JPH0823672A - Switching power unit and its insulating method - Google Patents

Abstract

PURPOSE:To avoid abnormal current caused by biased magnetization by insulating a switching power source circuit and load circuit from each other with the insulating barriers of capacitors. CONSTITUTION:An insulation circuit 21 is connected between a switching power source circuit 11 and frequency converting circuit 7. The insulation circuit 21 is composed of capacitors CF1 and CF2. Because of the insulating barriers 451 of the capacitors CF1 and CF2, the frequency converting circuit 7 and a load circuit 4 are electrically floated from the circuit 11. Since the capacitors CF1 and CF2 have low impedances against a high-frequency voltage of 1MHz outputted between connecting points A1 and B1, electric power can be transmitted without hindrance. However, the capacitors CF1 and CF2 show extremely high impedances against the frequency of commercial power supply. Therefore, a switching unit constituted in such a way can practically neglect very weak electric energy leakage at signal levels or lower against low frequencies.

Description

Description: TECHNICAL FIELD The present invention relates to a switching power supply device and its insulation method, and more particularly to electrostatic energy stored in a large-capacity or small-capacity AC or DC capacitor on the input side. The present invention relates to a switching power supply device that supplies power to a load via an insulating circuit to a switching power supply circuit that outputs a high-frequency voltage or power based on the above, and an insulating method thereof.

[Prior Art] FIG. 2 is an electric circuit diagram showing an example of a conventional switching power supply device. Referring to FIG. 2, the switching power supply circuit 11 is connected to a series circuit of a DC power supply E and a reactor L, and is also connected to a ripple absorbing capacitor CS. That is, in the switching power supply circuit 11, a voltage is input from the DC power supply E to the ripple absorbing capacitor CS via the reactor L, so that the ripple component of the high frequency voltage component is removed, and the ripple absorbing capacitor CS is removed. The electrostatic energy stored in is supplied to the switching power supply circuit 11. That is, the electrostatic energy of the capacitor CS becomes the direct input energy of the switching power supply circuit 11.

 The switching power supply circuit 11 includes switching elements SF1 to SF4 connected in a full bridge, and each switching element SF1 to SF4 is composed of a power MOSFET which is an extremely high speed self-extinguishing type switching element having a built-in freewheeling diode. The control terminals (gates) of the respective switching elements SF1 to SF4 are alternately supplied with control pulses from a control circuit (not shown).

To the connection point A1 between the switching elements SF1 and SF2 and the connection point B1 between the switching elements SF3 and SF4, the primary side terminals A and B of the insulation transformer T are connected, and the secondary side terminals C and D of the insulation transformer T are connected. The load circuit 4 is connected via the frequency conversion circuit 7. That is, the load circuit 4 with respect to the switching power supply circuit 11 is electrically suspended by the insulating barrier 44 constituted by the insulating transformer T.

 In the switching power supply device configured as described above, the electrostatic energy charged in the ripple absorbing capacitor CS from the DC power supply E via the reactor L becomes the input energy of the switching power supply circuit 11. By applying a high frequency pulse to each control terminal, switching elements SF1 to SF4 are alternately turned on and off repeatedly, and a high frequency AC voltage converted between connection points A1 and B1 is output. . Then, this high-frequency AC voltage is transmitted to the frequency conversion circuit 7 via the magnetic field passing through the insulation barrier 44 of the insulation transformer T, frequency-converted into DC power, and given to the load circuit 4.

[Problems to be Solved by the Invention] In the conventional switching power supply device shown in FIG. 2 described above, in order to electrically float the switching power supply circuit 11 and the frequency conversion circuit 7, insulation of the insulation transformer T is performed. The barrier 44 was used. Therefore, due to the difference in the storage time of the switching elements of the switching power supply circuit 11 or the difference in the switching speed, the DC or low frequency voltage that is output unnecessarily causes the excitation of the isolation transformer T to be biased and saturated, resulting in an abnormally large voltage. It was often the case that the switching element constituting the switching power supply circuit was damaged due to the demagnetization phenomenon in which the exciting current flows without passing through the load circuit 4.

 Therefore, an object of the present invention is to provide a switching power supply device capable of avoiding the generation of an abnormal current due to a magnetic bias phenomenon and an insulating method thereof.

[Means for Solving the Problems] The invention according to claim 1 is an output of a switching power supply circuit that switches electric power from a power supply through electrostatic energy and outputs electric power of a frequency higher than the electric power from the power supply. In a switching power supply device in which a load is connected to the load via an insulation circuit, the insulation circuit consists of an insulation barrier composed of a capacitor.

 An invention according to a second aspect includes a frequency conversion circuit which is connected between the load and the capacitor according to the first aspect of the invention and which frequency-converts electric power of a high frequency.

