JP3101487B2 - Amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit and, more particularly, to an improvement in an amplifier circuit such as an audio amplifier whose operation is switched according to a mode.

[0002]

2. Description of the Related Art An amplifier circuit according to a conventional example will be described below with reference to the drawings. 2. Description of the Related Art An amplifier circuit according to a conventional example is an audio amplifier that switches circuits according to each of a mute mode and a play mode. In the mute mode, power is supplied to an audio device (for example, stereo) including the amplification circuit.
The play mode is a state in which no sound is output to the outside (for example, from a speaker or the like) without flowing to the amplifier circuit.
A state in which a current flows through the amplifier circuit and a sound is output to the outside.

As shown in FIG. 3, the circuit includes a differential amplifier (1), an output amplifier (2), a pre-driver (Q5) comprising PNP transistors, and a mode switch (S).
W1, SW2), load resistors (R51, R52) and constant current sources (CS1, CS2), and amplifies an audio signal (SI) input from an input terminal (IN) and outputs it as an amplified signal (ZS). The signal is output to an external speaker (RL) connected to (OUT).

The operation of the circuit will be described below. In the case of the mute mode, the power supply voltage (+ Vcc) is applied to the circuit.
Is supplied, and both the mode changeover switches (SW1, SW2) are turned off. Then, the audio signal (S
Even when I) is input, none of the differential amplifier (1), the pre-driver (Q5) and the output amplifier (2) operate, so that no amplified signal (ZS) is output to the speaker (RL).

After that, when shifting to the play mode,
Set both mode select switches (SW1, SW2) to O
N. Then, the mode switch (SW1, SW
Since both the differential amplifier (1), the pre-driver (Q5) and the output amplifier (2) operate when both of them are turned on, the audio signal input from the input terminal (IN) (SI) is amplified by the differential amplifier (1) and the output amplifier (2), output as an amplified signal (ZS) to an external speaker (RL), and output as sound.

[0006]

However, according to the conventional amplifier circuit, the collector current does not flow through the transistors (Q1, Q2) at the input section of the differential amplifier section (1) in the mute mode. The base of the driver (Q5) is in a floating state, and is unstable as a non-operating condition.

Here, when a leakage current (ICBO) of about nA occurs in the transistor (Q1), as shown in FIG. 4, the positive power supply (+ Vcc) → the emitter base of the pre-driver (Q5) → the transistor (Q1). Leakage current (ICBO) in the path from collector-base to ground potential (GND)
) Flows, so that the pre-driver (Q5) attempts to turn on.

As a result, a collector current having a value of {leakage current (ICBO) × current amplification factor (hFE)} flows through the pre-driver (Q5), and the transistors (Q6, Q7) of the Darlington-connected output amplifier (2). ), The potential of the output terminal (OUT) shifts to the positive side due to the current amplification, and a DC current continues to flow through the load (RL), which is a speaker, which may cause a problem that the speaker may be damaged. .

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional disadvantages. As shown in FIG. 1, it does not operate in a first state in which an amplified signal (ZS) is not output to the outside. An input amplifier (11) for amplifying an input signal (SI) and outputting the amplified signal to a pre-driver (PD) in a second state for outputting an amplified signal (ZS) to the outside, and an emitter connected to the positive power supply (+ Vcc) A pre-driver (PD) having a base formed of a PNP transistor connected to an output of the input amplifier (11), amplifying the input signal (SI) and outputting the amplified signal to an output amplifier (12); In the first state, a constant current is supplied to the output amplifying unit (12) and the pre-driver (PD). In the second state, the pre-driver (P
D) A switching circuit (SW1) that does not supply a constant current to
2), and an output amplifying unit (12) for further amplifying the amplified input signal (SI) and outputting the amplified input signal (SI) to the outside as an amplified signal (ZS). By connecting the potential fixing resistor (RA) between the power supply (+ Vcc) and the power supply (+ Vcc), the DC current continues to flow through the speaker which is the load in the mute mode, and as a result, a situation in which the speaker is damaged is minimized. It is an object of the present invention to provide an amplifying circuit that enables the above.

[0010]

According to the amplifier circuit of the present invention, as shown in FIG. 1, a PNP transistor having an emitter connected to the positive power supply (+ Vcc) and a base connected to the output of the input amplifier (11). A resistor (RA) for fixing a potential is connected between a base of a pre-driver (PD) for amplifying an input signal (SI) and outputting it to an output amplifying section (12) and a positive power supply (+ Vcc). Become.

