JP3594522B2 - Audio signal amplifier circuit and television receiver using the same - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
This invention related to an audio signal amplifier circuit and a television receiver using the same.
[0002]
[Prior art]
If the protection circuit is not provided in the audio signal amplifying circuit of a television receiver or audio equipment, if the load is short-circuited for some reason and the state is left as it is, the withstand voltage of the circuit element will exceed or exceed There is a danger of ignition, smoking, or rupture of the circuit element due to heat generated by the current.
[0003]
[Problems to be solved by the invention]
Therefore, an IC incorporating a circuit capable of detecting a load short circuit has been proposed, but the cost is high.
When a signal of a certain level or more is input to the audio signal amplifier circuit, the output is limited (clipped) by the power supply voltage or the ground line, and a distorted audio is output. As described above, when the output is excessive, not only is it unpleasant to hear, but if such a state continues for a long time, the temperature of the audio signal amplifier circuit and its surroundings rises, and there is a risk of ignition or smoking.
As a means for preventing this, automatic volume control by AGC or the like can be considered, but this results in a large increase in cost.
[0004]
Therefore, a main object of the present invention is to provide an audio signal amplifier circuit capable of detecting a load short circuit at low cost.
Another object of the invention, and unpleasant sound when an excessive output of the audio signal amplifier circuits or al, the risk due to heat generation can be prevented at low cost, is to provide an audio signal amplifier circuit.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the audio signal amplifying circuit according to claim 1 amplifies an input audio signal and outputs the amplified audio signal to a load, and a power supply line for supplying power to the audio output means. includes an overcurrent detecting resistor connected to the power supply line, a short circuit detecting means for load based on the voltage across the over-current detection resistor is detected that short, and the power supply line based on an output of the short circuit detecting means Control means for controlling the supply of electric power from the audio output means to the audio output means, and the overcurrent detection resistor reduces the power supply voltage supplied to the audio output means via the power supply line, thereby reducing the maximum output level from the audio output means. It is also used as a dropper resistor for controlling
[0006]
The audio signal amplifying circuit according to claim 2 , wherein the audio signal amplifies an input audio signal and outputs the amplified audio signal to a load, a power supply line for supplying power to the audio output means, and an overcurrent connected to the power supply line. An overcurrent detection means for detecting that a current of a certain level or more has flowed to the load based on a voltage between both ends of the overcurrent detection resistor , and a voice output means based on an output of the overcurrent detection means. Control means for controlling the output signal level of the audio output means or the input signal level to the audio output means, and the overcurrent detection resistor lowers the power supply voltage supplied to the audio output means via the power supply line so that the audio output means Characterized in that it is also used as a dropper resistor for controlling the maximum output level.
[0007]
A television receiver according to a third aspect uses the audio signal amplifier circuit according to the first or second aspect .
[0008]
In the audio signal amplifying circuit according to claim 1, when the voltage between both ends of the overcurrent detecting resistor becomes equal to or higher than a predetermined level, it is determined that the load is short-circuited, and the control means is controlled based on the output from the short-circuit detecting means at this time. Cuts off the supply of power to the audio output means . Thereby, heat generation and ignition at the time of load short circuit are prevented. In this case, the short-circuit detection unit and the control unit including the overcurrent detection resistor can be included in the audio signal amplifier circuit without being integrated, and the load short-circuit can be detected at low cost.
Further, the cost can be reduced by sharing the dropper resistance and the overcurrent detection resistance.
[0009]
In an audio signal amplifier circuit according to claim 2, that a certain level or higher current to the load flows it is when it is detected by the overcurrent detection means, supplied with the output signal level or the audio output means from the voice output means input The signal level is reduced by the control means. Therefore, without using a different AGC like the traditional, unpleasant or sound when an excessive output from the audio signal amplifier circuit, it is possible to prevent the risk from heating at a low cost.
Further , since it is detected whether or not an overcurrent occurs based on the voltage across the overcurrent detection resistor connected to the power supply line, the cost can be reduced.
[0010]
Further, the cost can be reduced by sharing the dropper resistance and the overcurrent detection resistance.
