JPH04364327A - Power supply circuit - Google Patents

Abstract

PURPOSE:To ensure dielectric strength through a simple constitution wherein a current transformer is fed with primary current from an AC current supply circuit and a current/voltage converter is connected to the secondary of the current transformer. CONSTITUTION:Primary currents of current transformers(CTs) 5a, 5b are fed from an AC power supply circuit 4. Current/voltage converting circuits 6a, 6b for converting the secondary current into power supply voltage are connected to the secondary of the CTs in order to feed driving circuits 3a, 3b with regulated voltages. Since an insulating means comprises the CT, only several turns are required on the primary and thereby the inter-winding capacitance can be decreased remarkably. Consequently, resonance between isolated power supplies due to inter-winding parasitic capacitance or imbalanced voltage at the time of series connection of semiconductors can be eliminated.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an electric circuit device.
The present invention relates to a power supply circuit that simply and stably supplies isolated power from one potential point to a different potential point.

0002

2. Description of the Related Art In electric circuits, a voltage source is often supplied from a circuit placed at a certain potential point to a point at a different potential or a high potential point. Such a power supply method is often found particularly in power supply circuits for driving semiconductor elements, and an example thereof will be shown and explained below.

In circuits such as inverters, several series bodies of semiconductor elements such as transistors are connected in parallel as shown in FIG. Furthermore, in an electric circuit that switches high voltage, a large number of semiconductor elements are connected in series as shown in FIG. 9 in order to realize a high breakdown voltage.

FIG. 8 shows a DC power supply 17 and a transistor 2a.
~2d, a single-phase inverter circuit consisting of diodes 12a to 12d connected in antiparallel to the transistors, drive circuits 3a to 3d for driving the transistors, and a power supply circuit 18 for supplying power to the drive circuit. . Generally, AC voltage is generated at the output by turning on and off 2a and 2d, 2b and 2c at the same time, and turning on and off these two sets in an appropriate order.

FIG. 9 shows a series connection of five GTO thyristors, in which a DC high voltage power supply 17, a GTO thyristor 2
0a to 20e, drive circuits 3a to 3e that drive the GTO thyristors, and a power supply circuit 18 that supplies power to the drive circuits.
and a load 19. As mentioned above, since the thyristors are connected in series to achieve high voltage resistance, it is necessary for the series thyristors to operate as one switch, and of course, all the GTO thyristors 20a to 20e are repeatedly turned on and off at the same time.

The necessity of a power supply circuit for supplying an isolated power supply will be explained with reference to FIGS. 8 and 9.

In FIG. 8, at a certain point, transistor 2
Consider a transition from a state where transistors a and 2d are on and transistors 2b and 2c are off to a state where transistors 2a and 2d are off and transistors 2b and 2c are on. First, transistors 2a and 2
When d is on and 2b and 2c are off, point A shown in the figure is at the same potential as the power supply 17 voltage because transistor 2a is on, and point B is at the same potential as the power supply 17 voltage because transistor 2d is on. It is at zero potential. Next, the transistors 2a and 2d are turned off and the transistors 2b and 2c are turned on, but it takes some time for the semiconductor element to turn on and off, and when 2a and 2d are not completely turned off, the transistors 2b and 2c are turned on. When 2c is turned on, a short circuit occurs in the power supply 17, so a so-called dead time is provided in which all transistors are turned off. Therefore, the transistor 2a,
There is a dead time period when 2d is turned off, but since the load that is generally connected is often inductive, the power supply 17
, the current flowing in the direction of arrow C shown in FIG.
Even if d is turned off, the current continues to flow, so diodes 12b and 12c are turned on. Here, when the diode 12b is turned on, the point A is at zero potential, and when the diode 12c is turned on, the potential at the point B is changed to the voltage of the power supply 17, causing a potential fluctuation between the point A and the point B.

Similarly, when the transistors 2b and 2c are in the on state and the load current is being supplied in the direction opposite to the arrow C shown in FIG. 8 and the dead time is reached, a potential fluctuation occurs at point A and point B. become. Since the inverter circuit repeats the above-described operation, the points A and B go back and forth between zero potential and the power supply 17 voltage potential.

In this operation, the drive circuits 3a and 3c have the potential at point A and point B, respectively, so they must be insulated from the drive circuits 3b and 3d, which are always at zero potential. Of course, since the potentials between them are different from each other, it is necessary to insulate them. Therefore, the power supply circuit 18
Therefore, the power supplied to each drive circuit must also be insulated. However, the drive circuit 3b is always at zero potential.
, 3d power supplies are not limited to this.

