JPH03250453A - Muting circuit - Google Patents

Abstract

PURPOSE:To reduce the number of terminals to be used for the formation of an IC and to contract a mounting area by charging a capacitor when a power supply switch is ON and discharging the capacitor at the OFF of the capacitor to make a switch element conductive. CONSTITUTION:When the power supply switch 2 is turned on, the capacitor 15 is charged with electricity, transistors(TRs) 21, 24 are turned on and the switching element 28 is turned to the conductive state. When the switch 2 is turned off, the charged electricity of the capacity 15 is discharged, TRs 12, 18 are turned on and the element 28 is made conductive. Thereby, a signal (noise) from an input terminal 26 is allowed to flow into the earth side and a noise tone from a speaker is not discharged, so that only the capacitor is used for the muting circuit 50, the number of terminals to be used for the formation of an IC are reduced and the mounting area is contracted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a mute circuit suitable for application when, for example, a VTR audio circuit is made into a monolithic IC.

[Summary of the invention]

The present invention provides a monolithic IC for the audio circuit of a VTR, for example.
Regarding the mute circuit suitable for application when
One controlled electrode of the transistor is connected to one end of the DC power supply via a power switch, and the other controlled electrode of the first transistor is connected to the other end of the DC power supply via a first resistor. At the same time, the other controlled electrode of this first transistor is connected to the control electrode of the second transistor via a second resistor, and the one controlled electrode of this second transistor is connected to a third resistor. is connected to one controlled electrode of this first transistor and the connection point of this power switch through the other controlled electrode of this second transistor through a first diode for backflow prevention. A controlled electrode is connected to a signal line, the other controlled electrode is connected to a control electrode of a switching element connected to the other end of this DC power supply, and the control electrode of this first transistor is connected to a fourth resistor, A fifth resistor and a second diode for preventing reverse current are connected to the connection point of this power switch and this third resistor through a DC circuit, and the connection point of this fourth and fifth resistor is connected to the connection point of this power switch and this third resistor. It is connected to the other end of this DC power supply via a capacitor, and the connection point of the fourth and fifth resistors is connected to one controlled electrode of the third transistor, and the control electrode of this third transistor is connected to the other end of the DC power source. The other controlled electrode of this third transistor is connected to the other end of this DC power source via a seventh resistor. and the other controlled electrode of the third transistor is connected to the control electrode of the fourth transistor via the eighth resistor, and one controlled electrode of the fourth transistor is connected to the control electrode of the fourth transistor. The other controlled electrode of this fourth transistor is connected to the connection point of the fourth and fifth resistors via a resistor, and the control electrode of this switching element is connected to the other controlled electrode of this fourth transistor via a third diode for backflow prevention. By connecting the capacitor to the capacitor, the number of capacitors used can be reduced to one.

[Conventional technology]

Conventionally, for example, a mute circuit (monolithic IC) (50) implemented as an IC has a configuration as shown in FIG.

In Figure 2, (1) is a DC power supply, and this DC power supply (
1) One end (plus side) is connected to the power terminal (3) of the IC of the mute circuit (50) via the power switch (2), and the other end (minus side) is grounded. Therefore, when the power switch (2) is turned on, power is supplied to the power terminal (3).

The emitter of a PNP transistor (42) whose emitter and base are connected via a resistor (40) is connected to the power supply terminal (3), and the base of this transistor (42) is connected via a resistor (41). It is connected to a terminal (33) of the IC, and this terminal (33) is grounded via a capacitor (43). In this case, the mute time when the power switch (2) is turned on is determined by the time constant determined by the resistors (40), (41) and the capacitor (43). The collector of this transistor (42) is connected to two NPN transistors (28a) through a diode (25) for backflow prevention.
) and (28b) are connected to the respective bases of transistors (28a) and (28b) of a switch element (28) configured by connecting their respective collectors and emitters to each other.

(26) is an input terminal for audio signals, and this input terminal (26) is an input terminal for audio signals.
6) is connected to the output terminal (31) of the IC via a series circuit of resistors (27) and (29). Further, the connection point between this resistor (29) and the output terminal (31) is grounded via a signal output resistor (30).

