JP2878870B2 - Power circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an electric circuit device,
The present invention relates to a power supply circuit that simply and stably supplies insulated power from a certain potential point to a different potential point.

[0002]

2. Description of the Related Art In an electric circuit, a voltage source is frequently supplied from a circuit placed at a certain potential point to a point having a different potential or a high potential point. Since such a power supply method is particularly often used in a power supply circuit for driving a semiconductor element, an example thereof will be described below.

In a circuit such as an inverter, as shown in FIG. 8, several serial elements of semiconductor elements such as transistors are connected in parallel. In an electric circuit for switching a high voltage, a large number of semiconductor elements are connected in series as shown in FIG. 9 in order to realize a high withstand voltage.

FIG. 8 shows a DC power supply 17 and a transistor 2a.
To 2d, diodes 12a to 12d connected in anti-parallel to the transistor, drive circuits 3a to 3d for driving the transistor, and a power supply circuit 18 for supplying power to the drive circuit. . Generally, an AC voltage is generated at the output by turning on and off 2a and 2d and 2b and 2c at the same time, and turning on and off the 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 and a GTO thyristor 2 are connected.
0a to 20e, drive circuits 3a to 3e for driving the GTO thyristor, and a power supply circuit 18 for supplying power to the drive circuits
And load 19. As described above, the series connection of the thyristors is required to operate as one switch because the series connection is performed to increase the withstand voltage. Needless to say, all the GTO thyristors 20a to 20e repeatedly turn on and off at the same time.

The need for a power supply circuit for supplying insulated power will be described with reference to FIGS. 8 and 9.

[0007] In FIG.
It is assumed that transistors 2a and 2d are turned off and 2b and 2c are turned on from the state where a and 2d are on and the state where 2b and 2c are off. First, transistors 2a and 2a
When d is on and 2b and 2c are off, the point A shown in the figure is at the same potential as the voltage of the power supply 17 because the transistor 2a is on, and the point B is because the 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. However, it takes a little time for the semiconductor element to perform an on / off operation, and when the semiconductor elements 2a and 2d are not completely turned off, 2b, When 2c is turned on, the power supply 17 is short-circuited, so that a so-called dead time for turning off all transistors is provided. Therefore, the transistor 2a,
The dead time period occurs when 2d is turned off. However, since the connected load is often inductive, the power supply 1
7. The current supplied by the transistors 2a and 2d and flowing in the direction of arrow C shown in FIG.
Even if 2d is turned off, the diodes 12b and 12c are turned on in order to continuously flow. Here, when the diode 12b turns on, the point A changes to the zero potential, and the point B changes to the potential of the power supply 17 voltage when the diode 12c turns on, and the potential fluctuation at the point A and the point B occurs.

Similarly, when the transistors 2b and 2c are turned on and a load current is supplied in the direction opposite to the arrow C shown in FIG. become. Since the inverter circuit repeats the above-described operation, the point A and the point B alternate between the zero potential and the voltage potential of the power supply 17.

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

FIG. 9 shows a GTO thyristor 20a.
When 20e is off, a voltage obtained by dividing the power supply voltage by the number of series is applied to each of them, and the driving circuits 3a to 3e gradually become higher in potential in the order of those connected to the GTO thyristor near ground potential, The drive circuit 3a substantially reaches the power supply 17 voltage potential. Next, when the GTO thyristors are turned on all at once, the voltage is not applied to all the GTO thyristors connected in series, and all the driving circuits are also set to the ground potential. Therefore, all the power supplied from the power supply circuit 18 to the drive circuits 3a to 3e needs to be insulated. If so, the insulation must be very strong.

As described above, when an electric circuit is formed by using a series body of semiconductor elements, the gate drive power is increased by a large-capacity element such as a GTO thyristor or an electrostatic induction (SI) thyristor. In the case where the gate bias must be ensured in the voltage drive type as described above, it is common practice to provide a drive circuit for each element and supply an insulating power supply for driving.

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

FIG. 10 shows a circuit using an insulating transformer.
Generally, the commercial power supply 24 is insulated by a transformer 21a, stepped down to a required voltage, and supplied to the drive circuit 3a via an appropriate voltage regulator 22a. In addition, in the case of this circuit system, providing one insulating transformer for one element is disadvantageous in terms of space. Therefore, the secondary side of the insulating transformer is provided with multiple windings, and withstand voltage is provided between the secondary windings. Supplying insulated power is performed.