In FIG. 9, the GTO thyristor 20a
20e is off, a voltage obtained by dividing the power supply voltage by the number of series connections is applied to each of the drive circuits 3a to 3e, and the potential of the drive circuits 3a to 3e gradually becomes higher in the order of those connected to the GTO thyristor close to the ground potential. The drive circuit 3a reaches approximately the power supply 17 voltage potential. Next, when the GTO thyristors are turned on all at once, no voltage is applied to all the GTO thyristors connected in series, and all the drive circuits are also at ground potential. Therefore, all of the power supplied from the power supply circuit 18 to the drive circuits 3a to 3e must be insulated, and an insulated power supply is supplied to a portion where the power potential fluctuates from approximately the power supply potential to the ground potential, such as the drive circuit 3a. In this case, the insulation must be extremely strong.

As described above, when constructing an electric circuit using a series body of semiconductor elements, GTO thyristors and electrostatic induction (
SI) When the gate drive power is large for a large capacitance element such as a thyristor, or when gate bias must be secured for a voltage-driven type such as a MOSFET or IGBT, it is necessary to provide a drive circuit for each element. It is common practice to provide an isolated power supply.

Conventionally, a circuit as shown in FIG. 10 has been known as an insulated power supply circuit for driving a semiconductor as described above.

FIG. 10 shows a circuit using an isolation transformer.
Generally, the commercial power source 24 is insulated by a transformer 21a, stepped down to a required voltage, and supplied to the drive circuit 3a via a suitable voltage regulator 22a. In addition, in the case of this circuit system, providing one isolation transformer for one element would be disadvantageous in terms of space, so the secondary side of the isolation transformer should have multiple windings, and each secondary winding should have a withstand voltage. Supplying isolated power is performed.

FIG. 11 shows another method. This is an example in which the isolation transformer 21b is miniaturized by using the DC-AC converter 23 and increasing its AC output frequency. isolation transformer 2
The secondary side voltage of 1b is stabilized by the operation of a switching element placed in the DC-AC converter, and the secondary side of the isolation transformer 21b often does not have a voltage regulator, and is not equipped with a commercial isolation transformer. 2 of the transformer 21b as in the case where
Miniaturization is often achieved by using multiple windings on the next side.

[0015]

[Problems to be Solved by the Invention] In recent years, in power converters such as inverters that have semiconductor elements inside and adjust the output waveform by turning on and off the semiconductor elements, semiconductor elements are used for fine control of output and noise reduction. The trend is to increase the on/off switch frequency of Against this background, the speed of semiconductor devices has also increased, and devices with turn-on and turn-off times of several μs or less have been developed and are now available for use. It has become.

However, when such a high-speed semiconductor element is used to construct an inverter circuit operating at a high frequency, the high-speed nature of the semiconductor element causes potential fluctuations in the drive circuit as explained in FIG. 8, and accompanying drive power supply. Potential fluctuations between the isolated power supplies that are connected occur in an extremely short period of time and with high frequency.

On the other hand, in the transformer used as the insulating means in FIGS. 10 and 11, stray capacitance occurs between the windings due to the structure of one winding, an insulator, and the other winding. In Figures 10 and 11, the stray capacitance between transformer windings is as shown in Figure 1 when an isolation transformer with one element is used.
As shown in Figure 2, there is a stray capacitance Cp between the primary and secondary windings of the transformer, and when the secondary side has multiple windings to drive multiple elements, the capacitance between the primary and secondary windings increases as shown in Figure 13. Cp and the capacitance Cs between the secondary windings exist. Therefore, in FIG. 12, by the series connection of Cp through the primary side of the transformer, and in FIG.
3, the series connection of Cp and the parallel connection of Cs as in FIG. 12 connect the secondary windings of each transformer, that is, the isolated power supplies.

However, in the operation of an inverter circuit using high-speed semiconductors, when extremely short-term potential fluctuations occur between isolated power supplies, the frequency components of the potential fluctuations become high, and as shown in FIGS. 12 and 13. The impedance of such capacitive coupling decreases, causing a phenomenon in which current flows between the isolated power supplies. Since the impedance of the capacitive component decreases as the capacitance increases and the frequency increases, this phenomenon naturally becomes more likely to occur as the potential fluctuation between the insulated power supplies becomes steeper. This current also flows into the drive circuit and affects the drive signal of the semiconductor element, and in the worst case, there is a risk that the semiconductor element may be destroyed due to malfunction.

