JP3909407B2 - Electrically isolated switching element drive circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrically insulating switching element driving circuit.
[0002]
[Prior art and problems to be solved by the invention]
In general, a DC-DC converter and various inverter circuits are driven based on a reference potential different from the reference potential of the input circuit system. The most obvious example of such an application is the case where the high side element of the inverter circuit is driven as the potential of the output terminal of the inverter circuit. In this case, the control terminal of the high side element is connected to the output terminal of the inverter circuit. A control voltage based on (a connection point between the high-side element and the low-side element of the inverter circuit) must be applied. Further, not only the high-side element but also the low-side element of the inverter circuit is often driven on the basis of a reference voltage completely different from that of the input side circuit system. In addition, a circuit system in which the power supply voltage has an absolute potential (or reference potential) different from that of the input side circuit system is required not only for the above-described inverter circuit but also for various applications.
[0003]
In such a circuit system, when a signal is transmitted from the input side circuit to at least the first switching element of the output side circuit, it is easy to supply power from the input side circuit for at least the driving power of the first switching element. .
[0004]
In order to realize this, a transformer insulation type electric insulation type switching element driving circuit is conventionally known. In this circuit, the input side circuit oscillates to form an AC voltage format signal, which is transmitted to the output side circuit through a transformer, rectified by the output side circuit, and rectified high energy switching signal voltage. Therefore, a method of intermittently connecting the first switching element (hereinafter also referred to as a transformer insulation type switching element driving circuit) is frequently used.
[0005]
However, the conventional transformer-insulated switching element drive circuit is not easy to wind the coil because the transformer core is small, and can drive the switching element at a high frequency, although it can transmit power with a low intermittent frequency. There was a problem that could not. This is because, in the conventional transformer insulation type switching element driving circuit, the hysteresis loss of the transformer core is greatly increased by the increase of the frequency, and most of the high-frequency AC power input to the transformer is attenuated by the heating of the core. This is because the transmission efficiency is reduced due to the leakage inductance.
[0006]
In addition to the above-described transformer-insulated switching element drive circuit, there is a conventional electrical insulation type switching element drive circuit that uses a piezo transformer (piezocoupler) for input / output electrical insulation. Since the drive frequency is low, it is difficult to drive the output side switching element at a high frequency.
[0007]
In addition, as a conventional electrically isolated switching element driving circuit, a method of transmitting a signal accompanied by electric power while electrically insulating input / output using a photocoupler using an LED (light emitting diode) and a photodiode (PD) is also considered. However, in order to transmit the power necessary for directly driving the switching element on the output side, LEDs (light emitting diodes) and photodiodes (PD) need to have a large chip area, and the low voltage obtained by the PD can be reduced. Realizing a circuit for boosting power is not easy and practically difficult to implement.
[0008]
The present invention has been made in view of the above problems, and an object of the present invention is to provide an electrically isolated switching element driving circuit capable of directly driving a high-power switching element that requires a considerable amount of power for driving at a high frequency.
[0009]
[Means for Solving the Problems]
An electrically insulating switching element driving circuit according to claim 1 is an oscillation circuit that converts a binary signal voltage for intermittently driving the switching element into an AC voltage having a predetermined fundamental frequency, and each one primary coil and secondary A leakage transformer having a coil and the AC voltage applied to the primary coil; a resonance circuit that receives the output voltage of the secondary coil and resonates with the fundamental frequency as a resonance frequency; and is output from the resonance circuit A waveform shaping circuit that rectifies an AC voltage, converts it to a binary signal voltage, and applies it between a reference potential main terminal and a control terminal of the switching element, and the waveform shaping circuit outputs from the resonance circuit A rectifying circuit for rectifying the AC voltage to be generated, and converting the rectified voltage output from the rectifying circuit into a binary signal voltage to convert the reference potential of the switching element A comparison circuit to be applied between the main terminal and the control terminal, the resonance circuit has a resonance capacitor (C2) connected to both ends of the secondary coil, and the rectifier circuit has one end Is connected to one end of the capacitor (C2), a diode (D1) whose anode is connected to the other end of the capacitor (C1), and a cathode is connected to the other end of the capacitor (C1). A diode (D2), a diode (D3) whose cathode is connected to the anode of the diode (D2), and a smoothing capacitor (C3) connecting the cathode of the diode (D1) and the anode of the diode (D3) A voltage doubler rectifier circuit that applies a power supply voltage to the comparison circuit from between the cathode of the diode (D1) and the anode of the diode (D3). Made is, the comparison circuit,
The binary voltage is formed by comparing the anode voltage of the diode (D1) with the divided voltage (reference potential) of the double voltage rectified voltage output from the diode (D1) .
