JPS62269508A - Noise reduction reduction device - Google Patents

Abstract

PURPOSE:To reduce noise caused by a transformer by providing the ternary winding to the transformer, connecting a variable resistor to the windings, and connecting a capacitor between its slider and a shield of the transformer. CONSTITUTION:An LPF 13 is connected between the primary winding 11 and a commercial power supply 12. A variable resistor 32 is connected across the ternary winding 31 of the transformer 10 and its slider 32 is connected to a shield grounding point 25 of the transformer 10 via a capacitor 33 in a cancellation circuit 30. The equivalent circuit of the circuit 30 is shown in the figure. Thus, the polarity level of a common mode noise Vcom produced between terminals 24 and 25 is compensated over a wide range by adjusting the slider 32, on the condition of R/2+winding resistance << 1:/omegac, where R is the total resistance of the variable resistor 32. If the condition is lost, a harmonic signal of a proper angular frequency omega or over due to the LPF 13 is not supplied to the primary winding of the transformer 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a device that reduces noise in an electric circuit using a transformer.

[Prior Art] Fig. 3 is a block diagram showing a conventional transformer, and in the figure, an AC signal is input to the second winding (11) of the transformer (10). j-2L'
ky '14 beats/6111- IJ? l - tithe x
Mode noise appears. This level (size) largely depends on the structure of the transformer (10). Moreover, although this noise can be suppressed to some extent by the structure of the transformer,
Depending on the required specifications, it may be greatly influenced by variations in variables that are difficult to manage during manufacturing. Here, the common mode noise mentioned above refers to a certain reference point (for example, ground potential point)
This shows how much the output system as a whole is swayed in terms of potential relative to the voltage, and when this is shown in the equivalent circuit diagram of FIG. 4, it corresponds to ('/c). Note that (Ys) is a predetermined signal.

However, there are many processes for generating the above-mentioned noise.

For example, stray capacitance that exists between the primary winding (11) and the secondary winding (21), other stray capacitance coupling with the ground, or magnetically induced electromotive force that occurs in the winding or the lead wire of the shield, etc.
Most of the problems are caused by the structure of the transformer. There are also certain limits to the means for reducing this common mode noise. Furthermore, in recent years, as switching regulators have become smaller, switching operations have tended to operate at higher frequencies, so reduction of this common mode noise is becoming more and more important.

The object of the present invention is to obtain a device in which the above-mentioned noise is reduced.

[Means for Solving the Problems] A noise reduction device according to the present invention includes a third winding provided in a transformer, a variable resistor connected between the windings, and a slider of the third winding connected to the transformer. A capacitor is connected between the shield and the shield.

[Function] In the present invention, the positive and negative sides of noise can be compensated for over a wide range by adjusting the slider of the variable resistor.

[Embodiment of the Invention] FIG. 1 is a circuit diagram showing a noise reduction device according to an embodiment of the invention, and the same reference numerals as in FIG. 3 indicate the same parts. (13) is the primary winding (11) and commercial power supply (12)
A low-pass filter inserted and connected between (30)
is a cancellation circuit, in which a variable resistor (32) is connected between both terminals of the third winding (31) of the transformer (10),
The slider (32) is connected to the shield ground point (25) of the transformer (10) via a capacitor (33). Note that the intermediate taps of the windings (21) and (31) are commonly connected. Here, an equivalent circuit of the above cancellation circuit (3Q) is shown in FIG. That is, the terminal (
24), (25) common mode noise ('/c
on) is expressed by the following formula.

Vcom=Vc-i/(jωcc)=Vr-i
/(jωc)=0 However, this is (C4r=Cc4c
) holds true under the following conditions. Here, (C
) is the capacitance value of the capacitor (33), and (Vr) is the divided voltage of the variable resistor (32), so that positive and negative outputs can be obtained. (
Cc) is the stray capacitance value of the transformer (10) and ('/c) is the noise source generating common mode noise. As is clear from the above equation, by adjusting the variable f, t, (slider of the flow device (32)), the common mode noise (Yco*)
can be compensated to a small extent.

However, in order to obtain the above conditions, a forebank of (R/2+(winding resistance))<(1/ωC) is required. Here, (R) is the total resistance value of the variable resistor (32). If the surface conditions are violated, the phase error will increase and sufficient functionality will not be achieved. In order to correct this, a filter (13) is used in the present invention. In other words, if the commercial power supply (12) on the negative side of the transformer (10) is a sine wave signal, the circuit constants should be selected according to this frequency, and thereby the above canceling operation is possible. The signal becomes a rectangular wave, and high frequency components are generated at the rise and fall of the signal, making it impossible to achieve the initial intended operation. This result (R/2) (
The precondition of (1/ωC) is broken. Here, in order to obtain the above-mentioned conditions, a low-pass filter (13) is used to prevent harmonic signals having a suitable angular frequency (ω) or more from being supplied to the negative side of the transformer (10).

[Effects of the Invention] As detailed above, according to the present invention, no matter what level or phase of common mode noise appears, it is possible to cancel it over a wide range.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention in which noise reduction is performed.
Namazu M-Kan 9ML Sunken Kotokan's electrician H modified M whistle Figure 3 is a circuit diagram of the conventional device, and Figure 4 is its equivalent circuit diagram. In the figure, (10) is the transformer, (12) is the input AC power supply, (
13) is a low-pass filter, (30) is a cancellation circuit, (32) is a variable resistor, and (33) is a capacitor. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] In a transformer in which the primary and secondary windings are shielded, a commercial power supply is connected to the primary winding via a low-pass filter, and intermediate taps of the secondary winding and the third winding are connected. A noise reduction device characterized in that a variable resistor is connected between both ends of the third winding, and a slider of the variable resistor is connected to the shield via a capacitor to reduce common mode noise.