When the above-described audio signal amplifier circuit is used in a television receiver, the cost of the television receiver can be reduced.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, with reference to FIG. 1, a description will be given of an audio signal amplifier circuit 10 that can detect a short circuit of a load and cut off the supply of power.
The audio signal amplifying circuit 10 is used for a television receiver, for example, and includes an audio output circuit 12 for amplifying an audio signal as an input signal. As the audio output circuit 12, for example, an audio amplifier IC, LA4227 manufactured by Sanyo Electric is used.
[0012]
A power supply circuit 14 and a protection circuit 15 are connected to the audio output circuit 12 via a twelfth pin. The protection circuit 15 is for protecting the audio output circuit 12 when the load is short-circuited. The protection circuit 15 is provided between the power supply circuit 14 and the twelfth pin. And a control circuit 18 for controlling power supply to the power supply.
Power supply circuit 14 includes a rectifier circuit 20 for rectifying an AC voltage of, for example, 100V. A power transformer 22 is connected to the rectifier circuit 20, and an output of the power transformer 22 is supplied to a twelfth pin of the audio output circuit 12 via an audio amplifier power line 24.
[0013]
The dropper resistor R1 of the short-circuit detection circuit 16 is inserted between the audio amplifier power supply line 24 and the twelfth pin of the audio output circuit 12. The DC power supply voltage is lowered by a certain level by the dropper resistor R1, and the maximum output level of the audio output circuit 12 is adjusted. The dropper resistor R1 is also used to determine whether the DC power supply current supplied from the audio amplifier power supply line 24 is an overcurrent and to detect a load short circuit, thereby reducing costs.
The resistors R2 and R3 connected in series are connected between both ends of the dropper resistor R1, and the voltages across the dropper resistor R1 are divided by the resistors R2 and R3. The base and the emitter of the transistor Tr1 are connected between both ends of the resistor R3, the collector of the transistor Tr1 is connected to the overcurrent detection line 26 via the resistor R4, and the output of the short circuit detection circuit 16 is given to the control circuit 18. Can be
[0014]
The control circuit 18 includes a CPU 28, to which an output of the short-circuit detection circuit 18 is given via an overcurrent detection line 26. The CPU 28 outputs a control signal based on the output of the short circuit detection circuit 16. This control signal is supplied to the transistor Tr2 through the power supply control line 30 and the resistor R5, and controls on / off of the transistor Tr2. The switching operation of the relay 32 is controlled based on the operation of the transistor Tr2, whereby the opening and closing operation of the power supply circuit 14, that is, the supply of power to the audio output circuit 12, is controlled.
A speaker 34 is connected to the second and third pins of the audio output circuit 12 of the audio signal amplifier circuit 10 to output audio.
[0015]
The operation of the audio signal amplifier circuit 10 configured as described above will be described.
For example, when the audio output circuit 12 is used with a load of 8Ω and a rated output of 2 W × 2, the required power supply voltage is about 11 V and the power supply current at the rated output is about 500 mA.
Here, assuming that the DC voltage supplied from the power transformer 22 is 11.5 V with a certain number of turns, the voltage is increased by 0.5 V so that the output from the audio output circuit 12 does not become larger than the rated output. I have to descend. That is, when a current of 500 mA flows, a voltage drop of 0.5 V is required, so a dropper resistor R1 of 0.5 V ÷ 0.5 A = 1Ω is required.
Here, a current of about 500 mA flows through the dropper resistor R1 at the time of rated output, but when a current far exceeding this flows, the audio output circuit 12 determines that an abnormal situation such as a load short circuit has occurred. You may. Therefore, when the overcurrent detection level is set to a value corresponding to the power supply current when the load is short-circuited, the short-circuit of the load can be detected.
[0016]
In this embodiment, when the voltage obtained by dividing the voltage between both ends of the dropper resistor R1 by R2 and R3, that is, the base-emitter voltage Vbe of the transistor Tr1 becomes higher than the ON voltage of the transistor Tr1, the transistor Tr1 is turned on. , The collector voltage of the transistor Tr1 becomes HIGH.
