 12 based on the upper limit value Tth1 (= corrected upper limit value Tth2) corrected based on the ambient temperature of the auxiliary inductor Ls. Therefore, according to the DC-DC converter 10A according to this embodiment, it is possible to reliably prevent saturation of the auxiliary inductor Ls while improving efficiency through soft switching.

[Second embodiment]
7 shows a DC-DC converter 10B according to a second embodiment of the present invention. As shown in the figure, the DC-DC converter 10B differs from the DC-DC converter 10A in that it has a control unit 20B instead of the control unit 20A, but in other respects it is the same as the DC-DC converter 10A. The control unit 20B also differs from the control unit 20A in that it has a memory unit 23B instead of the memory unit 23A, a temperature correction unit 24B instead of the temperature correction unit 24A, and a second on-time setting unit 25B instead of the second on-time setting unit 25A, but in other respects it is the same as the control unit 20A.

The memory unit 23B stores a first upper limit value Ttha1 that corresponds to the rule shown in FIG. 5 and the upper limit value Tth1 described above, as well as a second upper limit value Tthb1 that is slightly smaller than the first upper limit value Ttha1.

The temperature correction unit 24B reads out the first upper limit value Ttha1 and the second upper limit value Tthb1 from the memory unit 23B, and corrects the two upper limit values Ttha1 and Tthb1 that have been read out based on the ambient temperature. As with the temperature correction unit 24A, if there is a tendency for saturation to occur earlier at higher temperatures, the temperature correction unit 24B decreases the upper limit values Ttha1 and Tthb1 as the ambient temperature rises. Conversely, if there is a tendency for saturation to occur earlier at lower temperatures, the temperature correction unit 24B increases the upper limit values Ttha1 and Tthb1 as the ambient temperature rises. In the following description, the corrected first upper limit value Ttha1 will be referred to as the "first corrected upper limit value Ttha2" and the corrected second upper limit value Tthb1 will be referred to as the "second corrected upper limit value Tthb2".

The second on-time setting unit 25B compares the first on-time Ton1 with the two corrected upper limit values Ttha1 and Tthb1, and if the first on-time Ton1 is less than or equal to the second corrected upper limit value Tthb2, it sets the second on-time Ton2, which is the final on-time, to the first on-time Ton1, if the first on-time Ton1 > the first corrected upper limit value Ttha2, it sets the second on-time Ton2 to zero, and if the second corrected upper limit value Tthb2 < the first on-time Ton1 is less than or equal to the first corrected upper limit value Ttha2, it sets the second on-time Ton2 to the first on-time Ton1 or zero.

More specifically, as shown in FIG. 8, the second on-time setting unit 25B is configured to keep the second on-time Ton2 at zero once the first on-time Ton1 exceeds the first corrected upper limit value Ttha2 until the first on-time Ton1 becomes equal to or less than the second corrected upper limit value Tthb2, and to keep the second on-time Ton2 at the first on-time Ton1 once the first on-time Ton1 becomes equal to or less than the second corrected upper limit value Tthb2 until the first on-time Ton1 exceeds the first corrected upper limit value Ttha2.

The DC-DC converter 10B according to this embodiment can prevent the auxiliary resonant circuit section 12 from frequently stopping and restarting operation. If the auxiliary resonant circuit section 12 frequently stops and restarts operation, the output voltage (voltage V2 when stepping up, voltage V1 when stepping down) will fluctuate, which may cause damage to the various load circuits connected to the high-voltage input/output terminals 14, 14 and the storage battery 30 connected to the low-voltage input/output terminals 13, 13.

In addition, the DC-DC converter 10B according to this embodiment provides the same effects as the DC-DC converter 10A.

[Modification]
Although the first and second embodiments of the DC-DC converter according to the present invention have been described above, the configurations of the present invention are not limited to these.

For example, the configuration of the converter main circuit is not limited to that shown in Figures 1 and 7. In particular, if the main switching elements Qm1 and Qm2 include body diodes, the main diodes Dm1 and Dm2 can be omitted.

The configuration of the auxiliary resonant circuit section is not limited to that shown in Figs. 1 and 7. In particular, when the auxiliary switching elements Qs1 and Qs2 include body diodes, the auxiliary diodes Ds1 and Ds2 can be omitted. Furthermore, when the auxiliary resonant circuit section is operated only during boosting, the first auxiliary switching element Qs1, the first auxiliary diode Ds1, the first auxiliary capacitor Cs1, and part of the first winding Tr1 can be omitted, and when the auxiliary resonant circuit section is operated only during stepping down, the second auxiliary switching element Qs2, the second auxiliary diode Ds2, the first auxiliary capacitor Cs1, and another part of the first winding Tr1 can be omitted.

The rules to be referred to when setting the first on-time Ton1 are not limited to those shown in FIG. 5. In the present invention, a graph, a formula, a map, a table, or the like that can univocally determine the first on-time Ton1 that provides the most efficient step-up/step-down operation, that is, the first on-time Ton1 that provides the most effective soft switching, can be used as the rules.

