JP5008632B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply device installed inside an electronic device.

  In recent years, switching power supplies have been strongly demanded to be smaller and more efficient with the reduction in price, size, performance and energy saving of electronic devices. As an input of the switching power supply device, a circuit that rectifies and smoothes a commercial power supply and outputs a DC voltage, or a battery is used. In particular, when a battery is used as an input, the battery has a voltage fluctuation range, and it is required to stably supply a DC stabilizing voltage higher than the input voltage to the load from an input DC power supply having the voltage fluctuation range. Is done.

  A conventional switching power supply device has a circuit configuration as disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-147436 (hereinafter referred to as Patent Document 1). In Patent Document 1, a first switch Q1 is connected between a pair of DC terminals 1a and 1b via a first inductor L1 and a first portion N1a of a primary winding N1 of a transformer T. The second switch Q2 is connected via the inductor L1 and the second portion N1b of the primary winding N1. Further, the full-wave full rectifier circuit 2 is connected to the secondary winding N2 of the transformer T, and a smoothing capacitor C is connected between the output terminals of the full-wave full rectifier circuit 2, and a backflow prevention diode D5 is connected in parallel to the smoothing capacitor C. A DC-DC converter in which a second inductor L2 that is electromagnetically coupled to the first inductor L1 is connected is disclosed. In addition, the code | symbol used in the patent document 1 is used for the code | symbol in the said description.

JP 2004-147436 A (summary column, FIG. 2)

  By adopting the circuit configuration disclosed in Patent Document 1, when the first switch Q1 and the second switch Q2 are turned off, the leakage inductances of the first inductor L1, the second inductor L2, and the transformer T are reduced. Due to the influence, a spike-like excessive surge voltage is generated between the drain and source of the first switch Q1 and the second switch Q2. That is, the element stress on the first switch Q1 and the second switch Q2 is large, and the switches Q1 and Q2 need to have a withstand voltage that can withstand the surge voltage. This will increase the withstand voltage. Increasing this withstand voltage increases the conduction resistance of the switches Q1 and Q2 and increases the conduction loss, and the switching loss increases due to an excessive surge voltage, and there is a problem that the efficiency cannot be increased.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a switching power supply device capable of removing an excessive surge voltage generated when a switch is turned off.

  In order to solve the above problems, a switching power supply according to the present invention includes a choke coil having a first winding and a second winding, a first winding connected in series to the first winding of the choke coil, A transformer having a second winding; first switching means connected in series to the first winding of the transformer; and second switching means connected in series to the second winding of the transformer; A switching circuit for applying a voltage to the choke coil and the transformer by turning on and off the input DC voltage, a first rectifier means and a transformer connected to a connection point between the transformer and the first switching means; A second rectifying means connected to a connection point with the second switching means, the first switching means or the second switching means; A rectifier circuit for rectifying a voltage output via the choke coil and the transformer and a second winding of the choke coil when the one is on and the other is off; The third rectifying means for rectifying the voltage supplied to the output through the choke coil, the first rectifying means, and the second rectifying means when both the switching means and the second switching means are in an OFF state. Rectifying means, smoothing means for smoothing the voltage rectified by the third rectifying means, and the first switching means and the second switching means so as to maintain the output voltage of the smoothing means at a predetermined value. And a control circuit for on / off control.

  According to the switching power supply according to the present invention, a switching power supply capable of removing an excessive surge voltage generated when the switching element is turned off can be obtained.

  Preferred embodiments of a switching power supply device according to the present invention will be described below with reference to the accompanying drawings. Note that the present invention is not limited to these embodiments.

Embodiment 1 FIG.
First, the circuit configuration of the switching power supply according to Embodiment 1 of the present invention will be described with reference to FIG.
As shown in FIG. 1, the input DC power supply 1 is connected to DC input terminals 2 a and 2 b of the switching power supply device 100 in order to supply a DC voltage to the switching power supply device 100. One terminal of the first winding 3a of the choke coil 3 is connected to one terminal of the second winding 3b, and the other terminal of the first winding 3a of the choke coil 3 is the first terminal of the transformer 4. It is connected to one terminal of the winding 4a and one terminal of the second winding 4b. Reference numeral 3c indicates the core of the choke coil 3, and reference numeral 4c indicates the core of the transformer 4.

