JP3359248B2 - Output power limiting circuit of power amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output power limiting circuit for a power amplifier, and more particularly to a power limiting circuit for limiting the output power of a power amplifier to prevent an overload of a power supply circuit for supplying a power supply voltage to the power amplifier. The present invention relates to an output power limiting circuit of an amplifier.

[0002]

2. Description of the Related Art As shown in FIG. 3, a power amplifier comprises a voltage amplifying stage 1 for amplifying an input signal and a power amplifying stage 2 for amplifying the output of the voltage amplifying stage 1, and a power supply circuit 3.
Generates a power supply voltage and supplies the generated power supply voltage to a plurality of power amplifiers.

In the above configuration, the output power limiting circuit of the power amplifier connects the series circuit of the Zener diode 31 and the Zener diode 32 between the output terminal of the voltage amplifying stage 1 and the ground, and connects the ground of the series circuit to the ground. The connection to the power supply circuit 3 is selectively performed by the transistor 33 to avoid an overload of the power supply circuit 3.

That is, by turning on the transistor 33, the level of the output voltage of the voltage amplifying stage is limited to a voltage level determined by a series circuit of the Zener diode 31 and the Zener diode 32. To avoid overloading the power supply circuit 3.

In the conventional power limiting circuit of the power amplifier configured as described above, the number of operated power amplifiers,
That is, based on the operation mode of the power amplifier, the on / off of the transistor 33 is controlled in advance, and the output terminal of the voltage amplification stage 1 is selectively grounded via the Zener diode to thereby reduce the output voltage of the voltage amplification stage 1. The amplitude is limited to the Zener voltage of the Zener diode, and the output power of the power amplification stage 2 is limited.

In another conventional output power limiting circuit of a power amplifier, as shown in FIG. 4, the output voltage of the power supply circuit 3 is switched based on the operation mode of the power amplifier.
Thus, the output power of the power amplification stage 2 is limited by selectively switching between the high voltage and the low voltage.

The output power is limited by the output power limiting circuits of the conventional two power amplifiers by setting ON / OFF of the transistor 33 in advance based on the number of power amplifiers to be operated, or by setting the switching circuit 41 When the number of power amplifiers to be operated is large, the transistor 33 is set to ON and the switch circuit 41 is set to the low voltage output side.

[0008]

However, in the above-described output power limiting circuit of the conventional power amplifier, when the output power is limited, not only the continuous maximum output but also the peak of the audio signal output whose output power level dynamically fluctuates. There is a problem that the power is also limited.

Also, in a multi-channel power amplifier comprising three or more power amplifiers, the output power obtained when the transistor 33 is turned off in a two-channel mode in which the two power amplifiers are operated. Or higher than the output power obtained when the switch circuit 41 is controlled to the H side, that is, the high potential side.
The output power obtained when the transistor 33 is turned on in the mode of the channel or higher, or the output power obtained when the switch circuit 41 is controlled to the L side, that is, the low potential side, becomes small, and the output power becomes small. There was a problem of being restricted.

According to the present invention, the operation of the output power limiting circuit is
It is an object of the present invention to provide an output power limiting circuit of a power amplifier which does not need to set a non-operation.

[0011]

According to a first aspect of the present invention, there is provided an output power limiting circuit for a power amplifier, comprising: a power amplifier having a voltage amplification stage and a power amplification stage for amplifying an output of the voltage amplification stage; Output power limiting circuit for a power amplifier having a power supply circuit for supplying a power supply circuit, wherein a time constant circuit that receives an output voltage from the power amplifier as an input and a power supply voltage level supplied from the power supply circuit to a voltage amplification stage are limited. and voltage limiting means, the output voltage level from the time constant circuit and a control means for limiting the power supply voltage value supplied to the voltage amplifier stage from the power supply circuit to limit the voltage value of the period in, voltage limit means exceeds a predetermined value , Is provided.