The ambient temperature of the auxiliary inductor Ls detected by the temperature sensor 15 is preferably also the ambient temperature of the transformer Tr. In other words, the ambient temperature detected by the temperature sensor 15 is preferably influenced not only by the temperature of the auxiliary inductor Ls but also by the temperature of the transformer Tr. With this configuration, it is possible to determine whether or not to stop the operation of the auxiliary resonant circuit unit 12, taking into account not only the saturation of the auxiliary inductor Ls but also that of the transformer Tr.

10A, 10B DC-DC converter 11 Converter main circuit section 12 Auxiliary resonant circuit section 13 Low voltage side input/output terminal 14 High voltage side input/output terminal 15 Temperature sensor 20A, 20B Control section 21 Duty setting section 22 First on-time setting section 23A, 23B Memory section 24A, 24B Temperature correction section 25A, 25B Second on-time setting section 26 Drive signal generation section 30 DC power supply (storage battery)
C1, C2 Capacitors Cs1, Cs2 Auxiliary capacitors Db1, Db2, Db3, Db4 Diodes Dm1, Dm2 Main diodes Ds1, Ds2 Auxiliary diode Lm Main inductor Ls Auxiliary inductor NB Reference node NH High voltage node NL Low voltage node NM1 First intermediate node NM2 Second intermediate nodes Qm1, Qm2 Main switching elements Qs1, Qs2 Auxiliary switching element Tr Transformer Tr1 First winding Tr2 Second winding

Claims (5)

A DC-DC converter that performs DC power conversion between a low voltage node and a high voltage node, the DC-DC converter comprising a converter main circuit section, an auxiliary resonant circuit section, and a control section that controls these sections,
The converter main circuit unit includes:
a main inductor provided between the low voltage node and a first intermediate node;
a main switch element provided between the first intermediate node and the high voltage node, and between the first intermediate node and a reference node,
The auxiliary resonant circuit unit includes:
an auxiliary inductor provided between the first intermediate node and the second intermediate node;
an auxiliary switch element provided at least one between the second intermediate node and the high voltage node and between the second intermediate node and the reference node;
a temperature sensor for detecting an ambient temperature of the auxiliary inductor;
The control unit is
a duty setting unit that sets an on/off duty of the main switch element;
a storage unit that stores a rule regarding an ON time of the auxiliary switch element in a predetermined switching period and an upper limit value of the ON time;
a first on-time setting unit that sets a first on-time, which is a temporary value of the on-time, based on the rule;
a temperature correction unit that obtains a corrected upper limit value by correcting the upper limit value based on an ambient temperature of the auxiliary inductor;
a second on-time setting unit that determines whether the first on-time is equal to or less than the corrected upper limit value, and when it is determined that the first on-time is equal to or less than the corrected upper limit value, sets a second on-time that becomes the on-time to the first on-time, and when it is determined that the first on-time exceeds the corrected upper limit value, sets the second on-time to zero;
a drive signal generating section that generates drive signals for the main switching element and the auxiliary switching element based on the duty and the second on-time. the storage unit stores a first upper limit value corresponding to the upper limit value and a second upper limit value smaller than the first upper limit value;
the temperature correction unit corrects the first upper limit value based on an ambient temperature of the auxiliary inductor to obtain a first corrected upper limit value and corrects the second upper limit value based on an ambient temperature of the auxiliary inductor;
2. The DC-DC converter according to claim 1, wherein, once the first on-time exceeds the first corrected upper limit value, the second on-time setting unit continues to set the second on-time to zero until the first on-time becomes equal to or less than the second corrected upper limit value, and, once the first on-time becomes equal to or less than the second corrected upper limit value, the second on-time continues to be the first on-time until the first on-time exceeds the first corrected upper limit value. The converter main circuit unit includes:
The main inductor;
a first main switching element provided between the first intermediate node and the high voltage node;
a second main switching element provided between the first intermediate node and a reference node;
a first main diode connected in anti-parallel to the first main switching element;
3. The DC-DC converter according to claim 1, further comprising a second main diode connected in anti-parallel to the second main switching element. The auxiliary resonant circuit unit includes:
The auxiliary inductor;
The temperature sensor;
auxiliary capacitors provided between the first intermediate node and the high voltage node, and between the first intermediate node and the reference node, respectively;
a first winding having a center tap connected to the second intermediate node;
a first auxiliary switch element provided between one end of the first winding and the high voltage node;
a second auxiliary switch element provided between the other end of the first winding and the reference node;
a first auxiliary diode connected in anti-parallel to the first auxiliary switch element;
a second auxiliary diode connected in anti-parallel to the second auxiliary switch element;
a second winding forming a transformer with the first winding;
4. The DC-DC converter according to claim 1, further comprising a diode bridge connected to one end and the other end of the second winding. 5. The DC-DC converter according to claim 4 , wherein the ambient temperature of the auxiliary inductor is also the ambient temperature of the transformer, and is affected not only by the temperature of the auxiliary inductor but also by the temperature of the transformer.

Images