JP2000165150A - Power amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a coil of a power supply voltage circuit in common, which changes an output level depending on a position of a glider of a variable resistor. SOLUTION: The power supply voltage circuit 7 acts like a voltage step-down chopper circuit by turning off a switch S2 and switching a switch S1 when a slider position of a variable resistor is set lower. The power supply voltage circuit 7 outputs a voltage Vb of a battery as it is by turning on the switch S1 and turning off the switch S2 when the slider position of the variable resistor 8 is set at the mid-position. The power supply voltage circuit 7 acts like a voltage step-up chopper circuit by turning on the witch S1 and switching the switch S2 when the slider of the variable resistor 8 is set high.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power amplifying device suitable for use in audio equipment.

[0002]

2. Description of the Related Art In general, in a power amplifying device, a technique of switching a power supply voltage of a power amplifying device in accordance with an output level of the power amplifying device in order to suppress unnecessary power loss and to prevent distortion of an output signal of the power amplifying device. Are known. The power supply voltage is reduced when the input or output of the power amplifying device is at a small or medium level, and is increased only when the input or output of the power amplifying device becomes large. FIG. 5 is a diagram showing a conventional power amplifying device as described above.

In FIG. 5, during the operation of the power amplifying device, the oscillator 2A inside the boost chopper circuit 2 is operated, and the switching transistor SW11 is turned on / off, whereby the boost chopper circuit 2 is operated. Is boosted to generate a boosted voltage.

At this time, the switching transistor SW2 is off, and the output amplifier 5 supplies the constant voltage Vb
Is applied as a power supply voltage via a bypass circuit.
In the output amplifier 5 using the voltage Vb as a power supply voltage, the input signal AS is amplified to generate an output amplified signal ZS.

During the above operation, the comparator 4
A indicates the potential Va at the point a in FIG. 5 and the reference voltage Vref.
Are compared with each other, and the potential Va at the point a is changed to the reference voltage Vre.
f or more is detected.

When the output amplified signal ZS of the output amplifier 5 is at a small or medium level and the potential Va at point a in FIG. 5 is equal to the reference voltage Vref.
In the following cases, the output signal of the comparator 4A becomes L level and the switching transistor SW2 is turned off, so that the constant voltage Vb is output from the output amplifier 5 via the bypass circuit 3.
As a power supply voltage.

When the output amplified signal ZS becomes a high level and the potential Va at the point a becomes higher than the reference level, the output of the comparator 4A becomes H level, so that the switch transistor SW2 is turned on and the boost chopper circuit 2 Is applied to output amplifier 5 as a power supply voltage.

When the output amplified signal ZS again becomes low or medium level and the potential Va in FIG. 5 falls below the reference voltage Vref, the output level of the comparator 4A becomes L level and the constant voltage Vb of the battery is changed to the output amplifier 5B. Is applied to

Therefore, the output level of the output amplifier 5 is Vr
Only when it becomes higher than ef, the boosted voltage Vu higher than the voltage Vb is applied as the power supply voltage of the output amplifier 5.

[0010]

In the power amplifying apparatus shown in FIG. 5, when the output level is small or medium, the output amplifier 5
Is a constant voltage Vb from the battery. When the output level is at the middle level, the power loss can be reduced. However, when the output level of the output amplifier 5 is low, 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 at a low output level of a power amplifying device.

[0011]

According to the present invention, there is provided a power amplifying apparatus having a volume for adjusting an output signal level of a power amplifying apparatus, wherein a power supply voltage of at least an output amplifier is variable, including a coil, and an external power supply. A boost chopper circuit that generates a first voltage obtained by boosting the fixed voltage, and a step-down chopper circuit that includes a coil and generates a second voltage that is reduced from the fixed voltage. A power supply voltage circuit for switching between the first voltage and the second voltage and outputting the same as the power supply voltage of the output amplifier is provided, and the coils of the step-up chopper circuit and the step-down chopper are shared.