[0019] Also, by connecting semiconductor elements in series, a voltage of several tens of kV can be achieved.
Even in circuits that switch high voltages, problems arise due to the influence of stray capacitance of isolation transformers. In the multi-series circuit of semiconductor devices shown in FIG. 9, when using the isolation transformer system shown in FIG. Generally, one isolation transformer is used for one element.

On the other hand, when the semiconductor element is off, it can be equivalently considered to be a capacitor due to its junction capacitance. Stray capacitance due to an isolation transformer is added to each of them. This situation is shown in FIG. (The primary side of the isolation transformer is shown as a ground potential which is sufficiently lower than the switch voltage.) In FIG. 14, C1 to C5 are semiconductor junction capacitance components, and Cz is a stray capacitance component of the isolation transformer. When the capacitance components of such connections are combined, the junction capacitance component of the series semiconductor elements is small on the high side and large on the low side. Therefore, there is a tendency that the shared voltage of the semiconductor element on the higher side is large and becomes smaller on the lower side, and this becomes more noticeable as the stray capacitance Cz with respect to ground becomes larger. As described above, due to the influence of the stray capacitance caused by the isolation transformer, the shared voltages of multiple semiconductor devices connected in series when they are off become unbalanced, and in the worst case, there is a possibility that the semiconductor devices may be destroyed due to overvoltage.

Furthermore, in the circuit shown in FIG. 9, when supplying an isolated power source for driving each element, the withstand voltage between the primary and secondary windings needs to be much higher than the switch voltage because the potential fluctuations are rapid. Therefore, especially when performing high-voltage switching with high repetitions, insulation deterioration due to corona discharge may occur, leading to dielectric breakdown. Therefore, the insulation transformer for this purpose needs to be sufficiently insulated in order to strengthen the withstand voltage between the windings.

However, in the circuit system shown in FIG. 9, an ordinary isolation transformer has a structure in which the primary and secondary windings are wound through an insulator, and the number of winding turns is large. Since a thin film or the like having a relatively low dielectric strength is used, a sufficient insulation distance cannot be secured, and reliability is greatly reduced, especially when a high withstand voltage is intended.

[0023]The above-mentioned structure for ensuring dielectric strength is complicated, and the external size is often large even if the capacity is small.Furthermore, the bushings for leading out the electrodes are determined by the dielectric strength. The problem arises that the transformer becomes large regardless of the transformer capacity, and as a result, the outer shape of the transformer becomes large. In this case, even if a high-frequency transformer is used, it is still necessary to strengthen the insulation of the windings in order to have sufficient dielectric strength, and the miniaturization of the isolation transformer, including the problems such as the bushing mentioned above, is necessary. It is difficult to plan.

Therefore, if the voltage is high and the number of series connections is large, the external shape of the isolation transformer will be correspondingly large, and as mentioned above, one isolation transformer must be used for each element, so the number of isolation transformers will also increase. This is a problem that leads to larger sizes.

The present invention has been made in order to improve the drawbacks of the conventional isolated power supply circuit, and it is possible to simply maintain the dielectric strength, reduce the influence of stray capacitance, and downsize the device. The purpose is to establish a stable power source.

[0026]

[Means for Solving the Problems] In the power supply circuit according to the present invention, one of the current transformers is controlled by the alternating current supply circuit.
It is carried out to supply a secondary current and to connect a current-voltage converter to the secondary side of the current transformer.

[0027]

[Operation] In a power supply circuit in which an alternating current supply circuit supplies the primary current of a current transformer and a current-voltage converter is connected to the secondary side of the current transformer, the insulation transformer is the main cause of insulation due to stray capacitance. It is possible to suppress mutual coupling between power sources and maintain sufficient dielectric strength with a simple structure. This makes it possible to secure a stable isolated power supply. Furthermore, since the insulation structure can be simplified, the insulation portion can be made smaller, and the circuit device can thereby be made smaller.

[0028]

[Embodiments] Examples of the present invention will be explained below with reference to the drawings. FIG. 1 shows a circuit configuration of a semiconductor drive power supply circuit equipped with a power supply circuit according to the present invention. Regarding the semiconductor elements 2a and 2b connected in series, the drive circuits 3a and 3b for the semiconductor elements, and the power supply circuit 1 that supplies isolated power to the drive circuit, an alternating current supply circuit 4, the alternating current supply circuit 4
The current transformer (hereinafter referred to as CT) 5a, 5b is inserted in series with the output of the CT, and current-voltage converters 6a, 6b are connected to the secondary side of the CT.

