JP3460041B2 - Amplifier circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power amplification stage in which the operation mode is higher than that of a class A power amplification operation mode such as a class A power amplification operation mode and a class AB power amplification operation mode. The present invention relates to an amplifier circuit configured to be switchable and controllable to a power amplification operation mode in which idle current is reduced. 2. Description of the Related Art A conventional amplification circuit of this kind, for example, an amplification circuit configured so that the operation mode of a power amplification stage can be switched between a class A power amplification operation mode and a class AB power amplification operation mode by an external signal and controlled. The circuit 1 has a resistor 6 as shown in FIG.
, One terminal is pulled up to a power supply, and the other terminal is grounded. The output voltage of the common terminal of the operation mode changeover switch 7 is detected by the bias control circuit 8A.
When it is determined that the common terminal of the operation mode changeover switch 7 is in contact with one terminal, the bias changeover switch 9 provided in the bias circuit 10 of the power amplification stage of the amplifier 2 is controlled by the bias control circuit 8A. When the power amplifier stage of the amplifier 2 is switched to the class A power amplification operation mode and the common terminal of the switch 7 is determined to be in contact with the other terminal, the switch 9 is switched to the bias control circuit. The power amplification stage is controlled to the ON state under the control of 8A to switch the power amplification stage to the class AB power amplification operation mode. On the other hand, with regard to the load side, the amplified output from the amplifier 2 which has amplified the input signal is transmitted as a speaker drive output via a switch 3 and the headphone can be driven by the output of the amplifier 2. The output of the amplifier 2 is supplied to the headphone jack 5A via the current limiting resistor 4, and a plug is inserted into the headphone jack 5A, that is, when driving the headphones, the switch 3 of the headphone jack 5A opens the switch 3 to disconnect the speaker load. It is composed. As a result, the speaker is disconnected when the headphone is driven, and the speaker is connected when the headphone is disconnected. In the conventional amplifier circuit 1 described above, an operation mode changeover switch for switching the operation mode of the power amplification stage of the amplifier 2 and a switch 3 controlled based on the use of headphones are independent. are doing. For this reason, when using headphones, the operation mode is set to A
Class power amplification operation mode can be selected. When selected in this way, the power amplifier stage performs class A power amplification operation, and the power loss of the amplifier circuit is always large regardless of the signal level. In addition, the headphone is light in load, so that the headphone is lighter than the speaker load. Further, current flows and heat generation increases. However, when a headphone is loaded, the above-described heat does not contribute to the required output, and there is a problem that only unnecessary heat is generated. Further, due to the above-mentioned problems, the power supply voltage ± Vcc of the amplifier may be reduced in order to reduce heat generation during the A-class power amplification operation.
As described above, when the power supply voltage of the amplifier is reduced, there is a problem that the output of the headphone is reduced. SUMMARY OF THE INVENTION It is an object of the present invention to provide an amplifier circuit which can suppress unnecessary heat generation under a headphone load, does not reduce the headphone output, and does not cause deterioration in sound quality. [0008] [0009] [0010] amplifier circuit according to claim 1, wherein the SUMMARY OF THE INVENTION The present invention, the operation mode is a class A power amplifier mode of operation of the power amplification stage and A class power amplifier operating mode An amplifying circuit configured to be switchable to a power operation mode in which an idle current is reduced by an external signal, and to switch a power amplification operation mode of a power amplification stage based on a switching instruction output of a manual switch; The speaker load is disconnected based on the detection output that detects that headphones are connected to the stage load, and the idle current is reduced in priority to the power amplification operation mode switching instruction of the power amplification stage based on the output of the manual switch. e Bei bias control means for switching the power amplifier mode of operation is, a-class power
The idle current is higher than the power supply voltage in the amplification mode.
Power supply voltage in the power amplification operation mode with reduced
The feature is that it is made. According to the amplifier circuit according to claim 1 of the present invention, electrostatic
Operation mode of power amplification stage is class A power amplification operation mode and class A
A power supply with a reduced idle current compared to the power amplification operation mode.
Switching control by external signal with force operation mode
Configured, headphones connected to the load of the power amplifier stage
When it is detected the based on the detection output, speaker
Power amplification operation mode in which the idle current is reduced in preference to the power amplification operation mode switching instruction of the power amplification stage based on the output of the manual switch while the load is disconnected.