The audio signal output from this output terminal (31) is supplied to a speaker (35) through an amplifier circuit (34).

In FIG. 2, the emitter of the transistor (28a) constituting this switch element (28) and the transistor (
The connection point of the collector of 28b) is connected to the resistor (27) and (2
9), and this transistor (2).
The connection point between the collector of transistor 8a) and the transmitter of transistor (28b) is grounded.

In addition, the emitter of a PNP type transistor (47) is connected to the power supply terminal (3) via a series circuit of a diode (46) and a resistor (45) for preventing backflow, and the emitter of this transistor (47) is IC terminal (14)
and this terminal (14) is grounded via a capacitor (48). In this case, the capacitor (48) determines the mute time when the power switch (2) is turned off.

The base of this transistor (47) is connected to the power supply terminal (3) via a resistor (44), and the base of this transistor (47) is connected to the power supply terminal (3) through a resistor (44).
The collector of 7) is connected to the control electrode of the sui-nochi element (28), that is, the bases of the transistors (28a) and (28b), through a diode (19) for preventing backflow.

In the above mute circuit (50), the power switch (
2) is turned on, current from the DC power supply (1) flows to the capacitor (43) via the power switch (2) and resistors (40) and (41), and this capacitor (43)
is charged. After this capacitor (43) is completely charged, the transistor (42) is turned off, but while the capacitor (43) is charging, the base voltage of the transistor (42) is lower than this emitter voltage, so the transistor (42) is turned on, current from the DC power supply (1) flows through the power switch (2), transistor (42) and diode (25), making the switch element (28) conductive and connecting the audio signal input terminal (26). Since the signal (noise) from the speaker (35) is sent to the ground side through this switch element (28), the signal (noise) from the power switch (2)
Noise is not emitted when the is turned on.

On the other hand, when the power switch (2) of the circuit (50) described above is turned on, the connection terminal (14) of the resistor (45), diode (46), and capacitor (48) is connected to the DC power supply (1).
) and charges the capacitor (48).

Next, when the power switch (2) is turned off, the base voltage of the transistor (47) becomes approximately ground potential, and the emitter of this transistor (47) is connected to the capacitor (4).
Since the charging voltage of transistor (8) is supplied, this transistor (4)
7) is turned on, a current due to the charge in the capacitor (48) flows through this transistor (47) and the diode (19), and as a result, the switch element (28) is turned on.
) is conductive, and at this time, the switch element (28) causes the signal (noise) from the audio signal input terminal (26) to flow to the ground side, so the power switch (2) is turned off from the speaker (35). When the noise is not emitted.

[Problem to be solved by the invention] By the way, when the above-mentioned mute circuit is integrated into an IC,
As mentioned above, there are two external capacitors (43),
(48) As a result, the number of IC terminals increases and the mounting area increases accordingly, which is disadvantageous in that the advantages of IC implementation are reduced.

In view of this point, the present invention proposes a mute circuit that can use only one capacitor.

[Means to solve the problem]

For example, as shown in FIG. 1, the present invention connects one controlled electrode (emitter) of a first transistor (21) to one end of a DC power source (1) via a power switch (2), and The other controlled electrode (collector) of the first transistor (21) is connected to the DC power supply (1) via the first resistor (22).
) and connect it to the other end of the first transistor (2nd type).
The other controlled electrode (collector) is connected to the second resistor (23
) is connected to the control electrode (base) of the second transistor (24), and one controlled electrode (collector) of the second transistor (24) is connected to the control electrode (base) of the second transistor (24) through a third resistor (4). The negative controlled electrode (emitter) of the first transistor (21) is connected to the connection point of the power switch (2), and the other controlled electrode (emitter) of the second transistor (24) is connected to the negative controlled electrode (emitter) of the second transistor (24). The first diode (25
), one controlled electrode is connected to the signal line, the other controlled electrode is connected to the control electrode of the switching element (28) connected to the other end of the DC power supply (1), and the first The control electrode (base) of the transistor (21) is connected to the power switch ( 2) and the third resistor (4), and connect the fourth and fifth resistors (20) and (11) to the connection point of the DC type #(1) via the capacitor (15). connected to the other end and the fourth and fifth resistors (20) and (1
1) is connected to one controlled electrode (emitter) of the third transistor (12), and the control electrode (base) of this third transistor (12) is connected through the sixth resistor (9). the other controlled electrode (collector) of the third transistor (12) via the seventh resistor (13). is connected to the other end of the DC power supply (1), and the other controlled electrode (collector) of the third transistor (12) is connected to the eighth
through the resistor (16) of the fourth transistor (18)
is connected to the control electrode (base) of the fourth transistor (
18) is connected to the fourth and fifth resistors (20) via the ninth resistor (17).
11) and the fourth transistor (
The other controlled electrode (emitter) of 18) is connected to the switching element (19) via a third diode (19) for backflow prevention.
28) is connected to the control electrode of 28).