In particular, when the position of the volume is small, the first voltage is applied to the output amplifier, and when the position of the volume is large, the second voltage is applied to the output amplifier. I do.

Further, when the position of the volume is in the middle, the power supply voltage circuit outputs the fixed voltage of the external power supply as it is.

The power supply voltage circuit includes a common coil, a first diode having a cathode connected to one end of the common coil, and a second diode having an anode connected to the other end of the common coil. A capacitor connected to the cathode of the second diode, a first switching means connected between one end of the common coil and the external power supply, and a second switch having one end connected to the other end of the common coil. 2 switching means, and first and second switch control circuits for controlling the first and second switching means according to the position of the volume.

In particular, when the position of the volume is small, the first switch control circuit switches the first switching means, and the second switch control circuit turns off the second switching means, and When the position is large, the first switching means is turned on and the second switching means is switched.

Further, when the volume is in the middle position, the first switching means is turned on,
The second switching means is turned off.

According to the present invention, when the output level of the output amplifier becomes high, a fixed boosted voltage generated from the booster circuit is applied to the output amplifier, and when the output level of the output amplifier becomes low, the output level becomes low. The step-down voltage of the step-down circuit that follows the output signal waveform of the amplifier is applied to the output amplifier.

[0018]

FIG. 1 is a diagram showing an embodiment of the present invention, in which 6 is a battery for providing a constant voltage Vb, 7 is a power supply voltage circuit, and a common coil L and a common coil L are provided. A first diode D1 having a cathode connected to one end of L
A second diode D2 having an anode connected to the other end of the coil L; a capacitor C connected to the cathode of the second diode D2;
And a second switching means S2 having one end connected to the other end of the coil L.
And comparison circuits OP1 and OP2 serving as first and second switch control circuits for controlling the first and second switching means S1 and S2 according to the position of a volume described later.
Consists of Further, 8 is a volume for adjusting the level of the input signal AS, 9 is a variable resistor for interlocking with the movable terminal of the volume 8, and a variable resistor for dividing the constant voltage Va by resistance, and 10 is based on the output voltage of the variable resistor 9. And a control circuit for controlling the first and second comparison circuits OP1 and OP2. In FIG. 1, the same circuit as in FIG.
The same reference numerals are given and the description is omitted.

In the power amplifying apparatus shown in FIG. 1, an output amplifier 5 amplifies an input signal AS and outputs an inverted and non-inverted amplified output signal to the speaker S with respect to the amplified input signal AS.
Apply to P. That is, the speaker SP is BTL-connected, and the output amplifier 5 drives the speaker SP by BTL.

Here, a feature of the present invention resides in that the power supply voltage Vcc of the output amplifier 5 is changed according to the output level of the output amplifier 5. Hereinafter, the operation of FIG. 1 will be described with reference to FIG.

In FIG. 1, when the volume is reduced and the position of the volume 8 is reduced, the movable terminal of the variable resistor 9 is set to the GND side in conjunction with the volume 8. Therefore, the output voltage of the variable resistor 9 becomes small, and the control circuit 10 detects that the position of the volume is small. In accordance with the detection result, the control circuit 10 sets the switch control signal S of “L” level.
S1 and the switch control signal SS2 of "H" level are output.

The switch control signal SS1 is supplied to the first comparison circuit O
Applied to the first positive input terminal of P1. First comparison circuit OP
1 has a second positive input terminal and a negative input terminal in addition to the first positive input terminal. In the first and second positive input terminals, the input terminal having the higher level of the applied input is given priority.
Since the switch control signal SS1 is at "L" level, the input signal of the second positive input terminal has priority. Here, since the input of the second positive input terminal is the output power supply voltage Vc of the power supply voltage circuit 7, the first comparison circuit OP1 performs a comparison operation between the power supply voltage + Vc and the reference voltage Vref1, and according to the comparison result. The first switch means S1 is switched on or off.

