JP2010041912A - Switching power supply apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid a decline in the efficiency of power supply conversion and restrict common mode noise while an insulating state is maintained between the primary side and the secondary side. <P>SOLUTION: A switching power supply apparatus 1 includes: a transformer 2 having windings 11, 12, which constitute a primary winding 13, and to which an input DC voltage Vin is applied to its one end A, and a secondary winding 16; a first switching element 3 connected to the other end A1 of the winding 11; a second switching element 4 connected to the other end A2 of the winding 12; and a rectifier smoothing circuit 5 connected to the secondary winding 16 for rectifying an AC voltage generated from the secondary winding 16 and generating voltages +Vout and -Vouts, wherein two resistors 31, 32 are connected in series between the other end A1 of the winding 11 and a position predetermined by the primary-side reference potential G1 on the side of the primary winding 13, and a capacitor 7 has one end connected to a connection point C of resistors 31, 32 and the other end connected to a position predetermined by the secondary-side reference potential G2 on the side of the secondary winding. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a switching power supply device, and more particularly to a switching power supply device that can reduce common mode noise.

  As this type of switching power supply, a switching power supply (DC-DC converter, see FIG. 5 for the outline of the configuration) disclosed in Patent Document 1 below is known. In the switching power supply 51, as shown in FIG. 5, the stray capacitance Cs existing between the primary winding 52a and the secondary winding 52b of the insulating transformer 52 is converted into the primary winding 52a of the transformer 52. Is repeatedly charged and discharged by the switching action of a switching element (for example, a transistor) 53 for driving the. Thereby, a noise voltage having a switching frequency as a fundamental wave is generated between the primary winding 52a and the secondary winding 52b, and this noise voltage is generated on the primary winding side of the transformer 52 (primary side of the switching power supply device). And the secondary winding side (secondary side of the switching power supply device). This common mode noise has an adverse effect on an external circuit (not shown) that operates by receiving a DC voltage Vout generated through a rectifier circuit 54 and a smoothing circuit 55 connected to the secondary side of the transformer 52. give. Therefore, normally, as in the switching power supply device 51, between the primary side and the secondary side of the transformer 52 (in FIG. 5, one end of the primary winding 52a and the reference potential of the secondary side (secondary side ground) ) To a few tens of nF to several hundreds nF of capacitor 56 to suppress common mode noise. Although not shown, this Patent Document 1 also discloses a configuration in which a coil is connected in series to the capacitor 56 and this series circuit is connected between the primary side and the secondary side of the transformer 52. ing.

JP-A-8-266054 (page 2, FIG. 2)

  However, the above switching power supply device has the following problems to be solved. That is, in this switching power supply device, there is a case where it is necessary to increase the capacitance value of the capacitor 56 connected between the primary side and the secondary side in order to increase the amount of suppression of common mode noise. In this case, since the AC impedance between the primary side and the secondary side is lowered, there is a problem that the insulation state between the primary side and the secondary side is deteriorated. Even in the above-described configuration in which the coil is connected in series with the capacitor 56, when the series resonance is performed to reduce the common mode noise, the impedance between the primary side and the secondary side is theoretically zero, and the insulation is also performed. The condition will get worse. To solve this problem, two switching rectifier outputs between the secondary side rectified output of the transformer and the secondary side reference potential (secondary side ground) as in the switching power supply device disclosed in Japanese Patent No. 3294251. It is conceivable to use a configuration in which resistors are arranged in series and a capacitor is arranged between the connection point of each resistor and the primary reference potential (primary side ground) of the transformer. As a result of the consumption of the generated DC voltage by the two resistors arranged on the secondary side, the loss in the transformer and switching element increases, resulting in a new problem that the power conversion efficiency of the power supply device decreases. appear.

  The present invention has been made to solve such a problem, and is capable of suppressing common mode noise while maintaining an insulation state between the primary side and the secondary side and avoiding a decrease in power conversion efficiency. The main purpose is to provide a power supply.