[Effect]

According to the present invention described above, when the power switch (2) is turned on, the capacitor (15) is charged and the transistor (21) is turned on, which makes the switch element (28) conductive and the signal When the power switch (2) is turned off, the charge in the capacitor (15) is discharged, the switch element (28) is made conductive, and the signal (noise) is emitted. Since no sound is generated, only one capacitor can be used.

[Embodiment] An embodiment of the mute circuit (monolithic IC) (50) of the present invention will be described in detail below with reference to FIG. In FIG. 1, parts corresponding to those in FIG. 2 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

Also in FIG. 1, the positive pole of this DC power supply (1) is connected to the power supply terminal (3) of the IC of the mute circuit (50) via the power switch (2), and its negative pole is grounded.

In this FIG. 1, (21) indicates a PNP type transistor, the emitter of this transistor (21) is connected to the power supply terminal (3), its collector is grounded via a resistor (22), and the resistor (21) is connected to the power supply terminal (3). (23) to the base of an NPN transistor (24).

The collector of this transistor (24) is connected to the power supply terminal (3) via a resistor (4), and the collector of this transistor (24) is connected via a resistor (5) to a PN
A diode (25) is connected to the base of the P-type transistor (6), and the emitter of the transistor (24) is connected to the base of the P-type transistor (6).
), the transistor (2
8a) and (28b).

(26) is an input terminal for audio signals;
) through a series circuit of resistors (27) and (29)
Connect to the output terminal (31) of C. Also, this resistor (
29) and the output terminal (31) are grounded via a signal output resistor (30). This output terminal (31)
The audio signal output from the speaker is supplied to the speaker (35) through the amplifier circuit (34).

The base of the transistor (21) is connected to the power supply terminal (3) through a DC circuit including a resistor (20), a resistor (11), and a diode (10) for preventing reverse current.
) and (11) are connected to the terminal (14) of the IC, this terminal (14) is grounded via the capacitor 15), and the connection point of the resistors (20) and (11) is connected to the terminal (14) of the IC. Connect to the emitter of the PNP transistor (12).

The emitter of the transistor (6) is connected to the power supply terminal (3), and the collector of this transistor (6) is connected to the resistor (7).
The collector of this transistor (6) is connected to the base of a PNP transistor (8). The emitter of the transistor (8) is connected to the power supply terminal (3), and the collector of this transistor (8) is connected to the resistor (
Connect to the connection points of 20) and (11). Further, these transistors (6) and (8) have the role of causing a large current to flow through the circuit when the power switch (2) is turned on.

The base of the transistor (12) is connected to the power supply terminal (3) via the resistor (9), and the collector of the transistor (12) is grounded via the resistor (13). is connected to the base of an N P N-type transistor (18) via a resistor (16).

Connect the collector of this transistor (18) to a resistor (17)
The emitter of this transistor (18) is connected to the switching element (
28), ie the bases of commonly connected transistors (28a) and (28b). In this case, the mute time when the power switch (2) is turned off is
This capacitor (15), resistor (17) and (13)
It is determined by the value etc.

In the above mute circuit (50), the power switch (2
) is turned on, the power terminal (3) is connected to the DC power supply (1).
), power is supplied to the mute circuit (50),
Diode (10), resistor (11), IC terminal (1)
4), current flows to the capacitor (15), and the capacitor (15) is charged. At the same time, the transistor (8) is turned on, and the connection terminal (
14), the capacitor (15) is charged.

