JP3913364B2 - Amplifier circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an amplifier circuit suitable for use in audio equipment.
[0002]
[Prior art]
In general, in an amplifier circuit, a technique for switching a power supply voltage of the amplifier circuit according to an output level is known in order to suppress useless power loss and prevent distortion of an output signal of the amplifier circuit. The power supply voltage of the amplifying unit is lowered when the input or output of the amplifying circuit is at a small or medium level, and the power supply voltage of the amplifying unit is increased only when the input or output of the amplifying unit becomes large. FIG. 4 is a diagram showing a conventional amplifier circuit as described above.
[0003]
In FIG. 4, during the operation of the amplifier circuit, the oscillator 2A inside the boost chopper 2 is operated, and the switching transistor SW1 is turned on / off to operate the boost chopper 2, whereby the constant voltage Vb from the battery is boosted. Thus, a boosted voltage is generated.
[0004]
At this time, the switching transistor SW2 is off, and the constant voltage Vb is applied to the output amplifier 5 as a power supply voltage via the bypass circuit 3. In the output amplifying unit 5 using the voltage Vb as the power supply voltage, the input signal AS is amplified to generate an output amplified signal ZS.
[0005]
During the operation as described above, the comparator 4A always compares the potential Va at the point a in FIG. 4 with the reference voltage Vref, and detects whether the potential Va at the point a is equal to or higher than the reference voltage Vref.
[0006]
When the output amplification signal ZS of the output amplifier 5 is small or medium level and the potential Va at the point a in FIG. 4 is equal to or lower than the reference voltage Vref, the output signal of the comparator 4A becomes L level, and the switching transistor SW2 is turned off. A constant voltage Vb is applied to the output amplifier 5 as a power supply voltage via the circuit 3.
[0007]
Further, when the output amplification signal ZS becomes a high level and the potential Va at the point a becomes equal to or higher than the reference level, the output of the comparator 4A becomes the H level, so that the switch transistor SW2 is turned on and the boost voltage from the boost chopper 2 is turned on. Vu is applied to the output amplifier 5 as a power supply voltage.
[0008]
When the output amplification signal ZS becomes small or medium level again and the potential Va in FIG. 4 falls below the reference voltage Vref, the output level of the comparator 4A becomes L level, and the constant voltage Vb of the battery 5 is supplied to the output amplification unit 5. Applied.
[0009]
Therefore, only when the output level of the output amplifier 5 becomes higher than Vref, the boosted voltage Vu higher than the voltage Vb is applied as the power supply voltage of the output amplifier 5.
[0010]
[Problems to be solved by the invention]
In the amplifier circuit of FIG. 4, when the output level is low or medium level, the power supply voltage of the output amplifier 5 is the constant voltage Vb from the battery. When the output level is a medium level, the power loss can be reduced. However, when the output level of the output amplifier 5 is a low level, the output level is much lower than the constant voltage Vb, so that the power loss is large. Therefore, an object of the present invention is to achieve high efficiency when the output level of the amplifier circuit is small.
[0011]
[Means for Solving the Problems]
The present invention has been made in view of the above-described problems. First, a power source, an amplifying unit, a booster circuit, a step-down circuit, a speaker, and a volume of the speaker are adjusted, and a divided voltage is set as the input signal. When the divided voltage is larger than the voltage corresponding to the constant voltage, the boosted voltage of the booster circuit is supplied as the power supply voltage of the amplifying unit. When the divided voltage is smaller than the voltage corresponding to the step-down voltage, the problem is solved by including a selection switching circuit that supplies the step-down voltage of the step-down circuit as the power supply voltage of the amplifying unit.
[0012]
Second, the booster circuit is constituted by a boost chopper provided with a switching circuit, and the step-down circuit is constituted by a step-down chopper provided with a switching circuit.
[0013]
In the third and fourth, the divided voltage of the volume is input to the microcomputer, and when the divided voltage is larger than the voltage corresponding to the constant voltage, the output of the microcomputer generated by the divided voltage Supplies the boosted voltage of the booster circuit as the power supply voltage of the amplifying unit, and supplies the stepped-down voltage of the step-down circuit as the power supply voltage of the amplifying unit when the divided voltage is smaller than the stepped-down voltage This problem is solved by having a selection switching circuit that performs this.
