JP2002198750A - Power amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power amplifier such as a power amplifier circuit that automatically detects the resistance of a load connected to the power amplifier and automatically selects a power supply voltage matching the resistance of the connected load. SOLUTION: The power amplifier is provided with an amplifier section that amplifies a received signal and outputs the amplified signal to the load, a power supply section that supplies power with a plurality of different power supply voltages to the amplifier section, a power supply voltage switching section that switches the output voltage of the power supply section, a test signal generating section that generates a test signal consisting of a plurality of pulses whose signal levels differ from each other, an input changeover section that selects the test signal or the input signal given to the amplifier section, a detection section that detects the resistance of the load on the basis of the test signal, and a control section that controls the power supply voltage switching section to select the power supply voltage on the basis of the load resistance detected by the detection section by allowing the test signal generating section to generate the test signal just after application of power.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power amplifier for amplifying a signal and outputting the amplified signal to a load such as a speaker.

[0002]

2. Description of the Related Art A power amplifier such as an audio device such as an audio power amplifier or an electronic musical instrument such as an electronic piano is used by connecting a speaker or the like to an output stage. Such a power amplifier uses a switching power supply that is a constant voltage power supply. A power amplifier equipped with a constant voltage power supply matches the power that can be supplied by the constant voltage power supply with the resistance (load impedance) of a load such as a speaker connected to the power amplifier.
It is necessary to set the output voltage value and the output current value of the constant voltage power supply.

In a power amplifier using a switching power supply, when the output voltage of a low-voltage power supply is designed to match a low load resistance, when a load having a high load resistance is connected, the power supply voltage of the constant-voltage power supply is increased. Cannot obtain the maximum output obtained by

For example, an output of 1 is applied to a load having a resistance value of 4Ω.
When a constant voltage power supply set to obtain 00 W is used, if a load having a resistance value of 8Ω is connected, only an output of 50 W can be obtained due to the limitation of the output voltage. In contrast, a power amplifier having an output stage designed to obtain an output of 100 W with respect to a load having a resistance of 8Ω has a resistance of 4Ω.
Is connected, only an output of 50 W can be obtained due to the limitation of the output current.

[0005] In a power amplifier (for example, an audio par amplifier, etc.) which is considered so as to obtain a maximum output corresponding to a load resistance value, a switch for switching a power supply voltage in accordance with a load resistance value of a connected speaker is provided. Provided on the back of the housing or the like, when connecting a speaker, the user checks the load resistance value of the speaker, and the user selects a power supply voltage suitable for the load resistance value using a switch.

In such a power amplifier, the user checks the load resistance value connected to the power amplifier and selects a power supply voltage suitable for the load resistance value using a switch. If the user forgets to switch the switch, the maximum output of the power amplifier may not be obtained.

As a power amplifier which has solved this problem, Japanese Patent Application Laid-Open No. 7-240636 discloses a power amplifier.
Determine the magnitude of the load impedance from the magnitude of the output current level relative to the input voltage level or output voltage level,
There is a power amplifier that switches a power supply voltage based on a load impedance.

[0008]

SUMMARY OF THE INVENTION Japanese Patent Application Laid-Open No. 7-24063
In the power amplifier disclosed in Japanese Unexamined Patent Publication No. 6 (1994), a load current value flowing through a load such as a speaker is compared with a reference value, and the load impedance is determined based on the magnitude of the load current value relative to the reference value. Until the value exceeds the reference value, switching of the power supply voltage is not performed even if the load impedance does not match.

Therefore, when the load current value is equal to or less than the reference value and is near the reference value, the power supply voltage is not switched, and when the same state continues for a long time, the analog element (for example, a transistor or the like) ) May be gradually heated and destroyed.

The detection of an output short circuit or the like is not a load resistance detection for detecting a load resistance value by flowing a predetermined current to a load, but a load current for detecting a load resistance value by flowing a maximum load current of the load to the load. Since the detection is performed, when the load resistance value is 0Ω or a value close to 0Ω, that is, when the output terminal is short-circuited, the maximum load current flows through the load when the load current is detected, and the load or the power amplifier may be damaged. There is.