FIG. 11 shows another method. This is an example in which the DC-AC converter 23 is used to increase the AC output frequency to reduce the size of the insulating transformer 21b. Insulation transformer 2
The secondary side voltage of 1b is stabilized by the operation of the switch element placed in the DC-AC converter, and the secondary side of the insulating transformer 21b often does not have a voltage regulator. As in the case of using
In many cases, the secondary side has multiple windings to reduce the size.

[0015]

In recent years, power converters such as inverters having a semiconductor element inside and adjusting the output waveform by turning on and off the semiconductor element have been used for the purpose of fine control of output and noise reduction. Tend to increase the on / off switch frequency. Against this background, the speed of semiconductor devices has also been increasing, and the time required for transition from the on-state to the off-state or from the off-state to the on-state, that is, turn-on time and turn-off time of several μs or less, has been developed and utilized. It has become

However, when an inverter circuit operating at a high frequency is constructed using such a high-speed semiconductor element, since the semiconductor element is high-speed, the potential fluctuation of the drive circuit described with reference to FIG. The potential fluctuation between the insulated power sources occurs in a very short time and with high repetition.

On the other hand, in the transformer used as the insulating means in FIGS. 10 and 11, a stray capacitance is generated between the windings due to the structure of one winding, an insulator, and the other winding. In FIG. 10 and FIG. 11, the stray capacitance between the transformer windings has a stray capacitance Cp between the primary and secondary of the transformer as shown in FIG. When a plurality of elements are driven by using windings, a primary-secondary inter-winding capacitance Cp and a secondary inter-winding capacitance Cs exist as shown in FIG. Therefore, in FIG. 12, by connecting Cp in series through the primary side of the transformer, and in FIG. 13 by connecting Cp in series and in parallel with Cs as in FIG. The connection will be made.

However, in the inverter circuit operation using a high-speed semiconductor, when a very short-time potential change occurs between the insulated power supplies, the frequency component of the potential change becomes high, and this is shown in FIGS. The impedance of such capacitive coupling decreases, and a phenomenon occurs in which a current flows between the insulated power supplies. Since the impedance of the capacitance component decreases as the capacitance increases and the frequency increases, the phenomenon becomes more likely to occur as the potential fluctuation between the insulated power sources 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.

Further, several tens of kV
In such a circuit for switching a high voltage, a problem arises due to the influence of the stray capacitance of the insulating transformer. In the multi-series circuit of the semiconductor elements shown in FIG. 9, when the drive power supply circuit employs a method using an insulating transformer as shown in FIG. In general, one insulating transformer is used for one element.

On the other hand, when the semiconductor element is off, it is considered equivalent to a capacitor due to its junction capacitance. Then, a stray capacitance due to an insulating transformer is added to each of them. This is shown in FIG. (The primary side of the insulating transformer is sufficiently lower than the switch voltage and is shown as the ground potential.) In FIG. 14, C1 to C5 are the junction capacitance components of the semiconductor, and Cz is the floating capacitance component of the insulation transformer. When the capacitance components of such connections are combined, the junction capacitance component of the series semiconductor element is small on the high side and large on the low side. Therefore, the shared voltage of the high-order semiconductor element tends to be high, and tends to decrease at the low-order side. This becomes more remarkable as the stray capacitance Cz to the ground increases. As described above, the shared voltage when the semiconductor elements are turned off in multiple series is unbalanced due to the influence of the stray capacitance caused by the insulating transformer, and in the worst case, there is a possibility that the semiconductor elements may be destroyed due to the overvoltage.

In the circuit shown in FIG. 9, when an insulated power for driving is supplied to each element, the withstand voltage between the primary and secondary windings needs to be much larger than the switch voltage due to a sudden change in potential. In particular, when a high voltage switch is performed at a high repetition rate, there is a possibility that insulation deterioration due to corona discharge occurs, which leads to insulation breakdown. Therefore, it is necessary for the insulation transformer for this application to perform sufficient insulation treatment in order to strengthen the withstand voltage between the windings.

However, in the circuit system shown in FIG. 9, an ordinary insulating transformer generally has a structure in which a primary and secondary winding is wound via an insulator and has a large number of winding turns. Since a thin film or the like having a relatively low dielectric strength is used, a sufficient insulation distance cannot be ensured. In particular, when a high breakdown voltage is to be achieved, the reliability is greatly reduced.