 The invention according to claim 3 is a switching power supply device for supplying electric power to a load, wherein the electric power from the power supply is switched via electrostatic energy to output electric power of a frequency higher than the electric power from the power supply. A switching power supply circuit, an insulation circuit that is connected between the switching power supply circuit and the load, and consists of a capacitor that forms an insulation barrier between the switching power supply circuit and the load, and suppresses or blocks common-mode current that passes through the insulation barrier. Includes a filter circuit connected as shown.

 An invention according to a fourth aspect is the switching power supply device according to the third aspect, wherein the filter circuit includes a common mode choke for suppressing a common mode current passing through the insulation barrier.

 An invention according to claim 5 is a switching power supply device according to claim 3, wherein the filter circuit includes a reactor for suppressing a common mode current passing through the insulation barrier.

 The invention according to claim 6 is a switching power supply device for supplying electric power to a load, wherein electric power from the power supply is switched via electrostatic energy to output electric power of a frequency higher than that of the electric power from the power supply. Switching power supply circuit, a frequency conversion circuit that is connected to the output of the switching power supply circuit, converts the high frequency power output from the switching power supply circuit into frequency, and supplies the load with a lower frequency power than the high frequency power. An insulation circuit, which is connected between the output of the power supply circuit and the input of the frequency conversion circuit and constitutes an insulation barrier between the output of the switching power supply circuit and the input of the frequency conversion circuit, and an insulation barrier. It includes a filter circuit connected to suppress or block the common-mode current that passes through.

 According to a seventh aspect of the present invention, there is provided the step of frequency-converting the electric power from the power supply through electrostatic energy to convert the electric power into a power having a frequency higher than that of the power from the power supply; Passing a number of electric powers.

 According to an eighth aspect of the present invention, there is provided a step of frequency-converting electric power from a power supply through electrostatic energy to convert it into electric power having a frequency higher than that of the electric power from the power supply, and an insulating barrier composed of the electric power having a high frequency. It consists of passing through the inside and switching the high frequency power that has passed through the insulation barrier and converting it to low frequency power.

 According to a ninth aspect of the present invention, there is provided a step of frequency-converting electric power from a power supply through electrostatic energy to convert the electric power into a power having a frequency higher than that of the power from the power supply; Passing a certain amount of power, and suppressing common mode current passing through the isolation barrier.

 According to a tenth aspect of the present invention, a step of frequency-converting electric power from a power source through electrostatic energy to convert the electric power into a power having a frequency higher than that from the power source, and an insulating barrier formed of a capacitor for the power having a high frequency. Through the insulation barrier, switching the high frequency power that has passed through the insulation barrier to frequency conversion into low frequency power, and further suppressing the common mode current that passes through the insulation barrier.

 The invention according to the eleventh aspect is an insulation method according to the seventh, eighth, ninth and tenth aspects, wherein the high frequency electric power is electric power equal to or higher than an audible frequency.

 A twelfth aspect of the present invention is an insulation method according to the seventh, eighth, ninth and tenth aspects, characterized in that high frequency electric power is electric power of 50 kHz or more. Method.

[Operation] According to the present invention, by insulating the switching power supply circuit and the load circuit by the insulating barrier of the capacitor, it is possible to avoid the occurrence of an abnormal current due to a biased magnetism when an insulating transformer is used.

[Embodiment] FIG. 1 is an electric circuit diagram of a first embodiment in which the idea of the present invention is embodied.

 The switching power supply device shown in FIG. 1 includes a DC power supply E, a reactor L, a ripple absorbing capacitor CS, a switching power supply circuit 11, a load circuit 4, and a frequency conversion circuit 7 as shown in FIG. It is constructed in the same way as the example. In this embodiment, an insulation circuit 21 is connected between the switching power supply circuit 11 and the frequency conversion circuit 7, and the insulation circuit 21 is composed of capacitors CF1 and CF2. The insulation barrier 451 of the capacitors CF1 and CF2 electrically floats the frequency conversion circuit 7 and the load circuit 4 with respect to the switching power supply circuit 11.

 Next, the operation of the embodiment shown in FIG. 1 will be described. Now, the control terminals (gates) of the switching elements SF1 to SF4 are turned on and off at the switching frequency of 1 MHz. First, for 400 nsec, the control terminals of the switching elements SF1 and SF4 are turned on, and the control terminals of the switching elements SF2 and SF3 are turned off. When the switching elements SF1 and SF4 are turned on and the switching elements SF2 and SF3 are turned off, the voltage of the capacitor CS is directly output between the connection points A1 and B1.

 Next, the control terminals of the switching elements SF1 and SF4 are turned off, the control terminals of the switching elements SF2 and SF3 are turned on, and the polarity of the output voltage is reversed. A dead time of 00 nsec is provided. That is, when the switching elements SF1, SF2 or SF3, SF4 above and below the arm are turned on at the same time regardless of the control pulse of turning on and off depending on the storage time of the switching elements SF1 to SF4, the capacitor CS is directly connected. Since a short circuit causes an excessive short circuit current to flow, the control terminals of all the switching elements SF1 to SF4 are turned off in advance so that the switching elements SF1 to SF4 are not turned on at the same time above and below the arm.