According to a first aspect of the present invention, there is provided an output power limiting circuit for a power amplifier, wherein an output voltage from the power amplifier is applied to a time constant circuit, and an output voltage level from the time constant circuit exceeds a predetermined value. The power supply voltage value supplied from the power supply circuit to the voltage amplification stage is limited by the control means to the limited voltage value of the voltage limiting means. Therefore, when the output power of the power amplifier exceeds a predetermined value, the power supply voltage of the voltage amplifying stage is limited to the limited voltage value of the voltage limiting means, and the output power is limited to the power value based on the limited voltage value. Is done. In this case, since the time constant circuit is provided, the peak power of the audio signal output whose output power level fluctuates dynamically is not limited.

According to a second aspect of the present invention, there is provided an output power limiting circuit for a power amplifier for supplying a power supply voltage to a plurality of power amplifiers each comprising a voltage amplification stage and a power amplification stage for amplifying the output of the voltage amplification stage. An output power limiting circuit of a power amplifier including a circuit, an adding circuit for adding output voltages from the respective power amplifiers, a time constant circuit for receiving the added output voltage of the adding circuit as an input, and a power supply circuit. and voltage limiting means for limiting the level of the power supply voltage supplied to the voltage amplifier stage, when the output voltage level from the constant circuit during a period that exceeds a predetermined value, electrodeposition pressure limiting means limit voltage value to each of the power supply circuit Control means for limiting a power supply voltage value supplied to the voltage amplification stage.

According to a second aspect of the present invention, there is provided an output power limiting circuit for a power amplifier, wherein output voltages from respective power amplifiers are added in an adder circuit, and an output voltage level from a time constant circuit having the added output voltage as an input. Is greater than the predetermined value, the control unit limits the power supply voltage value supplied from the power supply circuit to each voltage amplification stage to the limit voltage value of the voltage limiting unit. Therefore, when the sum of the output powers of the power amplifiers exceeds a predetermined value, the power supply voltage of the voltage amplifying stage is limited to the limited voltage value of the voltage limiting means, and the output power becomes the power value based on the limited voltage value. Is limited to In this case, since the time constant circuit is provided, the peak power of the audio signal output whose output power level fluctuates dynamically is not limited.

According to a third aspect of the present invention, there is provided an output power limiting circuit for a power amplifier according to the second aspect of the present invention, wherein the voltage limiting means comprises first and second voltage limiting means. Control means for dividing the output voltage of the time constant circuit, a first control means for selectively controlling the divided voltage of the voltage dividing means to zero level, and a divided voltage by the first control means. When the voltage is not controlled to zero level and the divided voltage level of the voltage dividing means exceeds a predetermined value, the power supply voltage supplied from the power supply circuit to each voltage amplification stage to the limited voltage value of the first voltage limiting means. A second control means for limiting the value, and a second voltage limiting means when an output voltage level from the time constant circuit exceeds a predetermined value when the divided voltage is controlled to a zero level by the first control means. Voltage limit Characterized in that a third control means for limiting the power supply voltage value supplied to each of the voltage amplification stage from the circuit.

According to a third aspect of the present invention, when the divided voltage is not controlled to the zero level by the first control means, the divided voltage level of the divided means is set to a predetermined value. Is exceeded, the power supply voltage value supplied from the power supply circuit to each voltage amplification stage is limited by the second control means to the limited voltage value of the first voltage limiting means. When the divided voltage is controlled to the zero level by the first control means, when the output voltage level from the time constant circuit exceeds a predetermined value, the third voltage limit means sets the third voltage limit value to the third voltage limit value.
The power supply voltage value supplied from the power supply circuit to each voltage amplification stage is limited by the control means. Therefore, the first
Under the control of the control means, the output power is limited to two types of power values.

BEST MODE FOR CARRYING OUT THE INVENTION

An output power limiting circuit of a power amplifier according to the present invention will be described below with reference to an embodiment.

FIG. 1 is a circuit diagram of an output power limiting circuit of a power amplifier according to an embodiment of the present invention.

