JP2000299233A - Transformer for power - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transformer for power which suppresses a peak value of current flowing non-controllable output system in a power circuit and can make a power circuit smaller and safer. SOLUTION: A second winding layer L2 is formed by bifilar-winding each wire so that two wires are disposed alternately in the bobbin BO width direction. One of the bifilar wound wires is used as a wire B3A connected to a uncontrolled output system of a power circuit while the other one is used as a winding N3B connected to another non-controllable output system in the power circuit. A third winding layer L3 is formed by winding a wire to a bobbin and the wire is used as a secondary winding N2 connected to a controlled output system in the power circuit. A fourth winding layer L4 has the same structure as that of the second winding layer L2. The third winding layer L3 for forming the secondary winding N2 is sandwiched between the second and fourth winding layers L2, L4 for forming the windings N3A, N3B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a winding technique capable of suppressing a peak value of a current flowing through an uncontrolled output system of a power supply circuit in a power supply transformer used in a multi-output type power supply circuit.

[0002]

2. Description of the Related Art In recent years, electronic equipment has a large number of functional circuits and devices, and it is natural that the drive voltage to be supplied to these functional circuits and devices is two or more types (voltage values). It became like. In order to obtain a plurality of output voltages having different voltage values, for example, a multi-output type switching power supply circuit having a circuit configuration as shown in FIG. 3 is used.

The power supply circuit shown in FIG. 3 has input terminals 1a, 1
Between b, the primary winding N1 of the transformer T and the switching transistor Q1 are connected in series, and the control circuit 4 is connected to the gate of the switching transistor Q1. Of the plurality of output windings, a secondary winding N2 is connected to output terminals 2a and 2b via a rectifying and smoothing circuit including a diode D1 and a capacitor C1. On the other hand, the tertiary winding N3 has an intermediate tap connected to the output terminal 3c, and each winding end has a diode D
2 is connected to the output terminal 3a or 3b via a rectifying / smoothing circuit comprising a capacitor C2 or a rectifying / smoothing circuit comprising a diode D3 and a capacitor C3. Further, for feedback control of the output voltage, a circuit configuration is provided in which a voltage detection circuit 5 and a photocoupler 6 are provided between the output terminals 2a and 2b and the control circuit 4.

The circuit of FIG. 3 having the above configuration uses a multi-output power supply transformer having a plurality of output windings in the transformer T in order to obtain a plurality of output voltages. As an example of such a multi-output power supply transformer, there is a transformer having a winding structure as shown in FIG. The winding structure of the power transformer shown in FIG. 4 is as follows. First, an electric wire is wound around a core portion of a bobbin BO constituting the power transformer in a single layer to form a first winding layer La. Wire layer L
a is covered with an insulating sheet SI. The insulation sheet SI
A second winding layer Lb is formed by further winding an electric wire on the upper surface of the second winding layer Lb, and the upper surface of the second winding layer Lb is covered with an insulating sheet SI. By repeating the operation of winding the electric wire and the insulating sheet around the bobbin BO, the third to fifth winding layers Lc and L
d and Le are sequentially formed to form a transformer winding NB.

Here, the third winding layer Lc is slightly different from the other winding layers. First, an electric wire is wound on an insulating sheet SI, and once outside the bobbin BO at an intermediate portion thereof. Pull out. The drawn wire is connected to a terminal pin (not shown) for tapping, and then the wire is returned to the bobbin BO again and wound on the insulating sheet SI. The third winding layer Lc thus formed is used as the tertiary winding N3 in the circuit of FIG. 3, and as shown in the lower part of FIG. 4, the first half of the third winding layer Lc has a winding N3A, The latter half is the winding N3B. Note that the first winding layer La and the fourth winding layer Ld are
Outside O, it is connected to the same terminal pin (not shown) so as to be connected in parallel, and is used as the primary winding N1 of the circuit of FIG. Further, the second winding layer Lb and the fifth winding layer Le are used as the secondary winding N2 and the drive winding N4 of the circuit of FIG. 3, respectively.