 As a matter of course, the length of the dead time needs to be longer than the switching time of the switching elements SF1 to SF4 used. In the case of this embodiment, the finite time when the switching elements SF1 to SF4 are turned on and off and turned on, that is, the switching time is estimated to be 50 nsec.

 During the dead time, the output voltage is uncontrolled, and the output voltage is uncertain because it is subtly affected by the switching characteristics of the switching elements and the load conditions. This dead time period is one of the main causes of generating DC or low frequency voltage components in the output voltage. As the switching frequency becomes higher, the ratio of the dead time to the time width of the switching period cannot be ignored, and the DC or low frequency voltage component contained in the output voltage tends to increase.

 After the dead time period ends, the control terminals of the switching elements SF1 and SF4 are turned off and the control terminals of the switching elements SF2 and SF3 are turned on for a time of 400 nsec. When the switching elements SF1 and SF4 are turned off and the state where the switching elements SF2 and SF4 are turned on is established, the connection point A1 becomes negative and the connection point B1 becomes positive. Therefore, the voltage of the capacitor CS is applied with the opposite polarity between the connection points A1 and B1.

After that, a dead time period of 100 nesc is provided again.

 By repeating the above operation, the high frequency voltage is output to the connection points A1 and B1. This high frequency voltage is transmitted to the frequency conversion circuit 7 via the electric field passing through the insulating barrier 451 constituted by the capacitors CF1 and CF2, and is frequency-converted into DC power, which is supplied to the load circuit 4. Here, the capacitors CF1 and CF2 have a low impedance with respect to the high frequency voltage of 1 MHz output between the connection points A1 and B1, and it is not a problem to provide the capacitors CF1 and CF2 for power transmission. It does not cause

 However, these capacitors CF1 and CF2 exhibit extremely high impedance with respect to the commercial power supply frequency (50 Hz or 60 Hz). That is, since the impedance value indicated by the capacitors CF1 and CF2 is inversely proportional to the frequency, the impedance value at 50 MHz is 1 MHz / 50 Hz = 20000 times higher than the impedance value at 1 MHz. Become. Therefore, for low frequencies, the leakage of electric energy that is as weak as the signal level can be substantially ignored as a switching power supply.

 Therefore, due to the higher frequencies, not only for DC but also for power frequencies around commercial frequencies, this insulation circuit can actually be used effectively as an insulation circuit as a switching power supply. In other words, it can be used as an insulation circuit for DC power source and commercial power source. This was achieved by increasing the frequency of the switching power supply device. If the output frequency of the switching power supply circuit is not very high compared to the commercial power supply frequency, for example, a frequency below the audible frequency of about 500 Hz. However, since the frequency ratio to the commercial frequency is as small as about 500Hz / 50Hz = 10 times, the capacitor that constitutes the barrier inevitably has an extremely large capacity, and in principle it cannot be used as an insulation circuit for the power supply of the commercial power supply. difficult.

 As described above, high frequency power is transmitted to the frequency conversion circuit 7 through the insulating barrier 451 that electrically floats the frequency conversion circuit 7 or the load circuit 4 with respect to the switching power supply circuit 11. On the other hand, due to the insulating barrier 451, direct-current power and low-frequency power of about commercial frequency cannot pass through the insulating barrier 451 at all or almost.

 In the embodiment shown in FIG. 1, the switching power supply circuit 11 is constructed by using the power MOSFET as the switching element, but it may be constructed by using other switching elements.

 FIG. 1A is a modification of the embodiment shown in FIG. 1, and is configured similarly to the above-described FIG. 1 except for the following points. That is, in FIG. 1A, the reactor L shown in FIG. 1 is removed and, instead of the switching elements SF1 to SF4, switching elements S1 to S4 composed of a power transistor having a freewheeling diode as a switching element are used. Thus, the switching power supply circuit 1 is configured. Further, instead of the capacitors CF1 and CF2 forming the insulating circuit 21 in FIG. 1, the insulating circuit 20 is formed by using the capacitors C1 and C2. The difference between the capacitors CF1 and CF2 and the capacitors C1 and C2 is that the capacitors C1 and C2 have a capacitance that is about three orders of magnitude larger than that of the capacitors CF1 and CF2.

 Next, the operation of the modification shown in FIG. 1A will be described. Now, the control terminals (bases) of the switching elements S1 to S4 are turned on and off at the switching frequency of 1 kHz. First, during 400 μsec, the control terminals of the switching elements S1 and S4 are turned on, and the control terminals of the switching elements S2 and S3 are turned off. When the switching elements S1 and S4 are turned on and the switching elements S2 and S3 are turned off, the voltage of the capacitor CS is output between the connection points A1 and B1 in the same polarity.