  To achieve the above object, a switching power supply according to claim 1 is a transformer having a primary winding and a secondary winding to which an input DC voltage is applied at one end, and a switching connected to the other end of the primary winding. A switching power supply device including a device and a rectifying and smoothing circuit connected to both ends of the secondary winding and rectifying an AC voltage output from the secondary winding to generate a DC voltage, the primary winding A plurality of resistors connected in series between the other end of the first coil and a portion defined by the primary reference potential on the primary winding side, and one end at a connection point between two of the plurality of resistors. And a capacitor having the other end connected to a portion defined by the secondary side reference potential on the secondary winding side.

  According to a second aspect of the present invention, there is provided the switching power supply device according to the first aspect, further comprising a surge absorbing element connected between the connection point and the primary side reference potential.

  In the switching power supply device according to claim 1, a resistance group including a plurality of resistors connected in series is connected between the other end of the primary winding of the transformer and a portion defined by the primary side reference potential, In addition, by connecting a capacitor between the connection point between two of the plurality of resistors (two resistors) and the portion defined by the secondary side reference potential, the primary side and the secondary side of the transformer The AC voltage component divided by the plurality of resistors is supplied to the secondary side reference potential via the capacitor while maintaining the insulation state between the two resistors at a predetermined resistance value or more. It is possible to reduce the voltage level of common mode noise generated on the secondary winding side. Also, by adjusting the resistance value of each resistor in the resistor group, the voltage level of the AC voltage component supplied to the secondary side reference potential via the capacitor can be finely adjusted, so the voltage level (amplitude) of the common mode noise is extremely low. It can be suppressed to a low level. Further, since the resistor group for reducing the voltage level of the common mode noise is connected to the primary winding of the transformer, the generated DC voltage is not consumed by the resistor group unlike the conventional example. Therefore, as a result of avoiding the loss in the transformer and the switching element, it is possible to avoid the decrease in power conversion efficiency in the switching power supply device due to the connection of the resistor group.

  In the switching power supply device according to claim 2, since the surge absorbing element is connected between the connection point and the primary side reference potential, a transient large common is provided between the primary side and the secondary side of the transformer. Even when mode noise occurs, the common mode noise is absorbed by the surge absorbing element. For this reason, according to this switching power supply device, the electrical resistance applied to the resistance connected between the connection point of the plurality of resistances and the primary side reference potential, that is, the resistance connected in parallel with the surge absorbing element. Therefore, it is possible to reliably prevent deterioration of resistance due to the stress.

1 is a configuration diagram of a switching power supply device 1. FIG. It is a block diagram of switching power supply device 1A. FIG. 5 is a voltage level diagram of common mode noise generated in a switching power supply device adopting a configuration in which a primary side reference potential G1 and a secondary side reference potential G2 are connected only by a capacitor 7; 3 is a voltage level diagram of common mode noise generated in the switching power supply device 1. FIG. It is a block diagram of the conventional switching power supply device 51.

  Hereinafter, an embodiment of a switching power supply device will be described with reference to the accompanying drawings.

  First, the configuration of the switching power supply device 1 will be described with reference to the drawings.

  For example, as shown in FIG. 1, the switching power supply device 1 includes a transformer 2, a first switching element 3, a second switching element 4, a rectifying / smoothing circuit 5, and a resistor composed of a plurality of resistors connected in series with each other. A positive voltage + Vout and a negative voltage − that are electrically insulated from the input DC voltage Vin based on the input DC voltage Vin. Vout (each DC voltage) is generated.

