JP3552509B2 - Amplifier circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an amplifier circuit that amplifies a voltage of an input signal and then amplifies power.
[0002]
[Prior art]
2. Description of the Related Art In recent years, the output required of an audio amplifier circuit has been increasing. However, the price is decreasing year by year, and it is necessary to achieve both an increase in the output of the amplifier circuit and a reduction in cost.
[0003]
[Problems to be solved by the invention]
To increase the output of the amplifier circuit without changing the basic circuit configuration, it is necessary to increase the voltage of the power supply. To this end, the transistors used in the constant voltage circuit must use parts having a high collector loss (Pc), which has caused a cost increase.
[0004]
SUMMARY OF THE INVENTION It is an object of the present invention to provide means for preventing a transistor used in a constant voltage circuit from having a high collector loss as in the related art even when a power supply voltage is increased to increase the output of an amplifier circuit. I do.
[0005]
[Means for Solving the Problems]
In order to solve the above problem, an amplifier circuit according to the present invention includes a voltage amplifying unit for amplifying a voltage of an input signal, a power amplifying unit for inputting an output of the voltage amplifying unit and amplifying power, and a power amplifying unit. Power supply means for supplying a DC power supply voltage to the power supply means, and constant voltage circuit means for converting the DC power supply voltage of the power supply means to a constant voltage and supplying the voltage as a constant voltage DC power supply voltage to the voltage amplification means, wherein the constant voltage circuit means The DC power supply voltage of the power supply means is detected, and when the DC power supply voltage is high, the DC output voltage is increased .
[0006]
As a result, the voltage drop, that is, the loss inside the constant voltage circuit means at the time of small output can be reduced, and a transistor having a small collector loss can be used, so that the cost can be reduced.
[0009]
According to a second aspect of the present invention, in the configuration of the first or second aspect, the output change of the constant voltage circuit means has a hysteresis characteristic with respect to the output change of the power amplifying means or the change of the DC power supply voltage of the power supply means. It acts to make it less susceptible to minute power supply voltage fluctuations.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
(Embodiment 1)
Hereinafter, the amplifier circuit according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an amplifier circuit according to Embodiment 1 of the present invention. For simplicity, only one channel of the four-channel amplifier is shown. The amplifying circuit 1 includes a voltage amplifying stage 2 serving as a voltage amplifying unit and a power amplifying stage 3 serving as a power amplifying unit. A power supply voltage for operating the amplifying circuit 1 is transformed by a transformer 4 into an rectifier circuit 7. The power is supplied to the power amplification stage 3 as a DC power supply voltage by the power supply means which rectifies the voltage, and is further converted to a constant voltage by the constant voltage circuit 5 on the positive voltage side and the constant voltage circuit 6 on the negative voltage side which are constant voltage circuit means. The voltage is supplied to the voltage amplification stage 2 as a DC power supply voltage. The control switching circuit 8 switches the output voltages of the constant voltage circuits 5 and 6 between the two channels and the four channels to reduce the maximum output of the amplifier circuit 1 during the four channels.
[0011]
The input signal is output after being amplified by the amplifier circuit 1. The amplifier circuit 1 generally amplifies the amplitude of the input signal in the voltage amplifier stage 2, and then amplifies the current in the power amplifier stage 3 and outputs the amplified signal. Configuration. Here, the maximum output voltage that can be output from the amplifier circuit 1 is determined by the voltage amplifier stage 2. The maximum voltage that can be output from the voltage amplifier stage 2 is the voltage supplied to the voltage amplifier stage 2, that is, the DC output voltage of the constant voltage circuit 5. It is. In other words, the maximum output of the amplifier circuit 1 is limited by this voltage.
