JP3604505B2 - Multi-output switching power supply - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multi-output switching power supply.AboutMore particularly, the present invention relates to a multi-output switching power supply device using a choke coil having a current-dependent magnetic characteristic that shares a magnetic core with each other and reduces the inductance when the load current increases.
[0002]
[Prior art]
As a power supply device for various electronic devices, it is inexpensive, compact and lightweight compared to the power capacity, and has high power conversion efficiency, so there is little power loss and accompanying heat generation, and multiple independent DC power can be obtained and constant voltage control A multi-output switching power supply device having a function is widely used.
[0003]
As shown in FIG. 23, for example, the most common conventional multi-output switching power supply device is a primary rectifying / smoothing circuit 2 comprising a diode bridge 4 and a large-capacity capacitor C1 for converting primary AC power input from an AC power supply 1. To convert it into primary DC power. A DC-DC converter 3a, which is a multi-output switching power supply including a transformer 6, a transistor Q, a switching control circuit 5, and three secondary rectifying / smoothing circuits 20a to 20c, receives primary DC power and is independent of each other. Three secondary DC powers are output from a pair of output terminals 8p and 8n, respectively.
[0004]
The choke coil CHc of the secondary rectification / smoothing circuit having the same configuration, for example, of the secondary rectification / smoothing circuit 20c is connected to the rectification diode Ds3 of the secondary AC power induced in the secondary winding N23 when the transistor Q is turned on. It is excited by the charging current of the capacitor C23 flowing through it, and converts the magnetic energy accumulated by the excitation when the transistor Q is off to current again, and further charges the capacitor C23 via the commutation diode Dt3.
[0005]
In this case, if a small amount of current always flows through the choke coil CHc, the output voltage of the secondary rectifying / smoothing circuit 20c is equal to the input voltage when the transistor Q is on (the voltage between the terminals of the secondary winding N23) and the output voltage of the transistor Q. Since the relationship of the product with the on-duty ratio is established (the same applies to the secondary rectifying and smoothing circuits 20a and 20b), the output voltage is fed back to the switching control circuit 5 so that the output voltage becomes a preset voltage. Can be controlled.
[0006]
However, when a discontinuous state in which no current flows through the choke coil CHc, that is, when a current cutoff occurs, the output voltage rises, so that the on-duty ratio of the transistor Q instantaneously becomes zero and switching stops. Intermittent oscillation occurs when switching is started again. When the intermittent oscillation starts, the frequency often falls within the audible frequency range, causing an unpleasant noise sound, and the output voltages of all the secondary rectifying / smoothing circuits 20a to 20c fluctuate at the intermittent oscillation frequency. And become unstable.
[0007]
In the secondary rectifying / smoothing circuit 20a or 20b that is not a feedback system, if a current cutoff occurs in the choke coil CHa or CHb, intermittent oscillation does not occur, but the output voltage of the secondary rectifying / smoothing circuit increases. Occurs. Therefore, the dummy resistors Rd1 to Rd3 are connected in parallel to the capacitors C21 to C23 of all the secondary rectifying / smoothing circuits 20a to 20c, respectively. It was necessary to always supply a dummy current that did not cut off the coil current.
[0008]
However, in general, the product of the inductance of the choke coil and the ripple of the current flowing therethrough has a constant, that is, an inversely proportional relationship. Further, the critical value at which the current flowing through the choke coil does not cut off even when there is no load is approximately の of the pp value of the current ripple, and the dummy current must be set to be larger than the critical value. Therefore, if the inductance of the choke coil is large, the dummy current is small, but if the inductance is small, the dummy current is large, so that the power loss and the heat generation due to it are not negligible.
[0009]
On the other hand, when the inductance of the choke coil is set to be large, the size and weight of the choke coil become large with respect to the output current of the secondary rectifying and smoothing circuit. This tendency is the same for all of the secondary rectifying and smoothing circuits 20a to 20c. Therefore, if the switching power supply has a large maximum output current and a large number of outputs (the number of secondary rectifying and smoothing circuits), the size and weight increase. And the cost increase was a big problem.
[0010]
Therefore, in the choke coils CHa to CHc independent from each other as shown in FIG. 23, the I-shaped core 16 shown in FIG. 20 and the winding frame around which the winding is wound (as will be described in detail later) are mounted. A normal magnetic circuit is constituted by the E-shaped core 17 having the central leg 17a. A step is provided on the upper surface of the central leg 17a which is a part of the magnetic circuit, and the inductance is large while the current is small, and the current is small. In some cases, a magnetic characteristic in which the inductance becomes smaller as the size becomes larger, the dummy current is reduced, and the core is made smaller and lighter.
