JP3351637B2 - Power amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power amplifying circuit suitable for use in audio equipment such as mini-components, CD radio cassette players, stereo equipment, and audio / video equipment, and more particularly to a power amplifying circuit capable of reducing power loss.

[0002]

2. Description of the Related Art In recent years, audio devices such as mini-components and CD radio-cassettes have been reduced in size and tend to have higher output. Power amplifier to increase output (power amplifier)
In addition to increasing the power supply voltage of the power amplifier, a power supply transformer having a large capacity corresponding to the power amplifier, a power IC, a radiator, or the like may be used.

However, the use of a large-capacity transformer leads to an increase in cost, and a high power supply voltage is applied to the power amplifier and the power transformer, so that the amount of heat generated increases, and as a result, the temperature inside the housing rises. The malfunction of the mechanism occurs, and the electrical characteristics of the element change (deterioration, etc.).

[0004]

In order to solve such a problem, attention is paid to the output voltage of the power amplifier. When the output voltage is low, a low power supply voltage is used, and when the output voltage is high, a high power supply voltage is used. It is conceivable to switch and use it. For example, as shown in FIG. 6, when the output voltage VO of the low frequency signal is low (section Lb), the low power supply voltage VPL (about 20 volts) is selected as the operating power supply, and when the output voltage VO is high (section La), the high power supply voltage is used. Voltage VPH
(40-45 volts) as its operating power source.

[0005] If the power supply voltage can be changed in accordance with the output voltage as described above, the capacity of the transformer can be suppressed, and the heat generation inside the housing can be suppressed. As a result, the cost of the apparatus can be reduced. As the power supply voltage switching means, a mechanical switching means such as a relay device can be used.

FIG. 7 shows the switching timing when the power supply voltage is switched using the relay device. Output voltage V
When O exceeds the reference level ± REF (time point a), at this time point a, the relay device is operated, and the voltage is switched from the low power supply voltage VPL to the high power supply voltage VPH almost simultaneously with the voltage detection time point a.

However, when the relay device is turned off, it cannot be switched quickly as in the case of the operation. That is, even if the operating voltage to the relay device is cut off, the relay does not operate immediately after the voltage cutoff. As a result, as shown in FIG.
After that, the power supply voltage is switched to the low power supply voltage VPH.

For this reason, as shown in FIG.
8 intermittently changes and the intermittent period is shorter than the above-mentioned time lag τ, in the example of FIG.
If the period is an intermittent period such as τ3, the power supply voltage cannot be effectively switched. Therefore, even if this relay device is actually mounted on an audio device, effective switching of the power supply voltage cannot be performed, and the problem of heat generation and the problem of power consumption remain unresolved.

In view of the above, the present invention has solved such a conventional problem. In particular, by using a high-speed power switching element as a power supply switching means, the power supply voltage can be switched in response to the output voltage. The present invention proposes a power amplifying circuit described above.

[0010]

In order to solve the above-mentioned problems, a power amplifier circuit according to the present invention comprises a low-voltage power supply or a high-voltage power supply.
Low-frequency power amplifier connected to the
Between the output voltage of the amplifier and the reference voltage generated from the low-voltage power supply.
Compare and based on the difference the low voltage to the low frequency power amplifier
Power supply switch to switch between power supply connection and high voltage power supply connection
And a power switching means for controlling the high voltage power supply.
Fast power switching element and output power of low frequency power amplifier
Voltage and the reference voltage generated from the low voltage power supply
Voltage ratio for on / off control of high-speed power switching element
And a high-speed power switch.
A transistor for on / off control of the switching element is provided,
The voltage to turn on the transistor and the
The operation to change the voltage to be turned
Power supply switching means, the high-voltage power supply
Is connected to the
If the pressure becomes lower than the pressure,
From the connection of the high-voltage power supply to the low-frequency power amplifier to the low-voltage power supply
Connection to the Internet .