  The other terminal of the first winding 4a of the transformer 4 is a drain terminal of a first MOSFET (Metal Oxide Field Effect Transistor) 5a which is a first switching means and a first rectifier diode which is a first rectifying means. 6a is connected to the anode terminal. The other terminal of the second winding 4b of the transformer 4 is connected to the drain terminal of the second MOSFET 5b that is the second switching means and the anode terminal of the second rectifier diode 6b that is the second rectifying means. ing. The first MOSFET 5 a and the second MOSFET 5 b are switching circuits that turn on and off an input DC voltage and apply a voltage to the choke coil 3 and the transformer 4. The first rectifier diode 6a and the second rectifier diode 6b are output via the choke coil 3 and the transformer 4 when one of the first MOSFET 5a or the second MOSFET 5b is in an on state and the other is in an off state. It is a rectifier circuit that rectifies the voltage.

  The other terminal of the second winding 3b of the choke coil 3 is connected to an anode terminal of a third rectifier diode 6c that is a third rectifier. The cathode terminals of the first rectifier diode 6a, the second rectifier diode 6b and the third rectifier diode 6c are connected together, and the connection point is one terminal of the output smoothing capacitor 7 which is a smoothing means and the switching power supply. The output terminal 8a of the device 100 is connected.

  The DC input terminal 2b, the source terminal of the first MOSFET 5a and the source terminal of the second MOSFET 5b are connected together, and the connection point is connected to the other terminal of the output smoothing capacitor 7 and the output terminal 8b of the switching power supply device 100. Has been. Output terminals 8 a and 8 b are connected to a load 9. The first MOSFET 5a and the second MOSFET 5b are on / off controlled by the control circuit 10.

The switching power supply apparatus 100 according to the first embodiment is configured as described above. Next, the operation thereof will be described with reference to FIGS. 1 and 2.
Here, FIG. 2 is a waveform diagram schematically showing a change over time in the voltage waveform of each terminal in the switching power supply apparatus 100, and (a) shows a time-dependent change in the voltage waveform between the gate and the source of the first MOSFET 5a. (B) is a voltage waveform diagram schematically showing the change over time of the gate-source voltage waveform of the second MOSFET 5b, and (c) is a first rectification. FIG. 4D is a current waveform diagram schematically showing a change with time of the current waveform after the merging of the diode 6a, the second rectifier diode 6b, and the third rectifier diode 6c, and FIG. 4D is a change with time of the input current waveform. Are respectively shown current waveform diagrams.

  When the input DC power supply 1 is applied to the DC input terminals 2a and 2b of the switching power supply device 100, the first MOSFET 5a is maintained so as to maintain the output voltage, which is the voltage across the output smoothing capacitor 7, from the control circuit 10 at a predetermined value. A control signal that alternately turns on and off is generated between the gate and source of the second MOSFET 5b. Here, the ON times of the first MOSFET 5a and the second MOSFET 5b are controlled to be the same, and the first MOSFET 5a and the second MOSFET 5b are both controlled to have a period in which they are always OFF.

  The operation state of the switching power supply device 100 is roughly divided into two. The first operation state is a state in which the first MOSFET 5a is on and the second MOSFET 5b is off. The operation of the entire circuit is the same when the first MOSFET 5a is off and the second MOSFET 5b is on. The second operating state is a state where both the first MOSFET 5a and the second MOSFET 5b are off.

  In the first operation state, that is, in the operation state in which the first MOSFET 5a is on and the second MOSFET 5b is off, the input DC power supply 1, the first winding 3a of the choke coil 3, and the second winding 4b of the transformer 4 are used. A current is supplied to the output via the second rectifier diode 6b. At this time, energy is accumulated in the choke coil 3 via the input DC power source 1, the first winding 3a of the choke coil 3, the first winding 4a of the transformer 4, and the first MOSFET 5a. The first rectifier diode 6a and the third rectifier diode 6c are reverse-biased.