  As shown in FIG. 1, the transformer 2 includes a primary winding 13 in which one ends of a winding 11 and a winding 12 are connected to each other, and each end is configured as a center tap (middle point) A; 14 and each end of the winding 15 are connected to each other, and each end includes a secondary winding 16 configured as a center tap (middle point) B. In the transformer 2, the windings 11, 12, 14, and 15 are wound around the core with the polarity indicated by black circles in FIG. 1. In addition, the primary winding 13 and the secondary winding 16 are electrically insulated from each other, but a stray capacitance Cs (for example, several tens of pF to several hundreds of pF) exists between them. A predetermined input DC voltage Vin is applied to the center tap A of the primary winding 13 (one end of each of the windings 11 and 12) between the primary side reference potential G1 (primary side ground).

  The first switching element 3 and the second switching element 4 are constituted by transistors (bipolar transistors or field effect transistors) as an example. In this case, as shown in FIG. 1, the first switching element 3 is connected between the other end A1 of the winding 11 constituting the primary winding 13 and the primary side reference potential G1. The second switching element 4 is connected between the other end A2 of the winding 12 constituting the primary winding 13 and the primary side reference potential G1. The switching elements 3 and 4 are respectively driven by drive signals S1 and S2 (pulse signals having a duty ratio of about 0.5) that are 180 degrees out of phase with each other. A switching operation that turns off (a switching operation that turns on for the same time alternately) is repeatedly executed.

  As an example, the rectifying / smoothing circuit 5 includes rectifying elements (diodes in this example) 21 and 22 and capacitors 23 and 24 as shown in FIG. In this case, the diode 21 has an anode terminal connected to the other end B1 of the winding 14 constituting the secondary winding 16, and the diode 22 has a cathode terminal connected to the winding 15 constituting the secondary winding 16. It is connected to the other end B2. The capacitor 23 has one end connected to the cathode terminal of the diode 21 and the other end connected to the secondary side reference potential G2 (secondary side ground). The capacitor 24 has one end connected to the anode terminal of the diode 22 and the other end connected to the secondary reference potential G2.

  As shown in FIG. 1, the resistor group 6 includes a plurality of resistors connected in series (in this example, two resistors 31 and 32 connected in series as an example), and constitutes a primary winding 13. 11 is connected between the other end A1 and the primary reference potential G1. Although the resistance values of the resistors 31 and 32 need to be changed in accordance with the capacitance of the capacitor 7, the resistance value of the transformer 2 is usually applied to the AC voltage component generated at the other end A 1 of the winding 11. The level of common mode noise generated on the secondary side is small. For this reason, for example, the resistance value of the resistor 32 is set to a high value of about several hundred ohms to several kiloohms, and the resistance value of the resistor 31 is several tens to several hundred times as large as the resistance value of the resistor 32 (this example) Is 100 times). One end of the capacitor 7 is connected to a connection point C (a connection point between two of the plurality of resistors) of the resistors 31 and 32, and the other end is connected to the secondary side reference potential G2. Further, the total resistance value of the resistor group 6 and the capacitance value of the capacitor 7 suppress the fluctuation of the voltage level of the secondary side reference potential G2 with respect to the primary side reference potential G1, and the primary side of the transformer 2 It is appropriately set so that the insulation state (insulation resistance value) between the secondary side can be maintained at a predetermined resistance value or more. In this example, as an example, the capacitance value of the capacitor 7 is defined within a range of several tens of pF to several hundreds of pF in correspondence with the capacitance of the stray capacitance Cs described above. Correspondingly, the total resistance value of the resistance group 6 is defined.

  Next, the operation of the switching power supply device 1 will be described.

  In the state where the input DC voltage Vin is applied to the transformer 2, when the drive signals S1 and S2 are supplied to the switching elements 3 and 4, the switching elements 3 and 4 are alternately turned on. repeat. As a result, a voltage is induced in the secondary winding 16 of the transformer 2, and the induced voltage is rectified and smoothed by the rectifying and smoothing circuit 5, so that the voltage becomes a positive voltage with reference to the secondary side reference potential G2. A positive voltage + Vout and a negative voltage −Vout that is a negative voltage based on the secondary side reference potential G2 are generated.

