JPH10294633A - Ac line filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the performance as an LPF and to block a leakage current concerning an AC line filter for removing noises on an AC power supply line. SOLUTION: On the next step of capacitor C2 on a neutral line 1N, a capacitor C0 for reducing common mode noises is connected through a switch 3 to a ground 1E. When the potential difference of live line 1L and neutral line 1N is more than a prescribed value, a potential difference detection circuit 4 sends a control signal to a switch circuit 3 and turns on the switch circuit 3. Since the neutral line 1N is connected with the ground line 1E on the power supply side, even when the switch circuit 3 is turned on, a large current does not flow to the capacitor C0. When the live line 1L and the neutral line 1N are not normally connected, since the potential difference gets lower than the prescribed value and the switch circuit 3 is turned off, the leak current does not flow through the capacitor C0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC line filter for removing noise on an AC power supply line, and more particularly to an AC line filter for reducing common mode noise.

[0002]

2. Description of the Related Art Conventionally, an AC line filter has been used as a measure to prevent unnecessary radiation through an AC power supply line or to prevent noise components from entering. The AC line filter can prevent common mode noise and normal mode noise from entering and exiting the AC line.
Here, the common mode noise refers to noise between the ground and the ground that flows from a noise source in the device to a power supply. on the other hand,
The normal mode noise is noise generated from the inside of the device, and is a loop noise passing between AC lines.

FIG. 6 is a circuit diagram showing a configuration of a general AC line filter. Live of AC line filter 100
Between the line 100L and the neutral line 100N,
Capacitor C1 for reducing normal mode noise
0 and C11 are connected in parallel. A common mode choke coil 101 for reducing common mode noise is connected between the capacitors C10 and C11. Further, two capacitors C12 and C12 for reducing common mode noise are provided next to the capacitor C11.
C13 are connected in series with each other and in parallel with the capacitor C11.

The connection point Ta between the capacitors C12 and C13 is connected to a frame ground FG. Therefore, a potential difference occurs between the power supply frame and the ground.
Therefore, when a person touches the frame, a so-called leakage current flows from the frame to the ground through the human body. In Japan, the safe current value for a person is specified to be 1 mA. In order to protect this with the AC line filter 100, the capacitors C12 and C13 both have a capacity of 2200 pF or more.
It is necessary to use a capacitor having a small capacity of 3300 pF.

However, the parameters for attenuating the common mode noise are the inductances of the coils L10 and L11 of the common mode choke coil 101 and the capacitance values of the capacitors C12 and C13.
When the capacitance value of the capacitor 13 is fixed as described above, it is necessary to increase the inductance of the coils L10 and L11 in order to increase the attenuation.

In general, the impedance of the AC line filter is set to 50 Ω to 150 Ω. When the capacitors C 12 and C 13 are set to the above-mentioned range, they hardly contribute to the characteristics of the filter.
00 is an LPF (Low Pass Filter) formed by the coils L10 and L11 and the line impedance. Therefore, also in this respect, the magnitude of the inductance of the coils L10 and L11 becomes important.

However, at present, even with super high μ materials,
At 15T, the inductance is at most 20 mH, the power loss due to the DC resistance is large, and the amount of heat generated is large. In addition, since the material is expensive, the entire power supply device becomes expensive. .

FIG. 7 is a circuit diagram showing a configuration of a high-output AC line filter used in an AV server or the like. AC
The line filter 110 includes a normal mode choke coil 11 next to the AC line filter 100 shown in FIG.
1 has a common mode choke coil 1
12 are connected. In the last stage, the capacitor C14 is connected to the live line 100L and the neutral line 100N.
Is connected between.

Such an AC line filter 110 is
The order of the filter is higher than that of the AC line filter 100 shown in FIG. This is because a power factor improving converter is placed in the first stage for harmonic regulation measures.
This is because the noise level is higher than the power supply of the conventional capacitor input rectifier circuit. Here, if a ferrite core is used for the common mode choke coil 101 and an amorphous wound toroidal core is used for the common mode choke coil 112, the respective inductances can be 3.5 mH and 20 mH, and the noise inductance can be increased. . However, capacitors C12 and C1
3 is as low as 2200 pF to 3300 pF.
The cutoff frequency of the entire C line filter does not decrease.

