JPS5919445Y2 - Volume switching circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a simple volume switching circuit with a small number of circuit components.

A conventional volume switching circuit is shown in FIG.

In Fig. 1, 1-1' is an audio signal input terminal, 2 is a volume adjuster, 3 is a selector switch as a switching circuit,
4 is a resistor, 5 is a capacitor, 6 is an audio power amplifier, and 7 is an output terminal to which a speaker is normally connected.

Reference numeral 8 indicates a control signal input terminal of the changeover switch 3, a indicates a ground terminal of the volume regulator 2, b indicates an output terminal of the volume regulator 2, and C indicates an input terminal of the volume regulator 2.

Generally speaking, each sound amplification device has a volume adjuster, and listeners adjust the volume to a level that is comfortable for them.

However, in the event of an emergency, such as a disaster prevention broadcast radio receiver or an in-place notification device, it is necessary to make a notification at a constant loud volume regardless of the position of the volume adjuster.

In order to achieve this, conventionally, as shown in FIG. By switching to the M side shown in the figure by the operation of the changeover switch 3 controlled by , the audio signal input is connected to the output side, that is, the resistor 4 side, regardless of the volume adjuster 2.

As the changeover switch 3, a transfer contact is required, and polarized relays are often used, and there are disadvantages such as the number of elements is large to configure the same function as a transfer contact with a semiconductor element, and the configuration is complicated. Ta.

Furthermore, while the changeover switch 3 is changing from M to B or from B to M as shown in the figure, the audio signal is cut off, and there is also a drawback that a switch impact sound is produced at the time of changeover.

The purpose of the present invention is to eliminate these drawbacks by using only a make contact or a switching circuit corresponding to a make contact in the changeover switch, and by creating an impedance between the output side of the make contact and the output side of the volume adjuster. A correction resistor is provided, and a volume switching circuit is obtained in which a connection point between the impedance correction resistor and the switching circuit is connected to the cutting edge side, and will be described in detail below.

Figure 2 is a diagram of the principle of the present invention, where 9 is a switching circuit with only a make contact, 10 is an impedance correction resistor,
Other signals are the same as in FIG.

As shown in the figure, a circuit in which a switching circuit 9 with only a make contact and an impedance correction resistor 10 are connected in series is connected between the input terminal C and the output terminal S of the volume adjuster 2, and an intermediate connection point A of the circuit is connected. This is a circuit configuration in which the point is connected to the output side, that is, to the resistor 4.

Therefore, in this figure, when the switch 9 is off, the volume of the output terminal 7 is determined by the position b of the volume adjuster 2, and when the switch 9 is on, the volume adjuster becomes a short-circuited circuit and the audio signal input is A constant output is applied to the audio amplifier 6 without attenuation and output from the output terminal 7.

The resistances between ac, al), and cl) of volume adjuster 2 are R, c, Rab, R, b (= Rc,, -R, b)
If the resistance of the impedance correction resistor 10 is RIO and the input impedance of the audio amplifier seen from point A is high, then the input impedance seen from the audio signal input terminal 1 is as follows.

Therefore, if the output impedance of the audio signal input source is approximately the same as the range of equation (4), the output of the output terminal 7 will be kept almost constant no matter where the position b of the volume adjuster 2 is.

The reason why the impedance correction resistor 10 is necessary is to prevent the input signal from becoming short-circuited to the ground when the output terminal of the volume adjuster 2 is at the ground terminal point a.

As explained above, the switching circuit only needs to be a make contact, and how to select the impedance correction resistor 10 (
3) It is sufficient to suitably set the conditions of the formula, and there is an advantage that the circuit configuration can be simplified.

Also, unlike conventional transfer contacts, no audio signal interruption occurs during operation.

Figure 3 shows an example using transistors as a switching circuit, where 11 is a transistor and 12 is a transistor.
1 is a base resistor, 13 is a DC blocking capacitor, and the capacitor 13 can be omitted depending on bias conditions.

In the example of FIG. 3, the switch control signal 8 may be a small current that drives the base current, and the transistor 11 may be a C-MOS analog IC or the like with low power consumption.

It is obvious that the transistor 11 is turned on by a signal from the switch control signal input terminal 8, and the same function as the switching circuit 9 with only the make contact shown in FIG. 2 can be realized.

The present invention is a volume switching circuit using a simple switching circuit that has the advantage of a simple circuit configuration and requires little control current, and is suitable for electronic equipment that requires low power consumption and communication equipment that requires emergency calls. You can use it.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional volume switching circuit, FIG. 2 is a principle diagram of the present invention, and FIG. 3 is a circuit diagram showing an embodiment of the present invention. 1.1'...Audio signal input terminal, 2...
・Volume adjuster, 3... Transfer contact switching circuit, 4... Resistor, 5...
Condenser, 6...Audio amplifier, 7...
...Audio output terminal, 8...Switch control signal input terminal, 9...Make contact switching circuit, 10...Impedance correction resistor, 11...
...Transistor, 12...Base resistance,
13...DC blocking capacitor.

Claims (3)

[Scope of utility model registration request] (1) A switching circuit is provided between the input terminal and the output terminal of the volume adjuster, and when the switching circuit is activated, a fixed amount of volume is output regardless of the adjustment position of the volume adjuster. In the volume switching circuit, only a make contact or a switching circuit corresponding to a make contact and an impedance correction resistor for correcting input impedance as seen from the input terminal side are connected in series between the input terminal and output terminal of the volume adjuster. 1. A volume switching circuit characterized by a circuit configuration in which a circuit is connected to the switching circuit and an intermediate connection point between the switching circuit and an impedance correction resistor is connected to an output side. (2) The volume switching circuit according to claim 1, wherein a transistor is used as the switching circuit. (3) C-MOS analog I as a switching circuit
The volume switching circuit according to claim 1, using C.