 Next, the control terminals of the switching elements S1 and S4 are turned off, the control terminals of the switching elements S2 and S3 are turned on, and the polarity of the output voltage is inverted. Before that, however, to prevent arm short circuit, 100 μs ec Dead time is provided. That is, when the switching elements S1, S2 or S3, S4 above and below the arm are turned on at the same time despite the control pulse being turned on and off depending on the storage time of the switching elements S1 to S4, etc., the capacitor CS is directly short-circuited. Since an excessive short-circuit current flows, the control terminals of all the switching elements S1 to S4 are previously turned off so that the switching elements S1 to S4 do not turn on at the same time above and below the arm.

 As a matter of course, the length of this dead time needs to be longer than the switching time of the switching elements S1 to S4 used. In the case of this embodiment, the finite time when the switching elements S1 to S4 are switched from on to off and from off to on, that is, the switching time is estimated to be 50 μsec.

 After the dead time period ends, the control terminals of the switching elements S1 and S4 are turned on and the control terminals of the switching elements S2 and S3 are turned on for a time of 400 μsec. When the switching elements S1 and S4 are turned off and the switching elements S2 and S4 are turned on, the connection point A1 becomes negative and the connection point B1 becomes positive. Therefore, the voltage of the capacitor C S is applied with the opposite polarity between the connection points A1 and B1. After that, a dead time period of 100 μsec is provided again, and by repeating the above operation, an AC voltage is output to the connection points A1 and B1. This AC voltage is given to the frequency conversion circuit 7 through the insulation barrier 45 constituted by the capacitors C1 and C2, frequency-converted to DC power, and supplied to the load circuit 4.

 Here, the capacitors C1 and C2 have a low impedance with respect to the AC voltage of 1 kHz output between the connection points A1 and B1, and therefore, the provision of the capacitors C1 and C2 causes a problem in power transmission. Not here. However, the insulating barrier 45 formed by the capacitors C1 and C2 exhibits an infinite impedance with respect to frequency zero, that is, direct current. Therefore, DC power cannot pass through this barrier 45.

 FIG. 3 is an electric circuit diagram showing a second embodiment of the present invention. Referring to FIG. 3, the DC power supply E, the switching power supply circuit 1, the insulating circuit 20, the load circuit 4, and the frequency conversion circuit 7 are constructed in the same manner as in FIG. 1A described above. FIG. 3 shows the connection between the direct current power source E and the capacitor CS shown in FIG. 1A via a filter circuit F. There are no other differences between FIG. 3 and FIG. 1A. The operation of the switching power supply circuit 1 is omitted because it is the same as that in FIG. 1A.

 The filter circuit F is formed by connecting terminals TA and TB and terminals TC and TD via reactors L1 and L2, respectively, and the terminals between the input terminals TA and TB of the filter circuit F and the output terminals TC and TD are reactors. It is cut off at a high frequency by L1 and L2. Therefore, the filter circuit F cuts off between the input side and the output side of the switching power supply device, that is, between the DC power supply E and the load circuit 4 at a high frequency.

 Here, the role of the filter circuit F will be described in detail. The filter circuit F basically has no impedance when the impedance between the ground on the input power supply side and the ground on the output load side is infinite, that is, when the input and output grounds are completely electrically independent. is necessary. However, for example, when the impedance between the input and output grounds is zero and the filter circuit F is not provided, an excessive common-mode current is isolated each time the switching operation of the switching power supply circuit 1 is performed. It flows between the input and output grounds via the circuit 20. As a result, an excessive current flows in the switching element that constitutes the switching power supply circuit 1, causing the switching element to be destroyed.

However, the provision of the filter circuit F solves this problem. That is, if the values of the reactors L1 and L2 forming the filter circuit F are high impedance with respect to the switching frequency of the switching power supply circuit 1, input / output of the input / output is performed via the insulating circuit 20 each time the switching power supply circuit 1 switches. The current flowing between the grounds, that is, the common mode current is effectively suppressed by the reactors L1 and L2 that form the filter circuit F. Therefore, the voltage of the capacitors C1 and C2 does not suddenly change due to the common mode current due to the reactors L1 and L2 of the filter circuit F, and the voltage of the capacitors C1 and C2 forming the insulation barrier 45 is reduced. Pressure stabilizes.

 FIG. 3A is an electric circuit diagram showing a modification of the embodiment shown in FIG. In the embodiment shown in FIG. 3A, instead of the installation location of the filter circuit F shown in FIG. 3, it is provided in the power line between the frequency conversion circuit 7 and the load circuit 4 in FIG. 3A. . In FIG. 3A, other main circuit configurations, that is, the switching power supply circuit 1, the insulating circuit 20, and the load circuit 4 are the same as those in FIG. 3, and therefore the description of the circuit configuration relating to them is omitted. The operation of the switching power supply circuit 1 will be omitted because it is the same as that in FIG. 1A. Similar to the filter circuit F of FIG. 3, the filter circuit F of FIG. 3A also has high impedance in the inductance of the reactors L1 and L2 with respect to the switching frequency of the switching power supply circuit 1. As a result, the voltages of the capacitors C1 and C2 that form the insulating circuit 20 do not suddenly change in response to the switching of the switching power supply circuit 1, and the impedance between the input and output grounds has a low resistance or zero impedance. However, the steep common-mode current that flows through the input / output grounds is effectively blocked by the filter circuit F even if it is a switch. Therefore, the filter circuit F prevents the voltages of the capacitors C1 and C2 from abruptly changing due to the common mode current.