The operation of the semiconductor drive power supply circuit equipped with the power supply circuit according to the present invention will be explained. The alternating current outputted by the alternating current supply circuit 4 is supplied as a primary current to the CTs 5a and 5b. As a result, a current determined by the current transformation ratio flows through the secondary side of the CT. A current-voltage conversion circuit 6 that converts the CT secondary current into a voltage source is provided on the secondary side of the CT.
A, 6b are connected and adjusted to the required voltage, and the drive circuit 3a,
3b.

The alternating current supply circuit 4 shown in FIG. 1, as shown in FIG. 2, uses a method of converting into current by connecting an impedance element such as a reactor 7a in series with an alternating current power source 24, as shown in FIG. In FIG. 2, when the current fluctuation due to load fluctuation is large, a capacitor 8a and a reactor 7b are connected in parallel to the output of the AC voltage source 9 as shown in FIG. There is a method of making the current of the reactor 8a approximately constant by matching the frequency of the source and supplying it as the primary current of the CT 5a.

In order to supply even more accurate current to the CT primary side, as shown in FIG. A conceivable circuit is an inverter circuit 11 made up of semiconductor elements 2a to 2d connected to each other, and a feedback diode 12e connected between the DC power supply 17 and the output of the chopper circuit 10.

In FIG. 4, the chopper circuit 10 connects the DC power supply 17 and the reactor 7 by turning on the semiconductor switch 2e.
Series circuit of c, diode 12f when semiconductor element 2e is off
A reflux circuit is formed with the reactor 7c and the reactor 7c, and current is supplied to the inverter circuit 11. At this time, the reactor 7c current increases when the semiconductor element 2e is turned on and decreases when the semiconductor element 2e is turned off. However, by repeating the on-off operation of the semiconductor element 2e finely compared to the degree of increase and decrease, the reactor current 7c, that is, the chopper circuit 1
An output current of 0 can be made constant.

The current made constant by the chopper circuit 10 is converted into an alternating current and output by alternately turning on and off the sets of semiconductor switches 2a and 2d and the sets of semiconductor switches 2b and 2c of the inverter circuit 11. Note that the feedback diode 12e closes the chopper circuit 1 when the chopper circuit 10 output becomes open due to abnormal operation of the inverter circuit 11.
This is connected to regenerate the energy of the reactor 7c of 0 to the DC power supply 17.

As described above, in the alternating current supply circuit shown in FIG.
This can be easily obtained by increasing the on/off operation repetition frequency.

The current-voltage conversion circuits 6a and 6b shown in FIG. 1 for converting the current into a voltage source are briefly shown in FIG.
As shown in the figure, a rectifier 1 rectifies the alternating current on the secondary side of the CT.
3. An impedance element 14 such as a resistor may be connected in series with the output of the rectifier 13, and a smoothing capacitor 8b connected in parallel with the impedance element 14. In FIG. 5, when the voltage fluctuation due to load fluctuation is large, a Zener diode 15 is inserted in parallel with the impedance element 14 as shown by the dotted line.

If higher voltage accuracy and higher efficiency are required, a configuration as shown in FIG. 6 may be considered. Figure 6 is a CT
A rectifier 13 that rectifies the alternating current on the secondary side, a semiconductor switch 2f connected in series to the output end of the rectifier 13, a series body of a diode 12g and a capacitor 8c connected in parallel with the semiconductor switch 2f, and both ends of the capacitor 8c as an output. It is to take out. The operation of the circuit shown in FIG. 6 is such that the semiconductor element 2f is first turned off, and the capacitor 8c is charged with the direct current obtained by the rectifier 13 via the diode 12g. When the voltage of the capacitor 8c reaches a predetermined voltage or higher, the semiconductor switch 2f is turned on to short-circuit the DC current obtained by the rectifier 13. At this time diode 12
g becomes a reverse bias state due to the voltage of the capacitor 8c and blocks the voltage of the capacitor 8c. When the semiconductor switch 2f is turned on, the DC current is short-circuited, and the capacitor 8c
charge energy is supplied to the load, and capacitor 8
When the c voltage becomes less than a predetermined voltage, the semiconductor switch is turned off again and DC current is supplied to the capacitor 8c to charge it. Then, in order to set the voltage of the capacitor 8c to a predetermined value, the semiconductor switch 2f repeats the above-described on/off operation. Therefore, by increasing the repetition frequency of the on/off operation of the semiconductor switch 2f, fine output voltage control is possible and voltage accuracy can be increased. Furthermore, since there are no loss elements such as resistance, high efficiency can be achieved.