[0012]
Assuming that the voltage on the input side of the constant voltage circuit 5 is Vc, the voltage on the output side is Ve, and the flowing current is Ice, the collector loss Pc required for the transistor in the constant voltage circuit 5 is
Pc = (Vc−Ve) * Ice
It becomes. However, the output voltage of the transformer 4 actually used is generally lower at the time of high load, that is, at the time of large output of the power amplification stage 3 than at the time of no load (at the time of small output) because of its internal resistance. . Here, assuming that the voltage at high load is Vload and the voltage at no load is Vload + Vα, the collector loss Pc required for the transistor at high load is
Pc = (Vload−Ve) * Ice
And at no load,
Pc = (Vload + Vα−Ve) * Ice
It becomes. Therefore, when there is no load, the collector loss Pc required for the transistor is larger than that at the time of high load by Vα * Ice, and a transistor having a large collector loss Pc must be used accordingly.
[0013]
If Ve can be set high here,
Pc = (Vload + Vα−Ve) * Ice
From this, it can be seen that the collector loss Pc of the transistor can be set low, but since Ve is a voltage limiting the maximum output of the voltage amplification stage 2, it cannot be set unconditionally high.
[0014]
Here, in the present invention, the voltage output from the constant voltage circuit is set high only when there is no load. That is, since there is no input signal when there is no load, there is no need to limit the output. Therefore, the output voltage Ve of the above-described constant voltage circuit may be set to be higher, which makes it possible to use a transistor having a smaller collector loss Pc than the conventional case, and to reduce the cost.
[0015]
FIG. 2 is an actual circuit diagram of the constant voltage circuit 5 in FIG. The transistor 51 controls the voltage Ve supplied to the voltage amplification stage 2. The constant voltage diodes 52 and 53 divide the voltage Vc on the input side of the constant voltage circuit 5 together with the resistor R1 to define the base potential of the transistor 51 and determine the voltage Ve on the output side. The transistor 54 changes the base potential of the transistor 51 by short-circuiting the constant voltage diode 53. A constant voltage diode 56 having the polarity shown in the figure is connected between the base of the transistor 55 connected between the base and the emitter of the transistor 54 and the middle point of the voltage comparator 57. It is connected between the input side voltage Vc and the ground. Further, a resistor R2 is connected between the collector of the transistor 54 and the middle point of the voltage comparator 57, and a capacitor C1 is connected between this connection point and the ground. The on / off control terminal from the control switching circuit 8 is connected to the base of the transistor 54.
[0016]
The operation is described below. Since it is not necessary to reduce the output power of the amplifier circuit 1 when using two channels, the control switching circuit 8 sets the on / off control terminal to low, turns off the transistor 54 irrespective of the input state of the transistor 55, and turns off the transistor 51. Is controlled by the voltage in which the constant voltage diodes 52 and 53 are connected in series, and the voltage Ve on the output side of the constant voltage circuit 5 is controlled to be high.
[0017]
When four channels are used, since four amplifier circuits are used, the total power consumption increases, and it is necessary to reduce the output of each amplifier circuit. The control switching circuit 8 sets the control voltage high to the on / off control terminal. In addition, the transistor 54 is turned on, the constant voltage diode 53 is short-circuited, the base of the transistor 51 is controlled by the voltage of the constant voltage diode 52, and the voltage Ve on the output side of the constant voltage circuit 5 is controlled to be low.
[0018]
In this state, when there is no input to the amplifier circuit 1, that is, when there is no load, if the voltage Vc on the input side of the constant voltage circuit 5 is high, the midpoint voltage of the voltage comparator 57 is also high, and exceeds the voltage of the constant voltage diode 56. Since the transistor 55 is turned on and the transistor 54 is turned off, the base of the transistor 51 is controlled by a high voltage in which the constant voltage diodes 52 and 53 are connected in series, and the voltage Ve on the output side of the constant voltage circuit 5 increases.
[0019]
When the input of the amplifying circuit 1 is large and the output of the power amplifying stage 3 is large, the voltage output from the transformer 4, that is, the voltage Vc on the input side of the constant voltage circuit 5 is lower than when the output is small, and Since the point voltage is also lowered and the voltage of the constant voltage diode 56 cannot be exceeded and the transistor 55 is turned off and the transistor 54 is turned on, the constant voltage diode 53 is short-circuited by the transistor 54, and the base of the transistor 51 is only the constant voltage diode 52. , The voltage Ve on the output side of the constant voltage circuit 5 becomes low, and the output voltage of the voltage amplification stage 2 is limited.