  Further, in the second operation state, that is, in the operation state in which both the first MOSFET 5a and the second MOSFET 5b are off, the energy stored in the choke coil 3 in the first operation state is released, thereby allowing the input. A current is supplied to the output via the DC power source 1, the second winding 3b of the choke coil 3, and the third rectifier diode 6c.

  As described above, according to the switching power supply device 100 according to the first embodiment, when the first MOSFET 5a is on and the second MOSFET 5b is off, the output between the drain and source of the second MOSFET 5b is output. The voltage is clamped by adding the forward voltage drop of the second rectifier diode 6b, and no further voltage is applied. When the first MOSFET 5a is off and the second MOSFET 5b is on, the voltage between the drain and source of the first MOSFET 5a is added to the output voltage by the forward voltage drop of the first rectifier diode 6a. And no further voltage is applied. That is, a voltage higher than the voltage obtained by adding the forward voltage drop of the first rectifier diode 6a or the second rectifier diode 6b to the output voltage is applied between the drain and source of the first MOSFET 5a and the second MOSFET 5b. There is nothing to do. Therefore, as the first MOSFET 5a and the second MOSFET 5b, it is possible to select a MOSFET having a significantly lower withstand voltage than the selection of the MOSFET when a surge voltage is generated. As a result, the conduction resistance of the MOSFET is small. Therefore, conduction loss can be reduced.

  Further, since excessive surge voltage can be removed, switching loss can be reduced, and a highly efficient switching power supply device can be provided.

  Further, since an excessive surge voltage generated in the MOSFET can be removed, an element stress applied to the MOSFET is small, so that an effect of providing a low-noise switching power supply device can be obtained.

  Note that although a MOSFET is used as a switching element in Embodiment 1, a bipolar transistor, an insulated gate bipolar transistor (IGBT = Insulated Gate Bipolar Transistor), a silicon carbide (Sic) transistor, or a silicon carbide MOSFET is used. Even if it is used, the same effect can be obtained. In the description of the first embodiment, the silicon diode is used as the rectifying element. However, the same effect can be obtained by using the silicon carbide diode.

Embodiment 2. FIG.
Next, a switching power supply device according to Embodiment 2 of the present invention will be described. FIG. 3 is a diagram illustrating a circuit configuration of the switching power supply apparatus 200 according to the second embodiment. As is apparent from FIG. 3, the switching power supply apparatus 200 according to the second embodiment is different from the configuration of the switching power supply apparatus 100 shown in the first embodiment in the following points.

  That is, in the switching power supply device 200 according to the second embodiment, the rectifier circuit (first to third rectifiers) includes the third MOSFET 11a, the fourth MOSFET 11b, and the fifth MOSFET 11c. The third MOSFET 11a, the fourth MOSFET 11b, and the fifth MOSFET 11c are configured by a synchronous rectifier circuit that synchronizes with the on / off timing of the first MOSFET 5a and the second MOSFET 5b. In addition, about another structure, it is the same as that of Embodiment 1, and duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  FIG. 4 is a waveform diagram schematically showing a change over time in the voltage waveform at each terminal in the switching power supply apparatus 200. FIG. 4A shows a change over time in the voltage waveform between the gate and the source of the first MOSFET 5a. A voltage waveform diagram schematically showing (b) is a voltage waveform diagram schematically showing a change with time of a gate-source voltage waveform of the second MOSFET 5b. (C) is a voltage waveform diagram schematically showing the change over time of the gate-source voltage waveform of the third MOSFET 11a, and (d) is the time-dependent change of the gate-source voltage waveform of the fourth MOSFET 11b. (E) is a voltage waveform diagram schematically showing changes with time of the gate-source voltage waveform of the fifth MOSFET 11c. Further, (f) is a current waveform diagram schematically showing a change with time of the current waveform after rectification by the third MOSFET 11a, the fourth MOSFET 11b, and the fifth MOSFET 11c, and (g) is a time chart of the input current waveform. Current waveform diagram schematically showing a typical change.

  As apparent from FIG. 4, the first MOSFET 5a and the fourth MOSFET 11b perform the on / off operation at the same timing, and the second MOSFET 5b and the third MOSFET 11a perform the on / off operation at the same timing. Further, when both the first MOSFET 5a and the second MOSFET 5b are off, the fifth MOSFET 11c is turned on.