The power supply circuit according to the present invention is constructed using the circuit elements as described above, and the effects of the semiconductor drive power supply circuit shown in FIG. 1 equipped with the circuit elements will be explained.

As mentioned above, it is said that the inter-winding capacitance of a transformer is mainly caused by the plurality of windings and the insulation between them. In other words, it is caused by the structure of one winding, an insulator, and the other winding, and generally increases in distributed capacitance as the number of turns in the winding increases. Therefore, when a conventional isolation transformer having a structure in which a large number of windings are wound on both the primary and secondary sides is used, the capacitance between the windings becomes large, and the problems described above cannot be avoided.

On the other hand, according to the present invention, the insulation means utilized is C
By using CT, the number of primary turns can be reduced to just a few turns, and in this case, one winding, an insulator,
Since the above-described structure of the other winding consists of only a number of sets of primary turns, it is possible to significantly reduce the capacitance between the windings (between the primary conductor and the secondary winding). Furthermore, by using a primary feed-through CT, the number of primary turns becomes only one, and it is clear that the capacitance between the primary conductor and the secondary winding can be further reduced. Therefore, in the semiconductor drive power supply circuit shown in FIG. 1 equipped with the power supply circuit according to the present invention, resonance phenomena between isolated power supplies due to stray capacitance between windings as described above, voltage imbalance phenomenon when multiple semiconductors are connected in series, etc. This can greatly improve the problem.

[0040] Regarding the dielectric strength voltage between the primary and secondary CT, if the required dielectric strength voltage is relatively low (about 2 to 3 kV), a dielectric strength of about several kV can be secured by the insulation structure of the CT main body mold, etc. Therefore, the CT primary conductor can be directly
It is sufficient to wrap it around the main body, but it can be made stronger by using an insulated wire as the primary conductor. Additionally, if higher dielectric strength is required between the CT primary and secondary conductors, this can be easily achieved by strengthening the sheathing of the insulated wire used as the CT primary conductor, and ultimately CT
It is possible to use a method in which an insulator pipe or the like with a CT primary conductor passed through the center hole is passed through the CT through hole.

As described above, according to the present invention using CT as an insulating means, the structure of the insulating part is simplified, and when a particularly high withstand voltage between transformer windings is required, thick insulating material as described above can be used. It is simple and highly reliable because the insulation distance can be easily secured.

Furthermore, as mentioned above, in a normal isolation transformer, increasing the frequency of the primary voltage does not have much effect on reducing the size of the transformer, but in this system, the insulation method is simple as described above, so CT can be made smaller by increasing the frequency of the primary current or by winding the primary side several turns.
This directly leads to the miniaturization of the external size and the miniaturization of the insulating part, and this can be easily achieved.

A high-voltage switch circuit using an electrostatic induction thyristor, which is equipped with such a semiconductor drive power supply circuit, is shown in FIG. 7, and the effects of the present invention will be explained.

In FIG. 7, a power supply circuit 1 according to the present invention
The drive circuits 3a to 3j supplied with drive power from the power supply circuit 1 have the same configuration as in FIG. Up to 12k in series configuration
Switch V. Further, the alternating current supply circuit 4 in FIG. 7 has the configuration shown in FIG. 4, and the current-voltage conversion circuits 6a to 6j have the configuration shown in FIG. 6.

First, when the semiconductor drive power supply circuit is constructed using a commercial frequency isolation transformer as shown in FIG. , a shared voltage difference of more than double occurred between the element with the maximum applied voltage and the element with the minimum applied voltage. Therefore, a capacitor with a different value was inserted in parallel with the electrostatic induction thyristor to correct the ground capacitance, one element at a time. In addition, the electrostatic induction thyristor has a fast switching speed, and the voltage of 12kV drops in 500ns, and this operation is repeated at 5kHz, so the primary and secondary of the isolation transformer that supplies power to the highest drive circuit The windings are exposed to approximately this voltage variation. For this reason, the outer shape of the transformer was large despite its capacity of 100VA, and the wiring to the voltage regulator had to be commensurate with this, making it complicated, and as a result, the entire device became large.