[0010]
The resonance circuit whose resonance frequency is the fundamental frequency is a resonance circuit whose resonance frequency is set to 0.8 to 1.2 times, more preferably 0.95 to 1.05 times the fundamental frequency. Alternatively, it means a resonance circuit that generates a secondary voltage larger than the theoretical secondary voltage value determined by the input voltage of the leakage transformer and the turn ratio. The capacitor mentioned here means all capacitors that are arranged on the secondary circuit side and constitute a resonance circuit together with the leakage inductance of the leakage transformer and the parasitic capacitance of the secondary coil. The leakage transformer here is a term that is distinguished from a closed magnetic circuit type transformer, and means that the electromagnetic coupling coefficient between the primary coil and the secondary coil is 50% or less. The above-mentioned closed magnetic circuit type transformer means a transformer having a core structure that has no air gap in the magnetic circuit or has only an air gap at the junction of a plurality of partial cores constituting the closed magnetic circuit. The transformer is a transformer having a large air magnetic path in a closed magnetic circuit and a very large leakage inductance of both coils.
[0011]
The transformer-insulated switching element driving circuit of the secondary side resonance type leakage transformer structure according to the present invention, more specifically, due to the resonance between the large leakage inductance (leakage inductance) of the secondary coil of the transformer and the capacitor, more specifically, the secondary of the transformer. A resonance phenomenon including an inductance-capacitance distributed constant circuit composed of coil inductance and parasitic capacitance (between turns) and the above capacitor reduces output voltage loss due to leakage inductance of the secondary coil of the transformer, thereby reducing the leakage transformer. Despite the structure, the effective electromagnetic coupling efficiency of the transformer can be dramatically improved.
[0012]
As a result, a switching element that is electrically isolated from the voltage system on the input side can be switched at high speed by the power supplied from the input side using a small, lightweight, and easy-to-coil winding transformer. The drive circuit can be configured simply and at low cost.
[0013]
Furthermore, the resonance can increase the output voltage of the transformer without setting the transformer turns ratio large (for example, even if it is set to 1: 1).
[0014]
According to a second aspect of the present invention, in the electrically insulating switching element driving circuit according to the first aspect, the leakage transformer is made of a core restaurant. In this way, since the core is not used at all, it is possible to increase the frequency without considering the increase in the loss of the core (for example, ferrite core) due to the hysteresis loss. With this higher frequency, it is possible to achieve a faster response of the switching element. Further, since the core restaurant coil and the resonance capacitor can be miniaturized by increasing the frequency, the apparatus can be significantly miniaturized. As a result, the electrically insulating switching element driving circuit can be significantly reduced in size and weight.
[0015]
In particular, when this core restaurant is adopted, the use of the resonance circuit is particularly important when an output voltage having an amplitude larger than the input voltage of the core restaurant needs to be applied to the switching element. In other words, the increase in the output voltage amplitude due to the adoption of this resonant circuit makes it possible to adopt a turns ratio close to 1: 1 that is effective in improving the electromagnetic coupling efficiency, and to improve the power transmission efficiency. To do.
[0016]
According to the present invention, the waveform shaping circuit includes a rectifier circuit that rectifies an alternating voltage output from the resonant circuit, and a rectified voltage output from the rectifier circuit that converts the rectified voltage into a binary signal voltage. Since it has a comparison circuit applied between the main terminal for reference potential and the control terminal, a pulse voltage with a steep edge can be applied to the switching element, and the switching loss in the transient state of the switching element Can be reduced.
[0017]
The comparison circuit is particularly important when the rectifier circuit has a smoothing capacitor (or a peak hold capacitor) that is charged through a rectifying diode. That is, in this circuit configuration, the core restaurant can quickly charge the smoothing capacitor through the rectifying diode when the switching element is driven, so that the switching element can be driven at high speed. However, in this case, even if the core restaurant stops charging of the smoothing capacitor through the rectifying diode when the switching element is turned off, the charge accumulated in the smoothing capacitor does not immediately disappear. It takes a long time to turn off the switching element due to the voltage drop, and the transient power loss and heat generation of the switching element during this period increase. This problem can be solved by using this comparison circuit. Note that, typically, the comparison circuit preferably compares a voltage at a predetermined portion between the smoothing capacitor and the secondary coil or a partial pressure thereof with a partial pressure of the smoothing capacitor. As a comparison circuit, a comparator is generally used. For example, a voltage of a predetermined portion between the smoothing capacitor and the secondary coil or a divided voltage thereof is applied to the gate, and a MOS transistor to which a predetermined threshold voltage is applied is applied. On and off may be used.
