JPH11252936A - High-voltage power supply and electronic device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-voltage power supply which suppresses a leakage current and improves the efficiency of the power supply by reducing the capacity coupling with peripheral parts. SOLUTION: A high-voltage power supply is provided with a printed circuit board 10 constituted of at least two layers of conductors and electrically insulated layers sandwiched between each conductor. Here, a high-voltage wiring pattern PA, on which a high voltage is impressed, faces a ground wiring pattern PG in proximity via the electrically insulated layer. When viewed from the vertical direction of the board, the ground wiring pattern PG is formed in such a way as to surround the outline of the high-voltage wiring pattern PA.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-voltage power supply including a transformer for generating high-frequency, high-voltage AC power, which is used, for example, for driving a cold-cathode tube at a high frequency or generating static electricity.

[0002]

2. Description of the Related Art A high-frequency high-voltage power supply is used in various fields such as a lighting circuit of a cold-cathode tube, which is widely used as a backlight source of a liquid crystal display panel and a lighting fixture, and a static electricity generating circuit in an electrophotographic copying machine. Used. Inside the high-frequency high-voltage power supply, a step-up transformer that operates with an alternating current of several tens of kHz to several hundreds of kHz is provided.

In a lighting circuit of a cold cathode tube, generally, several tens of kilohertz
In many cases, AC power having a voltage of several hundred volts is output at the frequency of z. However, recently, there is a tendency to increase the operating frequency in order to increase the brightness of the cold cathode fluorescent lamp.

The static electricity generating circuit employs a circuit system in which a rectifying element for rectifying the output of the step-up transformer is provided and a DC voltage is output. In order to reduce the size of the circuit, the operating frequency also tends to increase.

[0005] Each part in the device, including the high voltage power supply,
Design and evaluation are performed individually before they are incorporated into the equipment, and after these individual evaluations reach a certain level, an overall evaluation is performed with each part incorporated into the equipment at the final stage of equipment development. Will be

For example, a cold cathode tube is widely used as a backlight source of a liquid crystal display panel incorporated in a small personal computer, a so-called notebook personal computer. When developing a high voltage power supply for lighting a cold cathode tube, At the initial development stage, the design and evaluation are performed with only the load (lamp and reflector) connected.

However, even if the test passes only the evaluation of the load connection, the liquid crystal display panel, peripheral components, the device housing, and the like are close to the high-voltage power supply in a state of being incorporated in an actual notebook-type personal computer. Comes out.

[0008]

When a high-voltage power supply is housed in a small device, a sufficient space for the high-voltage power supply cannot be secured, and the high-voltage power supply and the metal frame of the liquid crystal display panel are arranged close to each other. More things. Then, capacitive coupling occurs between the high-voltage portion of the high-voltage power supply and the metal frame, so that the AC impedance decreases and a leak current flows.

Although the leakage current returns to the main power supply of the device, it does not pose a safety problem, but reduces the efficiency of the power supply circuit. Such a leakage current increases as the proximity distance between the high-voltage power supply and a metal component such as a metal frame decreases, and therefore some measure is required as the device becomes smaller.

In particular, when the leakage current increases in the lighting circuit of the cold cathode tube, the cold cathode tube may not be lit, or only the high voltage side of the cold cathode tube may be lit and the low voltage side may not be lit. It will not function as a light source.

Further, in order to improve the brightness of the cold-cathode tube and to downsize the power supply circuit, a power supply circuit operating at a high frequency is required. The higher the operating frequency, the lower the AC impedance tends to be.

An object of the present invention is to provide a high-voltage power supply capable of reducing leakage current and improving power supply efficiency by reducing capacitive coupling with peripheral components. It is another object of the present invention to provide an electronic device in which the efficiency of a high-frequency transformer does not decrease even when the device is made thin.

