JP2001284971A - Amplifier circuit and abnormality detecting method for switching means for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect abnormality in the switch means of an amplifier circuit. SOLUTION: A current limiter resistor R, a Zener diode 72 and a light emitting element respectively connected serially are parallel connected to a transistor Qa. The power amplifier voltage is impressed to the diode 72. When the voltage equal to or higher than a threshold voltage is impressed, the light emitting element 74 is turned on by the diode 72 and when the voltage lower than the threshold voltage is impressed, the light emitting element 74 is turned off. The threshold voltage is lower than the high power supply voltage and higher than the low power supply voltage. When a signal to be amplified by the power amplifier is not supplied, the low power supply voltage is impressed to the power amplifier and the light emitting element 74 does not emit. When a switch element Qc is short-circuited, however, even while the signal to be amplified by the power amplifier is not supplied, the high power supply voltage is impressed to the power amplifier and the light emitting element 74 is turned on. Namely, it can be detected the switch element Qc is short-circuited.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifying circuit and a method for detecting an abnormality in a switching means of the amplifying circuit.
Amplifying circuit including switching means for selectively applying to the amplifier a first high voltage of the high voltage power supply and a second low voltage lower than the first high voltage of the low voltage power supply, and abnormality detection of the switching means of the amplification circuit. About the method.

[0002]

2. Description of the Related Art Conventionally, an amplifier circuit provided with switching means for selectively applying a first high voltage of a high voltage power supply and a second low voltage of the low voltage power supply lower than the first high voltage to the amplifier has been known. It has been proposed (see JP-A-8-111615).
The switching means selectively applies the first high voltage and the second low voltage to the amplifier based on the magnitude of the signal to be amplified by the amplifier.

However, even if the switching means fails so as to always apply the first high voltage to the amplifier, the first high voltage is applied to the amplifier. It cannot be detected whether the switching means has failed.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and provides an amplifying circuit capable of detecting an abnormality of an amplifying circuit switching means and a method of detecting an abnormality of the amplifying circuit switching means. The purpose is to propose.

[0005]

In order to achieve the above object, according to the present invention, a first high voltage of a high voltage power supply and a second low voltage lower than the first high voltage of a low voltage power supply are selected. This is an amplifier circuit provided with a switching means for applying the voltage to an amplifier. The switching means may selectively apply the first high voltage and the second low voltage to the amplifier based on the magnitude of the signal to be amplified by the amplifier.

[0006] The amplifier circuit according to the present invention includes a notification element for notifying a predetermined state. The notification element is a light-emitting element, for example, a light-emitting diode (LE).
D) is preferable.

[0007] The amplifier circuit according to the present invention includes an operation control element for controlling the operation of the notification element. The operation control element may be a Zener diode.

Incidentally, the operation control element is applied with a voltage to the amplifier. The operation control element is turned on when a voltage equal to or higher than a threshold voltage is applied to operate the notification element, and is turned off when a voltage less than the threshold voltage is applied to turn off the notification element. Do not operate. The threshold voltage is lower than the first high voltage and higher than the second low voltage.

Here, when the switching means applies the second low voltage of the low-voltage power supply to the amplifier, a voltage smaller than the threshold voltage is applied to the operation control element, so that the notification element does not operate. On the other hand, when the switching means applies the first low voltage of the high-voltage power supply to the amplifier, a voltage higher than the threshold voltage is applied to the operation control element, so that the notification element operates.

As described above, the switching means controls the first high voltage and the second high voltage based on the magnitude of the signal to be amplified by the amplifier.
Is selectively applied to the amplifier.
The notification element is activated or deactivated according to the magnitude of the signal.

When the signal to be amplified is not supplied to the amplifier, the second low voltage is applied to the amplifier,
Therefore, the notification element should not operate.

However, if the switching means fails to always apply the first high voltage to the amplifier, the first high voltage is applied to the amplifier even when the signal to be amplified is not supplied to the amplifier. , The notification element operates.
Therefore, it is possible to detect that the switching means is abnormal.