An output power limiting circuit of a power amplifier according to one embodiment of the present invention includes a voltage amplifying stage 1 for amplifying an input signal and a power amplifying stage 2 for amplifying an output of the voltage amplifying stage 1 to a power supply circuit 3. The power supply voltage generated as described above is supplied to amplify the input signal by voltage and power. The output power limiting circuit of the power amplifier according to the present embodiment exemplifies a case where the output voltage from the power supply circuit 3 is supplied to two power amplifiers, and the power supply voltage supplied from the power supply circuit 3 to the voltage amplification stage 1 is illustrated. The case where the level is controlled to limit the output power of the power amplifier is shown.

The output voltage of the power amplification stage 2 is a diode D1
, And rectifies the output voltage of the power amplifier of another system (not shown) to the diode D2 to rectify the rectified output voltage of the two power amplifiers obtained by the diode D1 and the diode D2. ,
The addition is performed by an adding circuit 5 including resistors R1, R2, and R3. A capacitor C1 is connected in parallel to the resistor R2, and a time constant circuit 7 is formed by the addition circuit 5 and the capacitor C1.

The power supply voltage from the power supply circuit 3 to the voltage amplification stage 1 is supplied via a constant voltage control circuit 6. The constant voltage control circuit 6 includes a transistor Q that is turned on and off by applying a voltage across the resistor R2 via the time constant circuit 7 to the base.
2 and a transistor Q3 for controlling a power supply voltage level supplied to the voltage amplification stage 1 and the voltage amplification stage of another power amplifier.
And a resistor R connected between the collector and the base of the transistor Q3 to apply a bias voltage to the transistor Q3.
4, a zener diode D3 connected between the resistor R4 and the collector of the transistor Q2 and selectively energized through the resistor R4 by turning on and off the transistor Q2 to define an amplitude limiting voltage; and a base of the transistor Q3. And a capacitor C2 connected between the resistor R4 and the resistor C4 to form a ripple filter while the transistor Q2 is off.

On the other hand, a transistor Q1 is connected in parallel to the resistor R2, and the operation and non-operation of the output power limiting circuit are controlled by turning on / off the transistor Q1.

When the transistor Q1 is controlled to be on, the both ends of the resistor R2 are short-circuited by the transistor Q1, and the output power limiting circuit is controlled to be inactive. When the transistor Q1 is controlled to be in the off state, the short-circuit between both ends of the resistor R2 is released, and the voltage between both ends of the resistor R2 is applied to the transistor Q2, so that the output power limiting circuit is controlled to be in the operating state.

Hereinafter, the operation of the output power limiting circuit of the power amplifier according to the embodiment of the present invention will be described for the case where the output power limiting circuit is controlled to operate. The output voltage of the power amplification stage 2 is rectified by the diode D1,
The output voltage of the power amplification stage that constitutes another power amplifier is rectified by the diode D2, and the diodes D1 and D2,
The addition is performed by an adding circuit 5 including resistors R1, R2, and R3. The added output is applied to the time constant circuit 7 including the capacitor C1.

When the output voltage level from the time constant circuit 7 exceeds a predetermined value, that is, when the added output voltage level of the adder circuit 5 exceeds a predetermined value for a time determined by the time constant of the time constant circuit 7, the excess period is used. During this time, the transistor Q2 is controlled to be turned on, and the power supply voltage supplied from the power supply circuit 3 to the voltage amplification stage 1 is limited by the constant voltage control circuit 6 to the Zener voltage of the Zener diode D3.
Therefore, the Zener diode D3
Is no longer output, and the output power of the power amplification stage 2 is limited.

Similarly, in other power amplifiers whose output voltage is supplied as a power supply voltage from the power supply circuit 3, the output voltage level from the voltage amplification stage is limited, and the output power of the power amplifier is also limited. You.

When the output voltage level from the time constant circuit 7 does not exceed a predetermined value, the transistor Q2 is controlled to be turned off, the resistor R4, the capacitor C2 and the transistor Q3 act as a ripple filter. The ripple of the power supply voltage supplied to the voltage amplification stage 1 is reduced. The same applies to the voltage amplification stage of another power amplifier to which the output voltage of the power supply circuit 3 is supplied as the power supply voltage.

