JPS6115614B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier device, and particularly to an improvement in an amplifier device equipped with a protection circuit.

Conventionally, an amplifier device including a protection circuit configured as shown in FIG. 1 has been known. That is, this includes an input stage section 11 consisting of a differential pair transistor Q ₁ in a pair configuration, differential pair transistors Q ₂ and Q ₃ , current mirror transistors Q ₄ and Q ₅ , and bias circuit diodes D ₁ to D ₃ . The drive stage section 12 consists of
and an output stage section 13 consisting of complementary transistors Q ₆ to _{Q 9} each having a Darlington configuration,
A power amplifier 10 having a so-called push-pull configuration in which feedback is applied from the output terminal P to the reference side base of the input stage section 11 via resistors R _F and R _N outputs a power amplified output to a speaker SP serving as a load. In the supplying configuration, a protection circuit 14 that is driven by detecting an abnormal state at the output terminal P is provided, and the protection circuit 14
The output circuit is directly cut off in the event of an abnormality by the relay contact R _L1 , which is controlled on and off by the speaker.
It is designed to protect SP.

In addition, with such a configuration, the popping sound that occurs when the power switch (not shown) is turned on can be suppressed from the speaker SP.
It can also have a muting function to prevent it from coming out.

However, in the conventional amplifier device as described above, since the relay contact R _L1 is directly inserted into the output circuit, it has a drawback that characteristics such as sound quality are affected accordingly.

Therefore, if characteristics such as sound quality are important, it is required to be able to perform a protection function in the event of an abnormality and a muting function when the power switch is turned on without directly inserting a relay contact into the output circuit.

Therefore, the present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide an extremely good amplifying device that is simple and improved so that it can reliably meet the above-mentioned requirements.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

That is, in FIG. 2, the same reference numerals as in FIG. 1 are given to the parts configured similarly to those in FIG. 1 described above, and the configuration is omitted. In FIG. The relay contacts R _L2 and R _L3 are inserted in series with a low resistance R ₀ between the common emitter circuit of the differential pair transistors Q ₂ and Q ₃ of the drive stage section 12 and the output terminal P and ground. In this case, it is important that a resistor _Rx is inserted between the output terminal P and the lowest cathode terminal (or the highest anode terminal) of the bias circuit diodes _D1 to _D3 .

In the above configuration, first, assuming that a power switch (not shown) is turned on, one relay contact R _L2 is turned on by the protection circuit 14' after a certain period of time after the power switch is turned on. Ru. As a result, a bias current is supplied to each of the transistors Q ₂ to _{Q 5} of the drive stage section 12, and in turn, each of the transistors Q ₆ to _{Q 9} of the output stage section 13 is brought into an operating state. .

A muting signal is output from the protection circuit 14' so that the other relay contact R _L3 is turned off at the same time as the one relay contact R _L2 is turned on.

In other words, each of the above transistors Q ₂ to _{Q 9} during a certain muting period after turning on the power switch.
is in a non-operating state and can perform a muting function in which no output is generated.

Next, assuming that an abnormal state occurs in the power amplifier 10 or the like, one relay contact R _L2 is turned off by the protection circuit 14', and the transistors Q ₂ to _{Q 9} are rendered inoperable. At the same time, the protection circuit 14' causes the other relay contact R _L
3 is turned on, the output terminal P has low resistance.
As a result of being short-circuited to ground via R ₀ , abnormal current can be bypassed and prevented from flowing to the speaker SP. In other words, it is possible to perform a protective function that prevents damage to the speaker SP in the event of an abnormality.

Next, I will explain the action of the resistor Rx connected to the output terminal P and one end of the bias circuit.This has an important role in resolving the incompleteness of the muting function that occurs when the resistor Rx is not present. It is something.

That is, if there is no resistance Rx,
During the above-mentioned muting period, both transistors Q ₃ and Q ₅ of the drive stage section 12 are in the cut-off state, so their output impedance is extremely large.
The base potentials of Q ₆ and Q ₇ become unstable.