[0011]

[Action] In the power amplifier circuit 10 shown in FIG. 1, the positive side of the
Taking the output example, the voltage comparison means detects the positive output voltage.
ON of the diode 50 for high-speed power switching
・ Off-control transistor Qe, reference voltage generation constant
It comprises a voltage diode 32, a resistor 34 and the like. So
Then , when the level of the output voltage VO rises so that the potential Vr at the point r becomes equal to the difference between the low power supply voltage VPL and the reference voltage VS as shown in the equation (6), the transistor Qe is turned on for the first time. , And the transistor Qc is turned on.

Therefore, since the transistor Qc is off until the output voltage VO reaches the voltage level, the lower power supply voltage VPL is supplied as the power supply voltage of the power amplifier 18.

However, when the output voltage VO reaches the above-mentioned voltage level, the transistor Qe is turned on, and accordingly, the transistor Qc is turned on. Then, the higher power supply voltage VPH is applied to power amplifier 18 via transistor Qc, and the power supply voltage is switched.

After the transistor Qc is turned on, the output voltage VO starts to drop, and when the value approaches the value of the equation (6), the transistor Qc is turned off, so that the power supply voltage returns to the original lower power supply voltage VPL.

Here, when the power supply voltage is switched to the VPH side,
From that point on, the voltage Vr at the connection point r becomes
The power supply voltage changes from VPL to VPH. Therefore, the voltage level of the connection point r at which the transistor Qc turns off is higher than the voltage level at which the transistor Qe turns on.
This is because the value of the second term on the right side of equation (7) becomes larger than the value of the second term on the right side of equation (6). Therefore, as shown in FIG. 3, the output voltage VO at which the transistor Qe is turned on is different from the output voltage VO at which the transistor Qe is turned off. This is called the hysteresis characteristic of the power supply switching means 30.

Since a high-speed power switching element is used as a switching element for switching the power supply voltage to the higher power supply voltage VPH, the power supply voltage can be switched while correctly following the level fluctuation of the output voltage.

[0017]

Next, a case where an example of a power amplifier circuit according to the present invention is applied to a power output stage of the above-described audio device will be described in detail with reference to the drawings.

FIG. 1 shows a case where the present invention is applied to a power amplifier circuit provided in a final output stage of an audio device, and FIG. 1 shows the configuration of an R channel. This power amplifier circuit 10 has a voltage amplifier 14 and an input terminal 12 thereof.
Is amplified to a predetermined level. As the voltage amplifier 14, a voltage amplifier constituted by an operational amplifier 16 as shown in the figure can be used.

The voltage amplifier 14 is of a dual power supply drive type, and is supplied with a power supply voltage VPH (± VPH) having a higher voltage than the terminals 17 (17a, 17b). This is for a high-output amplifier (about 100 to 130 W).
An operating voltage of 45 volts is used.

The low frequency signal output from the voltage amplifier 14 is further supplied to a power amplifier 18. The power amplifier 18 is composed of a pair of power transistors Qa and Qb that are complementarily connected as shown in FIG. The output terminal 20 is connected to an R channel speaker (not shown) serving as a load.

The power supply of the power amplifier 18 is also of a dual power supply type, and the power supply voltage VPL applied via the terminal 22 (22a, 22b) is lower than the above-described power supply voltage VPH. In this example, ± 20 volts is selected. On the positive and negative power supply paths 28a and 28b with respect to the power supply voltage VPL, diodes 24 and 26 for preventing backflow when a higher power supply voltage is used as the power supply voltage are connected as described later.

In the present invention, the power amplifier 18 is driven not only by the low-voltage power supply voltage VPL but also by the high-voltage power supply voltage VPH. Therefore, the power amplifier 18
Power supply switching means 30 on power supply paths 27a and 27b for
Is provided.

First, a high-speed power switching element Qc is connected between the positive high-voltage power supply path 27a and the low-voltage power supply path 28a. Similarly, a high-speed power switching element Qd is connected between the high voltage power supply path 27b and the low voltage power supply path 28b on the negative side. As a power switching element that operates at high speed, a power MOS FET or the like can be used.