  The switching power supply device 200 according to the second embodiment is configured as described above, and in this configuration as well as the switching power supply device 100 according to the first embodiment, an excessive surge voltage generated when the MOSFET is turned off is removed. The effect that it is possible can be obtained.

  Further, by configuring the rectifying element with a synchronous rectifier circuit using a MOSFET, the loss can be greatly reduced as compared with the switching power supply apparatus of the first embodiment configured with a rectifier diode, and a more efficient switching power supply apparatus. Can be provided.

  In the second embodiment, the MOSFET is used as the switching element and the rectifying element. However, the same applies even when a bipolar transistor, an insulated gate bipolar transistor (IGBT), a silicon carbide transistor, or a silicon carbide MOSFET is used. An effect is obtained.

Embodiment 3 FIG.
Next, a switching power supply device according to Embodiment 3 of the present invention will be described. The circuit configuration and circuit operation of the switching power supply according to Embodiment 3 are the same as those of Embodiment 1, and the description of the configuration and operation thereof is omitted. In the third embodiment, an inductance setting method in the choke coil 3 that is a magnetic component constituting the switching power supply device 100 shown in FIG. 1 will be described in detail below.

The voltage of the input DC power supply 1 is Vin, the voltage of the output smoothing capacitor 7 is Vo, the forward voltage drop of the first rectifier diode 6a, the second rectifier diode 6b, and the third rectifier diode 6c is V _F , The switching frequency of the MOSFET 5a and the second MOSFET 5b is Fsw. The current after the rectification of the first rectifier diode 6a, the second rectifier diode 6b, and the third rectifier diode 6c is a current waveform in which an alternating current component is superimposed on a direct current (load current). If the output current ripple which is the current amplitude value in the critical mode or the current amplitude value in the critical mode is ΔIo, and the inductance of the second winding 3b of the choke coil 3 is L2, the relationship shown in Expression (1) is derived.

When the output voltage Vo, the forward voltage drop V _{F of} the rectifier diode, the switching frequency Fsw, and the desired output current ripple ΔIo are fixed values, the equation (1) represents the inductance L2 of the second winding 3b in the choke coil 3 as the input voltage. It is a function of Vin and has a maximum value within the range of the input voltage Vin. The relationship between the input voltage Vin and the inductance L2 is schematically shown in FIG. Moreover, L2max which is the maximum value of the inductance L2 is shown in Formula (2).

  That is, the expression (3) may be satisfied to keep the output current ripple ΔIo within a predetermined value.

  Further, the relationship between the inductance L2 and the efficiency is schematically shown in FIG. Increasing the inductance L2 leads to an increase in the size of the choke coil 3 and a reduction in efficiency due to an increase in loss. Therefore, the inductance L2 is desirably up to twice the L2max derived from the equation (2).

Further, regarding the turns ratio of the first winding 3a and the second winding 3b of the choke coil 3, the number of turns of the first winding 3a of the choke coil 3 is N1 and the inductance is L1 due to the continuity of the output current ripple waveform. When the number of turns of the second winding 3b is N2 and the inductance is L2, it is necessary to satisfy the relationship of Expression (4) and Expression (5).
N1: N2 = 1: 2 (4)
L1: L2 = 1: 4 (5)
In the above description, the relations of the expressions (4) and (5) are given as representative values, but the turns ratio N1: N2 between the first winding 3a and the second winding 3b of the choke coil 3 is approximately 1. : 2 is sufficient. Further, the ratio L1: L2 between the inductance L1 and the inductance L2 may be approximately 1: 4.

  That is, L2 shown in Expression (3) is the inductance of the second winding 3b of the choke coil 3, and the inductance L1 of the first winding 3a of the choke coil 3 obtained from Expression (4) and Expression (5). When the constituted choke coil 3 is used, a desired output current ripple ΔIo can be realized within the range of the input voltage Vin, and the ripple resistance current required for the output smoothing capacitor 7 can be reduced. The effect that 7 can be reduced in size is acquired.

  Moreover, since the excessive surge voltage applied to the switching element can be removed as in the first embodiment, the switching loss can be reduced, and an effect of providing a highly efficient switching power supply device can be obtained.

