JP3116565B2 - Line filter transformer and power supply circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line filter transformer for preventing noise from leaking from an electric device to an AC line, and more particularly to a lightning surge countermeasure.

[0002] The present invention also relates to a power supply circuit in which a line filter transformer is connected to an AC line, and is particularly suitable for a lightning surge countermeasure of a switching regulator of a pulse width modulation system.

[0003]

2. Description of the Related Art In recent years, switching regulators having relatively high efficiency have been frequently used as power supply circuits in order to reduce the size and weight of electronic devices and the like. As this switching regulator, there is a pulse width modulation type switching regulator whose design is advantageous with respect to the control range of the output amount.

This switching regulator of the pulse width modulation system performs pulse width modulation by driving a voltage-pulse width converter by an output voltage of an error amplifier at a constant chopping frequency determined by a repetition frequency of a pulse generator. The output value is stabilized by changing the conduction period in one cycle (reciprocal of the chopping frequency), that is, the ratio (duration) of the conduction period in one cycle.

That is, the conventional switching regulator of the pulse width modulation system has an input terminal φi as shown in FIG.
After once rectified by the supplied AC input voltage v bridge which is connected _in to the rear end of the AC line rectifier circuit 21 to n, and converted into an AC voltage using the on-off circuit 22 composed of a switching transistor, Then, the transformer 23
After the conversion into an AC voltage having a predetermined amplitude, the rectification and smoothing circuit 24 in the next stage converts the DC voltage into a DC voltage and outputs it as an output voltage Vout from an output terminal φout. The output terminal φout is connected to an electric device 32 such as a computer.

At this time, the output voltage Vout from the switching regulator is controlled by controlling the pulse width of the on / off circuit 22 by a feedback circuit 27 comprising an error amplifier 25 and a voltage-pulse width converter 26. Is to be stabilized. Reference numeral 28 denotes a photocoupler, 29 denotes a pulse generator that supplies a pulse signal having a constant chopping frequency to a voltage-pulse width converter 26, and V denotes a pulse signal supplied to an error amplifier 25.
r is a reference voltage.

The AC line is used to attenuate external noise and to prevent noise generated inside, for example, a high-frequency noise component generated from an electric device 32 such as a connected computer from jumping out through the AC line. For this purpose, an input filter 30 composed of a line filter transformer (hereinafter simply referred to as LFT) and capacitors (C ₁ , C ₂ , C ₃ , C ₄ ) is inserted. Note that L
The FT determines a rated current and an inductance value by a noise band to be suppressed by a transformer used for an input filter and a steady input current value.

According to the switching regulator of the pulse width modulation system, the switching transistor constituting the on / off circuit 22 performs class D amplification, that is, on / off operation with pulse width control. Only the switching loss in the switching transistor and the loss due to the voltage drop at the time of the ON operation can greatly improve the efficiency. Also, since the switching frequency is high, the transformer, choke coil, capacitor, and the like can be reduced in size and weight.

[0009]

However, in this type of conventional power supply circuit (pulse width modulation type switching regulator), there is a problem that countermeasures against a lightning surge voltage are insufficient.

When a lightning surge voltage is applied to the input side of the LFT, the voltage on the output side is expanded and boosted by the LFT, resulting in a higher voltage. In this case, a lightning surge voltage in the normal mode (negative-phase mode) can be prevented by inserting a varistor or the like between the AC lines in the preceding stage of the LFT, but a lightning surge voltage in the common mode (in-phase mode) can be prevented. The varistor 1
It cannot be inserted between the secondary side and FG (frame ground). In other words, between the transformer primary side and the FG, a withstand voltage (at the time of manufacture) of 1.8 kV _AC is required according to safety standards, so that the varistor (the highest operating voltage is 1.3 kV _AC).
) Cannot be inserted between them to take countermeasures against common mode lightning surge.

The countermeasures against the discharge gap are as follows. The discharge start voltage varies due to the manufacturing variation of the discharge gap. If the discharge gap does not discharge, the discharge is performed between the switching transistor (ON / OFF circuit 22) and the FG, and the switching is performed. There is a disadvantage that the transistor is destroyed.