Here, it is assumed that a power supply transformer having a winding structure as shown in FIG. 4 is actually applied to a power supply circuit having a circuit configuration as shown in FIG. The power circuit operates,
When the switching transistor Q1 shifts from the ON state to the OFF state, the winding N3 of the secondary winding N2 and the tertiary winding N3
A flyback voltage is generated in each output winding of A and N3B. Then, the switching transistor Q1 is turned off to the time after t _0, the diode D1 constitutes a rectifying smoothing circuit of the control output system, non-control output system of the rectifying smoothing circuit as shown in FIG. 5 the diode D2 and D3 constitutes a waveform Current flows.

In FIG. 5, first, two non-control output systems
Current I flowing through the diodes D2 and D3_3A, I_3BTo
About time t₀The maximum current I_P2Flows,
Decreases with time, and the time t₃Becomes zero at
A triangular current waveform (I_{3A 2}, I_3B2)
You. On the other hand, the diode D1 of the control output system of the power supply circuit flows.
Current I₂For the time t₀Prescribed at the time of
Value of current flows, time t₀To t₃Until the current I
_3A, I_3BThe current value gradually increases as the current value of
Add. And time t ₃Switching transistor from
Time t when Q1 turns on₄On the contrary, until
The current value gradually decreases with the lapse of time, and the time t₄And the current value
A pentagonal current waveform (I
₂₂).

[0008]

As can be seen from the current waveform in FIG. 5, the currents I _3A and I _3B flowing through the diodes D2 and D3 of the non-control output system have a short current flowing time but a peak value. It has a high, triangular current waveform. When such a current flows, the diodes D2, D3
Therefore, a diode element having a large current specification that can withstand the peak current value must be selected. When a current having such a waveform flows through the diodes D2 and D3,
The ripple component of the current flowing through the capacitors C2 and C3 also increases, and it is necessary to use a capacitive element having a large ripple resistance for the capacitors C2 and C3. as a result,
The power supply circuit is enlarged, which is not preferable in terms of safety of the power supply circuit.

For example, in order to keep the peak values of the currents I _3A and I _3B low, it is also conceivable to take measures in the circuit configuration such as inserting a choke coil in the circuit. However, this has a problem that, in addition to enlarging the outer shape of the power supply circuit, the number of components for configuring the power supply circuit increases. Accordingly, an object of the present invention is to provide a power transformer capable of suppressing the peak value of the current flowing through the non-control output system of the power circuit, thereby reducing the size of the power circuit and improving safety.

[0010]

A power transformer according to the present invention comprises an input winding, a first output winding connected to an output system to be subjected to feedback control of the power supply circuit, and a non-connected power supply circuit. A power transformer having second and third output windings connected to a control output system, wherein a first winding formed by winding an electric wire for forming the first output winding; A layer formed by winding each electric wire so that the layer, the electric wire for forming the second output winding, and the electric wire for forming the third winding are alternately arranged in the bobbin width direction. 2
Wherein the first winding layer and the second winding layer are wound on a bobbin such that one of them sandwiches the other.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In winding an electric wire around a bobbin and forming winding layers for an input winding and first to third output windings, a first winding layer and a second winding layer are formed. The winding layer is formed such that one sandwiches the other. Here, the first winding layer is 1
This electric wire is formed by winding a wire around a bobbin, and is used as a first output winding connected to a control output system of a power supply circuit. On the other hand, the second winding layer is formed by winding each wire by bifilar winding so that the two wires are alternately arranged in the bobbin width direction. It is used as a second output winding connected to an uncontrolled output system of the circuit, and the other wire is used as a third output winding connected to another uncontrolled output system of the power supply circuit.

[0012]

FIG. 1 shows a partial cross section of a bobbin and windings of a power transformer according to the present invention capable of suppressing a peak value of a current flowing through an uncontrolled output system of a power supply circuit, and a winding structure thereof.
In FIG. 1, the winding structure of the power transformer was as follows. First, one electric wire is wound around a core portion of a bobbin BO constituting the power transformer T in a single layer to form a first winding layer L1.
Is formed, and the upper surface of the first winding layer L1 is covered with the insulating sheet SI. Next, on the upper surface of the insulating sheet SI, two electric wires are wound in one layer by bifilar winding to form a second winding layer L
2 is formed, and the upper surface of the second winding layer L2 is covered with the insulating sheet SI. Here, the ends of the two wires wound by bifilar are connected to separate terminal pins (not shown) outside the bobbin BO, thereby forming two independent windings with each wire.