[0011]
Further, as shown in FIG. 3 of Japanese Patent Publication No. 7-50990 as a conventional example, two choke coils n1 and n2 of two secondary rectifying / smoothing circuits having capacitors 21 and 22, respectively, are connected to each other. There was an example in which a cooperative choke coil 19 sharing a magnetic core was used.
[0012]
Alternatively, as in the proposal shown in FIG. 1 of the publication, each of the choke coils of the three secondary rectifying / smoothing circuits including the capacitors 10 to 12 is constituted by the cooperative choke coil 9 and other than the feedback system. In the case where the inductors 7 and 8 are provided in series with the respective choke coils of the secondary rectifying / smoothing circuit, and the number of turns of each of the choke coils constituting the cooperative choke coil 9 cannot satisfy the special turns ratio determined by the circuit constant, There were also proposals to prevent troubles caused by such problems.
[0013]
When such a cooperative choke coil is used, if the winding ratio of the winding is set to the above-described special winding ratio, if the output voltage of any of the secondary rectifying / smoothing circuits is controlled to be a constant voltage, The output voltage of another secondary rectifying / smoothing circuit is also kept substantially constant by the cross regulation of the transformer.
In addition, if a current equal to or greater than the critical value flows through any one of the windings of the cooperative choke coil, current cutoff does not occur, so that an abnormal increase in the output voltage at light load can be prevented. Compared to the case where a coil is used, the whole core is smaller and lighter, and power loss due to a dummy current can be reduced.
[0014]
[Problems to be solved by the invention]
However, the switching frequency of the transistor Q is in a high frequency range of 100 kHz or more in order to reduce the size of the transformer and the choke coil. Since the frequency tends to be higher in recent years, the number of turns of the choke coil is reduced to about several turns. ing. Basically, the number of turns is an integral multiple of 1/2 turn, and cannot be set to a fraction less than 1/2 turn. Therefore, in actual design, it is difficult to obtain a required number of turns with a required inductance and a special turns ratio.
[0015]
If the special turns ratio is not satisfied, energy may be transferred between the windings of the cooperative choke coil, the desired output voltage may not be obtained, the output voltage may increase at light load, and unnecessary oscillation may occur. Trouble arises. To solve this problem, the proposal disclosed in Japanese Patent Publication No. 7-50990 is an extremely effective solution. However, by adding an inductor one less than the number of outputs, it is possible to increase the size of the multi-output switching power supply. There has been a problem that the cost and cost increase.
[0016]
Although the use of a cooperative choke coil certainly reduces the size and weight of the core as compared to a plurality of choke coils independent of each other, it can be said that the core is a cooperative choke coil in a high-power multi-output switching power supply device. Since a large core is required, and the winding wound accordingly becomes thick and long, power loss and heat generation due to copper loss and iron loss become a serious problem along with the weight.
[0017]
The present invention has been made in view of the above points, and further reduces the size and weight of a cooperative choke coil used in a multi-output switching power supply device, reduces power loss, suppresses heat generation, and improves power efficiency. The purpose is to:
[0018]
[Means for Solving the Problems]
According to the present invention, in order to achieve the above object, primary DC power is input to a series circuit of a primary winding of a transformer and a switching element, and the switching element is switched to induce a plurality of secondary windings of the transformer. The secondary AC power is supplied by a plurality of secondary rectifying and smoothing circuits each having a choke coil.Different output voltage from each otherFor secondary DC powerconversionMulti-output switching power supply device
Each of the choke coils of the plurality of secondary rectifying / smoothing circuits shares a magnetic core with each other, and when the load current is small, the inductance is large, and when the load current is large, the inductance is small.AndUpThe total value of the dummy currents flowing through the respective dummy resistors of the plurality of secondary rectifying / smoothing circuits is fixed, the dummy current of the secondary rectifying / smoothing circuit having a low output voltage is set large, and the secondary rectifying / smoothing circuit having a high output voltage is set. Reduced the dummy current ofThings.
[0019]
Also, the above-mentioned multi-output switching power supply deviceAnd each of the aboveA gap is formed in a part of the magnetic circuit formed by the magnetic core shared by the choke coil.Good to have.