The present invention automatically detects load resistance (load impedance) for various loads connected to a power amplifier, and automatically generates a power supply voltage suitable for the load resistance of the connected load. It is intended to provide a power amplifier for switching.

[0012]

According to the first aspect of the present invention, there is provided an amplifying section for amplifying an input signal and outputting the amplified signal to a load, and a power supply for supplying power of a plurality of different power supply voltages to the amplifying section. Unit, a power supply voltage switching unit for switching the output voltage of the power supply unit, a test signal generation unit for generating a test signal of a plurality of pulses having different signal levels, and an input input to the test signal and the amplification unit An input switching unit for switching a signal, a detection unit for detecting a resistance value of a load based on the test signal, and a load resistance detected by the detection unit by generating a test signal from the test signal generation unit immediately after power-on. A power supply voltage switching unit for controlling the switching of the power supply voltage based on the value.

According to a second aspect of the present invention, in the power amplifier according to the first aspect, the test signal includes an output short-circuit detection pulse for detecting whether an output terminal is short-circuited and a load resistance value. And a load resistance value detection pulse.

[0014]

FIG. 1 is a schematic diagram showing a schematic configuration of an embodiment of a power amplifier according to the present invention. In FIG.
The power amplifier 1 includes an input switching unit 2, an amplification unit 3, a power supply unit 4,
A test signal generator 5, a detector 6, a power supply voltage switcher 7, a controller 8, and a display 9 are provided. In this embodiment, the load 10 is a speaker.

The input switching unit 2 is controlled by the control unit 8 to
Either the input signal or the test signal input from the test signal generator 5 is selected and output to the amplifier 3. Further, the input switching unit 2 interrupts the input of the input signal and the test signal to the amplification unit 3 under the control of the control unit 8.

The amplifying unit 3 amplifies the signal input from the input switching unit 2 and outputs the amplified signal to the load 10. The maximum output of the power amplifier 1 is higher when the power supply voltage is higher than when the power supply voltage is lower.

The power supply unit 4 supplies power to each unit. The power supply unit 4 can supply power of a plurality of different power supply voltages, and supplies power to the amplification unit 3 with a power supply voltage selected by a power supply voltage switching unit 7 described later from the plurality of power supply voltages.

The test signal generator 5 includes a memory 11 and a digital-to-analog (DA) converter 12. The memory unit 11 is, for example, a ROM (Read Only)
Memory) and stores a test signal. The DA converter 12 converts the test signal output from the memory unit 11 from a digital signal to an analog signal, and outputs the analog signal to the input switching unit 2.

The detecting section 6 is for detecting the load resistance value of the load 10 based on a test signal, and includes, for example, a detecting resistor.

The power supply voltage switching section 7 switches the power supply voltage of the power supply section 4 under the control of the control section 8. In the present embodiment, the power supply voltage of the power supply unit 4 is switched by the power supply voltage switching unit 7, but a switching power supply or the like that can set the power supply unit 4 to an arbitrary output voltage value may be used.

The control unit 8 generates a test signal from the test signal generation unit 5 immediately after the power is turned on to the power amplifier 1, and the detection unit 6 detects the load resistance value of the load 10;
The power supply voltage switching unit 7 is controlled based on the detected load resistance value to switch the power supply voltage supplied to the power supply unit 4.

The control unit 8 outputs, from a plurality of pulses (for example, pulse a, pulse b, and pulse c) having different signal levels, a pulse a having the lowest signal level to a pulse c having the highest signal level. Let it.

The control unit 8 outputs the pulse a having the lowest signal level to the load to detect the load resistance value, and then outputs the pulse b to the load to detect the load resistance value. The pulse c having the highest level is output to the load resistance to detect the load resistance value.

If the load resistance is smaller than a predetermined load resistance by detecting the load resistance, the control unit 8 prevents the amplifying unit 3 and the load 10 from being damaged by the input signal.
The input switching unit 2 is controlled to cut off the supply of the input signal to the amplification unit 3 (the supply of the signal to the load).

Under the control of the control unit 8, the display unit 9 displays that the signal output is being cut off, that the load 10 connected to the power amplifier 1 has a low load resistance value, An indication that the load 10 connected to 1 has a high load resistance value is displayed.

