JP3447594B2 - Switching power supply and method of forming the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformer capable of reducing common mode noise by reducing the interwinding capacitance and a method of forming the same.

[0002]

2. Description of the Related Art Common mode noise from a switching power supply is caused by voltage fluctuation due to switching, and the fluctuation appears on the secondary side through a capacitance between a primary winding and a secondary winding of a transformer.

As a means for suppressing the outflow of such common mode noise, there is a switching power supply circuit disclosed in, for example, Japanese Patent Laid-Open No. 7-23562. As shown in FIG. 5, a common mode choke coil 56 is connected to the secondary output of a transformer 53 having a primary winding 54 and a secondary winding 55. This allows
Since the common mode choke coil 56 acts as a high impedance against the common mode noise, the outflow of the common mode noise to the secondary side is suppressed.

Further, in the switching power supply circuit disclosed in Japanese Patent Laid-Open No. 63-191890, as shown in FIG. 6, the primary side input of a transformer 75 having a primary winding 74 and a secondary winding 76. Common mode choke coil 7
2 are connected. As a result, the common mode choke coil 72 acts as a high impedance against the common mode noise, so that the outflow of the common mode noise to the secondary side is suppressed.

[0005]

As described above, in any of the prior arts, by connecting the common mode choke coils 56 and 72 to the secondary side output and the primary side input, common mode noise to the secondary side can be obtained. The outflow of water is controlled. However, these common mode choke coils 56 and 72 are required to suppress the outflow of the common mode noise to the secondary side, which causes a problem of increasing the number of parts.

The present invention has been made in view of such a situation, and can provide a transformer capable of reducing common mode noise without increasing the number of parts and a method for forming the transformer. To do so.

[0007]

A solution according to claim 1,
The switching power supply includes a power supply, a switching element, and a transformer.
And the transformer has one end connected to the power source
The other end is connected to the power source through the switching element.
Connected primary winding and secondary connected to secondary side output
A winding, the primary winding and the secondary winding,
It has a planar structure, and the other end of the primary winding and the
The capacitance between the secondary winding is one end of the primary winding.
And smaller than the capacitance between the secondary winding and
ing. Also, the distance between the other end of the primary winding and the secondary winding
Is wider than the distance between one end of the primary winding and the secondary winding.
You can make it easier. Also, secondary winding
Wind the wire so that it is biased toward one end side with respect to the winding width of the primary winding.
Can be turned around. Also, the primary winding
An insulator is interposed between the other end of the wire and the secondary winding
You can Switchon according to claim 5.
The method of forming the power supply is as follows:
A switch forming a switching power supply with a pressure device
A method for forming a power supply, the transformer comprising:
One end is connected and the other end is
Connect the primary winding connected to the power supply and the secondary output.
A secondary winding, and the primary winding and the secondary winding.
The feeder has a planar structure, and other than the primary winding
The capacitance between the end and the secondary winding is
Small compared to the capacitance between one end of the wire and the secondary winding
The method includes a first step formed so as to be drilled.
Also, in the first step, the other end of the primary winding and the secondary winding are
To the distance between one end of the primary winding and the secondary winding.
Compared to the second step of forming wider than
You can In addition, in the first and second steps, the secondary winding
Wind the wire so that it is biased toward one end side with respect to the winding width of the primary winding.
A third step of turning can be included.
In addition, in the first to third steps, the other end of the primary winding and the secondary
To include the step of interposing an insulator between the winding wire
can do.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

FIG. 1 is a circuit diagram showing an embodiment of the transformer of the present invention, FIG. 2 is a perspective view showing the primary winding and secondary winding of the transformer of FIG. 1, and FIG. 2 is a sectional view showing the primary winding and the secondary winding of the transformer of FIG. 2, and FIG. 4 is a sectional view for explaining the operation of the transformer of FIG.

The transformer 6 shown in FIG. 1 comprises a primary winding 6a and a secondary winding 6b. The DC power supply 1 is connected to one end (terminal 3) side of the primary winding 6a. The PMW control circuit 2 is provided on the other end (terminal 4) side of the primary winding 6a.
The switching element 5 whose switching is controlled by is connected.

Diodes 9 and 1 are provided on the side of the secondary winding 6b.
0, choke coil 11, capacitor 12 and resistor 13
Are connected. It should be noted that reference numerals 7 and 8 in the figure denote capacitances.

The transformer 6 has a planar structure, as shown in FIG. That is, the capacitance 7 is formed between the secondary winding 6b and the winding portion on the terminal 3 side which is drawn from the outer circumference of the primary winding 6a. Capacitance 8
Is formed between the secondary winding 6b and the winding portion on the terminal 4 side drawn out from the inner circumference of the primary winding 6a.

Here, the primary winding 6a and the secondary winding 6
b is wound as shown in FIG. That is, the secondary winding 6b has the terminal 3 with respect to the winding width of the primary winding 6a.
It is wound so that it is biased to the side. As a result, the distance between the terminal 4 of the primary winding 6a and the secondary winding 6b becomes wider than the distance between the terminal 3 of the primary winding 6a and the secondary winding 6b. It is made smaller than the electric capacity 7.

Next, the operation of the transformer 6 having the above structure will be described.

