JPS628600Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a noise reduction circuit for electrical equipment.

In electrical equipment, such as component-type audio equipment for automobiles, conventionally, as shown in Figure 1,
The equipment section 1, which is connected to each other and includes a tape deck, radio tuner, and preamplifier, and the amplifier 2, which uses an integrated circuit LA4060 manufactured by Tokyo Sanyo Electric Co., Ltd., are connected to each other from a common power supply (+B). The device is configured to receive an operating voltage. In the amplifier 2, the ground side line 4 of the preamplification stage (voltage amplifier) 3 and the ground side line 6 of the subsequent amplification stage (current amplifier) 5 are commonly connected, and the ground side line 7 of the preamplification stage (current amplifier) It is commonly connected to the ground side line 4 of the stationary amplifier stage 3. That is, each of the grounding lines 4, 6, and 7 of the amplifier 2 and the front-stage equipment section 1 is connected to a grounding conductor 8, which is the vehicle body of the automobile. The preamplifier stage 3, which is susceptible to noise, is supplied with power via a constant voltage circuit 11 to stabilize its operation.

However, the circuit shown in FIG. 1 has the disadvantage that it is susceptible to automobile engine noise (ignition noise, alternator noise, etc.). This will be explained with reference to the circuit of FIG. 2, which is an equivalent circuit of FIG. 1.

The pre-stage equipment section 1 and the amplifier 2 are connected to a common power supply (+
B) receives the operating voltage from amplifier 2.
On the preamplification stage 3 side of
→ Preamplification stage 3 → Earth side line 4 → Earth conductor 8
Current flows to. On the other hand, on the subsequent amplification stage 5 side, a current flows from the power supply line 9 to the ground conductor 8 through the choke coil 10, the subsequent amplification stage 5, and the ground side line 6.

Now, let us consider the resistance between each earth side line. The earth side line 4 of the preamplifier stage 3 and the earth side terminal 12 of the ripple elimination capacitor ( _C2 )
There is a resistance _r2 due to the pattern of the printed circuit board connecting the ground side line 6 of the subsequent amplifier stage 5 and the ground side terminal 12 of the capacitor ( _C2 ), and there is a resistance _r3 due to the pattern of the printed circuit board connecting the ground side line 7 of the previous equipment section 1 and the ground side line 4 of the pre-amplifier stage 3. There is also an internal resistance _r1 in the lead wire 13 connecting the ground side line 7 of the previous equipment section 1 and the ground side line 4 of the pre-amplifier stage 3.

Assuming that a noise voltage (VN) is generated due to engine noise and that this noise voltage (VN) is transferred to the power supply line 9, on the amplifier 2 side, as a loop through which the current due to the noise voltage (VN) flows, the chiyoke coil 10 and The first loop 14 flows through the ripple elimination capacitor (C ₂ ), then through the equivalent resistance (r ₃ ) according to the printed circuit board pattern, and flows to the ground conductor 8, and after passing through the ripple elimination capacitor (C ₂ ), the printed A second loop 1 flows through the equivalent resistance (r ₂ ) due to the board pattern and the internal resistance (r ₁ ) of the lead wire 13 to the ground conductor 8.
5 is possible. In addition, a third loop is also conceivable, which flows through the chiyoke coil 10 → constant voltage circuit 11 → ripple removal capacitor (C ₁ ) → internal resistance (r ₁ ) of the lead wire 13, and then flows to the ground conductor 8. Since the input impedance is sufficiently large compared to the second loop 14 and 15, most of the current due to the noise voltage (VN) flows to the first loop 14 and the second loop 15. However, it is assumed that noise is sufficiently suppressed in the front-stage equipment section 1.

Noise mixed into the input signal tends to affect the circuit handling the low signal level, that is, the circuit with a large voltage amplification factor (preamplifier 3 in Fig. 2), and in Fig. 2, the noise voltage (VN) is The voltage divided by the internal resistance (rL) of 10, the resistance components (r ₂ ) and (r ₃ ) due to the printed circuit board pattern, and the internal resistance (r ₁ ) of the lead wire 13 is applied to the preamplifier stage 3.
It is superimposed on the ground side line 4 of .

That is, the noise voltage (VN) is
The voltage is divided by the internal resistance (rL) of the circuit board and the resistance due to the pattern on the printed circuit board ( _r3 ) as shown in equation (1).

r ₃ /rL+r ₃・VN...(1), furthermore, this voltage is the resistance due to the pattern of the printed circuit board (r ₂ ) and the lead wire 1
The voltage is divided by the internal resistance (r ₁ ) of 3 as shown in equation (2). r ₁ /r ₁ +r ₂・r ₃ /rL+r ₃・VN…(2),
(However, r ₁ + r ₂ ≫ _{r 3.} ) Then, the voltage shown in equation (2) is superimposed on the ground line 4 of the preamplifier 3 as a noise voltage, and this voltage is amplified and sent to the amplifier 2. The signal appears at the output terminal 16 of , and is transmitted to a speaker (not shown) connected to this output terminal 16 . Therefore, as is clear from equation (2), the smaller the value of the internal resistance (r ₁ ) of the lead wire 13 and the larger the value of the internal resistance (rL) of the chiyoke coil 10, the more the noise is reduced. However, the internal resistance (r ₁ ) of the lead wire 13 inevitably exists, and if you try to increase the internal resistance (rL) of the chiyoke coil 10, not only will the chiyoke coil 10 become large, but the voltage due to the internal resistance (rL) will increase. The drop becomes large, and the power supply efficiency also deteriorates.