[0019]
In electrically insulated switching element driver circuit according to claim 2, wherein in the configuration of claim 3, wherein said primary coil and said secondary coil of said coreless transformer, the circuit board on which the input-side circuit and the output-side circuit is mounted In this case, the core restaurant can be easily mounted on the circuit board.
[0020]
In electrically insulated switching element driver circuit according to claim 3, wherein the arrangement of claim 4, around the primary coil and the secondary coil of said coreless transformer, a constant-voltage conductor region constant voltage with low impedance is applied Therefore, it is possible to improve the electromagnetic coupling cutoff with the outside, increase the parasitic capacitance in the distributed constant circuit of the core coil of the secondary coil, and improve its resonance. it can.
[0021]
According to a fifth aspect of the present invention, in the electrically insulating switching element driving circuit according to the fourth aspect , an inner end of the spiral printed coil is formed on the surface of the circuit board through a hole formed in the circuit board. because being connected to another via hole conductors to be drawn to the outside of the spiral printed coil, it is possible to simplify the structure for drawing out the end portion of the inner side of the spiral printed coil.
[0022]
According to a sixth aspect of the present invention, in the electrically insulating switching element driving circuit according to the fifth aspect , the other spiral printed coil is formed to be recessed inward at a portion close to the via-hole conductor. Therefore, the via-hole conductor can be easily drawn out of the other spiral printed coil, and the wiring structure can be simplified.
[0023]
According to a seventh aspect of the present invention, in the electrically insulating switching element driving circuit according to the sixth aspect , the via-hole conductor is formed at a corner of the other spiral printed coil formed in a square shape. In order to avoid the via-hole conductor while suppressing the decrease in the electromagnetic coupling coefficient, it is possible to suppress the increase in the turn length of the other spiral printed coil, and to reduce the resistance loss of the coil.
[0024]
In electrically insulated switching element driver circuit according to claim 2, wherein in the configuration of claim 8, wherein said primary coil and said secondary coil of said coreless transformer, the circuit board on which the input-side circuit and the output-side circuit is mounted The spiral printed coils are coaxially wound on each other, and a magnetic sheet is disposed on at least one surface side of both the spiral printed coils. As a result, it is possible to increase the inductance and the electromagnetic coupling coefficient while suppressing an increase in structure and process.
[0025]
In the configuration according to claim 9, in the electrically insulating switching element driving circuit according to claim 2, 80% or more of the conductor layers constituting the coils are at the same position (positions overlapping each other) in the main surface direction of the circuit board. It is characterized by being arranged in. In this way, since the electromagnetic coupling coefficient between the turns of both coils can be improved, the power transmission efficiency of Core Restaurant can be maximized.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of the electrically insulating switching element driving circuit of the present invention will be described below with reference to the drawings.
[0027]
[Example 1]
An electrically insulating switching element driving circuit of this embodiment will be described below with reference to FIG.
(Circuit configuration)
1 is an oscillation circuit, 2 is a modulation circuit, 3 is a current amplification circuit, 4 is a core restaurant, 5 is a rectification circuit, 6 is a comparison circuit, 7 is a current amplification circuit, and 8 is a voltage regulating constant voltage diode.
[0028]
The oscillation circuit 1 is a known circuit that outputs a high-frequency pulse voltage (basic frequency 9 MHz) having a phase difference of 180 degrees and a pulse width / pulse period of about 50%, and an AND gate 21 that constitutes the modulation circuit 2. 22 and the complementary emitter follower circuits 31 and 32 constituting the bridge type current amplifying circuit 3, the high frequency pulse only during the period when the switching element (not shown) is turned on at both ends of the series circuit of the primary coil 41 and the capacitor Co of the core restaurant 4. Apply voltage. As a result, a high-frequency pulse voltage having a peak value of about 5 V is applied to both ends of the primary coil 41. The series capacitor Co is for equivalently reducing the leakage inductance of the primary coil 41 of the core restaurant 4 and constitutes a series resonance circuit with the primary coil 41. The series capacitor Co can be omitted.