Therefore, the voltages of the capacitors C1 and C2 forming the insulation barrier 45 are stabilized. That is, the input terminals TA and TB and the output terminals TC and TD of the filter circuit F are cut off at high frequencies by the reactors LDC1 and LDC2. Therefore, the power supply E on the input side and the load circuit 4 on the output side of the switching power supply device are cut off at high frequencies by this filter circuit F, and the common mode currents are the reactors L1 and L2 forming the filter circuit F. Is suppressed by.

 FIG. 4 is an electric circuit diagram showing a third embodiment of the present invention. In the embodiment shown in FIG. 4, the filter circuit F shown in FIG. 3 is replaced with a filter circuit FC composed of a common mode choke. In this filter circuit FC, the terminal TA and the terminal TC are connected via one winding of the common mode choke, and the terminals TB and TD are connected via the other winding of the common mode choke. The input terminals TA and TB and the output terminals TC and TD of the filter circuit FC are cut off in a common mode by a common mode choke. That is, when the windings forming the common mode choke are completely connected, the filter circuit FC theoretically does not act as an impedance with respect to the normal mode. However, since the common mode choke exhibits a large impedance with respect to the common mode, it cuts off or suppresses the common mode current passing through the filter circuit FC. Therefore, the input side and the output side of the switching power supply device are shut off in a common mode by this filter circuit FC.

 Since the operation of FIG. 4 is the same as the drive operation of the switching elements S1 to S4 shown in FIG. 1A, a detailed description of the operation of the switching power supply circuit is omitted because it overlaps with that of FIG. 1A. Next, the role of the filter circuit FC will be described in detail. The filter circuit FC is basically unnecessary when the impedance between the ground on the input power supply side and the ground on the output load side is infinite, that is, when the input and output grounds are electrically completely independent. Is. However, for example, when the impedance between the input and output grounds is zero and the filter circuit FC is not provided, an excessive common mode current is isolated at every switching operation of the switching power supply circuit 1. Flow through circuit 20. As a result, the voltages of the capacitors C1 and C2 forming the insulation barrier 45 suddenly fluctuate. Then, an excessive current flows through the switching element that constitutes the switching power supply circuit 1, causing the switching element to be destroyed. However, this problem is solved by installing the filter circuit FC. That is, if the value of the inductance of the common mode choke forming the filter circuit FC is high impedance with respect to the switching frequency of the switching power supply circuit 1, the insulating circuit 20 is used every time the switching of the switching power supply circuit 1 is performed. The common-mode current flowing between the input and output grounds is effectively suppressed by the common-mode choke forming the filter circuit FC. Therefore, the voltage of the capacitors C1 and C2 does not suddenly change due to the common mode current. In other words, the common mode choke of the filter circuit FC cuts off the input power supply E and the load 4 in a common mode, and the filter circuit FC suppresses the common mode current flowing between the input and output of the switching power supply device. It

 The filter circuit FC may be connected between the frequency conversion circuit 7 and the load 4 as shown in FIG. 4A which is a modification of the embodiment shown in FIG. Further, the filter circuit FC may be connected between the switching power supply circuit 1 and the insulation circuit 20, or between the insulation circuit 20 and the frequency conversion circuit 7. Furthermore, one winding coil of the common mode choke constituting the filter circuit FC is provided between the terminal C of the insulating circuit 20 and the frequency conversion circuit 7, and the other winding coil is provided between the switching power supply circuit 1 and the insulating circuit 20. The common mode current passing through the insulating barrier 45 can be suppressed even if the common mode current is connected to the terminal B.

 FIG. 5 is an electric circuit diagram showing a fourth embodiment of the present invention. In the embodiment shown in FIG. 5, the frequency conversion circuit 7 shown in FIG. 4 is removed, and the insertion location of the filter circuit FC is moved between the insulating circuit 20 and the load circuit 4. Further, in FIG. 5, in order to clearly show the function of the filter circuit FC, the input power source E of the switching power supply device is grounded to the ground G1 and the load circuit 4 is grounded to the ground G2, and the electrically completely independent ground G1 is provided. Further, G2 and G2 are connected via the impedance Z, and the load circuit 4 is constituted by a resistor. The common mode choke of the filter circuit FC does not cut off the normal mode current flowing through the input terminals TA and TB of the filter circuit FC and the output terminals TC and TD of the filter circuit FC, but cuts off the common mode current. As a result, a steep common-mode excessive current does not flow through the insulating barrier 45 even if the impedance Z has a low resistance or zero. Moreover, the electric charges stored in the capacitors C1 and C2 forming the insulating barrier 45 do not suddenly become a steep common mode current via the input / output grounds G1 and G2 and are not charged / discharged. That is, since the input and output of the switching power supply unit are cut off in the common mode by the filter circuit FC, a steep common mode excessive current is suppressed by the common mode choke forming the filter circuit FC. And However, the filter circuit FC does not act as an impedance in principle for the normal mode, that is, the common mode choke has zero impedance for the normal mode.

