JPH0226230Y2 - - 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 3 is shown in Figure 4. .

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 4 has an anti-phase component (e1+e2)/2 and an in-phase component (e1-
e2)/2 and is represented as shown in Figures 5-a and 5-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.

[Means for solving the problems] This invention solves the drawbacks of the conventional example by:
Focusing on the fact that it is sufficient to reduce the currents Ic1 and Ic2 of in-phase components including frequency components, at least the primary winding to be connected to the commercial power supply, the secondary winding connected to the rectifier circuit, and the relevant secondary winding. a power transformer having an intermediate tap formed in a wire; a rectifier circuit connected to the secondary winding; and a smoothing circuit connected to the rectifier circuit and comprising two capacitors connected in series between at least the rectifier outputs. , a power supply circuit comprising a choke coil connected between an intermediate tap of the secondary winding and a mutual connection point of the capacitor.

[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.

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 connection point between the capacitors 4a and 4b is the intermediate tap 2c and the choke coil 6 (inductance).
connected via L1).

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. 3, 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+2L1)}Ib1 and Ib2 are each expressed as (e1+e2)/2(r+jωL).

[Effect of the invention] Therefore, the inductance of the common-mode component current is
It decreases by the amount that 2L1 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.

[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 power supply circuit diagram of the conventional example, Figures 4, 5-a and 5. Figure 1-b is an equivalent circuit diagram explaining the operation of the conventional power supply circuit. 1 is a commercial power supply, 2a is a primary winding, 2c is an intermediate tab, 2b is a secondary winding, 3 is a rectifier circuit, 4a, 4
b is a capacitor, 4 is a smoothing circuit, and 5 is a chiyoke coil.

Claims (1)

[Scope of utility model registration request] A primary winding 2a to be connected to at least the commercial power supply 1 and a secondary winding 2b connected to the rectifier circuit 3
and an intermediate tap 2 formed on the secondary winding 2b.
c and the secondary winding 2b.
a rectifier circuit 3 connected to the rectifier circuit 3, a smoothing circuit 4 connected to the rectifier circuit 3 and consisting of two capacitors 4a and 4b connected in series at least between the rectified outputs, and an intermediate tap 2c of the secondary winding. and a mutual connection point of the capacitors 4a and 4b, comprising a chiyoke coil 6.