[0020]
Alternatively, the magnetic core shared by the choke coils is formed by stacking a plurality of magnetic cores of different materials in the thickness direction.
Further, it is more preferable to provide a gap in a part of a magnetic circuit formed by a magnetic core formed by stacking choke coils.
[0021]
The gap between these choke coils may be formed by providing a step in a part of the cross section of the magnetic circuit.
Further, the gap may be formed by forming the whole or a part of the cross section of the magnetic circuit on a slope.
Alternatively, the gap may be formed by forming the whole or a part of the cross section of the magnetic circuit with a slope and a step.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.
FIG. 1 is a circuit diagram showing an example of a configuration of a multi-output switching power supply according to an embodiment of the present invention. In a DC-DC converter 3 which is a multi-output switching power supply device shown in FIG. 1, a primary rectifying / smoothing circuit 2 including a diode bridge 4 and a large-capacity capacitor C1 converts AC power input from an AC power supply 1. The secondary DC power is input, and three mutually independent (secondary) DC powers are output from respective positive and negative output terminals 8p and 8n.
[0023]
The DC-DC converter 3 is a high-frequency forward-type transformer 6 having three secondary windings N21, N22, and N23, and a transistor that is a switching element connected in series with the primary winding N1 of the transformer 6. (Or FETs) Q and secondary rectifying / smoothing circuits 21, 22 and 23 having a pair of output terminals 8 p and 8 n connected to the secondary windings N 21 to N 23, respectively, and outputs of the secondary rectifying / smoothing circuit 23. A switching control circuit (SWC) 5 for detecting a voltage and outputting a switching pulse having a pulse width corresponding to the detected voltage to the base of the transistor Q.
[0024]
The primary DC power converted by the primary rectifying / smoothing circuit 2 is input to both ends of a series circuit of the primary winding N1 of the transformer 6 and the transistor Q, and the switching pulse is input from the switching control circuit 5 to the transistor Q. , The current flowing through the primary winding N1 is turned on / off, and secondary AC power is induced in the secondary windings N21 to N23 by the on / off.
[0025]
Since the secondary rectifying / smoothing circuits 21 to 23 have the same configuration and operation, a description will be given of, for example, the secondary rectifying / smoothing circuit 23 which is a feedback system. When the transistor Q is on, an electromotive force is induced in the secondary winding N23. Then, the current flows through the rectifier diode Ds3 to charge the smoothing large-capacity capacitor C23 and to excite the choke coil CH3 to store magnetic energy.
[0026]
When the transistor Q is turned off, the polarity of the electromotive force of the secondary winding N23 is inverted, so that no current flows through the rectifier diode Ds3. On the other hand, the polarity of the choke coil CH3 is also inverted, and the stored magnetic energy is reconverted into a current, flows through the commutation diode Dt3, and similarly charges the capacitor C23. A dummy current according to the resistance value and the voltage between the terminals of the capacitor C23 flows through the dummy resistor Rd3 connected in parallel with the capacitor C23.
[0027]
The switching control circuit 5 detects the voltage between the terminals of the capacitor C23, that is, the output voltage of the secondary rectifying / smoothing circuit 23, and if the detected voltage is lower than a preset voltage, expands the ON width of the switching pulse. Raise the on-duty ratio to increase the output voltage. If the detection voltage is higher than the set voltage, the width of the pulse-on is narrowed, that is, the on-duty ratio is lowered to lower the output voltage. In this way, the output voltage of the secondary rectifying / smoothing circuit 23 is feedback-controlled so as to maintain the set voltage.
[0028]
Although the description of the configuration and operation of the DC-DC converter 3 is the same as that of the DC-DC converter 3a (FIG. 23), the choke coils CHa to CHc of the DC-DC converter 3a are independent of each other. On the other hand, since the choke coils CH1 to CH3 of the DC-DC converter 3 are cooperative choke coils 7 sharing a core (magnetic core) with each other, the operation and the effect are different.
[0029]
That is, as described above, by using the cooperative choke coil, the cross-regulation of the transformer 6 causes the output voltages of the secondary rectification / smoothing circuits 21 and 22 that are not feedback systems to be output from the secondary rectification / smoothing circuits 20a and 20b. Compared with the output voltage, the voltage fluctuation is reduced and stabilized, and the entire core is reduced in size and weight, and the cost is reduced. In this regard, a similar effect is obtained by the conventional multi-output switching power supply device using a cooperative choke coil and the proposal disclosed in Japanese Patent Publication No. 7-50990.