In view of this, the present invention proposes a noise reduction source circuit that reduces noise without increasing the size of the chiyoke coil.An embodiment of the present invention will be described below with reference to FIG. In addition, in Figure 3, the same parts as Figures 1 and 2 are shown in Figures 1 and 2.
The same figure numbers as in the figure will be used.

In the circuit of the present invention, the ground line 4 of the preamplification stage 3 and the ground line 6 of the subsequent amplification stage 5 are separated as shown in FIG. It is connected via a resistor (R ₄ ) to reduce noise.

Next, the reason why noise is reduced in the circuit shown in FIG. 3 will be explained. In the circuit shown in Fig. 3, when a noise voltage (VN) is generated and this noise voltage (VN) gets on the power supply line 9, if the ground side lines 4 and 6 are separated, the noise voltage (VN) flows to the ground conductor 8 through the chiyoke coil 10, the ripple removal capacitor (C ₂ ), and the resistor (r ₃ ). Also, considering the current flowing to the preamplifier stage 3 side, the current due to the noise voltage (VN) flows through the choke coil 10, the constant voltage circuit 11, the ripple removal capacitor (C ₁ ), and the resistance (r ₁ ) of the lead wire 13. A loop that flows through the ground conductor 8 can be considered. Therefore, the noise voltage (VN) is divided by the internal resistance (rL) of the chiyoke coil 10, the constant voltage circuit 11, and the resistor (r ₁ ), but the impedance of the constant voltage circuit 11 is the resistor (r ₁ ). Since the value of r 1 is sufficiently large compared to the value of r 1 , almost no voltage is generated across the resistor (r ₁ ), reducing noise.

On the other hand, if characteristics such as distortion rate deteriorate, even if it is not possible to separate the ground side lines 4 and 6, the internal resistance (r ₁ ) of the lead wire 13
Noise can be reduced by connecting via a resistor (R ₄ ) whose resistance value is sufficiently large compared to the value of (for example, a 1Ω resistor). That is, by connecting the ground side lines 4 and 6 via the resistor (R ₄ ),
The noise voltage (VN) is divided, and the ground line 4 of the preamplifier 3 has r ₁ /r ₁ +r ₄・r ₃ /rL+r.
Although the voltage represented by _3.VN (3) is superimposed, the noise is suppressed because the value of the resistance (R ₄ ) is sufficiently large.

If the circuit shown in FIG. 3 is used in this way, it is possible to use a chiyoke coil with a small internal resistance, so it is possible to downsize the device, and the voltage drop caused by the chiyoke coil is also reduced, so that the power supply efficiency is improved.

As described above, the noise reduction circuit according to the present invention includes an amplifier having a preamplification stage and a subsequent amplification stage, and a prestage equipment section connected to the input side of the amplifier, The equipment sections use a common power supply, and power is supplied to the preamplification stage of the amplifier via a constant voltage circuit, and the ground side line of the subsequent amplification stage and the ground of the preamplification stage are connected to each other. In an electrical device in which a side line is connected to a ground conductor, the ground side line of the preamplification stage is connected to the ground side line of the preceding stage equipment section, and the ground side line of the preamplification stage and the subsequent amplification stage are connected to the ground side line of the preamplification stage. The ground side line of the preamplifier stage is separated from the ground side line of the stage, or the ground side line of the preamplification stage and the ground side line of the preceding stage equipment section are connected via a resistor having a resistance value greater than the internal resistance value of the line connecting the line. , it is possible to reliably reduce the noise voltage generated on the ground side line of the preamplification stage, which is susceptible to the influence of noise.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a conventional audio device, FIG. 2 is an equivalent circuit diagram of FIG. 1, and FIG. 3 is an equivalent circuit diagram of an audio device using a noise reduction circuit according to the present invention. 1... Pre-stage equipment section, 2... Amplifier, 3... Preamplification stage, 5... Subsequent amplification stage, 4, 6, 7... Earth side line, 8... Earth conductor.

Claims (1)

[Scope of utility model registration request] an amplifier comprising the amplification stage and a subsequent amplification stage;
a preamplifier section connected to the input side of the amplifier, the amplifier and the preamplifier section use a common power source, and the preamplifier stage of the amplifier is provided with a power source via a constant voltage circuit. In an electrical device in which the grounding line of the subsequent amplification stage and the grounding line of the preamplification stage are connected to a ground conductor, the grounding line of the preamplification stage is connected to the grounding conductor of the preamplification stage. , and separate the ground side line of the preamplification stage and the ground side line of the subsequent amplification stage, or separate the ground side line of the preamplification stage and the ground side line of the preceding stage equipment section. 1. A noise reduction circuit for electrical equipment, characterized in that the circuit is connected via a resistor having a resistance value greater than the resistance value of an internal resistance of a line to be connected.