[0014]
As described above, when the output level is large, medium and small, the power supply of the amplifying unit is changed to large, medium and small, respectively, and high efficiency can be realized even when the output level is small.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing an embodiment of the present invention. 1 is a constant voltage power source (battery) for generating a constant voltage Vb, 2 is a step-up chopper circuit, 3 is a step-down chopper circuit, 4 is an amplifying unit, When the divided voltage of the volume BL to which the input signal AS is input is larger than the voltage corresponding to the constant voltage Vb, the first chopper circuit 2 is operated to supply the boosted voltage to the power supply of the amplifying unit. The selection switching circuit 6 operates the step-down chopper circuit 3 when the divided voltage of the volume BL to which the input signal AS is input is smaller than the voltage corresponding to the constant voltage V2, and supplies the step-down voltage to the power source of the amplifier unit. Is a second selection switching circuit for supplying. Further, the input signal AS is input via the volume BL, and as a result, the amplified output ZS of the amplifying unit 4 is output from the speaker SP.
[0016]
That is, as shown in FIG. 2, the power supply applied to the amplifying unit 4 is set to a constant voltage Vb, higher voltages V1 and V2 lower than Vb. When the output ZS is higher than Vb, the divided voltage generated from the volume BL corresponding to the output ZS is monitored, and the SW12 is turned on and the SW11 is turned on / off by an oscillator or the like. Is supplied with the voltage V1 generated in the above. When the output ZS is lower than V2, the divided voltage generated from the volume BL corresponding to the output ZS is monitored, the SW22 is turned on / off, and the voltage V2 generated at the point e is supplied to the amplifying unit 4. . If the SW 22 continues to be in the ON state, the voltage Vb is supplied.
[0017]
As described above, when the output level is large, medium, and small, the power of the amplifying unit can be changed to large, medium, and small, and V2 can be supplied as the power source even when the output level is small.
[0018]
Now, a specific description will be given with reference to FIG.
A DC voltage VbV is generated at the upper end (point a) of the constant voltage power supply 1 (for example, a battery), and 0 V (ground) is generated at the lower end. Between the point a and the point b of the amplifier 4, the first coil L11, the first diode D12, and the third switching element SW12 are connected in series. A first switching element SW11 is connected between the intersection of the first coil L11 and the first diode D12 (hereinafter referred to as the first intersection 11) and the ground line 10, and the first diode D12 is connected. A first capacitor C <b> 11 is connected between the intersection between the first switching element SW <b> 12 and the third switching element SW <b> 12 (hereinafter referred to as the second intersection 12) and the ground line 10. Also, a comparison circuit OP4 for controlling on / off of the first switching element SW11 is provided. An oscillator OSC that generates a triangular wave is connected to a negative terminal of the comparison circuit OP4, and a reference voltage Vref1 is connected to a first positive terminal. The second + terminal is connected to a point e1 between the resistors R1 and R2.
[0019]
The input signal AS is amplified by the amplifier 4 via the volume BL, and an output signal ZS is output. The divided voltage of the volume BL is connected to the negative terminal of the comparison circuit OP1 through the microcomputer M, and the reference voltage Vref3 connected to the positive terminal is compared with the output of the microcomputer to turn on and off the third switching element SW12. I have control. The third switching element SW12 controls whether to supply or not supply a boosted voltage as a power source for the amplifying unit.
[0020]
In the above configuration, the booster circuit 2 is configured by L11, D12, SW11, OP4, and C11 as surrounded by a dotted line. Further, OP1, SW12 and the microcomputer M constitute a first switching circuit 5 (see FIG. 1).