[0013]

SUMMARY OF THE INVENTION The present invention provides at least two
In a high-voltage power supply having a printed circuit board composed of a conductor layer of a layer and an electrical insulating layer interposed between the conductor layers,
The high-voltage wiring pattern to which a high voltage is applied and the ground wiring pattern face each other via the electric insulating layer, and the ground wiring pattern includes 80% or more of the contour of the high-voltage wiring pattern when viewed from the direction perpendicular to the substrate. This is a high-voltage power supply characterized by being formed in a simple shape.

According to the present invention, by arranging the high-voltage wiring pattern and the ground wiring pattern close to each other with the electric insulating layer interposed therebetween, even when the high-voltage power supply is incorporated in the device, the high-voltage wiring pattern and the peripheral components can be connected. Does not increase much. Therefore, the state change before and after the device is incorporated is reduced, and the development cost can be significantly reduced.

Further, by forming the ground wiring pattern viewed from the vertical direction of the substrate so as to include at least 80% of the contour of the high-voltage wiring pattern, capacitive coupling with peripheral components can be suppressed efficiently. . The distance between the high voltage wiring pattern and the ground wiring pattern in the direction perpendicular to the substrate is preferably 0.2 mm to 2 mm. More preferably, it is 0.2 mm to 1.6 mm.

The present invention is further characterized in that the distance from the contour of the ground wiring pattern to the contour of the high-voltage wiring pattern is in the range of -0.2 mm to 10 mm when viewed from the direction perpendicular to the substrate. The negative sign of the distance indicates that the contour of the ground wiring pattern is inside the contour of the high-voltage wiring pattern.

According to the present invention, as the contour of the ground wiring pattern is made wider than the contour of the high-voltage wiring pattern, the effect of suppressing the capacitive coupling with peripheral components becomes higher. It was found that the suppression effect was almost saturated when the ratio exceeded.

Further, the present invention is characterized in that the high-voltage wiring pattern is a wiring pattern for electrically connecting a high-frequency transformer and an output connector.

According to the present invention, as the frequency of the current flowing through the high-voltage wiring pattern increases, the effect of capacitive coupling with peripheral components increases, so that the effect of suppressing the ground wiring pattern becomes more remarkable.

Further, the present invention is characterized in that the high-frequency transformer is a piezoelectric transformer that boosts voltage by mutual conversion between an electric signal and mechanical vibration.

According to the present invention, by using a piezoelectric transformer utilizing a piezoelectric effect as a high-frequency transformer,
Small and highly efficient boosting becomes possible. Further, the output current of the piezoelectric transformer is not so large, and the effect of capacitive coupling with peripheral components increases, so that the suppression effect due to the arrangement of the ground wiring pattern becomes more remarkable.

According to the present invention, there is also provided an electronic device incorporating the above-mentioned high-voltage power supply, comprising a metal frame or a metal plate, wherein a closest distance between the wiring pattern and the metal frame or the metal plate is 0.4 mm to 10 mm. The electronic device is set in the range of:

The high-voltage power supply of the present invention has a particularly remarkable effect when used near a metal frame or a metal plate provided to reduce the thickness and the strength of the device.
For example, when a metal plate or a metal frame is used as a reinforcing member on the back surface or a part of the liquid crystal display panel of a notebook computer, the liquid crystal display panel can be made thinner. At this time, if the distance between the high-voltage wiring pattern on the printed board and the metal frame or metal plate is smaller than 0.4 mm, there is a possibility of discharge between the two. This distance is 1
If it is larger than 0 mm, it is difficult to make the electronic device thinner. Therefore, this distance is preferably in the range of 0.4 mm to 10 mm. The material of the metal frame or the metal plate is not particularly limited, and examples thereof include aluminum or an alloy thereof.

[0024]

FIG. 1 is a block diagram showing an embodiment of the present invention. The high-frequency high-voltage power supply includes a power circuit unit 1 that supplies a high-voltage output VH to a load Q such as a cold-cathode tube or a corona charger, and a control unit 5 that controls the operating frequency of the power circuit unit 1.