The switch control signal SS2 is applied to a second positive input terminal of the second comparison circuit OP2. The second comparison circuit OP2 includes a reference voltage Vre in addition to the first positive input terminal.
It has a second positive input terminal to which f2 is applied, a third positive input terminal to which the power supply voltage + Vc is applied, and a negative input terminal to which a triangular wave signal from the oscillator OSC is applied. Second comparison circuit O
Also at P2, similarly to the first comparison circuit OP1, a positive input terminal having a high input level is prioritized. Switch control signal S
Since S2 is at "H" level, the first positive input terminal has priority, and as a result, an "L" level output signal is generated from the second comparison circuit OP2, and the second switch means S2 is turned off. Therefore, it is considered that there is no second switch means S2, and the power supply voltage circuit 7 forms a step-down chopper circuit.

Power supply voltage circuit 7 serving as a step-down chopper circuit
, The first switch means S1 is turned on / off by the output signal of the first comparison circuit OP1, and the capacitor C is charged and discharged. The step-down chopper circuit is for stepping down the constant voltage Vb. The basic operation of the step-down chopper circuit is as follows. When the first switch means S1 is turned on / off, the cathode voltage of the first diode D1 becomes the voltage as shown by the solid line in FIG. Vb
And approximately 0 V are alternately switched, and the output voltage of the step-down chopper circuit is generated by smoothing the cathode voltage by the capacitor C. The step-down chopper circuit has an on / off duty ratio of the first switch means S1 of 50.
%, A voltage of Vb / 2 is generated as shown by the dotted line in FIG. When the duty ratio is not 50%, an average voltage corresponding to the duty ratio is generated from the step-down chopper circuit.
As shown by the dotted line in (a), the voltage becomes higher than the voltage Vb / 2, and if the off period is long, the output voltage VcL becomes lower than the voltage Vb / 2.

In the first comparison circuit OP1, when the output voltage VcL of the step-down chopper circuit is higher than the reference voltage Vref1, an "L" level output signal is generated, and the first switch means S1 is turned off. Therefore, the capacitor C is discharged, and the terminal voltage VcL of the capacitor C decreases. When the voltage VcL is lower than the reference voltage Vref1, "H" is set.
A level output signal is generated, the first switch means S1 is turned off, and the capacitor C is charged, so that the output voltage Vc
L increases. By the negative feedback as described above, the step-down voltage V
Since cL tends to be equal to the reference voltage Vref, the output voltage Vc of the power supply voltage circuit 7 becomes the output voltage VcL of the step-down chopper circuit. Note that the relationship between the output level of the output amplifier 5 and the power supply voltage VcL is as shown in FIG.

The volume is set to a medium level and the volume 8
When the position is set to the middle, the movable terminal of the variable resistor 9 is set to the middle between the GND side and the constant voltage VA side in conjunction with the volume 8. Therefore, the output voltage of the variable resistor 9 becomes medium, and the control circuit 10 detects that the position of the volume is medium. As a result, the control circuit 10 outputs the "H" level switch control signal SS1 and the "H" level switch control signal S1.
S2 is output.

In the first comparison circuit OP1, the "H" level switch control signal SS1 is prioritized.
The comparison circuit OP1 always generates an "H" level output signal. Therefore, the first switch means S1 is turned on, and the battery voltage Vb is directly conducted. In addition, the second comparison circuit OP2 has a switch control signal SS2 of “H” level.
Is applied, the second switch means S2 is turned off by the output of the second comparison circuit OP2. Therefore, the power supply voltage circuit 12 outputs the battery voltage Vb without processing. The output voltage of the power supply voltage circuit 7 when the volume is at the middle position becomes the voltage VcM (= Vb) as shown in FIG.

Further, the volume is increased and the volume 8
Is increased, the movable terminal of the variable resistor 9 is set to the constant voltage VA side in conjunction with the volume 8. Therefore, the output voltage of the variable resistor 9 becomes large, and the control circuit 10 detects that the position of the volume is large. Therefore, the control circuit 10 outputs an "H" level switch control signal SS1 and an "L" level switch control signal SS2.