[0021]
On the other hand, between the point a and the point b, the second switching element SW22, the second coil L22, and the third diode D22 are sequentially connected in series. A second diode D23 is connected between the second switching element SW22 and the second coil L22 (hereinafter referred to as the third intersection 13) and the ground line 14, and the second coil L22. And a third diode D22 (hereinafter referred to as a point e) and the ground line 14 are connected with a second capacitor C22. Furthermore, the second switching element SW22 is on / off controlled by the comparison circuit OP2. The reference voltage Vref2 is connected to the first + terminal of the comparison circuit OP2, and the second + terminal is connected to the output of the microcomputer M via the standby circuit STB. Further, resistors R21 and R22 are connected in parallel with the second capacitor C22, and the middle point e2 and the negative terminal of the comparison circuit OP2 are connected.
[0022]
In the above configuration, the step-down circuit 3 is configured by SW22, L22, D23, C22 and OP2 as surrounded by a dotted line, and the second switching is performed by the microcomputer M, the standby circuits STB, OP2, SW22 and Vref2. The circuit 6 (see FIG. 1) is configured.
[0023]
Next, the operation will be described. The output signal ZS is obtained by multiplying the voltage generated in the volume BL by the amplification factor.
[0024]
Here, when it is assumed that an output of about 40 to 60 W is generated in the speaker and power is supplied to the amplifier unit in large, medium, and small sizes of 18V, 13V, and 8V, the output signal ZS is generated between substantially 18V and 0V. . If the amplification factor is 100, the divided voltage generated from the volume is generated between 0.18V and 0V.
[0025]
When 8V is generated at the point e ′, 4V is set to be generated at e2, and 4V is applied to Vref2.
[0026]
First, when the output signal is between 13V and 8V, the divided voltage (0.13 to 0.08V) generated by the volume BL is supplied to the microcomputer M, and High (5V) is output from the microcomputer. In the comparison circuit OP2, the second + terminal and the-terminal are prioritized, and High is supplied from the comparison circuit OP2 to the second switching element SW22. The SW22 continues to be turned on to generate Vb = 13V. Supplied to the power supply.
[0027]
When the output signal is 8 V or less, the divided voltage of the volume is 0.08 V or less, and the microcomputer output is 0 V supplied to the standby circuit. At this time, the standby circuit does not generate a signal to the comparison circuit OP2, and the first + terminal and-terminal have priority. That is, Vref2 = 4V and the voltage at point e2 are compared. When e2 is 4V or less, OP2 becomes High, and SW22 is turned on to charge capacitor C22 to make point e 8V. When e2 becomes 4V or more, SW22 is turned OFF and C22 is discharged via the amplifying unit 4. This state is repeated, and the voltage at the point e generates a constant voltage of about 8V between 8V ± several milliV (or 8V ± tens of milliV).
[0028]
Next, the switching operation of the boosted constant voltage = 18V when the output voltage changes between 13V and 18V will be described. Corresponding to the voltage ZS output by the amplifying unit 4, the divided voltage of the volume BL changes between 0.13 and 0.18V substantially. In other words, when the divided voltage exceeds 0.13V, the microcomputer M outputs High (5V) from the lower output line to the comparison circuit OP1, and this divided voltage is compared with Vref3 = 4V, and OP1 becomes High. Output to SW11 and turn on SW11. As a result, the voltage of C11 is charged and tries to reach 18V.
[0029]
The oscillation circuit OSC is connected to the negative terminal of the comparison circuit OP4, the reference voltage Vref1 = 9V is connected to the first positive terminal, and the second positive terminal is connected to the point e1. Since the resistors R11 and R12 are set so that 9V is generated at the point e1 when the point 12 'is 18V, the 9V is adopted as the reference voltage.
[0030]
The first + terminal and the second + terminal are compared, the low voltage is prioritized and compared with the triangular wave of the triangular wave generating circuit OSC, and the ON / OFF control of SW11 is performed. That is, if the second intersection 12 is 17.5V, which is lower than 18V, the voltage 8.75V of the corresponding point e1 is compared with the triangular wave, and the second intersection 12 is 18.5V higher than 18V. If there is, the voltage of e1 becomes 9.25V, and the reference voltage 9V is compared with the triangular wave. In other words, if the second intersection 12 is 18V or higher with respect to the determined triangular wave, the ON / OFF control is performed at a constant duty ratio. When the second intersection 12 becomes lower than 18V, the point e2 becomes larger at SW11 as the difference increases. The duty is controlled so that the ON time becomes longer, and 18V is generated at the second intersection 12. In other words, the SW22 is turned on when it is low, and is turned on and off when it is high. The voltage at the second intersection 12 is about 18V between 18V ± several milliV (or 18V ± several tens of milliV). Generate constant voltage.