Therefore, basically, the AC power output from the switching power supply circuit 1 is not blocked from being transmitted to the load circuit 4. In other words, the filter circuit FC theoretically has zero impedance with respect to the normal mode AC current output between the connection points A1 and B1 by the switching power supply circuit 1, and thus the power transmission to the load circuit 4 is performed. In addition, the installation of the filter circuit F C does not cause any trouble. Therefore, the filter circuit FC prevents the power output from the switching power supply circuit 1 from leaking to the impedance Z and significantly lowering the efficiency of the switching power supply device.

 The filter circuit FC is provided between the switching power supply circuit 1 and the insulating circuit 20 as shown in FIG. 5A, which is a modification of the embodiment shown in FIG. 5, or the embodiment shown in FIG. Alternatively, as shown in FIG. 5B, which is another modified example, the DC power source E and the capacitor CS may be indirectly connected. Furthermore, one winding coil of the common mode choke forming the filter circuit FC is provided between the terminal C of the insulation circuit 20 and the load circuit 4, and the other winding coil of the switching power supply circuit 1 and the insulation circuit 20. Even if it is connected to the terminal B, the common mode current passing through the insulating barrier 45 can be suppressed.

 FIG. 6 is an electric circuit diagram showing a fifth embodiment of the present invention. In the embodiment shown in FIG. 6, a filter circuit F composed of reactors L1 and L2 is connected instead of the filter circuit FC composed of the common mode choke shown in FIG. 5B. Like the filter circuit FC shown in FIG. 5B, this filter circuit F also has a function of suppressing the common mode current.

 FIG. 7 is an electric circuit diagram showing a sixth embodiment of the present invention. In the embodiment shown in FIG. 7, a switching power supply circuit 10 is connected instead of the switching power supply circuit 1 shown in FIG. There is no other difference between FIG. 7 and FIG. The switching power supply circuit 10 is composed of self-extinguishing type switching elements S1 and S2, each of which is connected in series and connected in parallel to the capacitor CS. Each of the switching elements S1 and S2 is composed of a power transistor having a built-in freewheeling diode. Control pulses (not shown) are applied to the control terminals (bases) of the switching elements S1 and S2 from a control circuit (not shown). The primary side terminal B of the insulating circuit 20 is connected to the connection point A1 between the switching elements S1 and S2 of the switching power supply circuit 10, and the primary side terminal A is connected to the collector of the switching element S1.

 Next, the operation of the embodiment shown in FIG. 7 will be described. Now, the control terminals of the switching elements S1 and S2 are turned on and off at the switching frequency of 1 kHz. First, for 400 μsec, the control terminal of the switching element S2 is turned on and the control terminal of the switching element S1 is turned off. When the switching element S2 is turned on and the switching element S1 is turned off, the voltage of the capacitor CS is output between the terminals A and B. After that, the control terminal of the switching element S2 is turned off, the control terminal of the switching element S1 is turned on, and the output voltage becomes zero, but before that, a dead time of 100 μsec is provided to prevent arm short circuit. .

That is, when the switching elements S1 and S2 above and below the arm are turned on at the same time regardless of the control terminal signals that are on and off due to the accumulation time of the switching elements S1 and S2, the capacitor CS is directly short-circuited to cause an excessive short-circuit current. Therefore, the control terminals of all the switching elements S1 and S2 are turned off in advance so that the switching elements S1 and S2 do not turn on at the same time above and below the arm.

 After the dead time period ends, the control terminal of the switching element S2 is turned off and the control terminal of the switching element S1 is turned on for a time of 400 μsec. When the switching element S2 is turned off and the state where the switching element S1 is turned on is established, the terminals A and B have the same potential. Therefore, the voltage between terminals A and B becomes zero. After that, a dead time period of 100 μsec is provided again. By repeating the above operation, an AC voltage containing a large amount of DC voltage components is output to terminals A and B. Only the AC component of the AC voltage containing a large amount of this DC voltage component is supplied to the load circuit 4 via the insulating barrier 45 constituted by the capacitors C1 and C2.