For example, assuming that R1 = 1Ω, R2 = 1.8 kΩ, R3 = 5.6 kΩ, and the ON voltage of the transistor Tr1 = 0.6 V, the voltage across the dropper resistor R1 is Vr1 = (1.8 k + 5.6 k) / 5. When 6k × 0.6 ≒ 0.79V or more, that is, when the power supply current becomes Icc = 0.79V / 1Ω = 790mA or more, the transistor Tr1 is turned on and the audio output circuit 12 has an abnormality such as a load short circuit. Can be detected.
[0017]
By supplying this detection signal to the CPU 28 and turning off the relay 32 based on the control signal from the CPU 28, the supply of power to the audio output circuit 12 is stopped, and danger such as heat generation and ignition can be avoided.
Further, according to the audio signal amplifier circuit 10, the short-circuit detection circuit 16 including the dropper resistor R1 and the control circuit 18 can be included in the audio signal amplifier circuit 10 without being integrated, and the load short-circuit can be detected at low cost. And can cope.
Furthermore, according to the audio signal amplifying circuit 10, it is possible to detect a load short circuit in accordance with an arbitrary load impedance or a rated output only by changing the set values of the elements included in the short circuit detecting circuit 16.
[0018]
Next, an audio signal amplifier circuit 100 capable of detecting an overcurrent and controlling audio output will be described with reference to FIG.
The audio signal amplifying circuit 100 is used in, for example, a television receiver, and includes an audio output circuit 102 that amplifies an audio signal that is an input signal. As the audio output circuit 102, for example, an audio amplifier IC, LA4287 manufactured by Sanyo Electric is used. The audio output circuit 102 includes a switch 104, and the switch 104 selects either the first pin or the third pin according to a switching control signal from the fourth pin. The output from the switch 104 is amplified by an amplifier 108 via a DC volume 106 controlled by a DC volume control voltage, then output from a ninth pin, and a sound is output from a speaker 110. As described above, the audio output circuit 102 has a volume control function, and can control the audio output by controlling the volume control voltage input to the fifth pin of the audio output circuit 102 from 0 V to 5 V. .
[0019]
A power supply voltage Vcc and an overcurrent detection circuit 114 are connected to a 10th pin of the audio output circuit 102 via an audio amplifier power supply line 112.
The dropper resistor R11 of the overcurrent detection circuit 114 is inserted in the audio amplifier power supply line 112. The resistors R12 and R13 connected in series are connected to both ends of the dropper resistor R11, and the voltages across the dropper resistor R11 are divided by the resistors R12 and R13. Both ends of the resistor R13 are connected between the base and the emitter of the transistor Tr11, and the collector output of the transistor Tr11 is supplied to the transistor Tr12 via the resistor R14. When the transistor Tr12 is turned on, the volume control voltage is divided by the resistors R15 and R16 and applied to the fifth pin of the audio output circuit 102. Thus, the volume control voltage can be controlled by the transistor Tr12.
[0020]
The operation of the audio signal amplifier circuit 100 will be described.
For example, when the audio output circuit 102 is used with a load of 8Ω and a rated output of 5 W, the required power supply voltage is about 19 V, and the power supply current at the rated output is about 400 mA.
As in the previous embodiment, when the voltage obtained by dividing the voltage between both ends of the dropper resistor R11 by R12 and R13, that is, the base-emitter voltage Vbe of the transistor Tr11 becomes equal to or higher than the ON voltage of the transistor Tr11, the transistor Tr11 is turned on. Is turned on, and the collector voltage of the transistor Tr11 becomes HIGH.
For example, assuming that R11 = 1.5Ω, R12 = 560Ω, R13 = 5.6 kΩ, and the ON voltage of the transistor Tr11 = 0.6V, the voltage across the dropper resistor R11 is Vr11 = (560 + 5.6k) /5.6k× When 0.6 ≒ 0.66 V or more, that is, when the power supply current becomes Icc = 0.66 V / 1.5Ω = 440 mA or more, the transistor Tr11 is turned on, and the audio signal from the audio output circuit 102 becomes excessive. Output can be detected.