[0010] Further, since the amorphous core has a high magnetic permeability and a small leakage magnetic flux, it cannot be expected to reduce the normal mode noise. 111 are provided.

However, the common mode choke coil 1
To further increase the inductance of 01,112,
Since the number of windings of the coil must be increased, the size of components increases, the cost increases, and the power consumption also increases. For this reason, in the AC line filter 100 or the AC line filter 110, the capacitance of the capacitors C12 and C13 must be increased in order to lower the inductance of the common coil and lower the cutoff frequency. However, as described above, in this method, the leakage current increases, so that the safety decreases.

Therefore, there is an equivalent circuit in which safety is maintained even when the capacitance of the capacitor is increased. FIG. 8 is an equivalent circuit of the AC line filter 100 of FIG. In the AC line filter 120, the AC line filter 1
Neutral instead of capacitors C12 and C13
The capacitor C14 is connected to the line 100N.
When a ring core having a high magnetic permeability is used for the common mode choke coil 101, the coupling coefficient is almost 1, so that C14 = C12 + C13 makes the circuit equivalent.

Accordingly, if the other terminal of the capacitor C14 is connected to the frame ground, the neutral line 1
00N is usually connected to earth on the power transmission side,
Even if the capacity of the capacitor C14 is increased, almost no leakage current flows.

[0014]

However, this is a case where the lines are normally connected, and A
Live line 1 between the C line filter and the power supply side
When the 00L and the neutral line 100N are connected in reverse, or when the earth and the neutral line 100N are disconnected, a large current flows to the frame ground through the capacitor C14. Such a phenomenon,
This can occur, for example, when measuring leakage current.

FIG. 9 is a diagram showing a schematic configuration of a leakage current measuring system. In the measurement system 200, the measurement device 220 is connected to the next stage of the transformer 210 on the input side, and the power supply device 230 containing an AC line filter is connected to the output side of the measurement device 220. At this time, the earth and the frame ground are open.

In the measuring device 220, a live line and
Assuming that there is a mistake in the connection of the neutral line,
A changeover switch 221 is provided. The changeover switch 221 causes the transformer 210 and the power supply device 2 to operate.
The polarity is switched with 30. Then, at each switching position, the value of the leakage current from the earth terminal of the power supply device 230 is detected by the detector 221.

As described above, once the polarity of the power supply side and the polarity of the AC line filter are switched, once the live line and the AC line filter are switched.
The neutral lines are connected in reverse. When connected in reverse, a large current may flow to the frame ground side through the capacitor C14.

The present invention has been made in view of the above points, and has as its object to provide an AC line filter capable of improving the performance as an LPF and preventing a leakage current.

[0019]

According to the present invention, in order to solve the above-mentioned problems, an A for eliminating noise on an AC power supply line is provided.
A C-line filter, a common mode noise capacitor connected between the neutral line and earth;
A switch circuit for turning on / off a connection state between the common mode noise capacitor and the earth,
a potential difference detecting circuit for detecting a potential difference between the ve line and the earth, and turning on the switch circuit only when the potential difference is equal to or more than a predetermined value to connect the common mode noise capacitor to the earth. Is provided.

The potential difference detection circuit comprises a live line and an eart
The potential difference between h is detected, and only when the potential difference is equal to or more than a predetermined value, the switch circuit is turned on to connect the common mode noise capacitor to earth. Therefore, live line and ne
When the utral line is connected in reverse, or when earth is disconnected, the switch circuit does not turn on because the potential difference between the live line and earth is zero or close to it. Therefore, no leakage current flows through the common mode noise capacitor.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the principle of the AC line filter of the present invention. Between the live line 1L and the neutral line 1N of the AC line filter 1, capacitors C1 and C2 for reducing normal mode noise are connected in parallel. A common mode choke coil 2 for reducing common mode noise is connected between the capacitors C1 and C2. Further, a capacitor C0 for reducing common mode noise is connected to the earth 1E via the switch circuit 3 at a stage subsequent to the capacitor C2 of the neutral line 1N.

Further, a potential difference detecting circuit 4 for detecting a potential difference between the live line 1L and the earth 1E is connected. The potential difference detection circuit 4 is connected to the live line 1L.
neutral line 1N is connected normally and earth 1
If E is securely connected and the potential difference between them is equal to or greater than a predetermined value, a control signal is sent to the switch circuit 3 to turn on the switch circuit 3. Since the neutral line 1N is connected to the earth 1E on the power supply side, a large current does not flow through the capacitor C0 even when the switch circuit 3 is turned on. On the other hand, if the circuit is not normally connected, such as the live line 1L and the neutral line 1N are connected in reverse or the neutral line 1N and the earth 1E are disconnected, the switch circuit 3 is turned off. , Capacitor C0
No leakage current flows through the circuit.

Therefore, there is no fear of electric shock in any situation. For this reason, even if the capacitance value of the capacitor C0 is increased in order to reduce the common mode noise, the safety can be maintained.
Of low cost, high performance L
A PF can be configured.

Next, a specific embodiment of the AC line filter of the present invention will be described. FIG. 2 is a circuit diagram showing a configuration of the AC line filter of the present embodiment. The AC line filter 10 is a high-output AC line filter used for an AV server or the like. Here, the same components as those in FIG. 1 are denoted by the same reference numerals. Between the live line 1L and the neutral line 1N of the AC line filter 10, capacitors C1 and C2 for reducing normal mode noise are connected in parallel. A common mode choke coil 2 for reducing common mode noise is connected between the capacitors C1 and C2.

The next stage of the capacitor C2 is two capacitors C3 and C3 for reducing common mode noise.
C4 are connected in series with each other and in parallel with the capacitor C2. Further, a normal mode choke coil 5 and a common mode choke coil 6 are connected to the next stage. In the last stage, a capacitor C5 is connected between the live line 1L and the neutral line 1N.

The connection point T1 between the capacitors C3 and C4 is ea
Connected to rth 1E. Also, neutral line 1N
A capacitor C0 for reducing the common mode noise is connected to the earth 1E and the frame ground FG via the switch circuit 3 at the next stage of the capacitor C2.

The switch circuit 3 comprises a transistor 3a and a light emitting diode 3b. The light emitting diode 3b emits light in response to a control signal from the potential difference detection circuit 4, whereby a voltage is applied to the gate (G) of the transistor 3a, and the drain (D) and the source (S) conduct.

Between the live line 1L and the earth 1E,
The potential difference detection circuit 4 is connected. Potential difference detection circuit 4
, The voltage of the live line 1L is half-wave rectified via a diode D1 and input, and a voltage value determined by the resistors R1 and R2 is input to the input terminal (-) of the comparator 4a.
The voltage from the load side is applied to the potential difference detection circuit 4. The voltage from the load side is divided by the resistors R3 and R4, and is applied as the reference voltage Vx to the other input terminal (+) of the comparator 4a. Here, the values of the resistors R1 and R2 are set so that when the potential difference between the live line 1L and the earth 1E is equal to or greater than a predetermined value Va, the voltage input to the input terminal (−) is equal to or greater than the reference voltage Vx. I can decide. In addition, the predetermined value Va is a live line 1L, a neutral line 1
Li when N and earth 1E are connected normally
The voltage value of the ve line 1L is set to a value or an appropriately smaller value.

The output voltage of the comparator 4a is divided by the resistor R5 and the capacitor C6, and is divided by the input terminal (+) of the comparator 4b.
Is applied to The reference voltage Vx is applied to the input terminal (-) of the comparator 4b. The output of the comparator 4b is
It is connected to the cathode side of the light emitting diode 3b of the switch circuit 3.

The voltage from the load is connected to the anode of the light emitting diode 3b via the resistor R6. Next, the operation of the AC line filter 10 having such a configuration will be described.

First, live line 1L, neutral line 1
N, and when the earth 1E is normally connected, the potential difference between the live line 1L and the earth 1E is a predetermined value V
Therefore, the voltage applied to the input terminal (-) of the comparator 4a becomes equal to or higher than the reference voltage Vx, and the output of the comparator 4a is turned off. Then, the output of the comparator 4b is also turned off, a current flows through the light emitting diode 3b of the switch circuit 3, and the switch circuit 3 is turned on. Thereby, the capacitor C0
Are connected to the earth 1E and the frame ground FG, and function as components of the LPF.

At this time, the frame ground FG is
Since it is grounded to the earth 1E, the leakage current is very small, and there is no electric shock even if a person touches the frame ground FG. Therefore, since it is safe to increase the capacitance value of the capacitor C0, the common mode noise can be reduced without increasing the inductance of the common mode choke coil 2 and the common mode choke coil 6.

In addition, since ferrite cores can be used for the common mode choke coil 2 and the common mode choke coil 6, the cost can be reduced. Further, since the number of windings can be reduced, the power loss can be significantly reduced, the temperature rise of the power supply device can be reduced, and the reliability is improved. In particular, in the case of a ferrite core, since the leakage inductance is large, the inductance of the normal mode choke coil 5 can be reduced. Further, even if an amorphous core is used, the number of turns of the coil can be reduced, so that the power loss can be significantly reduced, and the shape of the core material can be reduced, so that the cost can be reduced.

On the other hand, in the AC line filter 10,
When the live line 1L and the neutral line 1N are connected in reverse to the power supply side, the potential of the live line 1L is almost zero because the live line 1L is grounded. Therefore, the voltage applied to the input terminal (-) of the comparator 4a is smaller than the reference voltage Vx, so that the outputs of the comparator 4a and the comparator 4b are turned on. Therefore, no current flows through the light emitting diode 3b, and the switch circuit 3 is also turned off. Therefore, no leakage current flows to the frame ground FG side via the capacitor C0.

Also, earth 1E and frame ground FG
Is not connected, a current return path is not formed, so that no current flows through the diode D1. Therefore, the switch circuit 3 is also turned off, and no leakage current flows to the frame ground FG side via the capacitor C0. Therefore, safety is ensured.

In this embodiment, since the operation source of the potential difference detection circuit 4 is pulled from the load side, when the power supply device is off, the switch circuit 3 is surely turned off, and the capacitor C0 is erroneously connected. Nothing.

Further, since the switch circuit 3 is constituted by the light emitting diode 3B and the transistor 3a which operates in response to the light emitting diode 3B, generation of noise at the time of switching can be prevented.

The AC line filter 10
Uses the capacitor C0 for common mode noise, so the capacitors C3, C
4 (see FIG. 8) can be omitted. By omitting the capacitors C3 and C4, the leakage current becomes
The current can be reduced to the detection current of the diode D1 and the resistors R1 and R2. In a normal design, for example, when the AC voltage is 230 V, it can be set to about 0.9 μA.

Next, the equivalence of capacitors for common mode noise will be described. FIG. 3 is a diagram showing an equivalent circuit of a capacitor for common mode noise.
FIG. 2B is a diagram illustrating a filter circuit in which two capacitors are connected between two C lines, and FIG. 2B is a diagram illustrating a filter circuit in which a capacitor is connected only to one AC line. Figure (A)
In the filter circuit 20, the two common mode choke coils 7 and the common mode choke coil 8 are provided between the live line La and the neutral line Na. Further, between the common mode choke coil 7 and the common mode choke coil 8, capacitors C01 and C02 for reducing common mode noise are connected in series with each other and straddle between the live line La and the neutral line Na. ing. Further, capacitors C01 and C0
The second connection point T2 is connected to the frame ground.

On the other hand, the filter circuit 30 of FIG. 2B also has two common mode choke coils 7 and 8. One terminal of a capacitor C03 is connected to a neutral line Na between these coils. The other terminal of the capacitor C03 is connected to the frame ground.

Filter circuit 20 and filter circuit 30
, The capacitance of the capacitor C03 is represented by C03 = C0
By setting 1 + C02, both are equivalent. FIG.
FIG. 4 is a diagram illustrating a frequency characteristic of a gain of the two filter circuits in FIG. 3. In the figure, the horizontal axis represents frequency [kHz] and the vertical axis represents gain [dB]. Here, the inductances of the common mode choke coil 7 and the common mode choke coil 8 are both 2 mH, the capacitances of the capacitors C01 and C02 are both 1200 pF, and the capacitance of the capacitor C03 is 2400 pF. And
In the figure, the characteristics of such a filter circuit 20 are shown as S1, and the characteristics of the filter circuit 30 are shown as Q1.

As can be seen from the figure, the characteristics of the two are almost the same and can be said to be sufficiently equivalent. FIG. 5 shows FIG.
FIG. 7B is a diagram illustrating a frequency characteristic of a gain when the value of the capacitor C03 in the filter circuit 30 of FIG. In the drawing, Q1a to Q1h are respectively obtained by setting the capacitor C03 to Q1a = 0, Q1b = 1200 pF, and Q1c =
2400 pF, Q1d = 3600 pF, Q1e = 480
0pF, Q1f = 6000pF, Q1g = 7200p
F, Q1h = 0.12 μF. The inductances of the common mode choke coil 7 and the common mode choke coil 8 are both 2 mH.

As can be seen from the figure, the capacitor C03
If the capacitance of the common mode choke coil 7 and the common mode choke coil 8 is small, the cutoff frequency can be reduced. That is,
Common mode noise can be reduced.

[0044]

As described above, according to the present invention, neutra
l Because a common mode noise capacitor is connected between the line and earth, even if the capacitance of the common mode noise capacitor is increased, the leakage current is large via the common mode noise capacitor in a normal connection state. Does not flow. Therefore, the performance as the LPF can be improved without increasing the inductance of the common mode coil. Further, the number of turns of the coil can be reduced, so that cost and power loss can be significantly reduced.

Further, a potential difference detecting circuit detects a potential difference between the live line and the earth, and turns on the switch circuit only when the potential difference is equal to or more than a predetermined value, thereby connecting a common mode noise capacitor connected to the neutral line to the earth.
Live line and neutral
If the line is reversed, the earth is disconnected,
If the line is not connected normally, the switch circuit can be turned off to cut off the leakage current via the common mode noise capacitor. Therefore, safety is ensured.

[Brief description of the drawings]

FIG. 1 is a diagram showing the principle of an AC line filter according to the present invention.

FIG. 2 is a circuit diagram showing a configuration of an AC line filter of the present embodiment.

3A and 3B are diagrams illustrating an equivalent circuit of a capacitor for common mode noise, in which FIG. 3A illustrates a filter circuit in which two capacitors are connected between two AC lines, and FIG. 3B illustrates only one AC line; FIG. 3 is a diagram showing a filter circuit in which a capacitor is connected to the filter circuit.

FIG. 4 is a diagram illustrating frequency characteristics of gains of the two filter circuits in FIG. 3;

FIG. 5 is a diagram illustrating a frequency characteristic of a gain when the value of a capacitor in the filter circuit of FIG. 3B is changed.

FIG. 6 is a circuit diagram showing a configuration of a general AC line filter.

FIG. 7 is a circuit diagram showing a configuration of a high-output AC line filter used for an AV server or the like.

FIG. 8 is an equivalent circuit of the AC line filter of FIG. 6;

FIG. 9 is a diagram showing a schematic configuration of a leakage current measuring system.

[Explanation of symbols]

1 ... AC line filter, 1L ... live line,
1N ... neutral line, 1E ... earth, 2 ...
· Common mode choke coil, 3 ··· switch circuit, 4 ··· potential difference detection circuit, 4a, 4b ··· comparator, C0 ··· capacitor for common mode noise, 10
... AC line filters

Claims (3)

[Claims] 1. A method for removing noise on an AC power supply line
In the C-line filter, a common mode noise capacitor connected between the neutral line and earth, a switch circuit for turning on / off a connection state between the common mode noise capacitor and the earth, a live line and earth And a potential difference detecting circuit for connecting the common mode noise capacitor to the earth by turning on the switch circuit only when the potential difference is equal to or more than a predetermined value. filter. 2. The switch circuit includes a light emitting element that emits light in response to a control signal supplied from the potential difference detection circuit, and a transistor that operates by receiving light from the light emitting element. Item 7. The AC line filter according to Item 1. 3. An apparatus according to claim 1, wherein an operation source of the potential difference detection circuit is supplied from a load side.
An AC line filter as described.