JPH0226232Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a power supply circuit, particularly a power supply circuit suitable for use in an amplifier.

[Prior Art] An example of a conventional power supply circuit will be explained with reference to FIG.
60Hz), 2 is a power transformer with a primary winding 2a connected to the commercial power supply, and a primary winding 2a connected to the rectifier circuit.
It has a secondary winding 2b, and the secondary winding 2b has an intermediate tap 2c.

3 is a rectifier circuit connected to the secondary winding 2b, which is a known bridge type rectifier circuit; 4 is a smoothing circuit connected to the output of the rectifier circuit, which is composed of two capacitors 4a and 4b connected in series; The mutual connection point of the capacitors 4a and 4b is connected to the intermediate tap 2c.

Further, the positive output terminal and negative output terminal of the smoothing circuit 4 are respectively connected to the +B terminal and -B terminal of the amplifier circuit 5, and the mutual connection point of the capacitors is connected to the ground E of the amplifier circuit 5. .

[Problems to be solved by the invention] In such a power supply circuit, when an AC signal such as an audio signal is input to the amplifier circuit 5, if the AC signal is positive, the discharge current of the capacitor 4a increases, and if it is negative, the discharge current of the capacitor 4a increases. The discharge current of 4b increases.

At this time, when the frequency of the AC signal becomes lower than the frequency of the commercial power supply (50/60Hz), the voltage drop across the capacitors 4a and 4b increases or decreases depending on the AC signal frequency, and the charging current of the capacitor increases or decreases depending on the increase or decrease in this voltage drop. Since the secondary current of the power transformer 2 increases and decreases, a signal frequency component is included.

The disadvantage is that the magnetic flux generated by this changing current couples with the amplifier circuit and other circuits, thereby impairing the fidelity of the amplifier and the entire audio equipment system.

This can be thought of as follows.

Since the charging current is proportional to the voltage drop across capacitors 4a and 4b, if we consider the voltage drop across capacitors 4a and 4b as voltage sources e1 and e2 of the charging current, the equivalent circuit of the circuit in Figure 4 is shown in Figure 5. .

However, r is the resistance of the winding and the rectifying diode, L is the leakage inductance, and the impedance of the capacitor is sufficiently small at the power supply frequency.

Note that the dotted arrow indicates the direction of electromotive force, and the solid arrow indicates the direction of current.

Furthermore, according to the superposition theory, the circuit in Figure 5 has an anti-phase component (e1+e2)/2 and an in-phase component (e1-
e2)/2 and is represented as shown in Figures 6-a and 6-b.

Here, the currents Ic1 and Ic2 flowing through each circuit network are respectively expressed as (e1-e2)/2(r+jωL), and the currents Id1 and Id2 are respectively expressed as (e1+e2)/2(r+jωL).

Further, the anti-phase component is considered to be a component proportional to the magnitude of the AC signal, and the in-phase component is considered to be due to the imbalance between positive and negative signals and includes a frequency component.

Therefore, as a means to solve this drawback, a power supply circuit shown in FIG. 7 (the same reference numerals as in FIG. 4 indicate the same parts) has been devised.

The circuit consists of a pair of coils 7a and 7b (the inductance of each coil is L2, and the mutual inductance is M), which are wound in the same direction (the mark indicates the winding start end) between a power transformer 2 and a rectifier circuit 3. show)
It has a configuration in which a transformer 7 consisting of the following is interposed.

Here, as in FIG.
Considering the equivalent circuits of the above embodiments for each of them, they are shown in FIGS. 8-a and 8-b.

The currents If1 and If2 of each circuit are respectively expressed as (e1-e2)/2{r+jω(L+L2+M)}, and g1 and Ig2 are respectively expressed as (e1+e2)/2{r+jω(L+L2-M)}.

Therefore, an increase in L2+M has the effect of reducing the common-mode current, and by making the coupling degree of the coil close to 1, L2≈M, which has no effect on the negative-sequence current and reduces the impedance for the common-mode current. The effect of increasing 2jωL2 was obtained.

However, in order to obtain this effect, a large value of inductance is required, which increases the size of the transformer 7 itself and causes an increase in component costs.

[Means for solving the problem] This invention solves the drawbacks of the conventional example, and in order to further improve the effect, it is necessary to further reduce the currents If1 and If2 of the in-phase components including frequency components. We focused on a power transformer having at least a primary winding to be connected to a commercial power source and a secondary winding forming an intermediate tap, a rectifier circuit, and a smoothing circuit consisting of at least two capacitors connected in series. ,
A transformer is provided, which is connected between the power transformer and the rectifier circuit, or between the rectifier circuit and the smoothing circuit, and the transformer has a first coil and a second coil wound in the same direction, and a first coil and a second coil wound in the opposite direction. The first coil and the second coil are connected between the power transformer and the rectifier circuit, or between at least one of the rectifier circuit and the smoothing circuit,
The power supply circuit is characterized in that the third coil is connected between an intermediate tap of the secondary winding and a mutual connection point of the capacitors.