  Furthermore, since an excessive surge voltage generated in the MOSFET can be removed, an element stress applied to the MOSFET is small, so that an effect of providing a low noise switching power supply device can be obtained.

In the third embodiment, the case where the rectifying element is configured by a diode has been described. However, the same effect can be obtained even when the rectifying element is configured by a synchronous rectifier circuit using MOSFET. The forward voltage drop _{V F} in this case is a voltage drop across the on-resistance of the MOSFET.

  In the third embodiment, the MOSFET is described as the switching element. However, the same effect can be obtained by using a bipolar transistor, an insulated gate bipolar transistor (IGBT), a silicon carbide transistor, or a silicon carbide MOSFET. It is done.

  In the third embodiment, the silicon diode is used as the rectifying element. However, the same effect can be obtained by using a silicon carbide diode.

  The switching power supply device according to the present invention is particularly applicable to power supplies for electronic devices that are required to be downsized, high performance, and energy saving.

1 is a circuit diagram of a switching power supply device according to Embodiment 1 of the present invention. FIG. It is a wave form diagram which shows typically change with time of a voltage and current waveform of each terminal in a switching power supply concerning Embodiment 1 of this invention. It is a circuit diagram of the switching power supply device concerning Embodiment 2 of this invention. It is a wave form diagram which shows typically change with time of a voltage and current waveform of each terminal in a switching power supply concerning a 2nd embodiment of this invention. It is a figure which shows typically the relationship between the input voltage in the switching power supply apparatus which concerns on Embodiment 3 of this invention, and the inductance of the 2nd coil | winding of a choke coil. It is a figure which shows typically the relationship between the inductance of the 2nd coil | winding of a choke coil, and efficiency in the switching power supply apparatus by Embodiment 3 of this invention.

Explanation of symbols

1 input DC power supply 2a, 2b input terminal 3 choke coil 3a first winding 3b second winding 3c choke coil core 4 transformer 4a first winding 4b second winding 4c transformer core 5a first MOSFET
5b Second MOSFET
6a First rectifier diode 6b Second rectifier diode 6c Third rectifier diode 7 Output smoothing capacitors 8a and 8b Output terminal 9 Load 10 Control circuit 11a Third MOSFET
11b Fourth MOSFET
11c fifth MOSFET
100, 200 switching power supply

Claims (3)

A choke coil having a first winding and a second winding;
A transformer connected in series to the first winding of the choke coil and having a first winding and a second winding;
A first switching means connected in series to the first winding of the transformer and a second switching means connected in series to the second winding of the transformer; A switching circuit for applying a voltage to the choke coil and the transformer;
A first rectifying means connected to a connection point between the transformer and the first switching means; a second rectifying means connected to a connection point between the transformer and the second switching means; A rectifier circuit for rectifying a voltage output via the choke coil and the transformer when one of the first switching means or the second switching means is in an on state and the other is in an off state;
A second circuit connected in series to the second winding of the choke coil and rectifies a voltage supplied to the output via the choke coil when both the first switching means and the second switching means are in an off state. 3 rectifying means;
Smoothing means for smoothing the voltage rectified by the first rectifying means, the second rectifying means, and the third rectifying means;
A control circuit for on / off controlling the first switching means and the second switching means so as to maintain the output voltage of the smoothing means at a predetermined value;
A switching power supply device comprising: The ratio of turns of the first winding and the second winding of the choke coil satisfies approximately 1: 2, and the inductance L2 of the second winding of the choke coil sets the output voltage of the smoothing means to Vo and the first winding. The forward voltage drop of the rectifying means, the second rectifying means, and the third rectifying means is V _F , the switching frequency of the first switching means and the second switching means is Fsw, and the first rectifying means is Fsw, When the AC component amplitude value of the current rectified by the rectifying means, the second rectifying means, and the third rectifying means or the current amplitude value in the critical mode is ΔIo, the following equation is satisfied: The switching power supply device according to claim 1.

  The first rectifying means, the second rectifying means, and the third rectifying means are each constituted by switching means, and are synchronized with on / off control of the first switching means and the second switching means. The switching power supply device according to claim 1, wherein the switching power supply device constitutes a synchronous rectifier circuit.

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