[0030]
However, the feature that the cooperative choke coil 7 used in the multi-output switching power supply according to the present invention is greatly different from the conventional cooperative choke coil is that it is performed in the conventional independent choke coil, but there is no example in the cooperative choke coil. In addition, it has "magnetic characteristics in which the inductance is large when the load current is small and the inductance is small when the load current is large".
[0031]
By providing the above-mentioned magnetic characteristics to the cooperative choke coil 7, the core can be reduced in size and weight to reduce the cost as well as the independent choke coil, and the dummy current can be reduced to reduce the power loss and improve the power efficiency. However, the cooperative choke coil 7 has an effect that the dummy current can be further reduced as compared with the independent choke coil.
Hereinafter, the reason will be described together with each embodiment.
[0032]
FIG. 20 is a perspective view showing an example of the configuration of a core used in a conventional choke coil having a constant inductance regardless of the magnitude of a current. In addition, in a choke coil using the core shown in FIG. 20, a current obtained by combining a dummy current Id flowing through the choke coil and a load current If is used as a choke current Ich. FIG. 21 shows a characteristic of an inductance L with respect to the choke current Ich (hereinafter referred to as “ch”). FIG. 22 is a waveform diagram showing an example of the choke current Ich at the time of no load and at the time of load, respectively.
[0033]
The core shown in FIG. 20 is constituted by a combination of an I-type core 16 shown by a two-dot chain line and an E-type core 17 shown by a solid line, and a winding (not shown) is mounted on a central leg 17 a of the E-type core 17. After the winding frame around which is wound is inserted, it is integrally formed with the I-shaped core 16. Since the center leg 17a of the E-shaped core 17 and the two side legs 17b and 17c are at the same height and their upper end surfaces are on the same plane, there is no gap between the center leg 17a and the I-shaped core 16.
[0034]
As shown in FIG. 21, the IL characteristic of a choke coil using a core having no gap has a constant value regardless of the current, and the choke current Ich exceeds a certain value, as shown in FIG. When the core becomes magnetically saturated (hereinafter simply referred to as "saturated"), the inductance L sharply decreases.
As shown in FIG. 22, the choke current waveform in this case is such that when there is no load, only the dummy current Id corresponding to the critical value corresponding to the inductance L flows, and when the load is applied, the current is the sum of the load current If and the dummy current Id. Flows, but the ripple (pp value) does not change because the inductance L is constant.
[0035]
There is also a core in which the upper end surface of the center leg 17a of the E-shaped core 17 is slightly lower than the upper side surfaces of the both side legs 17b and 17c to provide a parallel gap over the entire surface. A choke coil using a core having a parallel gap over its entire surface has a constant inductance L, but its IL characteristic is lower than that of the IL characteristic shown in FIG. Since the choke current Ich increases, it is often used for the purpose of reducing the size of a core in a circuit with a large current or for suppressing the occurrence of distortion due to saturation of the core in an audio circuit.
[0036]
The gap to which the present invention is directed is intended to reduce the inductance L of the choke coil when the load current If is small and the inductance L is small when the load current If is large. Therefore, as described above, the entire parallel gap for the purpose of increasing the choke current Ich with the constant inductance L is not included.
[0037]
FIG. 2 shows a gap provided for a cooperative choke coil 7 composed of choke coils CH1, CH2, and CH3 of each of the secondary rectifying and smoothing circuits 21 to 23 of the DC-DC converter 3 shown in FIG. It is a perspective view showing an example of composition of E type core which is a 1st embodiment of common core (illustrating a core omitted).
FIG. 3 is a diagram showing an example of the IL characteristic of the choke coil using the E-type core 10 shown in FIG. 2, and FIG. 4 is a waveform diagram showing an example of the choke current Ich of the choke coil. .
[0038]
The E-shaped core 10 shown in FIG. 2 has a step 10b provided in a part of a cross section (the upper end surface of the center leg 10a) which is a part of a magnetic circuit formed together with an I-shaped core (not shown). By providing such a step 10b, the IL characteristic of the choke coil using this core is such that, as shown in FIG. 3, the portion where the inductance L is constant becomes two steps, and the choke current Ich is small. In some cases, a characteristic is obtained in which the inductance L is large and the inductance L is small when the choke current Ich is large.