[0020]
Here, the operation of the resistor R2 will be described. This is to prevent the output voltage Ve from being finely changed by the fine change of the input voltage Vc of the constant voltage circuit 5, and when the voltage Vc is about to decrease. , The middle point of the voltage comparator 57 is supplied with the collector voltage of the transistor 54 by the resistor R2 and is maintained at a voltage higher than the voltage specified by the voltage comparator 57. 55 does not turn off. Also, once the transistor 54 is turned off, the transistor 54 is turned on, and a low voltage is applied to the middle point of the voltage comparator 57 by the resistor R2. The voltage switching is stably performed using a hysteresis phenomenon by positive feedback that the transistor 55 does not turn on unless the voltage becomes higher. The capacitor C1 is for eliminating the influence of the ripple of the power supply applied to the middle point of the voltage comparator 57.
[0021]
As described above, the transistor 51 needs only to output high Ve when Vc is high and output low Ve when Vc is low, so that a transistor having a lower collector loss Pc than a circuit having a constant Ve voltage can be used. , And the cost can be reduced.
[0022]
Although only the constant voltage circuit 5 has been described here, the constant voltage circuit 6 complementarily performs the same operation in a similar circuit. If the absolute value of -Vc increases when no load is applied, the absolute value of -Ve also increases. Work to be.
[0023]
In this embodiment, the constant voltage circuit 5 has been described to be able to change the DC output voltage in two stages. However, even if the constant voltage circuit 5 can be changed in three or more stages, the transistors 54 and 55 of the constant voltage circuit of FIG. The same effect can be obtained by changing the output voltage Ve of the transistor 51 continuously by changing the internal resistance of the transistor instead of the constant voltage diodes 52 and 53 so that the constituent part is configured to amplify the input voltage in an analog manner. Obtainable.
[0024]
As described above, in the present embodiment, the constant voltage circuit means detects the DC power supply voltage of the power supply means and acts to increase the DC output voltage when it is high, so that the DC output voltage of the constant voltage circuit means is increased. The internal loss of the constant voltage control transistor 51 can be reduced as compared with a fixed time, a transistor having a small collector loss Pc can be used, and the cost can be reduced.
[0025]
(Embodiment 2)
FIG. 3 is a block diagram of an amplifier circuit according to Embodiment 2 of the present invention. In the first embodiment, the output of the power amplification stage is detected by detecting a drop in the power supply voltage in order to increase the output voltage of the constant voltage circuit at the time of small output of the power amplification stage. It tries to detect the output itself. The overall configuration of the amplifier circuit is substantially the same as that of FIG. 1 except that the output signal is branched and the output of the power amplification stage 3 is detected in addition to the constant voltage circuits 5a and 6a. FIG. 4 shows an actual circuit diagram of the constant voltage circuit 5a in FIG. In FIG. 4, a transistor 51a controls a voltage Ve supplied to the voltage amplification stage 2. The constant voltage diodes 52a and 53a divide the voltage Vc on the input side of the constant voltage circuit 5a together with the resistor R1 to define the base potential of the transistor 51a and determine the voltage Ve on the output side. The transistor 54a changes the base potential of the transistor 51a by short-circuiting the constant voltage diode 53a. A constant voltage diode 56a having the polarity shown in the figure is connected between the base of the transistor 55a connected between the emitter of the transistor 54a and the ground and the midpoint of the voltage comparator 57a. Is connected in parallel with a capacitor C2 charged by a diode 58 that rectifies the output via a resistor R3. The on / off control terminal from the control switching circuit 8 is connected to the base of the transistor 54a.
[0026]
The operation is described below. Since it is not necessary to reduce the output power of the amplifier circuit 1 when using two channels, the control switching circuit 8 sets the on / off control terminal to low, turns off the transistor 54a, and turns on the base of the transistor 51a regardless of the state of the transistor 55a. Is controlled by a voltage in which the constant voltage diodes 52a and 53a are connected in series, and the voltage Ve on the output side of the constant voltage circuit 5 is controlled to be high.