 Here, the role of the filter circuit F will be described in detail. The filter circuit F is basically used when the impedance Z between the ground G1 on the input power supply side and the ground G2 on the output load side is infinite, that is, when the input and output grounds are completely electrically independent. Unnecessary. However, for example, when the impedance between the input and output grounds is zero and the filter circuit F is not provided, an excessive common mode current flows through the insulating circuit 20 every time the switching operation of the switching power supply circuit 10 is performed. Be done. As a result, an excessive current flows through the switching elements that make up the switching power supply circuit 10, causing destruction of the switching elements. However, the installation of the filter circuit F solves this problem. That is, if the reactors L1 and L2 forming the filter circuit F have high impedance with respect to the switching frequency of the switching power supply circuit 10, input / output graphs are output via the insulating circuit 20 each time the switching power supply circuit 10 switches. The common mode current flowing between the ends is effectively suppressed by the filter circuit F. Further, the filter circuit F has a function of preventing the power output from the switching power supply circuit 10 from becoming a common-mode current and leaking to the impedance Z, which lowers the power efficiency of the switching power supply device.

 FIG. 7A is a modification of the embodiment shown in FIG. 7, and is configured similarly to FIG. 7 described above except for the following points. That is, in FIG. 7A, the filter circuit F1 is configured by using reactors L11, L21 having a value that is about three digits smaller than the reactors L1, L2 that configure the filter circuit F shown in FIG. A switching power supply circuit 111 is configured by using switching elements SF1 and SF2 which are power MOSFETs having a built-in free-wheel diode instead of S1 and S2. Further, instead of the capacitors C1 and C2 forming the insulating circuit 20 in FIG. 7, an insulating circuit 21 is formed by using capacitors CF1 and CF2. The difference between the capacitors C1 and C2 and the capacitors CF1 and CF2 is that the capacitors CF1 and CF2 have a capacitance that is three orders of magnitude smaller than that of the capacitors C1 and C2. Therefore, the insulation circuit 21 can be used as a power insulation circuit for not only the DC power supply but also the commercial power supply. That is, the electric power of about the commercial frequency is cut off very effectively by the insulating circuit 21.

 Next, the operation of the modified example shown in FIG. 7A will be described, but it is basically the same as the operation described in FIG. The control terminals of the switching elements SF1 and SF2 are turned on and off at a switching frequency of 1 MHz. This on / off control pulse is the same as that of the switching elements SF1 and SF2 in FIG.

As a result, the switching power supply circuit 111 outputs a high-frequency AC voltage of 1 MHz, and the AC voltage contains many DC voltage components as in the operation of the embodiment shown in FIG.

 The basic role of the filter circuit F1 is also the same as that of FIG. 7, and it suppresses the common mode current passing through the insulation barrier 45 1 generated by the switching operation of the switching power supply circuit 111 1. As a result, the voltages of the capacitors CF1 and CF2 forming the insulating barrier 451 are stabilized. Further, since the excessive common mode current is suppressed by the filter circuit F1, the destruction of the switching element is avoided. Further, the filter circuit F1 can prevent the power output from the switching power supply circuit 111 from leaking to the impedance Z 1 between the input / output grounds G1 and G2.

 The present invention is not limited to the specific embodiment shown in FIGS. 1 to 7, but infinite variations and modifications are possible. That is, a person skilled in the art can realize various other embodiments without departing from the spirit and scope of the inventive idea by using a switching power supply circuit having other complicated or simple structure. it can. Furthermore, the insulation circuit, the frequency conversion circuit, and the load circuit are not limited to the illustrated embodiments, and the above-described invention can be implemented by using an insulation circuit and a frequency conversion circuit having other structures.

[Effects of the Invention] As described above, according to the embodiment of the present invention, an insulating circuit including a capacitor is connected between the switching power supply circuit and the load circuit, and insulation is performed by the insulating barrier of the capacitor. Therefore, it is possible to eliminate the need for an exciting current flowing through the insulating transformer for insulation, so that the phenomenon of magnetic bias does not occur.

 Therefore, even if the output of the switching power supply circuit contains a large amount of direct current voltage or low frequency components, an abnormally large current will not be generated due to the magnetic bias phenomenon of the insulating transformer.

 Therefore, there is no risk that the switching element will be destroyed by the abnormal current due to the demagnetization phenomenon of the insulation transformer.

 Furthermore, according to the embodiment shown in FIG. 3 to FIG. 7, the common circuit generated by the switching operation of the switching element inside the switching power supply device by the filter circuit constituted by the reactor or the common mode choke. Mode current is cut off or suppressed.

 Therefore, even if the input / output ground impedance is low resistance or zero, the common mode current passing through the insulation barrier is suppressed by the filter circuit composed of the common mode choke or reactor.

 Therefore, due to the filter circuit that suppresses the common mode current, the voltage of the capacitor that forms the insulation barrier does not change rapidly due to the common mode current.

 Further, since the common mode current is suppressed by the filter circuit, the switching element is prevented from being damaged by the excessive common mode current.