[Example] This invention will be explained with reference to the example shown in Fig. 1. In the figure, 1 is a commercial power supply (100V, 50/60
Hz), 2 is a power transformer having a primary winding 2a connected to the commercial power supply and a secondary winding connected to the rectifier circuit, and the secondary winding 2b is connected to an intermediate tap 2c.
has.

Reference numeral 6 denotes a transformer connected to the power transformer 2, which is composed of coils 6a and 6b wound in the same direction and a coil 6c wound in the opposite direction (the * mark on each coil indicates the winding start end) (coils 6a, The inductance of coil 6b is L1, the inductance of coil 6c is L2, the mutual inductance between coils 6a and 6b is M1, and the mutual inductance between coil 6a and coil 6c and between coil 6b and coil 6c is M2).

For example, bifilar winding is recommended so that each coil of the transformer 6 is preferably magnetically closely coupled.

3 is a rectifier circuit connected to the transformer 6, which is a well-known bridge type rectifier circuit; 4 is a smoothing circuit connected to the output of the rectifier circuit 3, which is composed of two capacitors 4a and 4b connected to DC; The mutual connection point of 4a and 4b is connected via the intermediate tap 2c and a coil 6c wound in the opposite direction.

Further, the positive output terminal and negative output terminal of the smoothing circuit 4 are respectively connected to the +B terminal and -B terminal of the amplifier circuit 5, and the mutual connection point of the capacitors is connected to the ground E of the amplifier circuit 5. .

[Effect] Here, as in Fig. 4, the in-phase component (e1-e2)/2
Considering the equivalent circuit of the above embodiment for each of
-b.

And the currents Ia1 and Ia2 of each circuit are respectively,
(e1−e2)/2{r+jω(L+L1+2L2+M1+
2M2)}, Ib1 and Ib2 are each expressed as (e1+e2)/2{r+jω(L+L1-M1)}.

[Effect of the invention] Therefore, the inductance of the common-mode component current is
It decreases by the amount that L1+2L2+M1+2M2 increases, and the signal frequency components of the charging current and winding current become smaller, and the influence on the amplifier circuit and other equipment can be reduced.

Also, if we set L1 = L2 and the degree of coupling between the coils is approximately 1, then approximately L1 = L2 = M1 = M2, and the inductance for the common mode current is approximately 6L1, which is the seventh
In order to obtain the same effect as the power supply circuit shown in the figure, each inductance may be reduced to approximately 1/3, and the transformer 6 can be significantly miniaturized.

Further, as shown in FIG. 3, the same effect can be obtained even if the transformer 6 is a power supply circuit placed between the rectifier circuit 3 and the smoothing circuit 4.

[Brief explanation of the drawing]

Figure 1 is a power supply circuit diagram of an embodiment of this invention, Figure 2
Figures -a and 2-b are equivalent circuit diagrams explaining the operation of the power supply circuit of the embodiment of this invention, Figure 3 is a block diagram of the main part of the power supply circuit of another embodiment of this invention, and Figure 4. The figure is a power supply circuit diagram of a conventional example, Figures 5, 6-a, and 6-b are equivalent circuit diagrams explaining the operation of the conventional power supply circuit of Figure 4, and Figure 7 is an equivalent circuit diagram of another power supply circuit. The power supply circuit diagrams of the conventional example, FIGS. 8-a and 8-b, are equivalent circuit diagrams illustrating the operation of the conventional power supply circuit of FIG. 7, respectively. 1 is a commercial power supply, 2a is a primary winding, 2c is an intermediate tap, 2b is a secondary winding, 3 is a rectifier circuit, 4a, 4b
are each a capacitor, 4 is a smoothing circuit, and 6 is a transformer.

Claims (1)

[Scope of utility model registration request] A primary winding 2a to be connected to at least a commercial power supply 1, and a secondary winding 2 forming an intermediate tap 2c.
b, a rectifier circuit 3, and at least two capacitors 4 connected in series.
a, 4b, and a transformer 6 connected between the power transformer 2 and the rectifier circuit 3, or between the rectifier circuit 3 and the smoothing circuit 4, the transformer 6 being connected in the same direction. A first coil 6a and a second coil 6b are wound in the opposite direction, and a third coil 6c is wound in the opposite direction. or connected between at least one of the rectifier circuit 3 and the smoothing circuit 4, and the third coil 6
c is the intermediate tap 1c of the secondary winding and the capacitor 4
A power supply circuit characterized in that it is connected between a and a mutual connection point of 4b.