The following configuration is added to control these switching elements Qc and Qd. Positive power supply terminal 22
a constant voltage diode 32 as a constant voltage element
And a series circuit of the resistor 34 are connected to generate a reference voltage for the connection midpoint p1. In this example, a Zener diode is used as a constant voltage diode. Similarly, a series circuit of a constant voltage diode 36 and a resistor 38 is connected between the negative power supply terminal 22b and the ground, so that a predetermined reference voltage is obtained at a connection midpoint p2.

Transistors Qe and Qf functioning as switching elements are connected between the connection middle points p1 and p2 and the switching elements Qc and Qd. A resistor 40 connected to the gates of the switching elements Qc and Qd,
Reference numerals 42, 44 and 46 denote voltage dividing resistors for obtaining an appropriate control gate voltage.

On the other hand, a pair of resistors 5 connected in series is connected between the low-voltage power supply path 28a and the output terminal 20 of the low-frequency signal.
4, 56 and 58, 60 are connected, and the base of the above-described transistor Qe is connected to one connection midpoint r via a diode 50 for detecting a positive output voltage. Similarly, the base of the transistor Qf is also connected to a connection midpoint s between the resistors 58 and 60 via a diode 52 for detecting a negative output voltage.

In this configuration, a circuit portion of the power supply switching means 30 surrounded by a chain line can also be used as a part of the power supply switching means of the power amplifier circuit on the L channel side.

According to the present invention, as shown in FIG.
Before the output voltage VO of the low-frequency signal obtained at 0 becomes a level that can no longer be driven by the low-voltage power supply voltage VPL, the power supply voltage applied to the power amplifier 18 is switched to the higher-power supply voltage VPH. Can be Since the high-speed power switching elements Qc and Qd are used as described above, the switching of the power supply voltage is performed at high speed. Therefore, when the waveform of the low-frequency signal is the output voltage waveform as shown by the curve L0 in FIG. 2, the power supply voltage applied to the power amplifier 18 corresponds to the output voltage waveform as shown by the curves L + and L- in FIG. Change.

Next, the power supply switching operation will be described in detail. Since the power switching operation on the positive side and the negative side is exactly the same, the power switching operation on the positive side will be described below.
The constant voltage value of the constant voltage diodes 32 and 36 is Vz, the base-emitter voltage of the transistors Qe and Qf is VBE, the drop voltage of the diodes 50 and 52 is VF, and the resistors 54 and 5
The resistance value of No. 6 will be described as Ra and Rb.

It is assumed that the voltage waveform of the output voltage VO obtained at the output terminal 20 is a curve Lo in FIG. The voltage Vr at the connection midpoint r can be expressed as in equation (1) since the voltage at the output terminal 20 and therefore at the connection midpoint q is VO.

[0031]

(Equation 1)

The condition for turning on the transistor Qe is as follows: Vr−VF ≧ VP1 + VBE (2) where VP1 = VPL−VZ (3) ∴Vr ≧ VPL− ( (VZ-VF-VBE) (4) Here, as the reference voltage VS, if VS = VZ-VF-VBE (5), the equation (4) becomes: Vr ≧ VPL-VS (6) That is, the voltage Vr at the connection midpoint r approaches the voltage of the difference between the low-voltage power supply voltage VPL and the reference voltage VS, and (6)
When the value satisfies the expression, the transistor Qe turns on. An increase in Vr means an increase in the output voltage VO itself, as can be seen from equation (1). Therefore, as shown in FIG. 3, the transistor Qe keeps the off state before the value of the output voltage VO satisfies the expression (6), that is, while Vr <VPL-VS. As a result, the switching element Qc also remains off, so that the power amplifier 18
Is supplied with the low-voltage power supply voltage + VPL from the terminal 22a as its operating voltage.

Here, the reference voltage VS is a value indicating how close the power supply voltage VPL and the curve LO (that is, VO) are to switch the power supply voltage VPL to the power supply voltage VPH. This value can be set by appropriately selecting the constant voltage diode 32, the transistor Qe, and the diode 50. In this embodiment, for example, VS is set to about 4 volts. From this, the voltage V for turning on the transistor Qe is
r is set based on a value obtained by subtracting the set voltage VS from the power supply voltage VPL as a reference (the output VO at this time is expressed by the following equation (1)).
). Vr is, for example, the ground point or output VO =
The reason why the absolute value such as the zero point is not set to a constant value from the following points is as follows.