While this capacitor (15) is being charged, the base voltage of the transistor (21) is
) is lower than the emitter voltage of this transistor (
21) is turned on, the current from the DC power supply (1) flows through this transistor (21) to the base of the transistor (24), and the transistor (24) is turned on, so the current from the DC power supply (1) flows through this transistor (21) to the base of the transistor (24). Transistor (24
) and (25) to the control electrode of the switch element (28), making the switch element (28) conductive.

Therefore, the signal (noise) from the audio signal input terminal (26) is routed to the ground side, and noise is prevented from being emitted from the speaker (35). And the capacitor (
When the charging potential of 15) reaches the potential between the resistors (11) and (20), the transistor (21) is turned off and the switching element (28) is also turned off.

In the above mute circuit (50), the power switch (
2) is turned off, the base voltage of the transistor (12) becomes approximately ground potential, and the charging voltage of the capacitor (15) is supplied to the emitter of the transistor (12), so this transistor (12) is turned on. Along with becoming
A current due to the charge in the capacitor (15) flows through the transistor (12) and the resistor (16).
Since the current flows to the base of this transistor (18),
) turns on, and the diode (10
), the DC circuit of the resistor (11), the resistor (17), the transistor (18), and the diode (19). A current flows to the control electrode of the switch element (28), and this switch element (28) becomes conductive. Since the signal (noise) from the input terminal (26) is sent to the ground side, the speaker (35)
) does not emit noise.

According to the above embodiment, when the power switch (2) is turned on, the capacitor (15) is charged and the transistor (21) is turned on, thereby making the switch element (28) conductive. In addition to preventing the signal (noise) from being emitted, when the power switch (2) is turned off, the charge in the capacitor (15) is discharged and the transistor (18) is turned on, thereby turning on the switch element (28). ) is made conductive to prevent the signal (noise) from being emitted, so only one capacitor can be used.

It goes without saying that the present invention is not limited to the above-described embodiments, and that various other configurations may be adopted without departing from the gist of the present invention.

[Effects of the Invention] According to the present invention, the number of capacitors used can be reduced to one, so when integrated into an IC, one terminal can be removed, the mounting area can be reduced, and the circuit can be simplified. The advantages of IC implementation can be enhanced.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional example. (1) is a DC power supply, (2) is a power supply switch, (3) is a power supply terminal, (12), (18), (21),
(24), (28a), (28b) are transistors, (15) are capacitors, (4), (9L(1
1), (13) (16), (17), (20)
, (22), (23) are resistors, (10),
(19). (25) is a diode, and (28) is a switch element.

Claims (1)

[Claims] One controlled electrode of the first transistor is connected to one end of the DC power supply via a power switch, and the other controlled electrode of the first transistor is connected to the other end of the DC power supply via a first resistor. and the other controlled electrode of the first transistor is connected to the control electrode of the second transistor via a second resistor, and the one controlled electrode of the second transistor is connected to the third controlled electrode. One controlled electrode of the first transistor is connected to the connection point of the power switch via a resistor, and the other controlled electrode of the second transistor is connected via a first diode for backflow prevention. One controlled electrode is connected to a signal line, the other controlled electrode is connected to a control electrode of a switching element connected to the other end of the DC power supply, and the control electrode of the first transistor is connected to a fourth resistor. a fifth resistor and a second diode for backflow prevention to a connection point between the power switch and the third resistor, and a connection point between the fourth and fifth resistors. A point connected to the other end of the DC power supply via a capacitor, and a connection point between the fourth and fifth resistors connected to one controlled electrode of the third transistor, and the control electrode of the third transistor is connected to the connection point of the power switch and the third resistor via a sixth resistor, and the other controlled electrode of the third transistor is connected to the seventh
connected to the other end of the DC power supply via a resistor, and the other controlled electrode of the third transistor is connected to the control electrode of the fourth transistor via an eighth resistor;
One controlled electrode of the fourth transistor is connected to the connection point of the fourth and fifth resistors via a ninth resistor, and the other controlled electrode of the fourth transistor is prevented from flowing backward. A mute circuit, characterized in that the mute circuit is connected to a control electrode of the switching element via a third diode.