It is switched on. As a result, A
Even if the switching to the class power amplification operation mode is instructed, when the headphone load is applied, the operation is switched to the power amplification operation mode in which the idle current is reduced prior to the instruction by the manual switch. Therefore, class A power increase
The headphone load and
Power, the idle current is reduced preferentially.
Switch to amplification operation mode to suppress unnecessary heat generation
It becomes possible. Furthermore, in the class A power amplification operation mode,
Power amplification that reduces idle current compared to power supply voltage
Because the power supply voltage in operation mode is set high,
Unnecessary power generation without reducing output power during phone load
Heat can be suppressed. Hereinafter, an amplifier circuit according to the present invention will be described with reference to embodiments. FIG. 1 is a block diagram showing a configuration of an amplifier circuit according to one embodiment of the present invention. An amplifier circuit 1 according to an embodiment of the present invention.
1, the same components as those of the conventional amplifier circuit 1 shown in FIG. 2 are denoted by the same reference numerals. The amplifying circuit 11 has a load
Similarly to the conventional amplifier circuit 1, the amplified output from the amplifier 2 that has amplified the input signal is sent out as a speaker drive output via the switch 3, and the amplifier 2 is driven so that the headphone can be driven by the output of the amplifier 2. Is supplied to a headphone jack 5 via a current limiting resistor 4, and a plug is inserted into the headphone jack 5, that is, when driving the headphones, the switch 3 of the headphone jack 5 opens the switch 3 to disconnect the speaker load. are doing. As a result, the speaker is disconnected when the headphone is driven, and the speaker is connected when the headphone is disconnected. The amplifier circuit 11 has a bias control circuit 8 which detects a common terminal output voltage of an operation mode changeover switch 7 in which one terminal is pulled up to a power supply via a resistor 6 and the other terminal is grounded. The output from the switch of the headphone jack 5 when the plug is inserted into the headphone jack 5 is detected by the bias control circuit 8. The bias control circuit 8 detects the output from the switch of the headphone jack 5 prior to the detection of the common terminal output voltage of the operation mode changeover switch 7. When the output from the switch of the headphone jack 5 is detected, Bias switch 9 regardless of the detection result of the common terminal output voltage of operation mode switch 7
Is turned on, the power amplification stage of the amplifier 2 is switched to the class AB power amplification operation mode, and the headphone jack 5 is turned on.
When the output from the switch is not detected, the output of the common terminal output voltage of the operation mode changeover switch 7 is detected, and based on the detected output of the common terminal output voltage of the operation mode changeover switch 7, similarly to the bias control circuit 8A, The bias switch 9 is configured to be switched. Here, as the bias control circuit 8, for example, a control circuit including a computer for controlling a device including the amplifier circuit 11 can be used. When the control circuit comprising the computer is used for the bias control circuit 8, the control circuit comprising the computer checks the output from the switch of the headphone jack 5 at predetermined time intervals. Is detected, the bias changeover switch 9 is turned on to switch the power amplification stage of the amplifier 2 to the class AB power amplification operation mode, and then skip the step of checking the output of the operation mode changeover switch 7. To perform other steps. In the above, the headphone jack 5
Only when the output from the switch of the headphone jack 5 is not detected when the output from the switch of the headphone jack 5 is detected, the step of checking the output of the operation mode changeover switch 7 is executed. When the output of the changeover switch 7 is at a high potential, the step of controlling the bias changeover switch 9 to the off state to switch the power amplification stage of the amplifier 2 to the class A power amplification operation mode is executed, and the output of the operation mode changeover switch 7 is checked. When the output of the operation mode changeover switch 7 is low potential when the step is executed, the step of controlling the bias changeover switch 9 to the ON state to switch the power amplification stage of the amplifier 2 to the class AB power amplification operation mode is executed. It is configured. When the plug of the headphone jack 5 is inserted in the amplifier circuit 11 configured as described above, the fact is detected by the bias control circuit 8 and the bias switch is performed regardless of the state of the operation mode switch 7. The switch 9 is turned on under the control of the bias control circuit 8, and the bias circuit 10
In the bias state of the class A power amplification operation, the power amplification stage of the amplifier 2 is controlled to the class AB power amplification operation. When the plug of the headphone jack 5 is inserted, the switch 3 is controlled to be turned off, the speaker load is removed, and the headphone is driven by the output of the amplifier 2. When the plug of the headphone jack 5 is removed from the inserted state or when it is not originally inserted, the bias control circuit 8 detects the fact and the state of the operation mode changeover switch 7 is checked. When it is determined by this check that the common terminal of the operation mode changeover switch 7 is in contact with one terminal, the bias changeover switch 9 is turned off under the control of the bias control circuit 8 and the amplifier 2 is turned off. The power amplification stage is placed in a class A power amplification operation mode. Since the plug of the headphone jack 5 is not inserted, the switch 3 is controlled to the ON state, and the speaker is driven by the output of the amplifier 2 in the class A power amplification operation. When the plug of the headphone jack 5 is removed from the inserted state or when it is not originally inserted, the bias control circuit 8 detects the fact and the state of the operation mode changeover switch 7 is checked. When it is determined by this check that the common terminal of the operation mode changeover switch 7 is in contact with the other terminal, the bias changeover switch 9 is turned on under the control of the bias control circuit 8, and the amplifier 2 is turned on. The power amplifying stage is placed in a class AB power amplifying operation mode.