The test signal of the test signal generator 5 will be described. FIG. 2 is a schematic diagram for explaining a test signal in the power amplifier according to the present embodiment. As shown in FIG. 2A, the test signal includes a plurality of pulses having different signal levels. These pulses are pulses having a width of time t, and the width of each pulse is time T.

The signal level of each pulse is, for example, signal level a for the first pulse, signal level b for the second pulse, and signal level b for the third pulse.
The pulse has a signal level c, and each signal level corresponds to a load resistance value (for example, 4
Ω (output short-circuit), 4 Ω, 8 Ω, etc.).

In this embodiment, the test signal is described as being composed of three pulses having different signal levels. However, the present invention is not limited to this. The test signal is composed of one or two pulses or four or more pulses. A test signal may be used. When the load resistance value is detected by a test signal having a large number of pulses, a more correct load resistance value can be detected.

In FIG. 2B, when a detection signal e is generated across the detection resistor R1 of the detection unit 6 by a test signal, the current I flowing through the detection resistor R1 becomes as shown in the equation (1). .

I = e / R1 (1)

In this case, the load resistance value R2 is obtained by equation (2).

R2 = A · E / I = A · E · R1 / e (2)

Based on the equation (2), the load resistance value R2 becomes
Less than 0.5Ω (output short circuit), less than 2Ω, less than 6Ω, 6Ω
In order to detect the above case, the amplification factor A of the amplification unit 3 = 2
0, detection resistance value R1 = 0.1Ω, detection voltage e = 0.1V
Then, the signal level E of each pulse becomes the signal level a =
0.03 V, signal level b = 0.1 V, signal level c =
0.3V.

The control unit 8 stores the threshold value ef as a criterion for determining the load resistance value R2, and compares the detected voltage e in each pulse of the test signal with the threshold value ef. In the present embodiment, the threshold value ef is the pulse a of the signal level a = 0.03 V.
Is output to a load having a load resistance R2 = 0.5Ω, a pulse b having a signal level b = 0.1 V is applied to the load resistance R2 = 2Ω.
When a pulse c having a signal level c = 0.3 V is output to a load resistance value R2 = 6Ω, the detection resistance R
1 (0.1 V).

In this embodiment, when the pulses a, b, and c are respectively output to the loads, whether or not the detection voltage e detected by the detection resistor R2 is larger than the threshold value ef is determined.
Whether the output terminal is short-circuited or the load resistance R2 is 2Ω
Whether the load resistance R2 is 4Ω or 8Ω.
Is determined.

In the present embodiment, one threshold value ef is set. However, the present invention is not limited to this, and two or more threshold values may be set. By setting two or more threshold values, the resistance values of more loads can be determined more accurately.

The controller 8 causes the test signal generator 5 to output pulses in order from pulse a to pulse c, and detects the load resistance value for each pulse.

The controller 8 causes the test signal generator 5 to output the pulse a. The detection voltage e due to the pulse a becomes the threshold ef
If it is larger, the control unit 8 determines that the load resistance value is less than 0.5Ω and the output terminal may be short-circuited.

For example, when the output terminal is short-circuited and the load resistance value R2 = 0.1Ω, the detection voltage e is 0.6 V
Becomes Since the detection voltage e is larger than the threshold value ef, the control unit 8 determines that the load resistance value is less than 0.5Ω and the output terminal is short-circuited.

In this case, the control unit 8 controls the input switching unit 2 to prevent destruction of an analog element (for example, a transistor) caused by inputting an input signal to the amplification unit 3, and to control the amplification unit 3. Is cut off, and the test signal generator 5 does not output the pulse after the pulse b.
Further, the control unit 8 displays on the display unit (not shown) and warns the user that the output is short-circuited.

When the detected voltage e due to the pulse a is equal to or less than the threshold value ef, the control section 8 causes the test signal generating section 5 to output the pulse b. When the detected voltage e due to the pulse b is larger than the threshold value ef, the control unit 8 determines that the load resistance is
Judge as less than Ω.

For example, when the load resistance value R2 = 1.5Ω, the detection voltage e is 0.13V. Since the detection voltage e is larger than the threshold value ef, the control unit 8 sets the load resistance value to 2Ω.
It is determined that a load having a low resistance value is connected.