[0029]
The core restaurant 4 is a transformer having no core, 41 is a primary coil, and 42 is a secondary coil.
[0030]
The rectifier circuit 5 includes a voltage doubler detection circuit (voltage doubler rectifier circuit) composed of a capacitor C1 and diodes D1 and D2, a capacitor C2, a diode D3, capacitors C3 and C4, and a resistor R1 .
[0031]
The secondary coil 42 of the core restaurant 4 constitutes a resonance circuit that resonates at the fundamental frequency together with the capacitors, particularly the capacitors C1 and C2, connected to the secondary coil 42. Particularly in this embodiment, the capacitor C1 constitutes a resonance circuit that resonates at the fundamental frequency together with the leakage inductance of the secondary coil 42 (more precisely, the impedance of the distributed constant circuit of the secondary coil 42) and the capacitor C2. Yes. The capacitor C1 functions as a basic component of a voltage doubler rectifier circuit, which will be described later, and the voltage drop of the capacitor C1 is 180 degrees out of phase with the voltage drop of the leakage inductance of the secondary coil 42. The voltage drop of the leakage inductance is effectively reduced, and the electromagnetic transmission efficiency and voltage loss of the core restaurant 4 are improved. The capacitor C1 and the leakage inductance as the distributed constant circuit may resonate at the basic frequency, and the capacitor C2 and the leakage inductance as the distributed constant circuit may resonate at the basic frequency.
[0032]
The diode D1 applies a power supply voltage that has been double-voltage rectified to a comparison circuit and a current amplification circuit 7 to be described later, and the capacitor C3 constitutes a smoothing capacitor (peak hold capacitor) for stably supplying this power supply voltage.
[0033]
The anode voltage of the diode D1 is applied to the capacitor C4 and the resistor R1. This anode voltage becomes a pulse voltage whose peak value is larger by the forward voltage drop than the peak voltage output from the cathode of the diode D1 in the positive half-wave period. The diode D3 and the capacitor C4 can be omitted.
[0034]
The rectifier circuit 5 includes diodes D1, D2, and D3, a smoothing capacitor C3, and a voltage dividing capacitor C4. The diode D1 is fed from one end of the secondary coil 41 through the capacitor C1 to charge the capacitor C3, and the capacitor C3 applies a power supply voltage to the subsequent circuit.
[0035]
The comparison circuit 6 includes a comparator 61 and a voltage dividing circuit formed by resistors R2 and R3. The divided voltage doubled rectified voltage output from the diode D1 is compared with the voltage of the resistor R1. When the AND gate 2 is cut off by the control voltage Vs, the voltage of the resistor R1 decreases rapidly, the output voltage of the comparator 61 becomes a low level, the complementary emitter-follower circuit output voltage of the comparator 61 forming a current amplifying circuit 7 Through this, the gate electrode voltage of the switching element (not shown) is rapidly reduced. R4 is a pull-up resistor that pulls up the input voltage of the current amplifier circuit 7 to a high level.
[0036]
FIG. 2 shows measured waveforms of the input voltage and output voltage obtained by this circuit. The power supply voltage applied to the current amplifier circuit 3 is 5V. Due to the effect of the resonance circuit, the output voltage is amplified beyond the limit voltage of 10 V of the voltage doubler rectifier circuit, and even in applications where high voltage is required, the output voltage is large without changing the turns ratio of the core restaurant 4. There is an advantage that the output voltage can be applied to the switching element. Note that the rectifier circuit and the resonance circuit can be replaced with other known circuits having a rectification effect and a resonance effect.
[0037]
Details of the core restaurant 4 will be described below with reference to FIGS.
[0038]
In FIG. 3, reference numeral 100 denotes a printed circuit board on which the circuit of FIG. 1 is mounted, and a primary coil 41 is printed on the front surface and a secondary coil 42 is printed on the back surface. As shown in FIG. 4, both the coils 41 and 42 are spiral printed coils having a turns ratio of 1, and the same turn of both the coils 41 and 42 is completely overlapped in the surface direction of the printed circuit board 100. It is formed in the same shape. Thereby, since each turn of both the coils 41 and 42 is each electromagnetically coupled satisfactorily, the electromagnetic coupling coefficient of both the coils 41 and 42 can be improved and the power transmission efficiency of the core restaurant 4 can be improved.