  In this case, the switching elements 3 and 4 repeat the switching operation at a predetermined switching frequency, so that the stray capacitance Cs existing between the primary winding 13 and the secondary winding 16 of the transformer 2 performs the switching operation. It is repeatedly charged and discharged with a period. For this reason, a noise voltage having the above switching frequency as a fundamental wave is generated between the primary winding 13 and the secondary winding 16 of the transformer 2. On the other hand, due to the switching operation of each switching element 3, 4, the AC voltage component having the above switching frequency as a fundamental wave is also transmitted to each end A 1, A 2 of the primary winding 13 in the same manner as the above noise voltage. It is generated based on the side reference potential G1. The resistors 31 and 32 constituting the resistor group 6 divide the AC voltage component and supply it to the secondary side reference potential G <b> 2 via the capacitor 7. The AC voltage component generated at each end A1, A2 of the primary winding 13 is composed of a fundamental wave having the same frequency as that of the noise voltage, and the phase is substantially the same, so this AC voltage component is divided. By supplying the secondary side reference potential G2 from the capacitor 7, fluctuations in the voltage level of the secondary side reference potential G2 with respect to the primary side reference potential G1 are suppressed. Unlike the conventional configuration in which the primary side and the secondary side of the transformer 2 are directly connected by a capacitor 7 or a series resonance circuit including a capacitor and an inductor, the resistors 31 and 32 constituting the resistor group 6 are used. Therefore, the insulation state between the primary side and the secondary side of the transformer 2 is reliably maintained at a predetermined resistance value or more by the resistors 31 and 32.

Furthermore, by adjusting the resistance values of the resistors 31 and 32, the voltage level of the AC voltage component supplied to the secondary side reference potential G2 via the capacitor 7 can be finely adjusted. For this reason, the voltage level (amplitude) of the common mode noise can be suppressed to an extremely low level. Specifically, in the configuration in which the primary side and the secondary side of the transformer 2 are connected by the capacitor 7 alone, common mode noise generated on the secondary winding 16 side of the transformer 2 (based on the primary side reference potential G1). The voltage level of the secondary side reference potential G2) is high (about 50 mVp-p) as shown in FIG. 3, but in the switching power supply 1 using the resistor group 6 and the capacitor 7, By adjusting the resistance values of the resistors 31 and 32, the voltage level of the common mode noise can be reduced to almost zero as shown in FIG. The specifications of each component of the test circuit that acquired the data of FIGS. 3 and 4 are as follows.
Winding of transformer 2: 10 turns for each primary side, 5 turns for each secondary side Input DC voltage Vin: 12V
Positive voltage + Vout: 6V
Negative voltage -Vout: -6V
Switching frequency: 120 kHz
Capacitor 7 capacitance: 100 pF
Measuring instrument: Waveform recorder (manufactured by 8870 Memory HiCorder Hioki Electric Co., Ltd.)
Measurement location: potential of secondary side reference potential G2 with reference to primary side reference potential G1

  As described above, according to the switching power supply device 1, a series connection is established between one end of the primary winding 13 (the other end A1 of the winding 11) and the portion defined by the primary reference potential G1 in the transformer 2. The resistor group 6 composed of the resistors 31 and 32 connected to each other is connected, and the capacitor 7 is connected between the connection point of each resistor 31 and 32 and the portion defined by the secondary side reference potential G2. Thus, the AC voltage component divided by the resistors 31 and 32 is passed through the capacitor 7 while maintaining the insulation state between the primary side and the secondary side of the transformer 2 at a predetermined resistance value or more by the resistors 31 and 32. Thus, the voltage level of the common mode noise generated on the secondary winding 16 side of the transformer 2 can be reduced by supplying the secondary side reference potential G2. Further, by adjusting the resistance values of the resistors 31 and 32, the voltage level of the AC voltage component supplied to the secondary side reference potential G2 via the capacitor 7 can be finely adjusted, so that the voltage level (amplitude) of the common mode noise. Can be suppressed to an extremely low level. Further, since the resistor group 6 for reducing the voltage level of the common mode noise is connected to the primary winding 13 of the transformer 2, the generated positive voltage + Vout and negative voltage −Vout are not consumed by the resistor group 6. Therefore, the loss in the transformer 2 and the switching elements 3 and 4 can be avoided, and as a result, a decrease in power conversion efficiency in the switching power supply device 1 due to the connection of the resistor group 6 can be avoided.