From the above, the following invention (the invention of claim 4) is proposed. That is, an abnormality detection method of the switching means of the amplifier circuit including the switching means for selectively applying the first high voltage of the high voltage power supply and the second low voltage lower than the first high voltage of the low voltage power supply to the amplifier. And a notifying element for notifying a predetermined state to the amplifier circuit, and a threshold voltage which is lower than the first high voltage and higher than the second low voltage when a voltage is applied to the amplifier. An operation control element that turns on when the voltage is applied to operate the notification element, and turns off when the voltage less than the threshold voltage is applied and does not operate the notification element. When the signal to be amplified is not supplied to the amplifier, the abnormality of the switching unit is detected based on the notification state of the notification element.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, a case where an example of an amplifier circuit is applied to a power output stage of an audio device will be described in detail.

FIG. 1 shows a case where the present invention is applied to a power amplifying circuit provided in a final output stage of an audio apparatus, and FIG. 1 shows a 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) higher than that of the terminal 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 a dual power supply system, and the power supply voltage VPL applied through the terminals 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 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.

[0028]

(Equation 1)

The condition for turning on the transistor Qe is as follows: Vr−VF ≧ VP1 + VBE (2) where VP1 = VPL−VZ (3) ΔVr ≧ VPL
− (VZ−VF−VBE) (4) Here, as the reference voltage VS, VS = VZ−VF−VBE.
(5), the expression (4) is expressed as Vr ≧ VPL−VS...
・ ・ (6) That is, the voltage Vr at the connection midpoint r is
When the voltage approaches the voltage difference between the low-voltage power supply voltage VPL and the reference voltage VS and satisfies the expression (6), the transistor Q
e 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 supplies the low-voltage power supply voltage + VPL from the terminal 22a.
Is applied as the 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 Vr for turning on the transistor Qe is determined based on the power supply voltage VPL from the set voltage Vr.
It is set based on the value obtained by subtracting S (the output VO at this time is represented by Equation 1). Vr, for example, the ground point or output VO
The reason why the absolute value was not set to a constant value such as the point of = 0 for the following reason.

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 VPH when the output VO reaches a certain voltage with respect to 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, Ra >> Rb.
... Selected as in (7). For example, VPL = 20
VVS = 4V, so Vr = 16VRa = 100KΩ R
b = 1KΩ, the voltage VO required to turn on the transistor Qe is approximately equal to Equation 1, VO = 15.
96 volts (point m in FIG. 3). That is, the output voltage V
When O rises 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.

[0037]

(Equation 2)

For this reason, using this equation (8),
The output voltage VO at which the transistor Qe turns 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 the 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, a pair of resistors 5
Hysteresis characteristics are provided by selecting 4, 56 and their values as described above, and a very stable power supply switching process resistant to noise can be realized by the hysteresis characteristics.

Here, as described above, since the switching element Qc uses an electric switching element such as a power MOSFET operating at a high speed, the switching of the power supply voltage is performed at a very high speed. Therefore, the power supply voltage can be switched immediately without a time lag following the level fluctuation of the low frequency signal as shown in FIG.

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, a region shown by oblique lines as shown in FIG.

On the other hand, when the power supply voltage is switched according to 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.

Although not shown in FIG. 1, the amplifier circuit 10 according to the present embodiment includes a current limiting resistor R, a Zener diode 72, and a light emitting element (a light emitting element) connected in series and in parallel with a transistor Qa. LED) 74 is connected. Similarly, for the transistor Qb, the current limiting resistor R, the Zener diode 72 and the light emitting element 7
4 are connected.

As described above, since the Zener diode 72 is connected in parallel to the transistor Qa, the amplifier 1
A voltage to 8 is applied. Also, the Zener diode 7
No. 2 turns on and activates the light emitting element 74 when a voltage higher than the threshold voltage is applied, and turns off and stops operation of the light emitting element 74 when a voltage lower than the threshold voltage is applied. I do. Here, the threshold voltage is lower than the high power supply voltage V _{PH and} higher than the low power supply voltage V _PL .