The first comparison circuit OP1 generates an "H" level output signal in response to the "H" level switch control signal SS1. Therefore, the first switch means S1 is turned on, and the battery voltage Vb is directly conducted.

On the other hand, in the second comparison circuit OP2, since the input level of the first positive input terminal becomes "L" level, the second comparison circuit OP2 outputs the triangular wave signal from the oscillator OSC, the reference voltage Vref2 and the power supply voltage. The comparison operation with the circuit Vc is performed. As a result, the power supply voltage circuit 7 starts operating as a boost chopper circuit.

In the power supply voltage circuit serving as the boost chopper circuit, the reference voltage Vref2 of the second comparison circuit OP2 is set to a voltage higher than the battery voltage Vb. When the output voltage Vc becomes lower than the reference voltage Vref2 of the second comparison circuit OP2, the output signal of the second comparison circuit OP2 becomes “L” level, and the second switch S2 is turned off. Therefore, the energy stored in the coil L is charged in the capacitor C, and the terminal voltage Vc of the capacitor C is changed as shown in FIG.
Rise as shown by the solid line. Then, when the output voltage Vc becomes higher than the reference voltage Vref2, the output signal of the second comparison circuit OP2 becomes “H” level, the second switch S2 is turned on, and the connection point between the coil L and the diode D2 becomes 0V. As a result, the capacitor C is discharged, and its terminal voltage Vc decreases as shown in FIG.
Stores energy. As described above, the boost chopper circuit operates so that the output voltage Vc becomes equal to the reference voltage Vref2. Therefore, the output voltage Vc of the power supply voltage circuit 7 is higher than the voltage Vb from the battery 6.
cH is obtained.

Further, a triangular wave oscillation signal is applied to the second comparison circuit OP2. When the output voltage Vc of the power supply voltage circuit 7 is higher than the reference voltage Vref2, the reference voltage Vref2
Is prioritized, and the triangular wave signal is compared with the reference voltage Vref2. According to the comparison result, the second switch means S2
Are turned on / off, thereby obtaining a boosted voltage VcH.

The output voltage Vc is equal to the reference voltage Vref2.
If the output voltage Vc is lower, the output voltage Vc is prioritized, and the second switching means S2
Is on / off controlled. In this case, the reference voltage Vref
2 and the triangular wave signal, the ON period becomes longer, so that when the boosted voltage VcH decreases, the boosted voltage can be quickly increased. Therefore, a remarkable decrease in the output voltage of the boost chopper circuit can be prevented.

When the position of the volume 8 is large, the output voltage VcH of the power supply voltage circuit 7 is applied to the output amplifier 5 as the power supply voltage Vcc as shown in FIG.

As described above, the power supply voltage of the output amplifier 5 can be changed depending on the position of the volume as shown in FIG. If the position of volume 8 is small,
Since the output waveform of the output amplifier 5 does not become large, the power supply voltage Vc can be set to the low voltage VcL, and as a result, the loss voltage in the output amplifier 5 can be reduced. When the position of the volume 8 is large, the output waveform of the output amplifier 5 becomes large, so that clipping can be prevented by setting the power supply voltage to VcH.

The volume 8 in FIG. 1 is assumed to be a manual volume. There is an electronic volume in the volume, which outputs a digital control signal from a microcomputer which is a control circuit, and decodes the digital control signal to adjust the volume. Since the adjustment position of the volume has already been determined by the control circuit, the microcomputer can control the power supply voltage circuit 7 without using the variable resistor 9.

FIG. 4 shows an actual circuit example of the boosting chopper circuit. The second comparison circuit OP2 includes a reference voltage Vref2.
And a divided voltage VcH 'obtained by dividing the output voltage Vc by the resistors 11a and 11b, and a triangular wave signal from the oscillator OSC, and an inverted output signal thereof is applied to the second switch means S2. You.