On the other hand, as shown in FIG. 7, when the power supply circuit according to the present invention was applied to a semiconductor drive power supply circuit using a primary feed-through type CT, the maximum element It was confirmed that the difference between the applied voltage and the minimum element applied voltage was about 1.2 times, and that a rated switch operation of 12 kV was possible without adding an adjustment capacitor. Also, insert a Teflon pipe with a wall thickness of about 10 mm through the CT body, and insert the C into the Teflon pipe hole.
Although it was insulated by passing the T primary conductor through it, corona discharge did not occur even in the CT connected to the highest element, which is subject to potential fluctuations as described above, and sufficient insulation strength was maintained even during long-term operation. I also understood that. In particular, the effect of miniaturizing the insulating portion using CT has made it possible to simplify the device configuration and downsize the device as a whole.

Above, a power supply circuit for driving a semiconductor has been shown and explained as an application of the power supply circuit according to the present invention, but regardless of this example, the power supply circuit according to the present invention is suitable for high potential points due to the simplicity of its insulation structure. It goes without saying that it can be widely applied, such as when supplying a voltage source or when there is a requirement to reduce stray capacitance in a power source such as an isolated amplifier.

[0048]

[Effects of the Invention] As described above, according to the present invention, stray capacitance can be significantly reduced compared to the conventional isolation transformer system, and C
Since insulation from the high voltage section is facilitated by using T, it is possible to simplify the circuit configuration and downsize the circuit device. When the power supply circuit according to the present invention is applied to a semiconductor drive power supply circuit, it is possible to prevent illegal oscillation between isolated power supplies due to stray capacitance, which was unavoidable with conventional systems, and to apply it to a circuit in which a large number of semiconductors are connected in series. can greatly improve the unbalance of shared voltage caused by stray capacitance with ground.

[Brief explanation of drawings]

FIG. 1 is an electrical circuit diagram of a semiconductor drive power supply circuit according to the present invention.

FIG. 2 is a diagram showing a circuit example of an alternating current supply device used in a semiconductor drive power supply circuit according to the present invention.

FIG. 3 is a diagram showing a circuit example of an alternating current supply device used in a semiconductor drive power supply circuit according to the present invention.

FIG. 4 is a diagram showing a circuit example of an alternating current supply device used in a semiconductor drive power supply circuit according to the present invention.

FIG. 5 is a diagram of a circuit example of a current-voltage conversion circuit used in a semiconductor drive power supply circuit according to the present invention.

FIG. 6 is a diagram of a circuit example of a current-voltage conversion circuit used in a semiconductor drive power supply circuit according to the present invention.

FIG. 7 is a diagram of an example of a high voltage switch circuit using the semiconductor drive power supply circuit according to the present invention.

FIG. 8 is a circuit diagram for explaining potential fluctuations.

FIG. 9 is a diagram of an example of a circuit configured with multiple semiconductors connected in series.

FIG. 10 is a diagram of an example of an electric circuit of a conventional semiconductor drive power supply circuit.

FIG. 11 is a diagram of an example of an electric circuit of a conventional semiconductor drive power supply circuit.

FIG. 12 is an explanatory diagram of the winding capacity of the transformer.

FIG. 13 is an explanatory diagram of the winding capacity of the transformer.

FIG. 14 is an equivalent circuit diagram when multiple semiconductor elements are connected in series.

[Explanation of symbols]

1 Semiconductor drive power supply circuits 2a to 2f Semiconductor elements 3a to 3j Drive circuit 4 AC power supply circuits 5a to 5j Current transformers 6a to 6j Current voltage conversion circuits 7a to 7c Reactors 8a to 8c Capacitor 9 AC voltage source 10 Chopper circuit 11 Single Phase inverter circuit 12a-12f Diode 13 Rectifier circuit 14 Impedance element 15 Zener diode 16a-16j Electrostatic induction thyristor 17 DC power supply 18 Power supply circuit 19 Load 20a-20j GTO thyristor 21 Isolation transformer 22a, 22b Voltage regulator 23 DC-AC converter 24 Commercial frequency AC power supply C1 to C2 Junction capacitance Cz, Cp, Cs Stray capacitance

Claims (1)

[Claims] 1. An alternating current supply circuit that outputs a substantially constant current, an insulating current transformer connected to the output of the alternating current supply circuit, and the current transformer connected to the secondary side of the current transformer. A power supply circuit comprising a current-voltage converter that converts a secondary current into a voltage source.