JPS6016076Y2 - Noise prevention device for radio wave application equipment - Google Patents

Description

[Detailed description of the invention] This invention relates to the improvement of a noise prevention device that can prevent interference waves generated from equipment and cause noise and communication interference, and reduce leakage current flowing from radio wave application equipment to the ground. be.

Currently, for example, microwave ovens are becoming popular and widely popular due to their ability to cook quickly by dielectric heating using radio waves of 2450 MHz. Or, in order to prevent adverse effects on communication equipment, not only must interference radio waves satisfy the regulatory values of technical standards stipulated in the Radio Act and the Electrical Appliance and Materials Control Act, etc., but also measures have been taken to ensure that no problems arise in actual situations. There is.

By the way, as a recent global trend, with the increase in radio wave application equipment, there is a tendency to strictly regulate jamming radio waves, and there is a need to further reduce jamming radio waves. Further reductions pose technical problems in that leakage current flowing from the equipment to the ground increases, potentially creating a risk of electric shock.

This point will be explained in detail below with reference to FIGS. 1 and 2.

As shown in Fig. 1, in a conventional microwave oven, a magnetron device 1 is attached to a heating box 5 made of a metal body, and a high DC voltage is supplied to the magnetron device to generate high frequency waves to heat the heated object. Heat item 8.

The heating box 5 is surrounded by an outer box 6 made of a metal body and a door device 7 that can be opened and closed, and an idle space 9 formed by the heating box 5 and the outer box 6 contains the magnetron device 1 and other devices. A power supply circuit 10 consisting of a transformer, a rectifier, etc. that supplies a high DC voltage to the magnetron device 1, and a control circuit 11 consisting of a door switch, a timer, etc. that control the supply of high voltage are arranged. For personal safety, a safety device 13 such as a current fuse and a grounding wire 15 extending from the outer box 6 to the ground are provided.

On the other hand, the interference radio waves generated by the magnetron device 1 cover a wide band and are of a considerably high level.

This interference radio wave may be radiated from the anode through the antenna 2, or may be radiated from the input side to the idle space 9, or propagated to the power supply 14 through the power supply circuit 10.

The former is emitted into the heating chamber 5, but since the heating chamber 5 is electrically sealed by the door device 7, it is absorbed by the object to be heated 8 and is not emitted to the outside, so there is no problem.

Regarding the latter, since the magnetron device 1 is surrounded by the shield case 4 made of a metal body, the interference radio waves radiated into the idle space 9 are suppressed to almost no problem, so there is no problem.

Also, most of the interference radio waves in the high frequency band (30 MH2 or more) propagated to the power supply circuit 10 through the connection line are blocked by the T-shaped filter circuit 3 constituted by a choke coil and a capacitor.

However, for low frequency band (30MH2 or less) jamming radio waves propagated to the distribution line 18 of the commercial power supply 14 through the power supply circuit 10, a C Prevention circuit 12
is used to block interference waves.

That is, in Fig. 2, capacitors 16, 17, 17'
Taking advantage of the fact that the high frequency impedance of is smaller than the commercial frequency impedance, the capacitor 16 short-circuits the symmetrical disturbance current 19 that flows through the distribution line 18 as a reciprocating line, and the capacitor 17 and 17' causes it to flow between one line of the distribution line 18 and the ground. The asymmetrical disturbance current 20 is connected from the outer box 6 to the grounding wire 1.
If the grounding conditions are poor, leakage current will flow from the outer box 6 to the ground through the user's human resistance, creating a risk of electric shock. Capacitance is 0.003-0.00
Although it is set at 5 μF, which satisfies the current legal regulation value and actual situation, the conventional C shadow prevention circuit 12 does not meet the requirement to suppress the value to a stricter value due to the risk of electric shock as described above. It is not possible to significantly reduce interference waves.