For this reason, the base potential of the pre-driver (PD) is fixed by the resistor (RA), and the base of the pre-driver (PD) does not enter a floating state in the mute mode as in the prior art. Even if a current flows through the transistor at the output of the input amplifier (11), the base potential of the predriver (PD) does not fluctuate, so that the predriver (PD) is not turned on.

As a result, the collector current of [current amplification factor of pre-driver (PD) × leakage current] does not flow to the pre-driver (PD) as in the prior art, so that the output terminal (OUT) of the output amplifying section (12). Does not shift to the positive side, and for example, it is possible to suppress as much as possible that a DC current continues to flow to a load such as a speaker, and to thereby prevent damage to the load such as a speaker.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an amplifier circuit according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 2, the amplifier circuit according to the embodiment of the present invention is an audio amplifier that switches circuits according to each of a mute mode and a play mode. Note that the mute mode refers to an audio device including the amplifier circuit (for example, stereo).
The power is turned on, but the sound does not flow to the amplifier circuit, and no sound is output to the outside (for example, from a speaker, etc.). In the play mode, the current flows to the amplifier circuit and the sound is output to the outside. The state that is done.

As shown in FIG. 2, the amplifier circuit according to the present embodiment includes an input amplifier (11), a pre-driver (Q15),
Output amplifying section (12), switching circuit (SW12),
An amplifier circuit comprising resistors (RA, RB) and a constant current source (CS12), wherein an input terminal (I) of an input amplifier (11) is provided.
N), and amplifies the audio signal (SI) inputted from the speaker (R) as an external load as an amplified signal (ZS).
L).

The input amplifier (11) is a circuit comprising a current mirror circuit (11A), a differential amplifier (11B), a switching circuit (SW11) and a constant current source (CS11), and does not operate in a mute mode. In the play mode, the audio signal (SI) is amplified and the pre-driver (Q
15). Current mirror circuit (1
1A), the base of the PNP transistor (Q13) and the base of the PNP transistor (Q14) are connected, and the emitters of the PNP transistors (Q13, Q14) are both connected to the positive power supply (+ Vcc). The collector and base of the transistor (Q14) are connected, the collector of the PNP transistor (Q13) is connected to the base of the pre-driver (Q15) and the collector of the NPN transistor (Q11), and the collector of the PNP transistor (Q14). Are NPN transistors (Q1
This is a circuit connected to the collector of 2).

The differential amplifier (11B) comprises NPN transistors (Q11, Q12), the emitter of the NPN transistor (Q11) and the NPN transistor (Q11).
12) is connected to the switching circuit (SW11), and the collector of the NPN transistor (Q11) is used as the output of the input amplifier (11) as the pre-driver (Q1).
5) and connected to the base of an NPN transistor (Q1).
The base of 1) becomes the input of the input amplifier (11), and NP
The base of the N-type transistor (Q12) is
This is a circuit connected to the output terminal (OUT) of 2).

The switching circuit (SW11) is turned off in the mute mode and does not supply the constant current from the constant current source (CS11) connected to the negative power supply (-Vcc) to the differential amplifier (11B). In the play mode, the circuit is turned on to supply a constant current to the differential amplifier (11B). The pre-driver (Q15) is a PNP transistor that drives the output amplifying unit (12) according to the input signal (SI), and has an emitter connected to a positive power supply (+ Vcc).
The base is connected to the collector of an NPN transistor (Q11) which is the output of the input amplifier (11), and the collector is the transistor (Q1) at the input stage of the output amplifier (12).
6) connected to the base.

The switching circuit (SW12) is turned off in the mute mode, and does not supply the constant current from the constant current source (CS12) connected to the negative power supply (-Vcc) to the output amplifying section (12). In the play mode, the circuit is turned on to supply a constant current to the output amplifier (12). The output amplifying unit (12) includes Darlington-connected NPN transistors (Q16, Q17), Darlington-connected PNP transistors (Q18, Q19), diodes (D11-D14), and resistors (R13, R14). This circuit amplifies the collector current of the pre-driver (Q15) and outputs the amplified signal from the output terminal (OUT) to a speaker (RL) as an external load as an amplified signal (ZS).

The resistor (RA) fixes the base potential of the pre-driver (Q15) by being connected between the positive power supply (+ Vcc) and the base of the pre-driver (Q15). High resistance. The resistor (RB) is connected between the emitter and the collector of the PNP transistor (Q14) and has a high resistance of about 20 kΩ which is the same resistance as the resistor (RA).