When the load resistance is 0.5 Ω or more and less than 2 Ω, the control unit 8 connects to the output terminal except for the speaker. The switching section 2 is controlled to cut off the input of the input signal to the amplification section 3 and the test signal generation section 5 does not output the pulse c. Further, the control unit 8 displays on the display unit (not shown) and warns the user that the load resistance value is low.

In the detection of the load resistance value by the pulse a and the pulse b, a load resistance value smaller than a predetermined resistance value (2 Ω in the present embodiment) is detected for each pulse. In the detection of the load resistance value, when a pulse b having a higher signal level than the pulse a is first output to the load, for example, if the output terminal is short-circuited, an excessive current flows through the load or the power amplifier, and The elements of the amplifier may be damaged.

For example, when detecting whether the load resistance value is less than 2Ω by only the pulse b, if the load resistance value is 2
Ω (when the load resistance is lower than the predetermined load resistance)
In this case, a current of about 1 A flows to the load, and when the output terminal is short-circuited and the load resistance value is 0.2Ω, a current of about 10 A flows to the load. Loads can carry up to about 10 A of current, which can damage the load or power amplifier.

Therefore, in detecting whether the load resistance value is less than 2Ω, a plurality of signal level pulses are used. That is, first, a pulse a having a low signal level is output to the load to detect whether the output terminal is short-circuited,
Next, a pulse b having a higher signal level than the pulse a is output to the load to detect whether the load resistance value is less than 2Ω. Thus, it is possible to prevent an excessive current from flowing through the load or the power amplifier, thereby preventing the load or the power amplifier from being damaged.

When the detected voltage e due to the pulse b is equal to or less than the threshold value ef, the control unit 8 causes the test signal generating unit 5 to output the pulse c. When the detected voltage e due to the pulse c is larger than the threshold value ef, the control unit 8 determines that the load resistance value is 2Ω or more and less than 6Ω.

For example, when the load resistance value R2 = 4Ω, the detection voltage e is 0.15V. Since the detection voltage e is larger than the threshold value ef, the control unit 8 determines that a load having a load resistance value of less than 6Ω is connected.

If the load resistance is not less than 2Ω and less than 6Ω, the control unit 8 determines that the speaker 10 having a load resistance of 4Ω is connected to the output terminal, controls the power supply voltage switching unit 7, and 3 is switched to the power supply voltage for low load resistance (for example, ± 28.3 V).

The detection voltage e due to the pulse c is equal to the threshold value e.
If f or less, the control unit 8 determines that the load resistance value is 6 Ω or more.

When the load resistance value is equal to or more than 6Ω, the control unit 8 determines that the speaker 10 having the load resistance value of 8Ω is connected to the output terminal, controls the power supply voltage switching unit 7, and controls the power supply unit 3. The power supply voltage is changed to the power supply voltage for high load resistance (for example, ±
40.0V).

The operation of the power amplifier 1 of this embodiment will be described. In FIG. 1, when the power is turned on to the power amplifier 1, the control unit 8 controls the input switching unit 2 to switch the signal output to the amplification unit 3 to a test signal. Thereafter, the controller 5 controls the test signal generator 5 to output a test signal (pulse a) to the load 10.

The test signal (pulse a) is supplied to the input switching unit 2
, And then passes through the load 10 and enters the detector 6.

A current flows through the detection resistor of the detection unit 6, and the control unit 8 determines the load resistance value from the voltage generated across the detection resistor. When it is determined that the load resistance value is less than 0.5Ω and the output terminal is not short-circuited, the control unit 8 controls the input switching unit 2 and shuts off the output of the signal to the amplification unit 3. At this time, the control unit 8 does not cause the test signal generation unit 5 to output the test signals (pulse b and pulse c) to the load 10.

When it is determined from the test signal (pulse a) that the output terminal is not short-circuited, the control section 8 causes the test signal generation section 5 to output the test signal (pulse b). When it is determined from the test signal (pulse b) that the load resistance value is less than 2Ω, the control unit 8 controls the input switching unit 2 and shuts off the signal output to the amplification unit 3. At this time, the control unit 8 does not allow the test signal generation unit 5 to output the test signal (pulse c) to the load 10.