One wire is further wound on the upper surface of the insulating sheet SI to form a third winding layer L3, and the upper surface of the third winding layer L3 is covered with the insulating sheet SI. And the second
Similarly to the winding layer L2, two electric wires are wound in one layer on the upper surface of the insulating sheet SI by bifilar winding to form a fourth winding layer L4. The ends of the two electric wires forming the fourth winding layer L4 are connected to the same terminal pins as the two electric wires forming the second winding layer L2, respectively. The respective windings formed by the winding layer L4 are connected in parallel. The operation of covering the upper surface of the winding layer with the insulating sheet SI, further winding one electric wire on the insulating sheet SI in one layer, and forming the winding layer is repeated. The wire layers L5 and L6 are sequentially formed, and the entire winding layers L1 to L6 wound around the bobbin BO are used as the windings NA of the transformer.

In the power transformer having the winding NA formed as described above, the first winding layer L1 and the fifth winding layer L5 are
The ends of the electric wires are connected to the same terminal pins (not shown) so as to be connected in parallel and used as the primary winding N1 of the circuit of FIG. Of the two wires wound by bifilar of the second winding layer L2 and the fourth winding layer L4, one is used as the winding N3A, and the other is used as the winding N3B. The third winding layer L3 and the sixth winding layer L6 are used as the secondary winding N2 and the drive winding N4 in the circuit of FIG.

In the power transformer having the winding structure shown in FIG. 1, two electric wires of the second winding layer L2 (or the fourth winding layer L4) used as the winding N3A and the winding N3B are used. With respect to the third winding layer L3 as the secondary winding N2,
Each is uniformly distributed in the width direction of the bobbin BO. Then, the third winding layer L3 may be sandwiched between the second winding layer L2 and the fourth winding layer L4, so that the secondary winding N2, the winding N3A, the winding N3B Will be further improved. When the power supply transformer having such a winding structure is applied to the power supply circuit of FIG. 3, the diodes D1, D2, and D3 constituting the rectifying / smoothing circuits of the control output system and the non-control output system are provided as shown in FIG. A current having a complicated waveform flows.

The diode D1 of the control output system of the power supply circuit is
Flowing current I₂For the time t ₀At the time of
The current flows and the time t₀To t₁Until the current value
Hardly changes. And time t₁Switch from
T when transistor Q1 is turned on₂For up to
The current value gradually decreases with time, and the time t₂
Pentagon-shaped electric current, the current value of which becomes zero
Flow waveform (I₂₁). The current I in FIG.₂of
The current waveform is the time t₀To t₁The current value between
Except that it has not changed much,
With a waveform shape similar to the current waveform in FIG.
is there. On the other hand, the two non-controlled output systems in FIG.
Current I flowing through nodes D2 and D3_3A, I_3BCurrent waveform
Is quite different from FIG.

[0017] That is, the current through the diode D2, D3 _{I 3A, I 3B,} the maximum current I at time _{t 0
P1} flows, decreases significantly over time as peak time of time t _0. When the current decreases to some extent (time t ₁ ), the slope of the current decrease becomes gentle, and the current value gradually decreases from time t ₁ to time t _{2 at} which the switching transistor Q 1 is turned on. And finally, said current becomes zero at time _{t 2,} L-shaped current waveform _{(I 3A1,} I _{3 B1)}
Becomes Such an L-shaped current waveform (I _3A1 , I _3A1
In _3B1), a current also flows through the diodes D2, D3 in the period between time _{t 1} of time _{t 2,} energy is supplied to the capacitor C2 and C3 by the current. Then, the peak value I _P1 of the current at the time point t ₀ is the peak value I _P of the current when the conventional power transformer is used.
_It is much lower than _P2 .

As a result, when the power supply transformer having the winding structure shown in FIG. 1 is applied to the circuit of FIG. 3, it becomes possible to use diode elements having small current specifications for the diodes D2 and D3. Further, as the peak value _IP1 of the current decreases, the ripple component of the current flowing into the capacitors C2 and C3 also decreases, so that a small-sized capacitive element can be used. As a result, the size of the power supply circuit can be reduced, which is advantageous in terms of safety of the power supply circuit. In addition, by improving the coupling between the secondary winding N2, the winding N3A, and the winding N3B, the effect of improving the regulation characteristics between the output voltages can be obtained.