As a solution to this problem, there is a method of double-insulating parts that users touch, such as the outer case of the equipment, with electrical insulators to reduce the risk of electric shock, and a method that reduces the leakage current between the equipment and the ground. There are possible ways.

First, as a method for the former, it is possible to increase the capacitance of the capacitors 17 and 17' of the C-type prevention circuit 12 by constructing the outer cover of the outer box 6 and the door device 7 with an electrical insulator such as plastic. Although it is possible, magnetron device 1. The antenna 2 of the microwave oven needs to be kept at zero potential, so it must be grounded through the heating box 5, and the microwave oven is not safe because it is used with a leaky hand in a humid place in the kitchen. It is not advisable to actually adopt it.

Next, as the latter method, an L-type prevention circuit shown in FIG. 3 can be considered.

In other words, the coils 21 and 21 inserted in series with the distribution line 18
This method uses the fact that the high frequency impedance of the series inductance becomes larger than the commercial frequency impedance due to ', to block the propagation of interference current. In order to keep the impedance voltage drop of the coil 21, 21' at a constant value, the inductance must be reduced, and the high frequency impedance to the interference current cannot be increased, so the interference cannot be significantly reduced. The method used is also inappropriate.

This invention provides a noise prevention device that solves the problem of reducing the risk of electric shock, which could not be solved by the various conventional methods mentioned above, and also reducing the propagation of interference waves to power distribution lines.The details are as follows. To explain this, as shown in FIGS. 4 and 5, the features of the present invention are that a capacitor 22 is connected between the lines, capacitors 23 and 23' are connected between each line and the outer box 6, and a coil 24 is connected between the outer box 6 and the ground. This coil is placed in the idle space 9 inside the outer box 6.

That is, the capacitor 22 short-circuits the symmetrical disturbance current 19 flowing through the distribution line 18 as a reciprocating line, and the capacitor 23, 23' short-circuits the asymmetric disturbance current 20 flowing between each line of the distribution line 18 and the outer box 6.

Further, the coil 24 prevents the propagation of the interference current flowing between the outer box 6 and the ground, and at the same time short-circuits the commercial frequency.

Note that the current flowing through the coil 24 is as small as 1 mA or less, and if the wire diameter of the coil 24 is set to 0.7 to 1.677El11, the impedance voltage drop of the coil 24 can be ignored.

Furthermore, the capacitor 23.23 reduces the asymmetric disturbance current 20.
' and the coil 24, so the capacitor 23
．． Since the capacitance of 23' can be set smaller than that of the shadow prevention circuit C, there is less leakage current flowing from the device to the ground, and the risk of electric shock can be prevented.

For example, when the capacitor 22 has a capacitance of 0.1μF, the capacitor 23 has a capacitance of 0.003.3μF, and the coil 24 has a capacitance of 0.003.3μF, and a choke coil with a wire diameter of 1 rnH is used. At the same time, the leakage current flowing from the device to the ground is only 0.5 mA or less, so there is almost no risk of electric shock.

It goes without saying that the present invention can be applied not only to microwave ovens but also to devices with a large amount of asymmetric interference current at full load current or higher.

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[Brief explanation of drawings]

Figure 1 is an electrical circuit diagram of a conventional microwave oven, Figure 2 is a noise prevention circuit diagram of Figure 1, Figure 3 is another conventional noise prevention circuit diagram, and Figure 4 is a diagram of the noise prevention device of the present invention. FIG. 5 is a diagram of the electric circuit configuration of the microwave oven used, and is a diagram of the noise prevention circuit shown in FIG. 4. In the figure, 1 is a magnetron device, 6 is an outer box, 16.17.
17' is a capacitor, 21.22' is a coil, 22,2
3.23' is a capacitor, and 24 is a coil. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of utility model registration request] Noise from radio wave application equipment in which capacitors are connected between each power distribution line to the equipment and the metal chassis of the equipment to reduce asymmetric interference current generated in the equipment, and the metal chassis is grounded via a coil. Prevention device.