  In the switching power supply device 1 described above, a configuration in which the resistor group 6 is connected between the other end A1 of the winding 11 constituting the primary winding 13 and the primary side reference potential G1 is adopted. A configuration in which the resistor group 6 is connected between the other end A2 of the winding 12 constituting the line 13 and the primary side reference potential G1 can also be adopted. Moreover, although the resistance group 6 is configured by the two resistors 31 and 32, it may be configured by a series circuit of three or more resistors. Further, a variable resistor can be provided in the resistor group 6 to adopt a configuration that can be finely adjusted.

  Moreover, although the example applied to the push-pull type switching power supply device 1 has been described above, as shown in FIG. 2, it can also be applied to a single-end type switching power supply device 1A. Hereinafter, the switching power supply device 1A will be described. In addition, about the structure same as the switching power supply device 1, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.

  As shown in FIG. 2, the switching power supply device 1A includes, as an example, a transformer 2A, one switching element (second switching element 4 in this example), a rectifying / smoothing circuit 5A, a resistor group 6, and a capacitor 7, and an input DC Based on the voltage Vin, one of a positive voltage and a negative voltage electrically insulated from the input DC voltage Vin (positive voltage + Vout as an example in this example) is generated.

  Specifically, as shown in FIG. 2, the transformer 2 </ b> A includes a primary winding 13 </ b> A composed of one winding 12 and a secondary winding 16 </ b> A composed of one winding 14. . In the transformer 2, the windings 12 and 14 are wound around the core with the polarity indicated by the black circles. Further, the primary winding 13A and the secondary winding 16A are electrically insulated from each other, but a stray capacitance Cs (for example, several tens of pF to several hundreds of pF) exists between them. Further, an input DC voltage Vin of a predetermined voltage is applied to one end A of the winding 12 with respect to the primary side reference potential G1 (primary side ground).

  The second switching element 4 is connected between the other end A2 of the winding 12 constituting the primary winding 13 and the primary side reference potential G1. The switching element 4 is driven by the drive signal S2 (pulse signal having a duty ratio of about 0.5), and repeatedly executes the switching operation. As an example, the rectifying / smoothing circuit 5A includes a rectifying element (in this example, a diode) 21 and a capacitor 23. In this case, the anode terminal of the diode 21 is connected to the other end B <b> 1 of the winding 14. The capacitor 23 has one end connected to the cathode terminal of the diode 21 and the other end connected to the secondary side reference potential G2. The resistor group 6 is connected between the other end A2 of the winding 12 and the primary side reference potential G1.

  In this switching power supply device 1A, similarly to the switching power supply device 1, the switching element 4 repeats the switching operation at a predetermined switching frequency, so that floating between the primary winding 13A and the secondary winding 16A of the transformer 2 occurs. Since the capacitor Cs is repeatedly charged and discharged at the cycle of the switching operation, a noise voltage having a switching frequency as a fundamental wave is generated between the primary winding 13A and the secondary winding 16A.