[0031]
【The invention's effect】
As described above, by adopting the switching circuit, the second switching element and the third switching element can be controlled ON / OFF, and when the output level is large, medium, or small, it is possible to change the power supply of the amplification unit to large, medium, or small, respectively. . Therefore, high efficiency can be realized even when the output level is small, and loss can be suppressed, so that the radiator can be downsized.
[Brief description of the drawings]
FIG. 1 is a circuit diagram illustrating an embodiment of the present invention.
FIG. 2 is a diagram for explaining the operation of FIG. 1;
FIG. 3 is a diagram illustrating a specific circuit of FIG. 1;
FIG. 4 is a circuit diagram illustrating a conventional amplifier circuit.
[Explanation of symbols]
L11 1st coil D12 1st diode SW11 1st switching element C11 1st capacitor SW22 2nd switching element L22 2nd coil D23 2nd diode L22 2nd coil C22 2nd capacitor SW12 3rd Switching element OP comparison circuit BL volume M microcomputer 1 constant voltage power supply 2 step-up circuit 3 step-down circuit 4 amplifying unit 5 first switching circuit 6 second switching circuit

Claims (3)

A power supply that generates a constant voltage;
An amplifier for amplifying the input signal and outputting the amplified signal;
A booster circuit for boosting the constant voltage and generating a boosted voltage;
A step-down circuit having a power supply for generating the constant voltage and a switching element connected in series on the power supply side of the amplifier ;
A speaker to which an output signal of the amplifying unit is input;
Adjust the volume of the speaker, the divided voltage becomes more and volume to said input signal,
In conjunction with the divided voltage of the volume, when the divided voltage is larger than the voltage corresponding to the constant voltage, the boosted voltage of the booster circuit is supplied as the power supply voltage of the amplification unit,
When the divided voltage is the same as or slightly lower than the voltage corresponding to the constant voltage,
Continue to turn ON the switching element, supply the constant voltage of the power supply as it is as the power supply voltage of the amplification unit through the switching element,
When the divided voltage is lower than the low voltage, the switching element of the step-down circuit is turned on and off to operate the step-down circuit , and the step-down voltage stepped down by the step-down circuit is supplied as the power supply voltage of the amplifying unit. An amplifier circuit characterized by the above. A first coil and the booster circuit connected to the positive side of the power source, a first diode, a first switching connected between the first intersection point between the first diode and the ground line more will first capacitor connected between the output of element and the first Daoodo and the ground line, said first boosted voltage said first capacitor through switching is charged and discharged the switching element Generated,
The step-down circuit includes a second switching element, a second coil, an intersection of the second switching element and the second coil, and a ground line that are connected in series to the positive side of the power source and the power source side of the amplification unit. And a second capacitor connected between an output of the second coil and a ground line, and keeps the switching element ON, and the switching element is turned on via the switching element. The constant voltage of a power supply is supplied as it is as a power supply voltage of the amplification section, and the second capacitor is charged and discharged by switching of the second switching element to generate a step-down voltage . Amplification circuit. The divided voltage of the volume is inputted to the microcomputer, and when the divided voltage is larger than the voltage corresponding to the constant voltage, the boosted voltage of the booster circuit is obtained by the output of the microcomputer generated by the divided voltage. When the divided voltage is the same as or slightly lower than the voltage corresponding to the constant voltage, the constant voltage of the power supply is supplied as it is as the power supply voltage of the amplifier. And a selection switching circuit for supplying a step-down voltage of the step-down circuit as a power supply voltage of the amplifying unit by an output of a microcomputer generated by the divided voltage when the divided voltage is lower than the low voltage. 2. The amplifier circuit according to claim 1.

Images