The above-described structure for securing the dielectric strength is complicated, and the outer shape is often increased even with a small capacity. Further, the bushing for leading the electrode is determined by the dielectric strength. Regardless of the transformer capacity, the transformer becomes large, and as a result, there arises a problem that the transformer outer shape becomes large. In this case, even if a high-frequency transformer is used, it is the same that the insulation of the windings must be strengthened in order to have the insulation withstand capability. It is difficult to plan.

Therefore, if the voltage becomes high and the number of series is large, the outer shape of the insulating transformer is correspondingly larger. Also, as described above, the insulating transformer has to be used one by one for each element, so that the number increases, and the number of devices increases. This is a problem that leads to an increase in size.

The present invention has been made in order to improve the above-mentioned drawbacks of the conventional insulated power supply circuit, and to simply maintain the dielectric strength, reduce the effect of stray capacitance, and reduce the size of the device. The purpose is to establish a stable power supply.

[0026]

In a power supply circuit according to the present invention, an AC current supply circuit uses one of current transformers.
A second current is supplied and a current-to-voltage converter is connected to the secondary side of the current transformer.

[0027]

In a power supply circuit in which a primary current of a current transformer is supplied by an AC current supply circuit and a current-voltage converter is connected to a secondary side of the current transformer, insulation by a stray capacitance which is a main factor of the insulation transformer is provided. It is possible to suppress the mutual coupling phenomenon between the power sources, and to sufficiently maintain the dielectric strength with a simple structure. This makes it possible to secure a stable insulated power supply. In addition, since the insulating structure can be simplified, the size of the insulating portion can be reduced, and the size of the circuit device can be reduced.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration of a semiconductor drive power supply circuit including a power supply circuit according to the present invention. For the semiconductor elements 2a and 2b connected in series, the driving circuits 3a and 3b for the semiconductor elements, and the power supply circuit 1 for supplying an insulating power to the driving circuit, an AC current supply circuit 4 and an AC current supply circuit 4
And a current transformer (hereinafter, referred to as CT) 5a, 5b inserted in series with the output of the first and second, and current-to-voltage converters 6a, 6b connected to the secondary side of the CT.

The operation of the semiconductor drive power supply circuit having the power supply circuit according to the present invention will be described. The AC current output from the AC current supply circuit 4 is supplied as the primary current of the CTs 5a and 5b. As a result, a current determined by the current transformation ratio flows on the secondary side of the CT. Current-voltage conversion circuits 6a and 6b for converting a CT secondary current into a voltage source are connected to the secondary side of the CT to adjust the voltage to a required voltage.
a, 3b.

The AC current supply circuit 4 shown in FIG. 1 simply converts the current into a current by connecting an impedance element such as a reactor 7a in series with an AC power supply 24, as shown in FIG. In FIG. 2, when the current fluctuation due to the load fluctuation is large, the capacitor 8a and the reactor 7b are connected in parallel to the output of the AC voltage source 9 as shown in FIG. 3, and the parallel resonance frequency by the capacitor 8a and the reactor 7b is changed to the AC voltage. There is a method of making the current of the reactor 8a substantially constant by adjusting the frequency of the source, and supplying the current as the primary current of the CT 5a.

In order to supply a more accurate current to the primary side of the CT, as shown in FIG. 4, a chopper circuit 10 including a DC power supply 17, a semiconductor switch 2e, a diode 12f and a reactor 7c, and an output of the chopper circuit 10 And a circuit comprising a feedback diode 12e connected between the DC power supply 17 of the chopper circuit 10 and the output.

In FIG. 4, the chopper circuit 10 turns on the DC power supply 17 and the reactor 7 by turning on the semiconductor switch 2e.
series circuit c, diode 12f with semiconductor element 2e off
A current is supplied to the inverter circuit 11 by forming a return circuit of the inverter 7 and the reactor 7c. At this time, the current of the reactor 7c increases when the semiconductor element 2e is turned on and decreases when the semiconductor element 2e is turned off. However, the on / off operation of the semiconductor element 2e is finely repeated as compared with the increase / decrease, so that the reactor current 7c, that is, the chopper circuit 1
The output current of 0 can be made constant.

The current converted into a constant current by the chopper circuit 10 is converted into an AC current by alternately turning on and off a set of semiconductor switches 2a and 2d and a set of 2b and 2c of the inverter circuit 11, and is output. When the output of the chopper circuit 10 is opened due to abnormal operation of the inverter circuit 11 or the like, the feedback diode 12e
It is connected to regenerate the energy of the zero reactor 7c to the DC power supply 17.