[0039]
That is, as shown in FIG. 3, while the choke current Ich is small, the lines of magnetic force flowing through the magnetic circuit are concentrated on the remaining portion 10c of the upper end surface of the central leg 10a having a smaller magnetic resistance than the step 10b, and the larger. The inductance L is obtained. As the choke current Ich increases and the remaining portion 10c of the upper end face approaches saturation, the magnetic flux lines also flow through the step 10b where the magnetic resistance is large, the inductance L starts to decrease, and the remaining portion 10c is completely removed. When saturated, all of the increase in the magnetic field lines flow through the step 10b, and the inductance value becomes low until the step 10b is saturated.
[0040]
As a result, as shown in FIG. 4, the choke current waveform has a large inductance L when no load is applied, so that the ripple component is small and the dummy current Id can be set small. On the other hand, when the load is loaded, the inductance L is small, so that the ripple is large. At this time, since the load current If is large,Dummy currentEven if Id remains small, no current cutoff occurs as shown. In addition, the provision of the gap increases the maximum choke current at which the core is saturated.
[0041]
Therefore, if the core size is the same, the maximum value of the choke current Ich increases, and the dummy current Id remains small, so that the maximum value of the load current If can be further increased. This effect can be applied to the choke coils independent of each other, but becomes more effective in the case of the cooperative choke coils 7 sharing the core with each other like the choke coils CH1 to CH3 shown in FIG.
[0042]
Generally, in a cooperative choke coil, the total amount of magnetic force lines generated in a core according to a product of a choke current, which is a sum of a dummy current and a load current flowing through a plurality of secondary rectifying and smoothing circuits, and the number of turns thereof, is a problem. The magnitude of the current flowing through each secondary rectifying and smoothing circuit does not matter. However, in the cooperative choke coil 7 shown in FIG. 1, each of the choke coils CH1 to CH3 is arranged to have the same turns ratio in order to clear a problem of a special turns ratio. Therefore, the sum of the dummy currents flowing through the respective dummy resistors Rd1 to Rd3 of the secondary rectifying / smoothing circuits 21 to 23 becomes the dummy current Id shown in FIG.
[0043]
Therefore, when the output voltages of the secondary rectifying / smoothing circuits 21 to 23 are different from each other, the dummy current of the secondary rectifying / smoothing circuit having the lowest output voltage is set to be large, and the dummy current of the secondary rectifying / smoothing circuit having the highest output voltage is set. , The power loss due to the dummy current can be minimized and the power conversion efficiency of the entire switching power supply can be improved without changing the dummy current Id shown in FIG. Further, in this case, the load current of the secondary rectifying / smoothing circuit in which the dummy current is suppressed is increased, and the inductance of the cooperative choke coil 7 is reduced. As a result, even if the ripple increases, the current cutoff does not occur. There is also an effect.
[0044]
FIG. 5 is a side view showing an example of the size of the step (only the tip of the center leg 10a is shown) of the embodiment of the stepped E-shaped core 10 shown in FIG. 2, and FIG. FIG. 4 is a diagram showing actually measured IL characteristics (corresponding to FIG. 3) of the choke coil using the E-shaped core shown. In this embodiment, the power capacity of the secondary rectifying / smoothing circuit 23 of the switching power supply shown in FIG. 1 is an output voltage of 24 V and a maximum current of 23 A. When the choke current Ich = 0, the inductance L = 320 μH and Ich = 0. 3A to obtain a choke coil with L = 215 μH and Ich = 23 A with L = 30 to 60 μH.
[0045]
Therefore, the core of the EI44 standard (the width of the center leg is 12 mm) is processed, as shown in FIG. 5, the depth of the step is set to 2.5 mm, and the lateral width is 5 mm ((1) broken line) and 6 mm ( (2) two-dot chain line) and 7 mm ((3) solid line). A cooperative choke coil was experimentally manufactured by combining the E-type core shown in FIG. 5 with the I-type core, and its IL characteristics were measured. As a result, FIG. 6 shows (1) broken line, (2) two-dot chain line, and (1) 3) The result indicated by the solid line was obtained.