[0021]
As described above, the power supply current at the time of the rated output is about 400 mA, and at this time, it is considered that the specified distortion rate is approximately 10% in the EIAJ standard. Therefore, the fact that the power supply current is flowing at 440 mA is considered to mean that the audio output is higher than the rated output and the audio output is higher than the specified distortion rate, that is, an unpleasant audio with a lot of distortion is output.
[0022]
In this embodiment, by supplying this detection signal to the base of the switching transistor Tr12, Tr12 is turned on when overcurrent is detected. Then, the volume control voltage of the audio output circuit 102 is divided by the dividing resistors R15 and R16, and the volume control voltage supplied to the audio output circuit 102 can be reduced. As a result, the output is limited to a certain level. can do. By setting the overcurrent detection level a little higher than at the time of the rated output level, an excessive output of the audio signal can be more reliably detected.
[0023]
By limiting the audio signal output level when the audio signal excessive output is detected in this way, it is possible to prevent unpleasant audio due to the excessive output from the audio output circuit 102. At the same time, the danger of heat generation and fire due to excessive output from the audio output circuit 102 can be prevented. Further, at this time, unlike the conventional case, since AGC or the like is not used, the cost can be reduced.
Further, the cost can be reduced by using the above-described overcurrent detection resistor and the dropper resistor R11 for adjusting the maximum output level of the audio output circuit 102 in common.
[0024]
When excessive output from the audio output circuit 102 is detected, the volume may be controlled by dividing the input signal supplied to the audio output circuit 102, or the volume may be automatically controlled by a CPU (not shown). May be controlled. Needless to say, in these cases, the same effect as in the above case can be obtained.
Further, if the above-described audio signal amplifier circuits 10 and 100 are used in a television receiver, the cost of the television receiver can be reduced.
The present invention can be applied to any drive circuit that drives a load with a signal obtained by amplifying an input signal.
[0025]
【The invention's effect】
According to the present invention, a short circuit of a load can be detected by an inexpensive circuit, and heat generation, ignition, and the like at the time of load short circuit can be prevented.
Further, according to the present invention, it is possible to detect the excessive output of the audio signal and limit the audio signal input level and the audio signal output level. Therefore, it is possible to prevent an unpleasant sound at the time of excessive output from the audio signal amplifying circuit, and at the same time, it is possible to prevent the danger of heat generation and ignition due to the excessive output.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an audio signal amplifier circuit according to an embodiment of the present invention.
FIG. 2 is a circuit diagram showing an audio signal amplifier circuit according to another embodiment of the present invention.
[Explanation of symbols]
10, 100 audio signal amplifier circuit 12, 102 audio output circuit 14 power supply circuit 15 protection circuit 16 load detection circuit 18 control circuit 24, 112 audio amplifier power supply line 34, 110 speaker 114 overcurrent detection circuit R1, R11 dropper resistance Tr1, Tr2 , Tr11, Tr12 Transistor

Claims (3)

Audio output means for amplifying an input audio signal and outputting it to a load;
A power line for supplying power to the audio output means,
Wherein an overcurrent detection resistor connected to the power line, on the basis of the short-circuit detecting means for the load based on the voltage across the over-current detecting resistor detects that shorted, and the output of said short circuit detecting means Control means for controlling supply of power from the power supply line to the audio output means ,
The overcurrent detection resistor is also used as a dropper resistor that controls a maximum output level from the audio output unit by lowering a power supply voltage supplied to the audio output unit via the power supply line. A sound signal amplifier circuit. Audio output means for amplifying an input audio signal and outputting it to a load;
A power line for supplying power to the audio output means,
An overcurrent detection resistor connected to the power supply line, wherein the overcurrent detection means detects that a current of a predetermined level or more flows to the load based on a voltage across the overcurrent detection resistor ; and Control means for controlling an output signal level from the audio output means or an input signal level to the audio output means based on an output of the current detection means ,
The overcurrent detection resistor is also used as a dropper resistor that controls a maximum output level from the audio output unit by lowering a power supply voltage supplied to the audio output unit via the power supply line. A sound signal amplifier circuit. A television receiver using the audio signal amplifier circuit according to claim 1 .

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