In the embodiment of the power transformer according to the present invention, only the third winding layer L3 is used for the secondary winding N2, but the winding layer having the same configuration as the third winding layer L3 is used. May be provided in plurality. In the winding structure shown in FIG. 1, the winding layer constituting the secondary winding N2 is sandwiched between the winding layers constituting the winding N3A and the winding N3B.
May be sandwiched between the winding layers constituting the windings N3A and N3B. Further, more winding layers having the same configuration as the second and fourth winding layers L2 and L4 may be provided. The number of various winding layers is not limited to the embodiment of FIG.

In the embodiment of the present invention, two windings N3A and N3B are assumed as non-control output system windings. However, three or more non-control output system windings may be used. In this case, the winding layer may be formed by a winding method such as a bifilar (trifiler).
Further, although the circuit shown in FIG. 3 is a flyback type power supply circuit, the power supply transformer according to the present invention can be applied to a power supply circuit of another type such as a forward type.

[0021]

As described above, the power supply transformer according to the present invention has the first winding layer formed by winding the electric wire for the secondary winding connected to the control output system and the non-winding layer. Each wire is bifilar wound so that the wire for one tertiary winding (N3A) and the wire for the other tertiary winding (N3B) connected to the control output system are alternately arranged in the bobbin width direction. And a second winding layer formed by winding the first winding layer and the second winding layer on one side when forming a winding by winding an electric wire around the bobbin. Is characterized by a winding structure formed on a bobbin so as to sandwich the other.

According to the power supply transformer having such a winding configuration, the coupling between the output windings is improved, and the peak of the current flowing through the rectifying / smoothing circuit of the non-control output system of the multi-output type power supply circuit is improved. You can lower the value. As a result, a rectifier element and a smoothing capacitor element having a small characteristic value can be used for the power supply circuit, and the power supply circuit using this power transformer can be reduced in size and improved in safety. Also incidentally,
Regulation characteristics between output voltages can also be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a partial cross section and a winding structure of a bobbin and a winding of a power transformer according to an embodiment of the present invention.

FIG. 2 is a current waveform flowing through each part of the circuit when the transformer having the winding structure of FIG. 1 is applied to the circuit of FIG. 3;

FIG. 3 is a circuit diagram of an example of a multi-output power supply circuit.

FIG. 4 is a diagram showing a partial cross section and a winding structure of a bobbin and a winding of a conventional power supply transformer.

FIG. 5 shows a conventional transformer having the winding structure of FIG.
The current waveform flowing through each part of the circuit when applied to the circuit of FIG.

[Explanation of symbols]

BO: bobbin L1: first winding layer L2: second
Winding layer (second winding layer) L3: third winding layer (first winding layer) L4: fourth winding layer (second winding layer) L5: fifth winding layer L
6: sixth winding layer N: transformer winding N1: primary winding (input winding) N2: secondary winding (first output winding) N3A: winding (second output winding) N3B : Winding (third output winding) SI: insulating sheet

Claims (3)

[Claims] 1. An input winding, a first output winding connected to an output system to be subjected to feedback control of a power supply circuit, and a second output winding connected to an uncontrolled output system of the power supply circuit. In a power transformer having a third output winding, a first winding layer formed by winding an electric wire for forming the first output winding, and a second output winding are formed. And a second winding layer formed by winding each of the wires so that the wires for forming the wires and the wires for forming the third winding are alternately arranged in the bobbin width direction. A power transformer, wherein the first winding layer and the second winding layer are formed on a bobbin such that one of them sandwiches the other. 2. The second winding layer is formed by winding a wire for forming a second output winding and a wire for forming a third winding by bifilar winding. The power transformer according to claim 1, wherein: 3. The second winding layer is formed as a single layer, and the second and third output windings are formed by a plurality of second winding layers in which respective electric wires are connected in parallel. The power transformer according to claim 1, wherein the power transformer is configured.