[0046]
That is, (1) the core having the step width of 5 mm indicated by the broken line was almost at the maximum at the maximum current Ich = 23 A, but the core having the step width of 6 mm and 7 mm indicated by the (2) two-dot chain line and (3) the solid line. Are L = 30 to 40 μH at Ich = 23 A, respectively, and almost satisfactory results are obtained at L = 300 to 400 μH when Ich = 0.3 A. As a result, the core is reduced from the EI50 standard to the EI44 standard by about 10%, the cost is reduced by about 20% from 600 yen to 500 yen, and the dummy current is reduced as compared with the conventional cooperative choke coil having the same capacity and no step. Id was reduced from 0.2 A to 0.1 A (energy saving 2.4 W).
[0047]
FIG. 7 is a perspective view showing a modification of the stepped E-shaped core shown in FIG.
The E-shaped core 11 shown in FIG. 7 has a step having the same depth and a width of 2/3 instead of the core having the step width shown in FIG. , Only 3/4 of the thickness (depth) thereof, and the remaining 1/4 of the thickness has no step.
Even if the gap is formed by the step as shown in FIG. 7, if the effective area and the depth of the step portion 11b when the upper end surface of the central leg 11a is viewed from above are the same, FIG. Functions and effects equivalent to those of the E-type core 10 are obtained.
[0048]
FIG. 8 is a perspective view showing an example of the configuration of an E-shaped core which is a second embodiment of the common core of the cooperative choke coil 7 of the DC-DC converter 3 shown in FIG.
FIG. 9 is a diagram showing an example of the IL characteristic of the choke coil using the E-type core 12 shown in FIG. 8, and FIG. 10 is a waveform diagram showing an example of the choke current Ich of the choke coil. .
[0049]
The E-shaped core 12 shown in FIG. 8 has a slope 12b as a gap in a cross section (upper surface of the center leg 12a) which is a part of a magnetic circuit, and one side thereof coincides with the upper surface to make the gap zero. As a result, the IL characteristic of the choke coil using this core is the highest when the inductance L is at the choke current Ich = 0 as shown in FIG. 9, and is linear with the increase of the choke current Ich. And finally reaches the saturation state.
[0050]
Therefore, as shown in FIG. 10, the choke current waveform has a large inductance L when no load is applied, and therefore the ripple component is small, and the dummy current Id can be set small. Decreases, the ripple increases, but the choke current Ich, which is the sum of the dummy current Id and the load current If, is always larger than (1/2) of the increasing ripple, so that the current cutoff is increased. Does not occur.
[0051]
FIG. 11 is a perspective view showing an example of the configuration of an E-shaped core which is a third embodiment of the common core of the cooperative choke coil 7 shown in FIG.
FIG. 12 is a diagram showing an example of the IL characteristic of the choke coil using the E-type core 13 shown in FIG. 11, and FIG. 13 is a waveform diagram showing an example of the choke current Ich of the choke coil. .
[0052]
The E-shaped core 13 shown in FIG. 11 is provided with a slope 13c as a gap and a step 13d at a part of the upper end surface 13b of the central leg 13a, so that an IL of a choke coil using this core is provided. As shown in FIG. 12, as compared with the IL characteristic shown in FIG. 3, the width of the two-stage large and small constant inductance L is narrower, but the middle part is smaller. They are connected by gentle diagonal lines. Therefore, the IL characteristic shows an intermediate characteristic of the IL characteristic shown in FIG. 3 and FIG.
[0053]
Therefore, the waveform diagram of the choke current Ich shown in FIG. 13 shows only the case of no load and the case of the load near the maximum load, and the difference from the choke current waveform diagrams shown in FIGS. Although it is not clear, the waveform of the choke current Ich for an intermediate load is also between the choke coils using the E-shaped cores 10 and 12.
[0054]
FIG. 14 is a perspective view showing an example of an E-shaped core according to a fourth embodiment of the common core of the cooperative choke coil 7 shown in FIG. 1, in which cores of different materials are stacked instead of providing a gap.
FIG. 15 is a diagram showing an example of the IL characteristic of the choke coil using the E-shaped core 14 shown in FIG. 14, and FIG. 16 is a waveform diagram showing an example of the choke current Ich of the choke coil. .
[0055]
The E-shaped core 14 shown in FIG. 14 is formed by stacking a plurality of cores 14a and 14b having the same size and different magnetic properties from each other in the thickness direction. For example, since the dust core and the ferrite core have different magnetic characteristics such as magnetic resistance and saturation limit, even if a magnetic circuit without a gap is formed, the IL characteristics of the dust core and the ferrite core are different from each other as shown in FIG. A two-stage L characteristic appears.