A negative feedback circuit (NF) is provided between the output terminal (OUT) and the base of the transistor (Q12) of the differential amplifier (11B). The operation of the circuit will be described below. In the case of the mute mode, the power supply voltage (+ Vcc) is supplied to the circuit, and the switching circuits (SW11, SW12) are both turned off.

Then, any audio signal (SI)
Is input, the input amplifier (11), the pre-driver (Q15), and the output amplifier (12) have a constant current source (CS).
11, CS12) is not supplied, so that none of them operates and no amplified signal (ZS) is output to the speaker (RL). Therefore, there is no sound from the speaker (RL).

After that, when shifting to the play mode,
Both switching circuits (SW11, SW12) are O
N. Then, the switching circuits (SW11, SW1)
2) are both turned on, so that the input amplifier (11),
Since both the pre-driver (Q15) and the output amplifier (12) operate, the input signal (SI) input from the input terminal (IN) is transmitted to the input amplifier (11) and the output amplifier (21). The signal is amplified and output to an external speaker (RL) as an audio signal (ZS).

According to the circuit according to the above embodiment, since the resistor (RA) having a high resistance of about 20 kΩ is connected between the positive power supply (+ Vcc) and the base of the pre-driver (Q15), In the mode, the pre-driver (Q
15) The base potential is fixed. As a result, the base of the pre-driver does not float in the mute mode as in the prior art.
Even if a small leak current flows through the transistor (Q11), the base potential of the predriver (Q15) does not fluctuate, so that the predriver (Q15) is turned on.
Not done.

As a result, the collector current of {current amplification rate of pre-driver (Q15) × leakage current} does not flow through the pre-driver (Q15) as in the prior art, so that the output terminal (OUT) of the output amplification section (12). Does not shift to the positive side, and for example, it is possible to suppress as much as possible that a DC current continues to flow to a load such as a speaker, and to thereby prevent damage to the load such as a speaker.

At the same time, the high-resistance resistor (RA) is also connected between the collector and the emitter of the transistor (Q13) of the current mirror circuit (11A). Since an error occurs in the mirror circuit (11A), the output offset voltage of the output amplifying unit (12) does not become 0 V, and adjustment for adjusting this to 0 V is required.

However, in this embodiment, as shown in FIG.
The resistance (RB) of about 20 kΩ which is the same as the resistance (RA) between the emitter and the collector of the PNP transistor (Q14) corresponding to a symmetric position with respect to the current mirror circuit (11A).
) Is connected, the current mirror circuit (11
A) The error of A) can be reduced, and the output offset voltage of the amplifier circuit during operation is automatically set to 0 V. Trimming for adjusting the output offset voltage of the amplifier circuit to 0 V becomes unnecessary. Becomes easier.

[0027]

As described above, according to the amplifier circuit of the present invention, the emitter connected to the positive power supply (+ Vcc) and the base connected to the output of the input amplifier (11) are connected.
A pre-driver (P) which is composed of an NP-type transistor and amplifies an input signal (SI) and outputs the amplified signal to an output amplifier (12)
Since a resistor (RA) for fixing the potential is connected between the base of D) and the positive power supply (+ Vcc), the potential of the output terminal (OUT) of the output amplifying section (12) becomes positive during muting. For example, it is possible to prevent a DC current from continuing to flow through a load such as a speaker as much as possible, so that damage to the load such as a speaker can be suppressed as much as possible.

[Brief description of the drawings]

FIG. 1 is a principle diagram of an amplifier circuit according to the present invention.

FIG. 2 is a circuit diagram of an amplifier circuit according to an embodiment of the present invention.

FIG. 3 is a circuit diagram of an amplifier circuit according to a conventional example.

FIG. 4 is a diagram illustrating a problem of a conventional example.