Since the plug of the headphone jack 5 is not inserted, the switch 3 is controlled to the ON state, and the speaker is driven by the output of the amplifier 2 in the AB class power amplification operation. Next, a specific example of amplification by the amplifier circuit 11 will be described in comparison with the case of the conventional amplifier circuit 1. The outputs of both amplifier circuits 1 and 11 are 10 W during class A power amplification operation and 40 W during class AB power amplification operation.
W, speaker load is 4Ω, headphone load is 32Ω,
It is assumed that the current limiting resistor 4 is 150Ω, the no-signal current of the power amplifying stage of the amplifier 2 is 1.12 A in the class A operation mode, the power supply voltage of the amplifier 2 is 13.2 V, and 5 in the AB class operation mode.
It is assumed that 0 mA and the power supply voltage of the amplifier 2 is 25.7 V. In the above description, when headphones are used, the maximum signal current in the AB class power amplification operation mode is 70 mA (rms) when headphones are used, and class A operation is possible by supplying 49 mA to the non-signal current of the power amplification stage. 158 mW can be output to the headphone load at that time. Therefore, sound quality similar to that in the class A power amplification operation mode can be obtained. Here, most of about 30 W consumed in the class A power amplification operation mode is converted to heat as loss. However, as described above, the amplifier circuit 11 uses the class AB power amplification operation when headphones are used. As a mode, the class A power amplification operation is performed with no signal current in the class AB power amplification operation mode, thereby reducing the loss of about 30 W as a loss. On the other hand, in order to reduce the loss of the power amplification stage in the class A power amplification operation mode in the amplifier circuit 1, the power supply voltage is reduced to 13.2 V in the class A power amplification operation mode. . When the power supply voltage is reduced in this way, only 39 mW can be output to the headphone load. However, as described above, when the amplifier circuit 11 is used, the power loss can be reduced, the headphone output can be increased, and the sound quality does not deteriorate. As described above, according to the amplifier circuit of the present invention, unnecessary heat generation can be suppressed when a headphone load is applied, the output of the headphone is not reduced, and the sound quality is degraded. The effect of not generating is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of an amplifier circuit according to one embodiment of the present invention. FIG. 2 is a block diagram illustrating a configuration of a conventional amplifier circuit. [Description of Signs] 2 Amplifier 3 Switch 4 Current limiting resistor 5 Headphone jack 7 Operation mode changeover switch 8 Bias control circuit 9 Bias changeover switch 10 Bias circuit 11 Amplification circuit

Claims (1)

(57) [Claim 1] An external signal is used to switch an operation mode of a power amplification stage between a class A power amplification operation mode and a power operation mode in which idle current is reduced as compared with the class A power amplification operation mode. In an amplifier circuit configured to be switchable, a power amplification operation mode of a power amplification stage is switched based on a switching instruction output of a manual switch, and a detection output that detects that headphones are connected to a load of the power amplification stage is output. based on, the disconnect the speaker load, comprising a bias control means for switching the manual switch in preference to switching instruction of the power amplifier operation mode of the power amplifier stage based on the output power amplifier mode of operation with reduced idle current of, a class Power supply voltage in power amplification operation mode
Power supply in power amplification operation mode with reduced dollar current
An amplifier circuit characterized by a higher voltage .