The power circuit section 1 includes an AC generator 3 for converting a DC low voltage input VL supplied through a noise filter 2 into an AC waveform of a predetermined frequency, and an AC from the AC generator 3 to a high voltage. It is composed of a booster circuit 4 for conversion. The booster circuit 4 includes a high-frequency transformer such as a coil transformer using electromagnetic induction of a coil or a piezoelectric transformer using a piezoelectric effect.

The control unit 5 includes an output detection circuit 8 for detecting a load current I flowing to the load Q, a reference voltage generation circuit 6 for generating a constant reference voltage, a reference voltage and a detection signal from the output detection circuit 8. And an error amplifier 7 that outputs an error signal by comparing the two, and an oscillator 9 whose frequency can be controlled by the voltage of the error signal.

Next, the operation will be described. When the oscillator 9 oscillates at a certain frequency, the AC generator 3 converts the low voltage input VL into an AC waveform based on the frequency, and the booster circuit 4 generates the high voltage output VH to drive the load Q. The fluctuation of the load current I is monitored by the output detection circuit 8, and the error amplifier 7 operates so as to decrease the frequency of the oscillator 9 when the load current I increases and to increase the frequency of the oscillator 9 when the load current I decreases. On the other hand, the output voltage of the booster circuit 4 has a characteristic that increases as the frequency increases. Therefore, when the load current I increases, the voltage of the high-voltage output VH decreases, and when the load current I decreases, the voltage of the high-voltage output VH increases. As a result, a feedback circuit that stabilizes the load current I is formed. Will be.

The operating frequency of such a high-voltage power supply is 20 k
Hz to 1 MHz, preferably 20 kHz to 200
It is set in the range of kHz. The output voltage of the high-voltage power supply is set in the range of 100 V to 10 kV.

FIG. 2 is a partial plan view showing an example of a wiring pattern on the output side of the high-frequency transformer 4a. The high-frequency transformer 4a is a component of the booster circuit 4, and is fixed on a printed board 10 such as a glass epoxy board. On the other hand, an output connector 11 for detachably connecting to an external load Q is also fixed on the printed circuit board 10.

A wiring pattern PA made of copper or the like is formed on the front surface of the printed board 10, and a wiring pattern PG made of copper or the like is formed on the back surface by etching or the like.
It is a conductor layer. The two are opposed to each other with the electric insulating layer of the printed circuit board 10 interposed therebetween.

Both ends of the wiring pattern PA to which a high voltage is applied are electrically connected to the terminal 4b of the high-frequency transformer 4a and the terminal 11a of the output connector 11 by soldering or the like. Is electrically connected to the terminal 4b by soldering or the like. Thus, the high-voltage output of the high-frequency transformer 4a is supplied to the output connector 11.

In such a configuration, the wiring pattern P
A, the length of PG is 10 mm, the width of wiring pattern PA is 2 mm, and the width of wiring pattern PG is changed from 1.6 mm to 22 mm, and the distance D from the outline of wiring pattern PA to the outline of wiring pattern PG is changed. Table 1 below shows the results of measuring the ratio of the power value of the low-voltage input VL to the power value of the high-voltage output VH as the power supply efficiency in a state where the power supply efficiency was changed and incorporated in the same device. An aluminum metal plate is placed 4 mm above the surface of the printed circuit board on which the high-frequency transformer is mounted, parallel to the printed circuit board, and another 0.1 mm thick insulating sheet is interposed between the printed circuit board and the opposite surface. An aluminum metal plate was placed. Thus, the measurement was performed with the printed board sandwiched between the two metal plates. The difference between the power efficiency (%) when each sample is placed in this state and the power efficiency (%) when there is no metal plate nearby is defined as the efficiency change.
The unit of the value was point. 120k as load Q
Ω resistors were used.

[0033]

[Table 1]

Here, in Comparative Example 1, as shown in FIG. 3, the ground wiring pattern PG is formed on the same surface as the wiring pattern PA and far from the wiring pattern PA. In Comparative Example 2, as shown in FIG. 4, the ground wiring pattern PG is formed on the back surface of the printed circuit board 10 so as to be close to the wiring pattern PA, but the width of the wiring pattern PG is smaller than that of the wiring pattern PA. It is formed.