First, in FIG. 1, the switching operation of the switching element 5 controlled by the PMW control circuit 2 causes a DC current from the DC power supply 1 to flow on the primary winding 6a side of the transformer 6. At this time, a DC current flows toward the diode 9 and the choke coil 11 due to the electromotive force generated in the secondary winding 6b of the transformer 6. The direct current flowing out from the choke coil 11 is smoothed by the capacitor 12 and then given to the resistor 13.

Here, when the DC current from the DC power supply 1 flows through the primary winding 6a side of the transformer 6, the primary winding 6a
The terminal 3 has a constant potential. On the other hand, on the terminal 4 side of the primary winding 6a, the potential changes due to the switching element 5 being turned on / off. This fluctuation of the potential causes a large voltage amplitude (common mode noise). The common mode noise passes through the electrostatic capacitance 8 between the primary winding 6a and the secondary winding 6b, and flows out to the secondary winding 6b as noise. Here, the capacitance 8 is, as described above, the terminal 3
Since it is smaller than the capacitance 7 on the side, the common mode noise flowing out to the side of the secondary winding 6b is reduced.

By the way, as shown in FIG. 4, when the secondary winding 6b is wound so as to have the same winding width as the primary winding 6a, the electrostatic capacitances 7 and 8 become equal. In this case, the common mode noise tends to flow out to the secondary winding 6b side through the capacitance 7 side, so that the common mode noise increases.

As described above, in the present embodiment, the capacitance 8 between the other end (terminal 4) of the primary winding 6a and the secondary winding 6b, which fluctuates due to the switching operation, is set to the primary winding 6a. Since the capacitance is made smaller than the capacitance 7 between the one end (terminal 3) and the secondary winding 6b, the common mode noise can be reduced without increasing the number of parts.

In this embodiment, as described with reference to FIG. 3, the case where the secondary winding 6b is wound so as to be biased toward the terminal 3 side with respect to the winding width of the primary winding 6a has been described. However, not limited to this example, it is possible to interpose an insulator or the like on the terminal 4 side of the primary winding 6a and increase the distance between the primary winding 6a and the secondary winding 6b on the terminal 4 side to obtain the capacitance 8 Can be reduced.

[0020]

As described above, according to the transformer and the method of forming the same according to the present invention, the capacitance between the other end of the primary winding and the secondary winding, which fluctuates due to the switching operation, is determined by the primary winding. Since the capacitance is made smaller than the electrostatic capacitance between one end of the secondary winding and the secondary winding, the common mode noise can be reduced without increasing the number of components.

[Brief description of drawings]

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

FIG. 2 is a perspective view showing a primary winding and a secondary winding of the transformer of FIG.

3 is a cross-sectional view showing a primary winding and a secondary winding of the transformer of FIG.

FIG. 4 is a cross-sectional view illustrating an operation of the transformer of FIG.

FIG. 5 is a circuit diagram showing an example of a conventional switching power supply circuit.

FIG. 6 is a circuit diagram showing another example of a conventional switching power supply circuit.

[Explanation of symbols]

1 DC power supply 2 PWM control circuit 3,4 terminals 5 switching elements 6 transformer 6a Primary winding 6b Secondary winding 7,8 capacitance 9,10 diode 11 choke coil 12 capacitors

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hideshi Matsuda               Tohoku NEC Corporation, 1 shellfish, Ichinoseki, Iwate Prefecture               Within the corporation                (56) Reference JP-A-4-137510 (JP, A)                 JP-A-5-62845 (JP, A)                 JP 7-23562 (JP, A)

Claims (8)

(57) [Claims] 1. A switching power supply including a power supply, a switching element, and a transformer, wherein the transformer has one end connected to the power supply and the other end.
Was connected to the power supply via the switching element
The primary winding and the secondary winding connected to the secondary output
The primary winding and the secondary winding have a planar structure.
, And the static Den'yo between the other end and the secondary winding of the primary winding
The amount is between the one end of the primary winding and the secondary winding.
A switch characterized by being made smaller than the capacitance.
Itching power supply. 2. The distance between the other end of the primary winding and the secondary winding is wider than the distance between one end of the primary winding and the secondary winding. The switching power supply according to claim 1. 3. The switching battery according to claim 1, wherein the secondary winding is wound so as to be biased toward the one end side with respect to a winding width of the primary winding.
Source . 4. The switching power supply according to claim 1, wherein an insulator is interposed between the other end of the primary winding and the secondary winding. 5. A switch forming a switching power supply comprising a power supply, a switching element and a transformer.
And a secondary winding connected to a primary winding, one end of which is connected to the power source and the other end of which is connected to the power source through a switching element. e Bei a secondary winding, said secondary winding and the primary winding are planar structures
And the capacitance between the secondary winding and the other end of the primary winding is smaller than the capacitance between the secondary winding and one end of the primary winding A method of forming a switching power supply , comprising the first step of forming as described above. 6. In the first step, the distance between the other end of the primary winding and the secondary winding is made wider than the distance between one end of the primary winding and the secondary winding. Second to form
Scan of claim 5, characterized in that includes the step
Forming method of switching power supply . 7. The first and second steps include a third step of winding the secondary winding so as to be biased toward the one end side with respect to the winding width of the primary winding. The method for forming a switching power supply according to claim 5 or 6, characterized in that. 8. The first to third steps include a step of interposing an insulator between the other end of the primary winding and the secondary winding. 8. The method for forming a switching power supply according to any one of 7 to 7.