(Additional explanation)
In addition, the parasitic capacitance of the core restaurant 4 is between each turn of the primary coil, between the primary coil and the ground, between each turn of the primary coil and each turn of the secondary coil, between each turn of the secondary coil, Exists between ground. Although high-frequency analysis of such a complicated circuit is not easy, a resonance point may be obtained by experiment.
[0039]
[Example 2]
Another embodiment of the core restaurant 4 will be described below with reference to FIG.
[0040]
In this embodiment, both the coils 41 and 42 are formed in a substantially square shape, and when the printed circuit board 100 is viewed from above, one corner portion 410 of the primary coil 41 is recessed in a square shape, and diagonally faces this. One corner 420 of the secondary coil 42 is recessed in a square shape.
[0041]
One end of the primary coil 41 is led out to the back side of the printed circuit board 100 through a through hole 411 provided in the printed circuit board 100. Since the through hole 411 is located outside the corner portion 420 of the secondary coil 42, Wiring can be performed without straddling any of the coils 41 and 42. Similarly, one end of the secondary coil 42 is drawn to the surface side of the printed circuit board 100 through a through hole 421 provided in the printed circuit board 100, and this through hole 421 is located outside the corner portion 410 of the primary coil 41. Therefore, wiring can be performed without straddling both the coils 41 and 42.
[0042]
[Example 3]
Another embodiment of the core restaurant 4 will be described below with reference to FIG.
[0043]
In this embodiment, the core restaurant 4 is a two-output type, and a pair of secondary coils 4200 and 4201 are arranged on the back side of the printed circuit board 10 along each turn of the primary coil 41. In this way, a pair of secondary voltages (see FIG. 7) that are electrically insulated from each other can be obtained. Therefore, the pair of secondary voltages is used to form a high-side element (upper arm element) of the inverter circuit. The first switching element and the second switching element forming the low side element (lower arm element) of the inverter circuit can be operated in reverse to each other with reference to different potentials. This circuit is shown in FIG. However, in FIG. 8, since the pair of secondary coils 4201 and 4202 outputs a voltage in the same direction, the pair of input voltages of the pair of comparators 611 and 612 are reversed so that the outputs of the pair are in reverse phase. I have to.
[0044]
[Example 8]
Another embodiment of the core restaurant 4 will be described below with reference to FIG.
[0045]
In this embodiment, four spiral printed coils 401 to 404 are arranged on a multilayer wiring printed circuit board 1000. These four spiral printed coils 401 to 404 can be used to generate an antiphase output voltage or to perform serial or parallel connection.
[0046]
[Example 9]
Another embodiment of the core restaurant 4 will be described below with reference to FIG.
[0047]
In this embodiment, two spiral printed coils 41, 42 are laminated as a primary coil and a secondary coil inside the multilayer printed circuit board 1000, and further, the spiral printed coils 41, 42 are covered so as to cover the multilayer printed circuit board. Electromagnetic noise radiation from the core restaurant 4 to other core restaurants or external circuits is reduced by arranging grounded copper foils 1003 and 1004 for electromagnetic shielding on the front and back surfaces of the circuit board 1000. . In this embodiment, the parasitic capacitance formed between the copper foils 1003 and 1004 for electromagnetic shielding and the secondary coil 42 reduces the voltage drop of the leakage inductance of the secondary coil 42 and reduces the electromagnetic resistance of the core restaurant 4. The effect of improving the transmission efficiency can also be expected.
(Modification)
In each of the above embodiments, the resonance frequency of the resonance circuit on the secondary coil side of the core restaurant is set to the fundamental frequency of the pulse voltage supplied from the primary side. Instead, the resonance of the resonance circuit on the secondary coil side of the core restaurant is used. The frequency may be three times the basic frequency of the pulse voltage supplied from the primary side. This is because the pulse voltage contains many third harmonic components.
(Modification)
A resonance capacitor may also be provided on the primary coil side of the core restaurant 4 to resonate with the leakage inductance of the primary coil 41 of the core restaurant 4.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a circuit configuration of a first embodiment.
FIG. 2 is a measured voltage waveform diagram showing input / output characteristics of the circuit of FIG. 1;
FIG. 3 is a schematic side view showing the core restaurant of FIG. 1;
4 is a schematic plan view showing the spiral printed coil of FIG. 3. FIG.