In the audio equipment of this embodiment, a commercial power supply from a household outlet is generally used as a power supply. Since the rectified output from the commercial power supply is used, the power supply voltage VPH or VPL
Naturally fluctuates. Further, the power supply voltage VPL causes a load change due to the output of the power amplifier 18, which also causes the power supply voltage VPL to change.

For example, if the output voltage VO is set to switch from the power supply voltage VPL to the voltage VPH when the output VO reaches a certain voltage based on the point 0, the output voltage VO increases when the power supply voltage VPL decreases. , The value of the output VO approaches the power supply voltage VPL, and the voltage between the collector and the emitter of the transistor Qa decreases, so that the HFE decreases. And the power supply voltage V
Waveform distortion occurs before PL switches to VPH.

In order to prevent this, in the present application, the transistor Qe is turned on, and the value of Vr when the power supply voltage VPL is switched to VPH is set based on the power supply voltage VPL.

On the other hand, when the level of the output voltage VO rises so as to satisfy the expression (6), the transistor Qe turns on. Then, since the current path of the transistor Qe is closed, the switching element Qc is turned on. As a result, a high power supply voltage + VPH is applied to the power amplifier 18 via the terminal 17a, and the power is amplified based on the power supply voltage + VPH (see FIG. 2).

In the configuration of FIG. 1, in order to provide a hysteresis characteristic to the detection of the output voltage VO, the following is selected: Ra >> Rb (7). For example, if VPL = 20V, VS = 4V, and thus Vr = 16V, Ra = 100KΩ, Rb = 1KΩ, the voltage VO for turning on the transistor Qe is approximately VO = 15.96 volts from equation (1). 3 point m). That is, when the output voltage VO increases to about 16 volts, the power supply voltage is switched to the high voltage + VPH.

On the other hand, the condition for turning off the transistor Qe is as follows. Equation (1) changes as in equation (8). This is because the power supply voltage has been switched.

[0040]

(Equation 2)

For this purpose, using this equation (8),
The output voltage VO at which the transistor Qe is turned off is approximately VO = 15.7 volts (point n in FIG. 3). That is, the voltage at which the transistor Qe is turned on is different from the voltage at which the transistor Qe is turned off. This means that the detection voltage for switching the power supply voltage is given a hysteresis characteristic.

Due to this hysteresis characteristic, even when noise N is mixed into the low frequency signal Lo as shown in FIG. 4, for example, the noise level becomes approximately 0.2 volts or more according to the above-described example. Otherwise, the transistor Qe does not turn off.

That is, by selecting the pair of resistors 54 and 56 and their values as described above, a hysteresis characteristic is provided, and the hysteresis characteristic realizes a very stable power supply switching process that is resistant to noise. it can.

Here, as described above, since the switching element Qc uses an electric switching element such as a power MOS FET which operates at a high speed, the switching of the power supply voltage is performed at a very high speed. Therefore, as shown in FIG. 2, it is possible to immediately switch the power supply voltage without a time lag following the level change of the low frequency signal.

By switching the value of the power supply voltage in accordance with the level of the low-frequency signal, a small radiator for the power amplifier 18 can be used. Can also be reduced in capacity. Incidentally, conventionally, the same power supply voltage (high voltage) VPH
5A, the area indicated by oblique lines as shown in FIG.

On the other hand, when the power supply voltage is switched in accordance with the level of the low frequency signal as in the present invention, the power loss area is reduced as shown by the hatched area in FIG. As a result, a radiator used in a 60 W class power amplifier, for example, even with a 120 W (watt) class power amplifier,
The corresponding small capacity power transformer can be used. Thus, the following effects can be obtained. (1) High-speed switching enables large power consumption
It is possible to realize a power-saving device with reduced power consumption. (2) Since the heating section in the device is common to the conventional
The operation section where the low-voltage power supply voltage can be used
It becomes the heat generation reduction area as it is, and the heat loss is greatly reduced
Wear. The radiator can be downsized. (3) Since power consumption of the power amplifier is reduced, power supply
Small size, lighter,
Furthermore, it contributes to cost reduction. (4) The circuit part shown by the chain line in FIG.
Can also be used, so that the overall circuit configuration can be simplified,
This contributes to downsizing of the entire device and cost reduction. And many more
Characteristic can be obtained .