When it is determined from the test signal (pulse b) that the load resistance value is 2 Ω or more, the control unit 8 causes the test signal generation unit 5 to output the test signal (pulse c).
When it is determined from the test signal (pulse c) that the load resistance value is 4Ω, the control unit 8 controls the power supply voltage switching unit 7 to switch the power supply voltage of the power supply unit 4 to a low load resistance voltage. After that, the input switching unit 2 is switched to the input signal side.

The input signal is supplied to the amplifier 3 via the input switch 2. The amplifier 3 amplifies the input signal and supplies the amplified signal to the load 10.

When it is determined from the test signal (pulse c) that the load resistance value is 8Ω, the control unit 8 controls the power supply voltage switching unit 7 to change the power supply voltage of the power supply unit 4. Switch to the voltage for high load resistance. After that, the input switching unit 2 is switched to the input signal side.

The input signal is supplied to the amplifier 3 via the input switch 2. The amplifier 3 amplifies the input signal and outputs the amplified signal to the load 10.

As described above, after the power is turned on, the power amplifier 1 automatically detects the load resistance using the test signal before the input signal is output to the load 10 via the amplifier 3. Select a power supply voltage suitable for the load resistance value. Then, the input signal is amplified based on the power supply voltage and the load 10 is amplified.
Can be output to For this reason, it is possible to obtain the maximum output suitable for the load resistance value without breaking the amplifier 3 or the load 10.

Further, it is possible to determine whether or not the output terminal is short-circuited by the test signal, thereby preventing the load or the power amplifier from being damaged due to an excessive current flowing through the load or the power amplifier.

In the above-described embodiment, the detection of the load resistance value is described as being performed after the power is turned on. However, the operation unit (not shown) is provided with an instruction button for detecting the load resistance value.
When the user operates the instruction button, the control unit 8 may detect the instruction and detect the load resistance value.

As a result, after the power of the power amplifier 1 is turned on and the load resistance at power-on is detected,
Even if the user replaces the load (speaker) 10,
Since the power supply voltage is set to the power supply voltage corresponding to the easily replaced load 10, there is no need for the user to confirm the load resistance value and reset the power supply voltage.

[0064]

According to the present invention, a load resistance (load impedance) is automatically detected for a plurality of loads connected to a power amplifier, and a power supply voltage suitable for the load resistance of the connected load is detected. Can be switched automatically.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of an embodiment of a power amplifier of the present invention.

FIG. 2 is a schematic diagram for explaining a test signal in the power amplifier according to the embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Power amplifier, 2 ... Input switching part, 3 ... Amplification part, 4 ... Power supply part, 5 ... Test signal generation part, 6
... Detection unit, 7 ... Power supply voltage switching unit, 8 ... Control unit, 9 ... Display unit, 10 ... Load (speaker), 1
1 ... memory unit, 12 ... DA conversion unit.

Continued on the front page F-term (reference) 5D020 AC02 5J091 AA02 AA41 CA36 CA56 CA81 FA18 FP02 FP04 FP06 GP05 HA25 HA38 KA12 KA17 KA28 KA49 KA62 MA11 MA20 SA05 TA01 TA06 5J092 AA02 AA41 CA36 CA56 CA81 FA18 KA12 KA38 KA17 MA20 SA05 TA01 TA06 VL03 VL08

Claims (2)

[Claims] An amplifier for amplifying an input signal and outputting the amplified signal to a load, a power supply for supplying power of a plurality of different power supply voltages to the amplifier, and a power supply for switching an output voltage of the power supply A voltage switching unit, a test signal generation unit that generates a test signal of a plurality of pulses having different signal levels, an input switching unit that switches between the test signal and an input signal input to the amplification unit, A detection unit for detecting the resistance value of the load, and a test signal is generated from the test signal generation unit immediately after power is turned on, and the power supply voltage switching unit detects the power supply voltage based on the load resistance value detected by the detection unit. A power amplifier comprising: a control unit that performs switching control. 2. The power amplifier according to claim 1, wherein the test signal includes an output short-circuit detection pulse for detecting whether an output terminal is short-circuited and a load resistance detection pulse for detecting a load resistance. A power amplifier comprising: