JP4265356B2 - DC-DC converter - Google Patents

Description

  The present invention relates to a DC-DC converter that suppresses a jumping voltage of a semiconductor switching element.

  FIG. 2A shows an explanatory diagram of a circuit of a step-up push-pull converter which is an example of a conventional DC-DC converter, and FIG. 2B shows an explanatory diagram of operation waveforms thereof. In FIG. 2A, reference numeral 1 is a DC power source, 2 is a reactor, 3 is a transformer, 4 is a capacitor, 5 is a load, 6a and 6b are switching elements, 7a and 7b are diodes, 9a, 9b, 10a and 10b are A diode 11 indicates a leakage inductance. In the conventional DC-DC converter, a jumping voltage is generated at both ends of the switching elements 6a and 6b due to the leakage inductance 11 when the switching elements 6a and 6b are turned off. In the prior art, the following three methods, namely, increasing the rated voltage of the switching element, absorbing and consuming the energy of the jumping voltage in the snubber circuit 15 shown in FIG. The jumping voltage of the semiconductor switching element has been suppressed. Non-patent document 1 discloses such a conventional DC-DC converter.

Semiconductor power conversion circuit, Institute of Electrical Engineers, Semiconductor Power Conversion Method Research Committee, P36-41, P300-301, Ohmsha

  Each of the above conventional techniques has the following problems. When the rated voltage of the switching element is increased, the switching element becomes expensive or the conduction loss of the switching element increases. Further, by absorbing and consuming the energy of the jumping voltage by the snubber circuit 15, the number of parts increases and the loss increases. Furthermore, the resonant converter increases the number of parts and complicates circuit control.

  An object of the present invention is to provide a DC-DC converter in which the loss is reduced and the efficiency is increased without increasing the rated voltage of the switching element.

  In the conventional DC-DC converter shown in FIG. 2, the secondary side rectifier circuits are only diodes 9a, 9b, 10a, 10b. On the other hand, the DC-DC converter of the present invention includes switching elements 8a and 8b as shown in FIG. 1A, and controls the switching elements 6a, 6b, 8a and 8b at the timing shown in FIG. 1B. To do. In the DC-DC converter of the present invention, the circuit shown in FIG. 1 (a) is controlled at the timing shown in FIG. 1 (b), so that the switching elements 8a, 6a and 6b are turned on and off. The secondary side of the transformer 3 is short-circuited by 8b so that no voltage is applied to the switching elements 6a and 6b. Thereby, in the DC-DC converter of this invention, the loss at the time of turn-on and turn-off of switching element 8a, 8b is suppressed small, and the jumping voltage which generate | occur | produces at the both ends of switching element 8a, 8b is suppressed.

  According to the present invention, since the jumping voltage of the switching elements 6a and 6b arranged on the primary side of the transformer can be reduced, the conduction loss is reduced even though it is a low-speed switching element without using a switching element that can perform high-speed switching with low conduction loss. A DC-DC converter without increasing the cost of the DC-DC converter by disposing low switching elements and switching elements capable of high-speed switching even with high conduction loss on the primary side and the secondary side of the transformer. High efficiency and downsizing can be realized.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1A is an explanatory diagram of a circuit of the step-up push-pull converter according to the present embodiment, and FIG. 1B is an explanatory diagram of operation waveforms of each part of FIG. FIG. 1B is associated with FIGS. 4A to 4E showing the current flow of the step-up push-pull converter of this embodiment. 1 (b) corresponds to FIG. 4 (a). Similarly, B is FIG. 4 (b), C is FIG. 4 (c), D is FIG. Corresponds to FIG.

  This embodiment is different from the prior art shown in FIGS. 2 (a) and 2 (b) in that switching elements 8a and 8b are newly provided on the secondary side of the transformer 3, which are shown in FIG. 1 (b). It is a point that is controlled at such timing. In addition to the bipolar transistor shown in FIG. 1A, a power MOSFET having an insulated gate, an IGBT, or the like can be used as the semiconductor switching element of the DC-DC converter of the present embodiment.

  In this embodiment, the switching elements 8a and 8b are controlled as shown in FIG. When the switching elements 6a and 6b arranged on the primary side of the transformer are turned off (FIGS. 4A to 4B), the secondary side of the transformer 3 is short-circuited by the switching elements 8a and 8b. Thereby, since the voltage applied to the switching elements 6a and 6b is reduced, the jumping voltage of the switching elements 6a and 6b is reduced. In addition, when the switching elements 6a and 6b are turned on (FIG. 4 (b) to FIG. 4 (a)), the switching elements 8a and 8b are short-circuited to reduce the switching loss when the switching elements 6a and 6b are turned on. To reduce.

  As described above, in this embodiment, when the switching elements 6a and 6b are turned on or turned off, no voltage is applied to the switching elements 6a and 6b due to the operation of the switching elements 8a and 8b. , 6b can be a low-speed switching element with low conduction loss. In addition, since the switching elements 8a and 8b have a short time during which the current flows during the turn-on and the turn-off, the switching elements 8a and 8b have higher continuity than the switching elements 6a and 6b. Even if it is a loss, it is applicable if it can be switched at high speed.

  Although the switching elements 8a and 8b are also turned-off, since the leakage inductance 11 does not affect the switching elements 8a and 8b, a large jump voltage is not generated at both ends of the switching elements 8a and 8b.

  As described above, according to this embodiment, a switching element that is a low-speed switching element but has a low conduction loss and a high-speed switching element that has a low conduction loss without using a switching element that combines high-speed switching and low conduction loss. A high-efficiency DC-DC converter in which the jumping voltage of the semiconductor switching element is suppressed can be realized by using a switching element having a high current for the primary side and the secondary side of the transformer.

  Although the present embodiment has been described with a circuit without the snubber circuit, it may be provided with a snubber circuit, in which case, for example, the conventional DC-DC converter shown in FIG. 2 is smaller than when the snubber circuit is provided. The snubber circuit is sufficient.

  FIG. 5 is an explanatory diagram of a circuit of the step-up full bridge converter according to the present embodiment. The present embodiment is different from the first embodiment in that the primary side of the transformer 3 is not provided with a mid-point tap, and that switching elements 6c and 6d and diodes 7c and 7d are newly provided.

  In this embodiment, the switching elements 8a and 8b operate so as to short-circuit the secondary side of the transformer 3 when the switching elements 6a, 6b, 6c and 6d are turned on and turned off. Thus, in the present embodiment as well as in the first embodiment, when the switching elements 6a to 6d are turned on or turned off, a voltage is applied to the switching elements 6a to 6d by the operation of the switching elements 8a and 8b. Therefore, the jumping voltage of the switching elements 6a to 6d can be reduced, and the rated voltage of the switching elements 6a to 6d can be lowered. As a result, the switching elements 6a to 6d can be low-speed switching elements with low conduction loss. In addition, since the switching elements 8a and 8b have a short time during which the current flows during the turn-on and the turn-off, the switching elements 8a and 8b have higher continuity than the switching elements 6a to 6d. Even if it is a loss, it is applicable if it can be switched at high speed. In addition, in this embodiment as well, the snubber circuit is unnecessary or downsized as in the first embodiment.

  FIG. 6A and FIG. 6B are explanatory diagrams of the circuit of the flyback converter of this embodiment. The difference between FIG. 6A and FIG. 6B is that the position of the diode 9a is different. In FIG. 6A, the loss of the diode 9a can be reduced. In FIG. 6B, the jumping voltage of the switching element 8a is low, and the rated voltage of the diode 10a can be lowered.

  In the present embodiment, the switching element 8a operates so as to short-circuit the secondary side of the transformer 3 when the switching element 6a is turned on and turned off. Thus, in the present embodiment as well as in the first embodiment, when the switching element 6a is turned on or turned off, no voltage is applied to the switching element 6a due to the operation of the switching element 8a. Can be reduced, and the rated voltage of the switching element 6a can be lowered. As a result, a low-speed switching element with low conduction loss can be applied to the switching element 6a. Also in this embodiment, the switching element 8a has a short time during which the current flows during the turn-on and the turn-off. Therefore, even if the conduction loss is higher than that of the switching element 6a, the switching element 8a is switched at a higher speed. Any element can be used. Also in this embodiment, the snubber circuit can be made unnecessary or downsized as in the first embodiment.

