JPH04170205A - power amplifier - Google Patents

Abstract

PURPOSE:To increase a collector loss of a transistor(TR) by switching a voltage fed to a power amplifier from a low voltage to a high voltage before an input signal is clipped even at reduction in a power supply voltage. CONSTITUTION:An input voice signal is subject to current amplification by a transistor(TR) 12, its output audio signal is fed to a speaker 13, from which a voice is outputted. Since a voltage of a low level input voice signal fed to a base via a diode D1a is low, TRs 18a, 19a are nonconductive. When the voltage of the input voice signal is gradually increased and a base voltage of the TR 18a gets higher via the diode D1a, the TR 18a is conductive. Succeedingly, the TR 19a is conductive succeedingly and a voltage of a high voltage power supply 16a is fed to a TR 12a and a high output amplifier signal is fed to a speaker 3. Thus, even when the power supply voltage is low, normal operation is kept and the power supply is effectively used.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a power amplifying device used in loudspeakers installed in poles, gymnasiums, etc.

BACKGROUND OF THE INVENTION FIG. 3 shows a conventional complementary-connection power amplifier device that switches the power supply voltage according to the level of an input audio signal to reduce collector loss.

In FIG. 3, the part in parentheses shows the configuration of the negative side amplification section.

Sv is a human-powered audio signal source such as a preamplifier that amplifies the audio signal from a microbon or the like. 2a (2b) is a complementary connected transistor for current amplifying the input audio signal from the input audio signal source Sv, 3 is a speaker connected to the output terminal of the emitter of the transistor 2a (2b), and outputs audio. It is something to do. 4a (4
b) is a low voltage supply power supply for supplying a low voltage via a diode D2a (D2b), and 6a (6b) is a high voltage supply power supply.

Reference numeral 7a (7b) is a switching reference power supply that applies a voltage serving as a reference for switching between high and low power supply voltages.

8a (8b) indicates that the input audio signal from the input audio signal source Sv is connected to the resistor R1a (Rlb) and the diode Dla (
9a (9b) is a high voltage is applied and is an on/off transistor that switches the supply of high voltage to the transistor 2a (2b).

Next, the operation of the above conventional example will be explained.

In FIG. 3, the input audio signal is transmitted through the transistor 2a (
2b), and this output signal is amplified by the speaker 3.
is supplied to output audio.

Here, when the input audio signal is of positive polarity, the positive polarity side amplifier section operates. That is, since the voltage supplied to the base via the diode Dla is low, the transistors 8a and 9a become non-conductive, and the transistor 2at becomes low voltage, voltage supply source 4.
A voltage of a is applied via diode D2a. In this case, the collector loss is small. Subsequently, the input audio signal becomes high and the voltage at the base of transistor 8a becomes high. This causes transistor 8a.

9a is conductive, and the transistor 2a is connected to the high voltage power supply 6.
A voltage a is applied, and a high output amplified signal can be supplied to the speaker 3. Note that when the input audio signal becomes negative, the negative amplification section operates in the same manner as the positive amplification section.

In this way, even in the above conventional power amplifier device, the collector loss of the transistor of the amplifier can be reduced by switching the power supply voltage depending on the level of the input audio signal.

゛ Problem to be Solved by the Invention However, in the above conventional power amplifier device, the low voltage supply power 4a applied to the transistor 2a (2b)
(4"b'), since the switching timing of the high voltage supply power source 6a (6b) is determined by the voltage of the input audio signal and the voltage of the power supply voltage switching reference power source 7a (7b), the low voltage power source 4 When the voltage of 'a (4b) decreases, it switches to the high voltage supply power supply 6a (6b), which has the disadvantage that the output signal clips before the output signal. Also, the low voltage supply power supply 4a (
When the voltage of transistor 2a (2b
) has the problem of significantly increasing collector loss.

The present invention solves such conventional problems, and aims to provide an excellent power amplification device that can appropriately switch the power supply voltage in response to fluctuations in the power supply voltage. be.

Means for Solving the Problems □ In order to achieve the above object, the present invention includes a reference voltage generation section that generates a switching reference voltage lower than the low voltage supplied from the power supply, and a switching section that generates a switching reference voltage that is lower than the low voltage supplied from the power supply. and switching means for switching the voltage applied to the power amplifier from a low voltage to a high voltage when the voltage is higher than the reference voltage.

Effects The present invention has the following effects due to the above structure. In other words, when the voltage generated from the input signal is higher than the switching reference voltage, the voltage applied to the power amplifier is switched from a low voltage to a high voltage, and even when the power supply voltage drops, the voltage applied to the power amplifier is applied to the power amplifier before the input signal clips. The voltage to be used changes from low voltage to high voltage. In addition, normal operation is maintained even when the power supply voltage drops, allowing effective use of the power supply.
This has the effect of preventing an increase in collector loss of a power amplifier, for example, a transistor, even when the voltage of the power supply increases.

Embodiment FIGS. 1 and 2 are schematic block diagrams of a power amplifying device in an embodiment of the present invention.

In FIG. 1, the part in parentheses shows the configuration of the negative side amplifying section.

Sv is an input audio signal source such as a preamplifier that amplifies the audio signal from a microphone or the like. 12a (12b) is a complementary connected transistor I for current amplifying the input audio signal from the input audio signal source SV.
'3 is a speaker connected to the output terminal of the emitter of the transistor 12a (12b), which outputs audio.