As a result of the measurement, when the distance D between the contours of the wiring pattern PA and the wiring pattern PG was set to 10 mm or less, a small change in the power supply efficiency of -3 points or less was obtained. On the other hand, the wiring pattern P
In Comparative Example 1 in which G was not brought close to and in Comparative Example 2 in which the width of the wiring pattern PG was reduced, the change in power supply efficiency was 7 points or more.

By making the ground wiring pattern PG close to and opposed to the wiring pattern PA in this manner, the effect of capacitive coupling with peripheral components can be greatly suppressed, so that leakage current to the peripheral components is suppressed and power efficiency changes. Becomes sufficiently small.

[0037]

As described in detail above, according to the present invention, by arranging a high-voltage wiring pattern and a ground wiring pattern close to each other with an electric insulating layer interposed therebetween, a high-voltage power supply can be obtained even when the high-voltage power supply is incorporated in the device. Since the capacitive coupling between the voltage wiring pattern and the peripheral components does not increase so much, the state change before and after the incorporation of the device is reduced, and the development cost can be greatly reduced.

Further, by forming the ground wiring pattern as viewed from the vertical direction of the substrate so as to include the contour of the high-voltage wiring pattern, capacitive coupling with peripheral components can be suppressed efficiently, and power supply efficiency can be reduced. The change could be reduced.

Further, by using a piezoelectric transformer utilizing a piezoelectric effect as the high-frequency transformer, a compact and highly efficient boosting is possible.

In an electronic device using a metal frame or a metal plate, the closest distance between the high-voltage wiring pattern on the printed board and the metal frame or the metal plate is set to 0.
By setting the thickness in the range of 4 mm to 10 mm, the thickness of the device can be reduced while reliably preventing discharge.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2A is a partial plan view showing an example of a wiring pattern on the output side of a high-frequency transformer 4a, and FIG.
Is a cross-sectional view along the wiring pattern PA.

FIG. 3A is a partial plan view showing Comparative Example 1, and FIG. 3B is a cross-sectional view taken along a wiring pattern PA.

FIG. 4A is a partial plan view showing Comparative Example 2, and FIG. 3B is a cross-sectional view taken along a wiring pattern PA.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power circuit part 4 Booster circuit 4a High frequency transformer 4b, 11a, 12a Terminal 5 Control part 10 Printed circuit board 11 Output connector PA, PG Wiring pattern

Claims (5)

[Claims] 1. A high-voltage power supply having a printed circuit board comprising at least two conductive layers and an electrical insulating layer interposed between the conductive layers, wherein a high-voltage wiring pattern to which a high voltage is applied and a ground wiring. A high-voltage wiring pattern, wherein the pattern is opposed to the pattern via an electrical insulating layer, and the ground wiring pattern is formed to have a shape including at least 80% of the contour shape of the high-voltage wiring pattern when viewed from the substrate vertical direction. Voltage power supply. 2. The high voltage according to claim 1, wherein a distance from a contour of the ground wiring pattern to a contour of the high voltage wiring pattern is in a range of −0.2 mm to 10 mm when viewed from a direction perpendicular to the substrate. Power supply. 3. The high-voltage power supply according to claim 1, wherein the high-voltage wiring pattern is a wiring pattern for electrically connecting a high-frequency transformer and an output connector. 4. The high-voltage power supply according to claim 3, wherein the high-frequency transformer is a piezoelectric transformer that raises a voltage by mutual conversion between an electric signal and mechanical vibration. 5. An electronic device incorporating the high-voltage power supply according to claim 1, further comprising a metal frame or a metal plate, wherein a closest distance between the wiring pattern and the metal frame or the metal plate is provided. Is 0.4mm
An electronic device characterized by being set in a range of 10 to 10 mm.