Therefore, at present, the transformer primary side -F
Measures have been taken to increase the insulation distance between G,
There are limitations on the size of parts, surge withstand voltage, and the like, and there is a limit in expanding the allowable range of lightning surge voltage application.

A similar problem with respect to such a lightning surge voltage may occur in a line filter transformer connected to an AC line in another circuit configuration, for example, as a noise filter.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a line filter transformer capable of coping with a common mode lightning surge.

Further, the present invention is to increase a surge applied potential at least in a power supply circuit in which a line filter transformer is connected to an AC line until a switching transistor is destroyed or malfunctions against a common mode lightning surge voltage. It is an object of the present invention to provide a power supply circuit capable of performing the following.

[0016]

SUMMARY OF THE INVENTION The present invention relates to an electric device
Como in order to prevent the noise from leaking to the AC line from
Absorber that clamps at a constant voltage between the input side of the line filter transformer and the output side in phase or between the input side and the output side out of phase in a line filter transformer (LFT) that reduces 11 are connected.

The surge absorbing component 11 can be constituted by a varistor.

Further, the surge absorbing component 11 can be constituted by a discharge tube, for example, a discharge tube containing gas or a Zener diode.

The present invention also relates to a power supply circuit in which a line filter transformer (LFT) for reducing at least common mode noise is connected to an AC line as an input filter 1; The surge absorbing component 11 is connected between different poles before and after the above.

[0020]

The line filter transformer (LF) according to the present invention
In T), the common mode noise is removed, and the surge absorbing component 11 is connected between the input side of the LFT and the output side of the same phase or between the input side and the output side of the different phase . 3, the input side of the LFT
When a common mode lightning surge voltage is applied to
With the so-called LC resonance due to the FT inductance and stray capacitance
The removal of the enlarged and boosted voltage that occurs after the LFT is eliminated.
It is. That is, the voltage generated before and after the LFT can be clamped, and the voltage applied between the transformer primary side and the FG after the LFT can be reduced. Therefore, the allowable range of lightning surge voltage application can be expanded as compared with the related art.

In particular, when the surge absorbing component 11 is connected between the input side of the LFT and the output side of the out-of-phase, it can cope with both the common mode and normal mode lightning surge voltages.

As the surge absorbing component 11, a varistor,
A discharge tube, a Zener diode, or the like can be used. When the discharge tube or the Zener diode is used, since the capacitance component is small, it is possible to sufficiently prevent the leakage of the high-frequency noise component from the electric device 13 in the LFT.

In the power supply circuit according to the present invention,
In AC line, between same poles before and after LFT or L
Since the surge absorbing component 11 is connected between different poles before and after the FT, as shown in FIG.
When a common mode lightning surge voltage is applied to the
So-called LC resonance due to LFT inductance and stray capacitance
In this way, the expanded and boosted voltage components occurring after the LFT are removed.
It is. That is, the applied voltage (V ₃ , V ₄ , V ₅ ) between the transformer primary side and the FG after the LFT can be reduced. As a result, the application tolerance lightning surge voltages V ₁ can be expanded than the conventional, it is possible to achieve high reliability of the power supply circuit.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a circuit diagram showing a power supply circuit according to the present embodiment using the line filter transformer of the present invention, particularly a switching regulator of a pulse width modulation system.

This switching regulator has a feedback circuit for controlling the pulse width of an input filter 1, a bridge type rectifier circuit 2, an on / off circuit 3, a transformer 4, a rectifying / smoothing circuit 5, and an on / off circuit 3, as shown in the figure. 6.

The operation will now be described.
After once rectifying the supplied AC input voltage v _in at the bridge rectifier circuit 2 connected to the rear end of the AC line in, using the on-off circuit 3 composed of switching transistors, for example, several tens of kHz for Convert to AC voltage.
The AC voltage appears on the primary side of the transformer 4. Then, on the secondary side of the transformer 4, the voltage is converted into an AC voltage having a predetermined amplitude, and then converted into a DC voltage by a rectifying and smoothing circuit 5 in the next stage, and the output terminal φout is output as an output voltage Vout.
Output from t. The output terminal φout is connected to an electric device 13 such as a computer.