As described above, in the AC current supply circuit shown in FIG. 4, the output current is a substantially constant rectangular wave AC, and the accuracy of the output current is the same as that of the semiconductor element 2 of the chopper circuit 10.
e can be easily obtained by increasing the on / off operation repetition frequency.

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

When further high voltage accuracy and high efficiency are required, the configuration shown in FIG. 6 can be considered. FIG. 6 shows CT
A rectifier 13 for rectifying the secondary-side AC current, a semiconductor switch 2f connected in parallel to an output terminal of the rectifier 13, a series body of a diode 12g and a capacitor 8c connected in parallel with the semiconductor switch 2f, and a capacitor 8c as an output. It takes out both ends. In the operation of the circuit shown in FIG. 6, first, the semiconductor element 2f is turned off, and the DC current obtained by the rectifier 13 charges the capacitor 8c via the diode 12g. When the voltage of the capacitor 8c becomes higher than a predetermined voltage, the semiconductor switch 2f is turned on and the rectifier 13
Short-circuit the DC current obtained by the above. At this time, diode 1
2g is in a reverse bias state by the voltage of the capacitor 8c and blocks the voltage of the capacitor 8c. The DC current is short-circuited by turning on the semiconductor switch 2f, and the capacitor 8
When the charge energy of c is supplied to the load and the voltage of the capacitor 8c becomes equal to or lower than a predetermined voltage, the semiconductor switch is turned off again and a direct current is supplied to the capacitor 8c to be charged.
Then, in order to set the voltage of the capacitor 8c to a predetermined value, the semiconductor switch 2f repeats the above on / off operation.
Therefore, by increasing the on / off operation repetition frequency of the semiconductor switch 2f, fine output voltage control can be performed, and voltage accuracy can be increased. Also, since there is no loss element such as resistance, high efficiency can be realized.

The power supply circuit according to the present invention is constructed using the above circuit elements, and the effect of the semiconductor drive power supply circuit shown in FIG. 1 having the circuit element will be described.

As described above, it is said that the inter-winding capacitance of a transformer is mainly generated by a plurality of windings and insulation therebetween. That is, it is caused by a structure such as one winding, an insulator, and the other winding, and generally increases in distribution capacity as the number of turns of the winding increases. Therefore, when a normal insulating transformer having a structure in which a large number of windings are wound on both the primary side and the secondary side as in the related art is used, the capacity between the windings increases, and the above-described problem cannot be avoided.

On the other hand, according to the present invention, the insulating means used is C
T, and the number of primary turns can be reduced to only a few turns by using CT, in which case one winding, an insulator,
Since the above-mentioned structure of the other winding has only a few sets of primary turns, the capacity between the windings (between the primary conductor and the secondary winding) can be significantly reduced. It is obvious that the use of the primary penetration type CT reduces the number of primary turns to only one, and further reduces the capacitance between the primary conductor and the secondary winding. Therefore, in the semiconductor drive power supply circuit shown in FIG. 1 including the power supply circuit according to the present invention, the resonance phenomenon between the insulated power supplies due to the stray capacitance between the windings as described above, the voltage imbalance phenomenon at the time of semiconductor multi-series, etc. Can be greatly improved.

As for the withstand voltage between the first and second CTs, when the required withstand voltage is relatively low (about 2 to 3 kV), the insulation withstand voltage of about several kV can be secured by the insulating structure such as the CT body mold. Therefore, the CT primary conductor is directly connected to C
Although it is sufficient to wind it around the T body, it can be made stronger by using an insulated wire for the primary conductor. Further, when further insulation withstand voltage between the CT primary and the secondary is required, it can be easily realized by strengthening the coating of the insulated wire used as the CT primary conductor as necessary, and ultimately the primary penetration type is used. C
By using T, a method of passing an insulator pipe or the like having a CT primary conductor through a center hole through a CT through hole can be used.

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

Furthermore, although it has been described above that increasing the primary voltage to a high frequency in a normal insulating transformer is not very effective in terms of miniaturization of the transformer, the method of insulation is simple in this method as described above. It is necessary to reduce the size of the CT core by increasing the frequency of the primary current or winding the primary side several turns.
This directly leads to a reduction in the size of the outer shape and, consequently, a reduction in the size of the insulating portion, which can be easily realized.