  In this case, also in this switching power supply device 1A, the resistors 31 and 32 that constitute the resistor group 6 are generated based on the above switching frequency in the same manner as the noise voltage generated at the end A2 of the primary winding 13. The voltage level of the secondary-side reference potential G2 when the primary-side reference potential G1 is used as a reference is suppressed by dividing the AC voltage component) and supplying it to the secondary-side reference potential G2 via the capacitor 7. can do. Further, since the resistor group 6 is used, the insulation state between the primary side and the secondary side of the transformer 2 can be reliably maintained at a predetermined resistance value or more by the resistors 31 and 32. Furthermore, since the voltage level of the AC voltage component supplied to the secondary side reference potential G2 via the capacitor 7 can be finely adjusted by adjusting the resistance values of the resistors 31 and 32, the voltage level (amplitude) of the common mode noise can be adjusted. ) Can be suppressed to an extremely low level. Further, the generated positive voltage + Vout is not consumed by the resistor group 6. Therefore, the loss in the transformer 2 and the switching element 4 can be avoided, and as a result, a decrease in power conversion efficiency in the switching power supply device 1A due to the connection of the resistor group 6 can be avoided.

  Further, as a result of further examination of the switching power supply devices 1 and 1A by the inventor of the present application, a transient high voltage is applied to the common mode (that is, the primary-side reference potential G1 and In this case, a large current flows through the resistor 32, so that an electrical stress is applied to the resistor 32. We found that the phenomenon occurred. Since it is not preferable that such electrical stress is applied to the resistor 32, the inventor of the present application reduces the stress as shown by broken lines in FIGS. A configuration in which the surge absorbing element 8 is connected in parallel to each resistor 32 is adopted. That is, a configuration in which the surge absorbing element 8 is connected between the connection point C of the resistors 31 and 32 (a connection point between two of the plurality of resistors) and the primary side reference potential G1 is adopted. As the surge absorbing element 8, a surge absorbing Zener diode, a varistor element, a glass tube arrester, a micro-type gap absorbing element, a surge absorbing capacitor (capacitance of about several tens of pF), or the like can be used. Even when a surge absorbing capacitor is used as the surge absorbing element 8, the capacitance thereof is about several tens of pF as described above, so that a reduction in common-mode signal rejection ratio (CMRR) is avoided. ing.

  By adopting this configuration, with respect to the non-transient common mode noise generated on the secondary windings 16 and 16A side of the transformer 2, the resistor 32 and the resistor 32 of the surge absorbing element 8 connected in parallel are mainly used. The common mode generated on the secondary winding 16 side of the transformer 2 when the AC voltage component divided by the resistors 31 and 32 is supplied to the secondary side reference potential G2 via the capacitor 7 by functioning. Reduce the voltage level of noise. Further, with respect to the transient high voltage common mode noise generated on the secondary windings 16 and 16A side of the transformer 2, the surge absorbing element 8 of the resistor 32 and the surge absorbing element 8 connected in parallel mainly functions. Thus, by reducing the inflow of the transient common mode noise into the resistor 32, it is possible to reduce the electrical stress applied to the resistor 32, thereby reducing the deterioration of the resistor 32 due to the stress. It can be surely prevented.

1,1A switching power supply
2 transformer
3 First switching element
4 Second switching element
5,5A rectification smoothing circuit
6 resistance groups
7 capacitors
8 Surge absorbing element 13, 13A Primary winding 16, 16A Secondary winding 31, 32 Resistance
C Connection point G1 Primary side reference potential G2 Secondary side reference potential Vin Input DC voltage + Vout Positive voltage -Vout Negative voltage

Claims (2)

A transformer having a primary winding and a secondary winding to which an input DC voltage is applied to one end, a switching element connected to the other end of the primary winding, and the second connected to both ends of the secondary winding A switching power supply device having a rectifying and smoothing circuit for generating a DC voltage by rectifying an AC voltage output from a next winding,
A plurality of resistors connected in series between the other end of the primary winding and a portion defined by a primary reference potential on the primary winding side;
A switching device comprising: a capacitor having one end connected to a connection point between two of the plurality of resistors and having the other end connected to a portion defined by the secondary side reference potential on the secondary winding side Power supply.   The switching power supply device according to claim 1, further comprising a surge absorbing element connected between the connection point and the primary reference potential.

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