[0027]
When four channels are used, since four amplifier circuits are used, the total power consumption increases, and it is necessary to reduce the output of each amplifier circuit. The control switching circuit 8 sets the control voltage high to the on / off control terminal. In addition, the transistor 54 is turned on.
[0028]
In this state, when there is no input (therefore, output) of the amplifier circuit 1, that is, when there is no load, the transistor 55a is turned off because the midpoint voltage of the voltage comparator 57a does not exceed the Zener voltage of the constant voltage diode 56a, and the transistor 54a Can be turned on, the collector of the transistor 54a is open, the base of the transistor 51 is controlled by a high voltage in which the constant voltage diodes 52 and 53 are connected in series, and the voltage Ve on the output side of the constant voltage circuit 5 increases. .
[0029]
When the control voltage of the on / off control terminal is high and the transistor 54 can be turned on and the output of the power amplification stage 3 increases, the capacitor C2 is charged via the resistor R3 and applied to the voltage comparator 57a. When the voltage at the midpoint exceeds the Zener voltage of the constant voltage diode 56a, the transistor 55a is turned on, so that the collector of the transistor 54a is at the ground potential, the constant voltage diode 53a is short-circuited, and the base of the transistor 51a is at a constant voltage. It is controlled by the voltage of the diode 52a, and the voltage Ve on the output side of the constant voltage circuit 5 is controlled to be low.
[0030]
As described above, in the present embodiment, the constant voltage circuit means detects the output of the power amplifying stage, and when the output is small, acts to increase the DC output voltage, so that the DC output voltage of the constant voltage circuit means is constant. In this case, the internal loss of the constant voltage control transistor 51a can be reduced as compared with the case of the above case, a transistor having a small collector loss Pc can be used, and the cost can be reduced. In the present embodiment, the modification in the first embodiment is also possible. For example, the output voltage of the constant voltage circuit means may have a hysteresis characteristic with respect to a slight change in the output.
[0031]
【The invention's effect】
As described above, in the amplifier circuit of the present invention , the constant voltage circuit means detects the DC power supply voltage of the power supply means and acts to increase the DC output voltage when it is high. The output can be detected to detect the output, the voltage drop inside the constant voltage circuit means at the time of small output , that is, the loss can be reduced, and a transistor having a small collector loss can be used, so that the cost can be reduced.
[0033]
Further, since the output change of the constant voltage circuit means has a hysteresis characteristic with respect to the output change of the power amplifying means or the change of the DC power supply voltage of the power supply means, it is possible to obtain the effect of not being affected by minute power supply voltage fluctuations.
[Brief description of the drawings]
1 is a block diagram of an amplifier circuit according to a first embodiment of the present invention; FIG. 2 is a circuit diagram of a constant voltage circuit 5 in FIG. 1; FIG. 3 is a block diagram of an amplifier circuit in a second embodiment; 4 is a circuit diagram of the constant voltage circuit 5a in FIG.
1 amplifying circuit 2 voltage amplifying stage 3 power amplifying stage 4 transformer 5 constant voltage circuit (positive voltage side)
6 Constant voltage circuit (negative voltage side)
7 Rectifier circuit 8 Control switching circuit 51, 51a Output transistor 52, 52a of constant voltage circuit Zener diode 53, 53a Zener diode 54, 54a Transistor 55, 55a Transistor 56, 56a Zener diode 57, 57a Voltage comparator 58 Diode R1, R2 , R3 Resistors C1, C2 Capacitor

Claims (2)

Voltage amplifying means for amplifying the voltage of the input signal;
Power amplifying means for inputting the output of the voltage amplifying means and amplifying the power,
Power supply means for supplying a DC power supply voltage to the power amplification means,
Constant voltage circuit means for converting the DC power supply voltage of the power supply means to a constant voltage and supplying it as a constant voltage DC power supply voltage to the voltage amplification means,
The amplifying circuit, wherein the constant voltage circuit means detects a DC power supply voltage of the power supply means, and increases the DC output voltage when the voltage is high . 2. The amplifier circuit according to claim 1, wherein the output change of the constant voltage circuit means has a hysteresis characteristic with respect to the output change of the power amplification means or the change of the DC power supply voltage of the power supply means .

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