When the transistor Q1 is controlled to be on, the transistor Q2 is controlled to be off, which is the same as when the output voltage level from the time constant circuit 7 does not exceed a predetermined value. The resistor R4, the capacitor C2 and the transistor Q3 act as a ripple filter, and reduce the ripple of the power supply voltage supplied to the voltage amplification stage 1.

In the output power limiting circuit of the power amplifier according to the embodiment of the present invention described above, 2
The case where the output voltage from the power supply circuit 3 is supplied to the power amplifier of the system is illustrated, but the case where the output voltage from the power supply circuit 3 is supplied to the power amplifier of three or more systems also corresponds to the diode D1 and the resistor R1. This can be achieved by adding a circuit to rectify and add the output voltage of the power amplification stage.

According to the output power limiting circuit of the power amplifier according to the embodiment of the present invention described above, the sum of the output voltage from the power amplification stage 2 and the output voltage from the other power amplification stages is obtained. Since the output power is limited based on the voltage, it is not necessary to set in advance whether to limit the output power based on the number of operating power amplifiers. The time constant circuit 7
Since the output power limiting circuit does not operate due to a peak of a signal whose output power level fluctuates dynamically like an audio signal, the margin for power limitation is greatly increased as compared with the conventional case.

According to the output power limiting circuit of the power amplifier according to the embodiment of the present invention, the output power can be further limited so that the power supply circuit 3 is not overloaded. It is sufficient that the power supply capacity is designed based on the limited output power, and the power supply transformer in the power supply circuit 3 can be reduced in size. Furthermore, the case of increasing the number of power amplifiers can be handled by adding a diode and a resistor constituting the adder circuit, and this is very convenient when applied to a surround amplifier such as Dolby Pro Logic.

Next, a modified example of the output power limiting circuit of the power amplifier according to one embodiment of the present invention will be described.

FIG. 2 is a circuit diagram of an output power limiting circuit of a power amplifier according to a modification of the embodiment of the present invention.

The output power limiting circuit of the power amplifier according to the modification of the embodiment of the present invention exemplifies a case in which the output voltage from the power supply circuit 3 is supplied to three systems of power amplifiers. The output voltages from the power amplification stages of the three power amplifiers are diodes D5, D6 and D7 and resistors R5 and R5.
6, R7, and R8 are added by an adding circuit 51. That is, the output voltages from the power amplification stages of the three power amplifiers are diodes D5, D6 and D7.
And rectifies the rectified output separately with a resistor R5,
The addition is performed by R6, R7, and R8. Here, the addition circuit 51 corresponds to the addition circuit 5.

A capacitor C5 is connected in parallel with the resistor R8, and a time constant circuit 71 is constituted by the addition circuit 51 and the capacitor C5. Here, the time constant circuit 71 corresponds to the time constant circuit 7.

The power supply voltage from the power supply circuit 3 to the voltage amplification stage is supplied through a constant voltage control circuit 61 corresponding to the constant voltage control circuit 6. The constant voltage control circuit 61 includes a transistor Q8 whose voltage is applied to the base via a Zener diode D8 to be turned on and off, and a power supply voltage supplied from the power supply circuit 3 to a voltage amplification stage of the power amplifier. , A resistor R11 and a resistor R12 connected between the collector and the base of the transistor Q7 to apply a bias voltage to the transistor Q7, and a resistor R11
Diodes D9 and D1 which are connected between the common connection point of the resistor 12 and the collector of the transistor Q8 and are energized through the resistor R11 to define the amplitude limiting voltage.
0 and the base of the transistor Q7 and the ground while the transistor Q8 is off,
7. A capacitor C6 which constitutes a ripple filter in cooperation with the resistors R11 and R12, resistors R9 and R10 for dividing the voltage of the time constant circuit 71, and a collector connected to a common connection point between the Zener diodes D9 and D10. And
And a transistor Q6 whose emitter is grounded and whose divided output applied to the resistor 10 is applied to the base to be turned on / off.