Here, when the switching element Qc is turned off, a voltage lower than the threshold voltage is applied to the Zener diode 72, so that the light emitting element 74 does not emit light. On the other hand, when the switching element Qc is turned on, a voltage higher than the threshold voltage is applied to the Zener diode 72, so that the light emitting element 74 emits light.

As described above, the switching element Qc
Is based on the magnitude of the signal to be amplified by the amplifier 18,
Since the power supply voltage V _PH and the power supply voltage V _PL are selectively applied to the amplifier 18, the light emitting element 74 emits light or does not emit light according to the magnitude of this signal. That is, the light emitting element 74 emits light, so that the power supply voltage V _PH is
8 is notified of the state being applied.

By the way, when the signal to be amplified is not supplied to the amplifier, the power supply voltage _VPL is applied to the amplifier 18, so that the light emitting element 74 should not emit light. However, when the switching element Qc is short-circuited, the power supply voltage V _PH is applied to the amplifier 18 even when the signal to be amplified is not supplied to the amplifier 18, and the light emitting element 74 emits light. Therefore, it is possible to detect that the switching element Qc is abnormal (short). Although a light emitting element is used in the above description, the present invention is not limited to this, and an element that outputs sound may be used.

[0048]

As described above, according to the present invention, when the voltage is applied to the amplifier and the threshold voltage is lower than the first high voltage of the high voltage power supply and higher than the second low voltage of the low voltage power supply, When the voltage is applied, it turns on to operate the notification element, and, when a voltage lower than the threshold voltage is applied, the operation control element is turned off and does not operate the notification element. This has the effect that an abnormality of the switching means for switching the low-voltage power supply can be detected.

[Brief description of the drawings]

FIG. 1 is a system diagram illustrating an example of an amplifier circuit.

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 as in FIG. 3;

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

FIG. 6 is an explanatory diagram of an element for detecting an abnormality of a switching element.

[Explanation of symbols]

 72 Zener diode (operation control element) 74 Light emitting element (notifying element) R Current limiting resistor

Continued on the front page F-term (reference) 5J091 AA02 AA18 AA41 AA51 CA00 FA18 HA08 HA10 HA18 HA19 HA20 HA25 HA39 HA44 KA01 KA49 KA67 MA24 SA05 TA06 UW09 5J092 AA02 AA18 AA41 AA51 CA00 FA18 HA08 HA10 HA18 KA19 HA25 HA25 SA05 TA06

Claims (4)

[Claims] 1. An amplifier circuit comprising switching means for selectively applying to a amplifier a first high voltage of a high voltage power supply and a second low voltage of the low voltage power supply which is lower than the first high voltage, A notifying element for notifying a predetermined state, and turned on when a voltage that is lower than the first high voltage and higher than a threshold voltage that is higher than the second low voltage is applied while a voltage is applied to the amplifier. And an operation control element that is turned off when a voltage less than the threshold voltage is applied and does not operate the notification element. 2. The amplifier circuit according to claim 1, wherein said notification element is a light emitting element. 3. The amplifier circuit according to claim 1, wherein the operation control element is a Zener diode. 4. A switching means for an amplifier circuit comprising switching means for selectively applying to a amplifier a first high voltage of a high voltage power supply and a second low voltage lower than the first high voltage of a low voltage power supply. An abnormality detection method, comprising: a notification element that notifies a predetermined state to the amplifier circuit; and a threshold that is applied to the amplifier and that is lower than the first high voltage and higher than the second low voltage. An operation control element that turns on when the voltage equal to or higher than the value voltage is applied to operate the notification element, and turns off when the voltage less than the threshold voltage is applied and does not operate the notification element. When the signal to be amplified is not supplied to the amplifier,
An abnormality detection method for a switching unit of an amplifier circuit, comprising: detecting an abnormality in the switching unit based on a notification state of the notification element.