At this time, the output voltage Vout is supplied to the error amplifier 7 to which the reference voltage Vr is input, and the output voltage Vc from the error amplifier 7 is supplied to the voltage-pulse width converter 8 through the photocoupler 8. The supply causes the voltage-pulse width converter 9 to be driven. The voltage-pulse width converter 9 outputs a pulse signal Pr having a constant chopping frequency from the pulse generator 10 and a pulse signal P having a pulse width corresponding to the amplitude from the output voltage Vc from the error amplifier 7. , On / off circuit 3. These error amplifier 7 and voltage-pulse width converter 9
Is a feedback circuit 7 for controlling the pulse width of the on / off circuit 3.
And the output voltage Vout from the switching regulator is controlled by the pulse width control by the feedback circuit 7.
Is to be stabilized.

The AC line is used to attenuate external noise and to prevent noise generated inside, for example, a harmonic noise component generated from an electric device 13 such as a connected computer from jumping out through the AC line. To prevent this, an input filter 1 composed of a line filter transformer (hereinafter simply referred to as LFT) and capacitors (C ₁ , C ₂ , C ₃ , C ₄ ) is inserted. In addition,
Is the stray capacitance between the switching element and ground.
(Capacitance) voltage change is the cause
Common mode noise and noise generated between two AC lines
-There is normal mode noise. LFT is common mode noise
To remove noise. About normal mode noise
Has no effect.

In this embodiment, as shown in FIG. 1 and FIG. 2 in which the input filter 1 is shown in an enlarged manner, in the AC line, between the same poles before and after the LFT, that is, the output side in phase with the input side. , Or between different poles before and after the LFT, that is, between the input side and the output side with a different phase. When a surge voltage is applied from the outside, the surge absorbing component 11 clamps with an operating voltage and functions to protect the internal elements.

As the surge absorbing component 11, any component can be considered, and an optimal component can be used in accordance with the surge absorption amount of the component, restrictions on the shape, and the like. As the surge absorbing component 11, for example, a varistor, a discharge tube (for example, a gas-containing discharge tube), a Zener diode, or the like can be used.

Here, when a common mode lightning surge voltage V ₁ is applied to the input terminal φin, the voltage between the FG (frame ground) before the LFT is V ₂ , the voltage between the FG after the LFT is V ₃ , The voltage between the primary side and the secondary side is V ₄ , and the voltage between the input and output terminals of the photocoupler 8 is V ₅ .

Then, for example, the lightning surge voltage V₁= 4kV
If no countermeasures are taken (that is, surge absorbing component 11
When no lister is inserted), each voltage V_Two, V_Three, V_FourPassing
And V _FiveAppears as shown in FIG. 3A. Note here
The point to be noted is that the FG voltage V_TwoAnd after LFT
Stage FG voltage V_Three(Before and after LFT)
That is, there is a difference. This is the voltage
LFT is caused by the
From the transformer primary side to the FG (V_Three, V_Four, V_Five)so
It can be seen that about 8 kV is applied.

On the other hand, as in this embodiment,
Before and after the same pole or before and after LFT
The surge absorbing component 11, for example, the operating voltage is about
When a 470V varistor is inserted, as shown in FIG.
The primary side of the transformer after the LFT by the varistor 11
-Each voltage between FG (V_Three, V_Four, V_Five) Before the LFT
Voltage V_TwoAbout 470V is clamped to
Each of the above voltages (V_Three, V _Four, V_Five) Has a peak value of about 5.5.
kV, and each voltage in the case of no countermeasure shown in FIG. 3A
(V_Three, V_Four, V_FiveAbout 2.5 kV lower than
I have.

In the configuration of the present embodiment, the peak value of each of the voltages (V ₃ , V ₄ , V ₅ ) is the peak value of each of the voltages (V ₃ , V ₄ , V ₅ ) in the case where no measures are taken. Value (about 8k
Become substantially the same as V), as shown in FIG. 3C, is when the value of the lightning surge voltage V ₁ is a 6kV, it is understood that the ability for lightning surge voltage is increased to 6kV from 4 kV.

As described above, according to the present embodiment, the AC line
Medium, same pole before and after LFT or before and after LFT
For example, a varistor of the surge absorbing component 11 between different poles
Are connected, so the common mode lightning surge
Pressure V₁Can be absorbed by the LFT,
Applied voltage between transformer primary side and FG (V_Three, V_Four,
V _Five) Can be lowered. As a result, lightning surge voltage
V₁Can increase the allowable range of
High reliability of switching regulator with pulse width modulation
Can be achieved.

The measures against the lightning surge voltages V _1, when used varistor as the surge absorbing component 11, to obtain positive, negative, live, the effects in the neutral all combinations in lightning surge of the common mode in one varistor Can be.

[0037] Incidentally, the varistor of the above example, since it has a capacitive component C _B between the terminals, as shown in FIG. 4, originally LFT
The high frequency noise component suppressed by
It is conceivable that the noise will pass through _B and deteriorate the noise terminal voltage and the level of radiation noise.

If an element having a small inter-terminal capacity, such as a discharge tube or a Zener diode, is used as the surge absorbing component 11 and a device that clamps at a constant voltage value when a voltage higher than a certain value is applied, high frequency noise components are difficult to pass. Become
Without increasing the levels of noise terminal voltage, radiated noise, etc., lightning surge voltage can be suppressed and surge immunity can be increased.

The above-described example shows an example in which the present invention is applied to a pulse width modulation type switching regulator. However, the present invention can be applied to all power supply circuits in which at least LFT is inserted as an input filter 1 in an AC line.

The above example is applied to a pulse width modulation type switching regulator. However, the present invention is not limited to such a power supply circuit.
Can be applied to other circuit configurations in which is inserted.

[0041]

According to the line filter transformer of the present invention, the common mode noise can be removed, the common mode lightning surge voltage can be suppressed, and the surge immunity can be improved. In other words, lightning surge voltage application
The range can be expanded more than before. Surge absorber
By using a varistor, the lightning surge voltage
Voltage generated before and after the LFT
Can be clamped to a low constant voltage,
The lightning surge voltage of the circuit can be suppressed. Surge absorption
Components must be composed of discharge tubes or zener diodes
By reducing the capacitance component of the surge absorbing component, the LFT
Enough to prevent high frequency noise components from leaking from electrical equipment
Can be fulfilled.

According to the power supply circuit of the present invention, it is possible to increase the surge applied potential up to the destruction and malfunction of the power supply circuit with respect to the common mode lightning surge voltage, thereby improving the reliability of the power supply circuit. be able to.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a pulse width modulation type switching regulator according to an embodiment.

FIG. 2 is an enlarged circuit diagram showing a switching regulator according to another example of the present embodiment, focusing on an input filter.

FIG. 3 is a characteristic diagram showing an effect of the switching regulator according to the embodiment as a countermeasure against lightning surge.

FIG. 4 is a circuit diagram of a line filter transformer part used for describing the present invention.

FIG. 5 is a circuit diagram showing the configuration of a pulse width modulation type switching regulator according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input filter 2 Bridge type rectifier circuit 3 ON / OFF circuit 4 Transformer 5 Rectifier smoothing circuit 6 Feedback circuit 7 Error amplifier 8 Photocoupler 9 Voltage-pulse width converter 10 Pulse generator 11 Surge absorption component LFT Line filter transformer FG Frame ground

Claims (4)

(57) [Claims] 1. A line filter transformer for reducing common mode noise for preventing noise from leaking from an electric device to an AC line, wherein a line filter transformer has an input side and an in-phase output side. A line filter transformer, characterized in that a surge absorbing component that clamps at a constant voltage is connected between the input side and an input side and an out-of-phase output side. 2. The line filter transformer according to claim 1, wherein the surge absorbing component comprises a varistor. 3. The line filter transformer according to claim 1, wherein the surge absorbing component comprises a discharge tube or a Zener diode. 4. An at least common mode as an input filter.
The line filter transformer that reduces the load noise is AC
A power supply circuit connected to a line, wherein a surge absorbing component is connected between the same pole before and after the line filter transformer or between different poles before and after the line filter transformer in the AC line. circuit.