FIG. 5 is a schematic plan view showing another embodiment of the spiral printed coil of FIG.
6 is a schematic plan view showing another embodiment of the spiral printed coil of FIG. 4. FIG.
7 is a measured voltage waveform diagram showing input / output characteristics of a circuit using the spiral printed coil of FIG. 6; FIG.
8 is a circuit diagram showing a circuit configuration using the spiral printed coil of FIG. 6. FIG.
FIG. 9 is a schematic plan view showing another embodiment of the spiral printed coil of FIG.
10 is a schematic plan view showing another embodiment of the spiral printed coil of FIG. 4. FIG.
[Explanation of symbols]
1 Oscillation circuit 4 Core restaurant (leakage transformer, resonance circuit)
C1, C2 capacitors (resonance circuit)
5 Waveform shaping circuit

Claims (9)

An oscillation circuit that converts a binary signal voltage for intermittently driving the switching element into an AC voltage having a predetermined fundamental frequency;
A leakage transformer having each one primary coil and secondary coil and the alternating voltage being applied to the primary coil;
A resonance circuit that receives an output voltage of the secondary coil and resonates with the fundamental frequency as a resonance frequency;
A waveform shaping circuit that rectifies an alternating voltage output from the resonance circuit, converts the alternating voltage into a binary signal voltage, and applies between the reference potential main terminal and the control terminal of the switching element;
With
The waveform shaping circuit is
A rectifier circuit for rectifying an AC voltage output from the resonant circuit;
A comparison circuit that converts the rectified voltage output from the rectifier circuit into a binary signal voltage and applies the voltage between the reference potential main terminal and the control terminal of the switching element;
The resonant circuit is:
A resonance capacitor (C2) connected to both ends of the secondary coil;
The rectifier circuit has a capacitor (C1) having one end connected to one end of the capacitor (C2), a diode (D1) having an anode connected to the other end of the capacitor (C1), and a cathode having the capacitor (C1). ), The diode (D2) connected to the other end, the diode (D3) whose cathode is connected to the anode of the diode (D2), and the smoothing connecting the cathode of the diode (D1) and the anode of the diode (D3). A voltage doubler rectifier circuit having a capacitor (C3) and applying a power supply voltage to the comparison circuit from between the cathode of the diode (D1) and the anode of the diode (D3);
The comparison circuit is
Electrically isolated switching characterized in that the binary voltage is formed by comparing the anode voltage of the diode (D1) with the divided voltage (reference potential) of the double voltage rectified voltage output from the diode (D1). Element drive circuit. The electrically insulating switching element driving circuit according to claim 1,
The electrical isolation switching element driving circuit according to claim 1, wherein the leakage transformer is made of a core restaurant . The electrically insulating switching element driving circuit according to claim 2 ,
The primary coil and the secondary coil of the core restaurant are spiral printed coils that are laminated in a thickness direction across an insulating layer or the circuit board on a circuit board on which the input side circuit and the output side circuit are mounted. An electrically insulated switching element driving circuit comprising: The electrically insulating switching element driving circuit according to claim 3 ,
An electrically insulated switching element driving circuit, wherein a constant voltage conductor region to which a constant voltage is applied with a low impedance is formed around the primary coil and the secondary coil of the core restaurant. The electrically insulating switching element drive circuit according to claim 4 ,
The inner end portion of the spiral printed coil is connected to a via-hole conductor drawn out of the other spiral printed coil formed on the surface of the circuit board through a hole formed in the circuit board. An electrically insulating switching element driving circuit. The electrically insulating switching element driving circuit according to claim 5 ,
The other insulated spiral printed coil is formed to be recessed inward at a portion close to the via-hole conductor. The electrically insulating switching element driving circuit according to claim 6 ,
The electrically insulated switching element driving circuit, wherein the via-hole conductor is formed at a corner portion of the other spiral printed coil formed in a square shape. The electrically insulating switching element driving circuit according to claim 2,
The primary coil and the secondary coil of the core restaurant are each composed of a spiral-type printed coil wound coaxially around a circuit board on which the input-side circuit and the output-side circuit are mounted. An electrically insulating switching element driving circuit, wherein a magnetic sheet is disposed on at least one side of the printed coil. The electrically insulating switching element driving circuit according to claim 2,
80% or more of the conductor layers composing the coils are disposed at the same position in the main surface direction of the circuit board.

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