[0047]

As described above , according to the power amplifier circuit of the present invention, the output voltage of the low-frequency power amplifier and the low-voltage power supply
Is compared with the reference voltage generated from the
Connecting a low-voltage power supply to the low-frequency power amplifier or connecting a high-voltage power supply
Power supply switching means for switching connection;
The stage is for ON / OFF control of high-speed power switching element
Transistors are provided, and the power switching means
When a high-voltage power supply is connected to the power amplifier,
If the output voltage becomes lower than the reference voltage,
High voltage to the low frequency power amplifier based on the teresis characteristics
The connection from the power supply to the low-voltage power supply is made
You. With this configuration, the high-speed power switching element
Voltage to turn on the transistor
Low frequency noise above the voltage difference that turns off the transistor
When the signal is mixed into the wave signal, the transistor is turned off.
Therefore, even when noise is mixed in,
The connection of the high voltage power supply can be maintained by the
And realizes a very stable power supply switching process.
be able to.

According to this, the following effects can be obtained. (1) Since high-speed switching is possible, power consumption is greatly reduced, and a power-saving device can be realized. (2) Since the heat generating portion in the device is common to the conventional one, the operation section in which a low-voltage power supply voltage can be used by the switching operation becomes the heat generation reducing region as it is, and the heat loss can be greatly reduced. The radiator can be downsized. (3) Since the power consumption of the power amplifier is reduced, a small power transformer can be used.
Furthermore, it contributes to cost reduction. (4) Since the circuit portion shown by the chain line in FIG. 1 can be shared by the R and L2 channels, the entire circuit configuration can be simplified, which also contributes to downsizing and cost reduction of the entire device. And many other features.

Therefore, the present invention is extremely suitable for application to a power amplification system of various audio equipment and video equipment as described above.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an example of a power amplifier circuit according to the present invention.

FIG. 2 is an explanatory diagram of a power supply voltage switching operation.

FIG. 3 is a detailed explanatory diagram of a power supply voltage switching operation.

FIG. 4 is a detailed explanatory diagram of a power supply voltage switching operation similarly to FIG. 3;

FIG. 5 is an explanatory diagram of heat loss due to power supply switching.

FIG. 6 is an explanatory diagram of power supply voltage switching.

FIG. 7 is an explanatory diagram showing an example of conventional power supply voltage switching.

FIG. 8 is an explanatory diagram showing an example of conventional power supply voltage switching.

[Explanation of symbols]

 Reference Signs List 14 voltage amplifier 18 power amplifier 30 power supply switching means Qc, Qd high-speed power switching element Qe, Qf switching transistor VPL low-voltage power supply voltage VPH high-voltage power supply voltage

Claims (1)

(57) [Claims] A low frequency power supply connected to a low voltage power supply or a high voltage power supply.
Wave power amplifier and the output voltage of the low frequency power amplifier and the low voltage power supply.
With the reference voltage, and based on the difference,
Disconnect the low-voltage power supply or high-voltage power supply to the power amplifier.
Power supply switching means for switching, the power supply switching means includes a high-speed power switching element for controlling a high- voltage power supply, and an output voltage and a low-voltage power supply generated from the low-frequency power amplifier.
The high-speed power switch based on the difference from the reference voltage
Voltage comparing means for controlling on / off of the switching element , wherein the voltage comparing means includes a transistor for controlling on / off of the high-speed power switching element.
A transistor is provided, a voltage for turning on the transistor and the transistor
The hysteresis characteristic makes the operation to turn off the voltage different
When a, in the power supply switching means, when the high voltage power supply is connected to the low-frequency power amplifier
And the output voltage becomes lower than the reference voltage.
The low frequency power increase based on the hysteresis characteristic.
Connect the high-voltage power supply to the low-voltage power supply
Power amplifier circuit, characterized in that Uninasa be.