[0056]
Therefore, as shown in FIG. 16, the waveform diagram of the choke current Ich also suppresses the ripple component when there is no load, reduces the dummy current Id, and prevents the current cutoff from occurring even when the ripple component becomes large under load. The same effects as those of the E-shaped cores 10 to 13 provided with gaps can be obtained.
The E-shaped cores 10 to 13 provided with a gap have an advantage that an arbitrary IL characteristic can be obtained by changing the shape of the gap as described above. In the case of the E-shaped core, the degree of freedom in selecting the IL characteristics tends to be somewhat narrowed even when the combination and type of the materials are changed.
[0057]
FIG. 17 is a fifth embodiment of the common core of the cooperative choke coil 7 shown in FIG. 1, and is a perspective view showing an example of an E-type core in which cores made of different materials are stacked and a gap is further provided. It is.
FIG. 18 is a diagram showing an example of the IL characteristic of the choke coil using the E-type core 15 shown in FIG. 17, and FIG. 19 is a waveform diagram showing an example of the choke current Ich of the choke coil. .
[0058]
The E-type core 15 shown in FIG. 17 is similar to the E-type core 14 shown in FIG. 14 except that E-type cores 15a and 15b made of different materials are stacked in the thickness direction. A gap having a slope 15c similar to the slope 12b of the E-shaped core 12 shown in FIG.
As a result, the IL characteristics of the choke coil using the E-shaped core 15 decrease as the choke current Ich increases as shown in FIG. ing. Since the waveform diagram of the choke current Ich shown in FIG. 19 has many overlapping portions, the description is omitted.
[0059]
Needless to say, the entire slope 15c of the E-shaped core 15 shown in FIG. 17 is an example of a gap, and the gap is not limited to the entire slope, but a step (FIGS. 2 and 7). , A combination of a slope and a step (FIG. 11), or a slope not shown but leaving a part of the upper end face of the center leg. Alternatively, a gap may be provided in at least one of the E-shaped cores made of different materials.
[0060]
As described above, the E-type cores 10 to 15 shown in FIGS. 2, 7, 8, 11, 14, and 17 are assumed to be combined with the I-type core similarly to the E-type core 17 shown in FIG. Although described, the core to be combined is not necessarily limited to the I-type core, and may be, for example, a combination of an E-type core and an E-type core. Further, the same effect can be obtained even if the shape of the center leg of the E-shaped core is not a prismatic shape as shown, but a cylindrical shape, for example.
[0061]
In using the cooperative choke coil 7 having the above-described various E-shaped cores as a common core, the DC-DC converter 3 shown in FIG. 1 connects each of the choke coils CH1 to CH3 to the ground of the secondary rectifying and smoothing circuit. Although provided on the line side, it goes without saying that a similar effect can be obtained by providing each on the hot line side.
Also, if for some reason each of the choke coils CH1 to CH3 is provided separately for the ground line and the hot line of each secondary rectifying and smoothing circuit, the transistor Q is turned on and each choke coil is turned on. A similar effect can be obtained if the respective windings are wound in the direction of magnetizing the common core in the same direction when the exciting current flows.
[0062]
【The invention's effect】
As described above, the present inventionMulti outputSwitching power supplyBy dummy currentReduce power loss and heat generation,Switching power supplyPower efficiency can be improved.Further, the load current of the secondary rectifying / smoothing circuit in which the dummy current is suppressed is increased, and the inductance of the cooperative choke coil 7 is reduced. As a result, even if the ripple increases, the current cutoff does not occur.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a DC-DC converter which is an embodiment of the present invention and is a multi-output switching power supply device, together with a primary rectifying and smoothing circuit.
FIG. 2 is a perspective view showing an example of a configuration of a first embodiment of an E-type core used as a common core of a cooperative choke coil of the DC-DC converter shown in FIG.
FIG. 3 is a diagram illustrating an example of an IL characteristic of a choke coil using the E-type core illustrated in FIG. 2;
4 is a waveform diagram showing an example of a current flowing through a choke coil having the IL characteristic shown in FIG.