In the constant voltage control circuit 61, a resistor R9 and a resistor R10
Transistor Q that selectively grounds the common connection point with
5 is connected.

As is clear from a comparison between FIG. 1 and FIG. 2, the components of the constant voltage control circuit 61 and the constant voltage control circuit 6
In view of the correspondence with the constituent elements, the Zener diode D1
0 corresponds to the Zener diode D3, the resistor R11 corresponds to the resistor R4, and the transistor Q7 corresponds to the transistor Q3.
, The transistor Q8 corresponds to the transistor Q2, and the capacitor C6 corresponds to the capacitor C2.

In the constant voltage control circuit 61, the components of the corresponding constant voltage control circuit 6 further include resistors R9 and R10, a transistor Q6, and a Zener diode D8.
And D9 are added. Here, the resistors R9 and R10 are voltage-dividing resistors for changing the output power limiting level, and the resistor R10 cooperates with the resistor R9 when the transistor Q5 is off to turn on / off the transistor Q6. This is a voltage-dividing resistor for adjusting the level, and substantially determines the on / off sensitivity of the transistor Q6 with respect to the output voltage level of the time constant circuit 71. Transistor Q6
And Q8 are transistors for switching the power supply voltage supplied from the power supply circuit 3 to the voltage amplification stage between the Zener voltage of the Zener diode D9 and the Zener voltage of the Zener diode D10. Zener diode D8 is a level shifting diode for setting the control voltage for turning on and off the transistor Q8, when the sensitivity of the on-off of the transistor Q8 to the output voltage level of the time constant circuit 71 substantially defined I have.

Hereinafter, the operation of the output power limiting circuit of the power amplifier according to the modification of the embodiment of the present invention will be described.

The output voltages from the three power amplifiers are rectified by diodes D5, D6 and D7, respectively, added by resistors R5, R6, R7 and R8 and applied to a time constant circuit 71 of a resistor R8 and a capacitor C5. .
When the transistor Q5 is controlled to be off,
The output voltage of the time constant circuit 71 is divided by a voltage dividing circuit including the resistors R9 and R10. The divided voltage applied to the resistor R10 is applied to the base of the transistor Q6. When the divided voltage level applied to the resistor R10 exceeds a predetermined value, the transistor Q6 is controlled to be turned on, and the voltage from the power supply circuit 3 is The power supply voltage supplied to the amplification stage is limited to the zener voltage of the zener diode D9, and the output power of the power amplifier is limited to a power level based on the zener voltage of the zener diode D9.

When the transistor Q5 is controlled to be turned on, both ends of the resistor R10 are short-circuited by the transistor Q5, the transistor Q6 is controlled to be turned off, and the resistors R8 and R9 are connected in parallel. The resistor R9 in addition to the resistor R8 constitutes the time constant circuit 71. The output voltage of the time constant circuit 71 is level-shifted by the Zener diode D8, and when the output voltage level of the time constant circuit 71 exceeds the Zener voltage of the Zener diode D8, the transistor Q8 is controlled to be on.

When the transistor Q8 is turned on, the power supply voltage supplied from the power supply circuit 3 to the voltage amplification stage is limited to the sum of the Zener voltage of the Zener diode D9 and the Zener voltage of the Zener diode D10. The output power of the power amplifier is limited to a power level based on the sum of the Zener voltage of Zener diode D9 and the Zener voltage of Zener diode D10.

Similarly, in the other power amplifiers whose output voltage is supplied from the power supply circuit 3 as the power supply voltage, the output voltage level from the voltage amplification stage is limited, and the output power of the power amplifier is also limited. You.

When the transistor Q5 is controlled to be on, the transistor Q6 is controlled to be off. In this state, the output voltage level of the time constant circuit 71 does not exceed the zener voltage of the zener diode D8. Sometimes, the transistor Q8 is controlled to be off, and the resistors R11 and R12, the capacitor C6 and the transistor Q7 act as a ripple filter, and the ripple of the power supply voltage supplied to the voltage amplification stage is reduced. The same applies to the voltage amplification stage of another power amplifier to which the output voltage of the power supply circuit 3 is supplied as the power supply voltage.