In an actual circuit, it is difficult to create a reference voltage higher than the battery voltage Vb. Therefore,
The second reference voltage Vref2 is set to a voltage lower than the battery voltage Vb, and the voltage VccH of the power supply voltage circuit 7 is divided by the resistances of the resistors 11a and 11b.
The voltage is divided to a value lower than b and applied to the second comparison circuit OP2. According to this, the boost chopper circuit can be operated at a voltage lower than the battery voltage Vb, and a voltage sufficiently higher than the battery voltage Vb can be generated. Also, in the step-down chopper circuit, the power supply voltage VcL may be divided by the resistance and then applied to the first comparison circuit OP1.

[0039]

According to the present invention, the power supply voltage of the power amplifier can be changed depending on the position of the volume, so that the power loss can be reduced and the output waveform can be prevented from being clipped. it can. In practical use,
Since the power loss can be reduced, the size of the radiator can be reduced.

In particular, by controlling the power supply voltage circuit, both the step-up chopper circuit and the step-down chopper circuit can be operated, and the coil can be shared. By using a common coil, the size of the power amplifying device can be reduced and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 shows an output waveform of an output amplifier of FIG. 1 and a power supply voltage Vcc.
FIG. 4 is a characteristic diagram showing a relationship between

FIG. 3 is a characteristic diagram for explaining an operation of the power supply voltage circuit 7 of FIG.

FIG. 4 is a circuit diagram showing another example of the boost chopper circuit 2.

FIG. 5 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 5 Output amplifier 6 Battery 7 Power supply voltage circuit 8 Volume 9 Variable resistance

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Satoshi Sugimoto 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. F-term (reference) 5J092 AA02 AA21 AA22 AA41 AA51 CA32 CA36 CA37 CA87 CA92 CA94 FA01 FA14 FA18 GR07 GR08 GR09 HA19 HA26 HA40 KA01 KA04 KA12 KA17 KA32 KA48 KA49 KA51 KA56 KA62 MA22 SA05 TA01 TA02 TA06 VL01 VL03 VL08

Claims (6)

[Claims] 1. A power amplifying device having a volume for adjusting an output signal level of a power amplifying device, wherein at least a power supply voltage of an output amplifier is variable, comprising a coil and a first boosted fixed voltage from an external power supply.
Including a boost chopper circuit that generates voltage and a coil,
A step-down chopper circuit for generating a second voltage obtained by stepping down the fixed voltage, according to the position of the volume,
A power supply voltage circuit for switching between the first voltage and the second voltage and outputting as a power supply voltage of the output amplifier, wherein a coil for the boost chopper circuit and a coil for the step-down chopper are shared. . 2. The method according to claim 1, wherein the first voltage is applied to the output amplifier when the position of the volume is small, and the second voltage is applied to the output amplifier when the position of the volume is large. The power amplifying device according to claim 1. 3. When the position of the volume is inside,
The power amplifier according to claim 3, wherein the power supply voltage circuit outputs a fixed voltage of an external power supply as it is. 4. The power supply voltage circuit includes: a common coil; a first diode having a cathode connected to one end of the common coil; and a second diode having an anode connected to the other end of the common coil. A capacitor connected to the cathode of the second diode, a first switching means connected between one end of the common coil and the external power supply, and a second switch having one end connected to the other end of the common coil. 2. The power amplifying device according to claim 1, further comprising two switching means, and first and second switch control circuits for controlling the first and second switching means according to the position of the volume. 5. When the position of the volume is small, the first switch control circuit switches the first switching means, and the second switch control circuit turns off the second switching means. The power amplifying device according to claim 4, wherein when the position is large, the first switching means is turned on and the second switching means is switched. 6. The apparatus according to claim 5, wherein when the volume is in the middle position, the first switching means is turned on and the second switching means is turned off.
A power amplifying device according to claim 1.