FIG. 5 is a side view showing an example of the size of the embodiment of the E-shaped core shown in FIG. 2;
6 is a diagram showing actually measured IL characteristics of a choke coil using the E-shaped core shown in FIG. 5;
FIG. 7 is a perspective view showing another example of the configuration of the first embodiment of the E-shaped core shown in FIG. 2;
FIG. 8 is a perspective view showing an example of a configuration of a second embodiment of the E-shaped core.
FIG. 9 is a diagram illustrating an example of an IL characteristic of a choke coil using the E-type core illustrated in FIG. 8;
FIG. 10 is a waveform chart showing an example of a current flowing through the choke coil having the IL characteristic shown in FIG.
FIG. 11 is a perspective view showing an example of the configuration of an E-shaped core according to a third embodiment.
12 is a diagram showing an example of an IL characteristic of a choke coil using the E-type core shown in FIG.
FIG. 13 is a waveform chart showing an example of a current flowing through the choke coil having the IL characteristic shown in FIG.
FIG. 14 is a perspective view showing an example of the configuration of a fourth embodiment of the E-shaped core.
FIG. 15 is a diagram illustrating an example of an IL characteristic of a choke coil using the E-type core illustrated in FIG. 14;
16 is a waveform chart showing an example of a current flowing through the choke coil having the IL characteristic shown in FIG.
FIG. 17 is a perspective view showing an example of the configuration of a fifth embodiment of the E-shaped core.
FIG. 18 is a diagram illustrating an example of an IL characteristic of a choke coil using the E-shaped core illustrated in FIG. 17;
19 is a waveform chart showing an example of a current flowing through the choke coil having the IL characteristic shown in FIG.
FIG. 20 is a perspective view showing an example of the configuration of a core of a conventional choke coil having a fixed inductance.
FIG. 21 is a diagram showing an example of an IL characteristic of a choke coil using the core shown in FIG. 20;
FIG. 22 is a waveform chart showing an example of a current flowing through the choke coil having the IL characteristic shown in FIG.
FIG. 23 is a circuit diagram showing an example of a configuration of a conventional multi-output switching power supply device.
[Explanation of symbols]
1: AC power supply 2: Primary rectification smoothing circuit
3: DC-DC converter (multi-output switching power supply)
5: Switching control circuit 6: Transformer
7: Cooperative choke coil
11 to 15: E type core (magnetic core)
21 to 23: secondary rectifying and smoothing circuit
C21 to C23: Capacitor
CH1 to CH3: Choke coil
N1: primary winding N21 to N23: secondary winding
Q: Transistor (switching element)

Claims (7)

Primary DC power is input to a series circuit of a primary winding of a transformer and a switching element, and secondary AC power induced in a plurality of secondary windings of the transformer by switching the switching element is respectively converted into In a multi-output switching power supply device, a plurality of secondary rectifying / smoothing circuits having choke coils convert and output secondary DC power having different output voltages from each other .
Each choke coil of the plurality of secondary rectifying smoothing circuit is configured to share the magnetic core to each other, the inductance is large when the load current is small, have a magnetic property inductance becomes small when the load current is large, the plurality of 2 The total value of the dummy currents flowing through the respective dummy resistors of the secondary rectification / smoothing circuit is fixed, the dummy current of the secondary rectification / smoothing circuit having a low output voltage is set large, and the dummy current of the secondary rectification / smoothing circuit having a high output voltage is set. A multi-output switching power supply characterized by being kept small . Oite the multiple-output switching power supply device according to claim 1, multiple-output switching power source device, wherein the providing the gap portion of the magnetic circuit shared magnetic core is formed of the choke coil. Oite the multiple-output switching power supply device according to claim 1, wherein the multiple output switching power supply the shared magnetic core of the choke coil, characterized by being formed by stacking a plurality of different cores of material to each other in the thickness direction thereof Equipment . In multiple-output switching power supply device according to claim 3, multiple-output switching power supply apparatus characterized by having a gap in a part of the magnetic circuit shared magnetic core of each choke coil is formed. In multiple-output switching power supply device according to claim 2 or 4, wherein the multi-output switching power source device, wherein said gap is provided with a step on a part of the cross section of the magnetic circuit. In multiple-output switching power supply device according to claim 2 or 4, wherein the multi-output switching power source device, wherein the gap is obtained by forming all or part of the cross section of the magnetic circuit on the slopes. In multiple-output switching power supply device according to claim 2 or 4, wherein the multi-output switching power source device, wherein the gap is that the whole or part of the cross section of the magnetic circuit formed by the slope and the step.

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