14a (14b) is a low voltage supply power supply for supplying low voltage via diode D2a (D2b), 16a
(16b) is a high voltage supply power source.

18a (18b) indicates that the input audio signal from the input audio signal source Sv is connected to the resistor R1a (Rlb) and the diode Dla.
The transistor 19a (19b) is a transistor to which the high voltage from the high voltage supply power source 16a (16b) is applied to the collector through the resistor R2a (R2b). This is a transistor to which a voltage is applied and which switches on/off the supply of high voltage to the transistors 12a (12b).

22a (22b) is a constant voltage diode to which resistor R3a (R3b) is connected, and 24a (24b) is a high voltage supply power source 16a through resistor R4a (R4b).
(16b) is applied, and a constant voltage is generated by the constant voltage diode 22a (22b),
This is a constant voltage generating transistor for turning on/off the transistor 18a (18b), that is, switching between high and low power supply voltages.

Next, the operation of the above embodiment will be explained.

In FIG. 1, the input audio signal is transmitted to the transistor 12a (
12b), and this output audio signal is supplied to the speaker 13 and output as audio.

Here, when the input audio signal is of positive polarity, the positive polarity side amplifier section operates. For low level input audio signals, the diode Dla
Since the voltage supplied to the base via
A low voltage from a low voltage supply power source 14a is applied to the collector of the transistor a via a diode D2a. In this case, the collector loss is small. On the other hand, the constant voltage generating transistor 24a
Since the constant voltage diode 22a is connected to the base of the constant voltage diode 22a, a voltage lower than the voltage of the low voltage supply power source 14a by the Zener voltage of the constant voltage diode 22a is always applied. Therefore, a switching reference voltage that is always lower by a fixed voltage than the voltage of the low voltage supply power source 14a is generated at the emitter of the constant voltage generating I transistor 24a.

Then, when the voltage of the input audio signal gradually increases and the base voltage of the transistor 18a increases via the diode Dla, the transistor 18a becomes conductive. Subsequently)・Langister 19a
conducts, and the transistor 12a receives the high voltage supply power 16.
A voltage a is applied, and a high output amplified signal can be supplied to the speaker 3.

Note that when the input audio signal becomes negative, the negative amplification section operates in the same manner as the positive amplification section.

In this way, when the voltage based on the input audio signal is always higher than the switching reference voltage generated from the low voltage power supply 14a (14b) regardless of the voltage fluctuation of the low voltage power supply 14a (14b), the transistor 12a (1
2b) is the low voltage supply power supply 14a (14
b) to the high voltage supply power source 16a (16b).

Also, if the Zener voltage of the constant voltage diode 22a (22b) is set appropriately, the transistor 12a (12b)
Regardless of the power supply voltage, the supply voltage is always switched immediately before the high output amplified signal supplied to the speaker I3 clips.

FIG. 2 shows the configuration of another embodiment.

In this other embodiment, one end of the resistor R1a (Rlb) is connected to the emitter of the transistor 12a (12b) and the speaker 13, and the other end is connected to the emitter of the transistor 18a (18b) through the diode Dla, as in the above embodiment. )
The other configurations are the same as in the previous embodiment. In this other embodiment, the only difference from the above embodiment is the extraction position of the audio signal (input audio signal), and therefore the operation is similar to that of the above embodiment, and a high level input audio signal is supplied. Therefore, the operating characteristics are improved.

In addition, in the above two embodiments, the constant voltage diode 22a (
Although a Zener diode is used for 22b), a normal diode or an I transistor may also be used.

In addition, the power supplies include two sets of low voltage supply power supplies 14a (14b),
Although the high voltage power supply 16a (16b) is used, three or more sets may be used.

Effects of the Invention As is clear from the above embodiments, the present invention has the following effects. In other words, when the voltage generated from the input signal is higher than the switching reference voltage, the voltage applied to the power amplifier is switched from a low voltage to a high voltage, so even when the power supply voltage drops, the voltage applied to the power amplifier is applied before the input signal clips. The voltage can be switched from low voltage to high voltage, normal operation can be maintained even when the power supply voltage drops, and the power supply can be used effectively, and the collector loss of a transistor, for example, can be increased as the power supply voltage increases. It has the advantage of being able to prevent

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a power amplifier according to an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of another embodiment, and FIG. 3 is a block diagram showing the configuration of a conventional power amplifier. It is a diagram. 12a, 12b...transistor, 13...speaker, 14a, 14b-=low voltage supply power source, 16a, 16
b-=high voltage supply power supply, 18a, 18a. 19a, 19b...-transistor, 22a, 22b...
... Constant voltage diode, 24a, 24b... Transistor for constant voltage generation, D... Diode, R... Resistor, Sv... Input audio signal source

Claims (1)

[Claims] A power amplifier that amplifies an input signal, a power supply for supplying a low voltage or a high voltage to the power amplifier, and a switching reference voltage generation section that generates a switching reference voltage lower than the low voltage. 1. A power amplifier device comprising: switching means for switching a voltage applied to a power amplifier from a low voltage to a high voltage when a voltage generated from an input signal is higher than a switching reference voltage.