Figure 3 is an equivalent circuit to explain this situation, and rQ ₃ and rQ ₅ are the output impedances of transistors Q ₃ and Q ₅ during the muting period, and have extremely large values;
It fluctuates significantly depending on the leakage current Icx at cut-off of Q ₃ and Q ₅ .

Now, right after turning on the power switch (positive power +
B and the state immediately after the negative power supply -B is applied), if rQ ₃ = rQ ₅ , the base potential V _B of transistors Q ₆ and Q _7
6 , V _B7 satisfies V _B6 = V _B7 ≒ 0, and no power-on noise that causes a flop is output from the output terminal P, so that a perfect muting function can be achieved without any problem.

However, if rQ ₃ > rQ ₅ , then V _B7 = rQ ₃ - rQ ₅ / rQ ₃ + rQ ₅ (-
B)≠0, and in this state, |V _B7 |>|V _BE7 |+|V _BE9 | (however, V _BE7 and V _BE9 are transistors
When the base-emitter voltage of Q ₇ and Q ₉ is satisfied, a voltage corresponding to |V _B7 |-(|V _BE7 |+|V _BE9 |) will be output as noise from the output terminal P. It can only perform incomplete mutating functions.

Therefore, in this invention, the resistor Rx as described above is
is connected to the output terminal P and one end of the bias circuit, and according to this, in Fig. 2 or 3, ( _RN + R _F + R _X ) << rQ ₃ (R _N + R _N + R _X ) << Since the relationship is rQ ₅ , even if rQ ₃ and rQ ₅ take different values, the signal source impedance Z ₀ on the base side of the transistor Q ₇ is Z ₀ ≒R _N +R _F +R _X ≪rQ ₃ becomes. As a result, even if the above-mentioned leakage current Icx flows, this Icx is very small and there is a relationship of Z ₀ ≪ rQ ₃ , so the voltage drop Z ₀ · Icx is very small Z ₀・Since Icx≪2V _BE , essentially V _BE6 ≒ V _BE7 ≒ V _BE8 ≒ V _BE9 , so no noise is emitted from the output terminal P when the power is turned on, and a perfect muting function is performed. It's something you get.

Note that in the above, R _N and R _F are resistors for applying feedback from the output terminal P to the reference side space of the input stage section 11, and V _BE6 and V _BE8 are transistors.
This is the base-emitter voltage of Q ₆ and Q ₈ .

Therefore, as detailed above, according to the present invention, it is possible to simply and reliably provide a protection function in the event of an abnormality and a muting function when the power switch is turned on, and in particular, a relay contact is not inserted directly into the output circuit. In particular, it becomes possible to provide an amplifier device equipped with an extremely good protection circuit suitable for cases where characteristics such as sound quality are important.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing a conventional amplifier device, FIG. 2 is a circuit configuration diagram showing an embodiment of the amplifier device according to the present invention, and FIG. 3 is an equivalent circuit diagram of the main part of FIG. 2. . 11... Input stage section, 12... Drive stage section, 13... Output stage section, 10 ... Power amplifier, 14'... Protection circuit, R _L
2 , R _L3 ...Relay contact, _Q1 ...Pair configuration differential pair transistor, _Q2 , _Q3 ...Differential pair transistor,
Q ₄ , Q ₅ ... Current mirror transistor, D ₁ ,
_D3 ...Bias circuit diode, _Q6 to _Q9 ...Darlington configuration complementary transistor, SP...speaker, P...output terminal, R _F , R _N , R _X ... resistor.

Claims (1)

[Claims] 1 An input stage section made up of a first differential pair transistor, a drive stage section made up of a second differential pair transistor, a current mirror transistor, a bias circuit diode, and an output stage section made up of complementary transistors, A power amplifier having a push-pull configuration in which feedback is applied from an output end to the base of a feedback side transistor in the input stage section via a resistor, a first switch means inserted into a common emitter circuit of a drive stage section in this power amplifier, and a second switch means inserted between the output end and the ground; and a second switch means for controlling the first and second switch means to turn on and off after a certain period of time from turning on the power switch, and detecting an abnormal state of the power amplifier. a protection circuit that controls the off state and on state when the
An amplifier device comprising: a resistor inserted between an output end of the power amplifier and one end of a bias circuit in the drive stage section.