  FIGS. 7A and 7B are explanatory diagrams of a circuit of the step-up forward converter according to the present embodiment. In this embodiment, as in the third embodiment, the loss of the diode 9a can be reduced in FIG. 7A, and the jumping voltage of the switching element 8a is low in FIG. 7B, so that the rated voltage of the diode 10a can be reduced. Similarly to the third embodiment, the switching elements 6a and 6b can be applied with a low speed switching element and a low conduction loss. Also in this embodiment, the switching element 8a has a higher conduction loss than the switching elements 6a and 6b. However, any element capable of switching at a higher speed than this can be applied.

  FIGS. 8A and 8B are explanatory diagrams of the circuit of this embodiment. The difference between the present embodiment and the third embodiment is that the primary side and the secondary side of the transformer 3 are connected by a ground potential that is a common potential. Other than this, it is the same as in the third embodiment, and the switching element 6a can be a low-speed switching element with a low conduction loss. Any element can be used.

  FIG. 9A to FIG. 9D are explanatory diagrams of the circuit of this embodiment. In this embodiment, switching elements 8a and 8b are arranged on the secondary side of the transformer 3 as shown in the figure. Also in the present embodiment shown in each of FIGS. 9A to 9D, the switching elements 6a and 6b arranged on the primary side of the transformer 3 are applied with low-speed switching elements having low conduction loss, For the switching elements 8a and 8b arranged on the secondary side of the transformer 3, an element capable of switching at a higher speed than that of the switching elements 6a and 6b is applied.

  Also in this embodiment, since the jumping voltage of the switching elements 6a and 6b arranged on the primary side of the transformer can be reduced, the conduction loss is low although it is a low-speed switching element without using a switching element capable of high-speed switching with low conduction loss. By arranging the switching elements and switching elements capable of high-speed switching even with high conduction loss on the primary side and the secondary side of the transformer, the cost of the DC-DC converter is increased without increasing the cost of the DC-DC converter. High efficiency and downsizing can be realized.

It is explanatory drawing of the circuit and operation | movement waveform of the pressure | voltage rise type push pull converter of Example 1. FIG. It is explanatory drawing of the circuit and operation | movement waveform of a boost type push pull converter of a prior art. It is explanatory drawing of the circuit of another boost technology push-pull converter. It is explanatory drawing of the flow of the electric current of the pressure | voltage rise type push pull converter of Example 1. FIG. It is explanatory drawing of the circuit of the pressure | voltage rise type full bridge converter of Example 2. FIG. It is explanatory drawing of the circuit of the flyback converter of Example 3. FIG. It is explanatory drawing of the circuit of the pressure | voltage rise type forward converter of Example 4. FIG. FIG. 10 is an explanatory diagram of a circuit of a DC-DC converter of Example 5. FIG. 10 is an explanatory diagram of a circuit of a DC-DC converter of Example 6.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... DC power supply, 2 ... Reactor, 3 ... Transformer, 4 ... Capacitor, 5 ... Load, 6a, 6b, 6c, 6d, 8a, 8b ... Switching element, 7a, 7b, 9a, 9b, 10a, 10b ... Diode DESCRIPTION OF SYMBOLS 11 ... Leakage inductance, 12 ... Primary current, 13 ... Secondary current, 15 ... Snubber circuit.

Claims (1)

In a DC-DC converter comprising a transformer, a first switching element arranged on the primary side of the transformer, and a rectifying means arranged on the secondary side of the transformer,
When the DC-DC converter is on the secondary side of the transformer and the first switching element of the first switching means is switched from conduction to non-conduction, it occurs at both ends of the first switching element due to leakage inductance. A predetermined period until it is no longer affected by the jumping voltage, or a predetermined period until it is not affected by the jumping voltage generated at both ends of the first switching element due to leakage inductance when switching from non-conduction to conduction. A circuit for short-circuiting the secondary side of the transformer by a second switching element during a period;
The DC-DC converter characterized in that the conduction loss of the second switching element is higher than that of the first switching element, and the switching speed of the second switching element is faster than that of the first switching element.

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