 Furthermore, even if the input and output of the switching power supply device are connected with a resistor, the power output from the switching power supply circuit leaks significantly to this resistor, which significantly deteriorates the efficiency of the switching power supply device. Is prevented by. That is, the loss caused by the common mode current is suppressed by installing the filter circuit that suppresses the common mode current.

[Brief description of drawings]

 FIG. 1 is an electric circuit diagram of the first embodiment of the present invention. FIG. 2 is an electric circuit diagram showing an example of a conventional switching power supply device. 3 and 3A are electric circuit diagrams showing a second embodiment of the present invention. 4 and 4A are electric circuit diagrams showing a third embodiment of the present invention. FIG. 5, FIG. 5A, and FIG. 5B are electrical circuit diagrams showing a fourth embodiment of the present invention. FIG. 6 is an electric circuit diagram showing a fifth embodiment of the present invention. 7 and 7A are electric circuit diagrams showing a sixth embodiment of the present invention. In the figure, 1, 10, 11, 111 are switching power supply circuits, 2, 20, 21 are insulation circuits, 4 are load circuits, 7 is a frequency conversion circuit, 44, 45, 451 are insulation barriers, E is a DC power supply, L, L1, L2, L11 and L21 are reactors, CS, C1, C2, CF1 and CF2 are capacitors, F, F1 and FC are filter circuits, and S1 to S4 and SF1 to SF4 are switching elements.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Date of submission] 2.10.22 Specification, page 41, line 17, "FIG. 1 is this invention" is amended to "FIG. 1, FIG. 1A is this invention".

Claims (12)

[Claims] 1. A switching power supply in which a load is connected to an output of a switching power supply circuit that switches electric power from a power supply via electrostatic energy and outputs electric power of a frequency higher than the electric power from the power supply via an insulating circuit. In the device, the insulating circuit includes an insulating barrier formed of a capacitor. 2. The switching power supply device according to claim 1, further comprising a frequency conversion circuit connected between the load and the capacitor, the frequency conversion circuit performing frequency conversion of the high frequency power. 3. A switching power supply device for supplying electric power to a load, wherein the switching power supply circuit switches electric power from a power supply through electrostatic energy and outputs electric power having a frequency higher than that of the electric power from the power supply. An insulation circuit that is connected between the switching power supply circuit and the load and that forms an insulation barrier between the switching power supply circuit and the load; and a common mode current that passes through the insulation barrier is suppressed. Or it includes a filter circuit connected to shut off. 4. A switching power supply device according to claim 3, wherein the filter circuit includes a common mode choke for suppressing common mode current passing through the insulation barrier. 5. The switching power supply device according to claim 3, wherein the filter circuit includes a reactor that suppresses a common mode current passing through the insulation barrier. 6. A switching power supply device for supplying electric power to a load, wherein the switching power supply outputs electric power of a frequency higher than the electric power from the power supply by switching electric power from the power supply through electrostatic energy. A circuit, a frequency conversion circuit connected to the output of the switching power supply circuit, for frequency-converting the high-frequency power output from the switching power-supply circuit, and supplying the load with a lower-frequency power than the high-frequency power. An insulation circuit comprising a capacitor connected between the output of the switching power supply circuit and the input of the frequency conversion circuit and forming an insulation barrier between the output of the switching power supply circuit and the input of the frequency conversion circuit, And a filter circuit connected to suppress or cut off the common mode current passing through the insulation barrier. . 7. A step of switching electric power from a power source through electrostatic energy to perform frequency conversion into electric power of a frequency higher than that of the electric power from the power source, and the electric power of the high frequency using an electric field as a medium in the insulating barrier. A method of insulating a switching power supply device, which comprises the steps of 8. A step of frequency-converting electric power from a power source through electrostatic energy to convert it into electric power of a frequency higher than the electric power from the power source, and the electric power of the high frequency into an insulating barrier composed of a capacitor. A method of insulating a switching power supply device, comprising the steps of: passing the high frequency power that has passed through the insulation barrier and frequency converting the high frequency power into a low frequency power. 9. A step of switching electric power from a power source through electrostatic energy to perform frequency conversion into electric power of a frequency higher than the electric power from the power source, and the electric power of the high frequency using an electric field as a medium in the insulating barrier. And a step of suppressing a common mode current passing through the insulation barrier, the method of insulating a switching power supply device. 10. A step of frequency-converting electric power from a power supply through electrostatic energy to convert it into electric power of a frequency higher than the electric power from the power supply, and the electric power of the high frequency in an insulating barrier composed of a capacitor. Passing through the insulation barrier, converting the high frequency power passing through the insulation barrier into a low frequency power, and suppressing a common mode current passing through the insulation barrier. A method for insulating a switching power supply device, which is characterized in that 11. An insulating method according to any one of claims 7, 8, 9, and 10, wherein the power of the high frequency is power of an audible frequency or higher. 12. An insulating method according to claim 7, 8, 9, or 10, wherein the high-frequency power is power of 50 kHz or more.