FIG. 7 shows a high-voltage switch circuit using an electrostatic induction thyristor provided with such a semiconductor drive power supply circuit, and the effects of the present invention will be described.

FIG. 7 shows 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 that of FIG. 1, and the semiconductor elements driven by the drive circuits 3a to 3j are 10 in electrostatic induction thyristors 16a to 16j. Up to 12k as a series configuration
Switch V. 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.

First, when the semiconductor drive power supply circuit employs a system using an insulation transformer having a commercial frequency as shown in FIG. 10, the voltage balance when the electrostatic induction thyristor is turned off is lost due to the stray capacitance of the insulation transformer as described above. In addition, the shared voltage difference between the maximum applied voltage element and the minimum applied voltage element was twice or more. For this reason, a capacitor for correcting the ground capacitance has been inserted in a different value for each element in parallel with the electrostatic induction thyristor. In addition, the switching speed of the electrostatic induction thyristor is high, and the voltage of 12 kV drops during 500 ns, and this operation is repeated at 5 kHz. Therefore, the primary and secondary insulation transformers that supply power to the highest-order drive circuit are used. The windings are substantially exposed to this voltage fluctuation. For this reason, the outer shape of the transformer was large despite the capacity of 100 VA, and the wiring up to the voltage regulator was commensurate with the wiring.

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 penetration type CT, the maximum element was removed with the capacitor for correcting the ground capacitance removed. The difference between the applied voltage and the minimum element applied voltage was about 1.2 times, and it was confirmed that a 12 kV rated switch operation was possible without adding an adjusting capacitor. A Teflon pipe with a thickness of about 10 mm is inserted through the CT body, and a Ceflon pipe hole is inserted into the Teflon pipe hole.
Although insulation was performed by passing the T primary conductor, no corona discharge or the like occurs even in the CT connected to the highest-order element having the above-described potential fluctuation, and a sufficient insulation resistance is maintained even during long-time operation. I understood that. In particular, due to the effect of miniaturization of the insulating portion using CT, the configuration of the device has been simplified, and the overall size can be reduced.

As described above, the power supply circuit for driving a semiconductor has been shown and described as an application of the power supply circuit according to the present invention. Regardless of this example, the power supply circuit according to the present invention has a high potential point due to the simplicity of the insulating structure. Naturally, it can be widely applied, for example, when supplying a voltage source or when there is a request to reduce stray capacitance with a power supply such as an insulating amplifier.

[0048]

As described above, according to the present invention, the stray capacitance can be greatly reduced as compared with the conventional insulating transformer system, and
The use of T facilitates insulation from the high voltage section, so that the circuit configuration can be simplified and the circuit device can be downsized. When the power supply circuit according to the present invention is applied to a semiconductor drive power supply circuit, illegal oscillation between isolated power supplies due to stray capacitance, which was inevitable in conventional methods, is prevented. Can greatly improve the imbalance of the shared voltage generated by the stray capacitance with the ground.

[Brief description of the drawings]

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

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

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

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

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

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

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

FIG. 14 is an equivalent circuit diagram in the case of multiple series semiconductor devices.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor drive power supply circuit 2a-2f Semiconductor element 3a-3j Drive circuit 4 AC power supply circuit 5a-5j Current transformer 6a-6j Current voltage conversion circuit 7a-7c Reactor 8a-8c Capacitor 9 AC voltage source 10 Chopper circuit 11 Single Phase inverter circuit 12a to 12f Diode 13 Rectifier circuit 14 Impedance element 15 Zener diode 16a to 16j Static induction thyristor 17 DC power supply 18 Power supply circuit 19 Load 20a to 20j GTO thyristor 21 Insulation 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)

(57) [Claims] 1. A power supply circuit for supplying a driving power supply to a plurality of power semiconductor elements connected in series, an AC current supply circuit for outputting a substantially constant current, and an AC current supply circuit connected to an output of the AC current supply circuit. A plurality of insulating current transformers provided in each of the plurality of power semiconductor elements connected in series, a rectifier on the secondary side of each of the current transformers, a switch element connected in parallel to an output of the rectifier, and a current-voltage converter Circuit, controlling the output voltage of the current-voltage conversion circuit by the on / off operation of the switch element, and supplying the output voltage of the controlled current-voltage conversion circuit to the power semiconductor element as a driving power supply. Power supply circuit.