As described above, when using the output power limiting circuit of the power amplifier according to the modification of the embodiment of the present invention, a level (also referred to as a first limit level) corresponding to the Zener voltage of the Zener diode D9; Zener voltage of Zener diode D9 and Zener diode D1
Level corresponding to the sum voltage of the zener voltage of 0 (second
The output power can be limited to two levels (also referred to as a limit level), and each level can be set independently. In addition, by setting the resistance values of the resistors R9 and R10, it is possible to operate with higher sensitivity when limiting to the first limit level than when limiting to the second limit level.

As described above, according to the output power limiting circuit of the power amplifier according to the modification of the embodiment of the present invention, the same effect as that of the embodiment of the present invention can be obtained, and the surround power amplifier can be obtained. Left channel of channel 1
By allocating the center to the channel 2 and the right channel to the channel 3 and selecting the first limit level when the speakers are connected in parallel, the optimum output power can be limited in various modes of the power amplifier. .

[0048]

As described above, according to the output power limiting circuit of the power amplifier according to the present invention, the output voltage of the power amplifier is supplied to the time constant circuit, and the output power is controlled based on the output of the time constant circuit. Since the limitation is performed, it is not necessary to set the operation and non-operation of the output power limiting circuit in advance.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an output power limiting circuit of a power amplifier according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of an output power limiting circuit of a power amplifier according to a modified example of one embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of an example of an output power limiting circuit of a conventional power amplifier.

FIG. 4 is a circuit diagram showing a configuration of another example of the output power limiting circuit of the conventional power amplifier.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Voltage amplification stage 2 Power amplification stage 3 Power supply circuit 5 and 51 Addition circuit 7 and 71 Time constant circuit 6 and 61 Constant voltage control circuit

Claims (3)

(57) [Claims] An output power limiting circuit for a power amplifier, comprising a power supply circuit for supplying a power supply voltage to a power amplifier comprising a voltage amplification stage and a power amplification stage for power amplifying an output of the voltage amplification stage, comprising: A time constant circuit that receives the output voltage from the input, a voltage limiting unit that limits the level of the power supply voltage supplied from the power supply circuit to the voltage amplification stage, and the output voltage level from the time constant circuit exceeds a predetermined value.
Control means for limiting a power supply voltage value supplied from the power supply circuit to the voltage amplifying stage to a limit voltage value of the voltage limiting means during the period, the output power limiting circuit of the power amplifier. 2. An output power limiting circuit for a power amplifier, comprising: a power supply circuit for supplying a power supply voltage to a plurality of power amplifiers each comprising a voltage amplification stage and a power amplification stage for power amplifying an output of the voltage amplification stage, An adder circuit for adding output voltages from the respective power amplifiers; a time constant circuit for inputting the added output voltage of the adder circuit; and a voltage limiter for limiting a power supply voltage level supplied from the power supply circuit to each voltage amplifier stage Means and the output voltage level from the time constant circuit exceeds a predetermined value
Control means for limiting a power supply voltage value supplied from the power supply circuit to each voltage amplifying stage to a limit voltage value of the voltage limiting means during a period, an output power limiting circuit of the power amplifier. 3. The output power limiting circuit of a power amplifier according to claim 2, wherein the voltage limiting means includes first and second voltage limiting means, and the control means divides the output voltage of the time constant circuit. First control means for selectively controlling the divided voltage of the voltage dividing means to zero level, and the divided voltage level of the voltage dividing means when the divided voltage is not controlled to zero level by the first control means. Control means for limiting the power supply voltage value supplied from the power supply circuit to each of the voltage amplification stages to the limited voltage value of the first voltage limiting means when the voltage exceeds the predetermined value, and the divided voltage by the first control means Is controlled to zero level, and when the output voltage level from the time constant circuit exceeds a predetermined value, the power supply voltage supplied from the power supply circuit to each voltage amplification stage to the limited voltage value of the second voltage limiting means. Restrict values Output power limiting circuit of a power amplifier characterized by comprising 3 control unit.