[Explanation of symbols]

 (11) Input amplifier (11A) Current mirror circuit (11B) Differential amplifier (12) Output amplifier (RA) Resistance (RB) Resistance (PD) Predriver (CS11, CS12) Constant current source (SW11, SW12) Switching circuit

Claims (2)

(57) [Claims] 1. A first circuit which does not output an amplified signal (ZS) to the outside.
Does not operate in the state of (1), an input amplifier (11) that amplifies the input signal (S1) in the second state of outputting the amplified signal (ZS) to the outside and outputs the amplified signal to the pre-driver (PD); + Vcc), a first PNP transistor (Q15) having an emitter connected to the output of the input amplifying section (11) and a base connected to the input signal (S1).
A pre-driver (PD) that amplifies the current and outputs it to an output amplifying unit (12). In the first state, a constant current is not supplied to the output amplifying unit (12) and the pre-driver (PD). In the second state, a first switching circuit (SW12) for supplying a constant current to the output amplifying unit (12) and the pre-driver (PD), and an input signal (S) amplified by the pre-driver (PD).
And an output amplifying section (12) for amplifying 1) and outputting the amplified signal to the outside as an amplified signal (ZS), wherein the input amplifying section (11) is connected to a constant current source (-Vcc) side. CS11) and a constant current from the constant current source (CS11) in the first state in which no amplified signal (ZS) is output to the differential amplifier (1).
1B), a second switching circuit (SW11) that supplies a constant current to the differential amplifier (11B) in the second state in which the amplified signal (ZS) is output to the outside without being supplied to the second and third third circuits. NPN transistors (Q11, Q1
2) and the second NPN transistor (Q1
1) and the emitter of the third NPN transistor (Q12) are connected to the second switching circuit (SW11), and the collector of the second NPN transistor (Q11) is used as an output unit as a pre-driver (PD). And the second NPN transistor (Q1
The differential amplifier (1) whose base is the input terminal (IN)
1B), the base of the fourth PNP transistor (Q13) and the fifth
And the collector of the fourth PNP transistor (Q13) is connected to the base of the first PNP transistor (Q15) and the second NPN transistor (Q11). The collector of the fifth PNP transistor (Q14) is connected to the collector of the third NPN transistor (Q12), and the fourth and fifth PNP transistors (Q1)
3, Q14) having a current mirror circuit (11A) connected to a positive power supply (+ Vcc). The base of the first PNP transistor (Q15) of the pre-driver (PD) and the positive power supply (+ Vcc) and a potential fixing resistor (RA) connected thereto. 2. A first circuit which does not output an amplified signal (ZS) to the outside.
Does not operate in the state of (1), an input amplifier (11) that amplifies the input signal (S1) in the second state of outputting the amplified signal (ZS) to the outside and outputs the amplified signal to the pre-driver (PD); + Vcc), a first PNP transistor (Q15) having an emitter connected to the output of the input amplifying section (11) and a base connected to the input signal (S1).
A pre-driver (PD) that amplifies the current and outputs it to an output amplifying unit (12). In the first state, a constant current is not supplied to the output amplifying unit (12) and the pre-driver (PD). In the second state, a first switching circuit (SW12) for supplying a constant current to the output amplifying unit (12) and the pre-driver (PD), and an input signal (S) amplified by the pre-driver (PD).
And an output amplifying unit (12) for amplifying 1) and outputting the amplified signal to the outside as an amplified signal (ZS). The input amplifying unit (11) has a constant current source (-Vcc) connected to the negative power supply (-Vcc) CS11) and a constant current from the constant current source (CS11) in the first state in which no amplified signal (ZS) is output to the differential amplifier (1).
1B), a second switching circuit (SW11) that supplies a constant current to the differential amplifier (11B) in the second state in which the amplified signal (ZS) is output to the outside without being supplied to the second and third third circuits. NPN transistors (Q11, Q1
2) and the second NPN transistor (Q1
1) and the emitter of the third NPN transistor (Q12) are connected to the second switching circuit (SW11), and the collector of the second NPN transistor (Q11) is used as an output section of a pre-driver (PD). And the second NPN transistor (Q1
The differential amplifier (1) whose base is the input terminal (IN)
1B), the base of the fourth PNP transistor (Q13) and the fifth
And the base of the fourth PNP transistor (Q13) is connected to the base of the first PNP transistor (Q15) and the collector of the second NPN transistor (Q11). The collector of a fifth PNP transistor (Q14) is connected to the collector of a third NPN transistor (Q12), and the fourth and fifth PNP transistors (Q1) are connected to the collector of a third NPN transistor (Q12).
3, Q14) having a current mirror circuit (11A) connected to a positive power supply (+ Vcc). The base of a first PNP transistor (Q15) of the driver (PD) and the positive power supply ( + Vcc), and a resistor (RB) having the same resistance as the resistor (RA) is connected between the emitter and collector of the fifth PNP transistor (Q14). An amplifier circuit, which is connected.