JPS58104510A - Power amplifier - Google Patents

Abstract

PURPOSE:To attain a large output simply and to reduce heat loss, by connecting ground side of a load to a positive or negative terminal of both polarity power supply with a large input signal and connecting the ground of the load to the common point of the power supply with a small input signal. CONSTITUTION:When an input signal ei is smaller than a positive power supply Vcc, a switch circuit SW is connected to a common point (b) of both polarity power supplies Vcc, Vcc', and the amplifier acts like a conventional class B amplifier. When the signal ei is higher than the power supply Vc, the circuit SW is connected to the negative terminal (c) of the power supply Vcc'. When the signal ei is larger than the power supply Vcc', the circuit SW is connected to a positive terminal (a) of the power supply Vcc. Thus, the maximum output is four times in using the same power supply voltage. Since the power supply voltage is low with a small output and the power supply voltage is larger with a large output, the same efficiency as that at the maximum output can be obtained with the small output. Thus, the heat loss is small, and large output, high efficiency and low loss can be realized at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power amplifier, and provides a power amplifier that can easily obtain a large output and has little heat loss.

Conventionally, as a power amplifier, there is a class amplifier as shown in FIG. In Figure 1, 1 is a long sword terminal, 2 is an output terminal,
Q, Q1' are power amplification transistors Vcc, Vcc'
are positive and negative power supplies, RL is load resistance, ei is input signal, eO
is the output voltage.

In this circuit, the maximum output power is determined by the power supply voltage and load resistance, and is as follows.

Po=CVac+Vcc'>2/BRL------
---(1) At the output, the output transistor Q1. Q
Since a large DC voltage is constantly supplied to 1', heat generation increases and efficiency becomes extremely poor. Furthermore, the higher the output power of the amplifier, the greater the amount of heat generated, and therefore the heat dissipation device becomes larger and more expensive.

The present invention solves the above-mentioned problems and realizes a power amplifier that can easily obtain a large output power and has low heat loss.

The principle of the invention is shown in FIG. In FIG. 3, SW is the positive side a of the positive power supply V c a and the positive and negative power supplies Vcc.

The midpoint of Vcc' is a switch circuit for switching three contacts on the negative side C of negative power supply Vcc', and the rest is the same as in FIG. 1.

Next, the operation shown in FIG. 3 will be explained. When the input signal ei is smaller than the positive power supply Vcc, the switch circuit SW is connected to the midpoint between the positive and negative power supplies Vca and Vcc', and in this case it operates in the same way as the conventional class B amplifier shown in Fig. 1. . On the other hand, when the input signal ei becomes higher than the positive power supply Vcc, the switch circuit SW is connected to the negative side C of the negative power supply VCC'.As a result, the collector voltage of the transistor Q1 becomes vCC + vCC/, and the switch circuit SW1 Negative power supply Vcc', positive power supply Vca transistor Q1゜load RL
Current flows through the path.

Further, when the input signal ei becomes C larger than the negative power supply Vcc', the switch circuit SW is connected to the positive side a of the positive power supply Vcc, and the collector voltage of the transistors Q,' becomes Vcc+
Vcc', and a current flows through the path of the switch circuit SW1 positive source Vcc, the negative power source Cd transistor Q1', and the load RL.

FIG. 4 shows voltage waveforms at various parts at this time. That is, the maximum output of this circuit is as follows.

Po=(2x(Vcc+Vcc'))/RL ・---
-(2) Therefore, when compared with the above equation (1), it can be seen that the maximum output is four times greater at the same power supply voltage.

Conventionally, BTL was used as a method to obtain high output with the same power supply voltage.
It is well known that the maximum output is four times that of a class B amplifier with the same load and the same power supply voltage. It is no different from a class B amplifier. However, in the power amplifier of the present invention shown in FIG. 3, when the output is small, the power supply voltage is low, and when the output is large, the power supply voltage is high.
At a small output (maximum output K), the same efficiency as at maximum output can be obtained. Therefore, heat loss is approximately %, and high output, high efficiency, and low loss can be achieved at the same time.

FIG. 5 shows a specific embodiment of the present invention. In Fig. 5, R1, R1', R2, R2' are resistances, Dl, D1
'D2, D2', Da, D3' are diodes, Q2, 02' are transistors forming a comparison circuit, Q3, Q3' and Q4.

Q4' is a switching transistor, vT, vr' are positive,
The negative reference tortoise pressure and other details are the same as in FIG.

Next, the operation shown in FIG. 5 when the input signal ei is a positive voltage will be explained. When the input signal ei is smaller than the reference voltage vr, the bias resistor R2' causes the transistor Q4' to
is turned on, the load voltage 11 flows through the path of the transistor Q4'J, the diode D3', the positive power supply Vcc, the transistor Q4, and the load RL. Next, the input signal ei
When becomes larger than the reference voltage vr, a current flows through the emitter of the transistor Q2 constituting the comparator circuit, and this current flows through the transistor Q3', turning on the transistor Q3'. This transistor Q3
Since the current flowing through Vac' flows through the diode D2, the transistor Q4, which had been on until now, is turned off. Furthermore, since the negative side of the negative power supply Vac' becomes equal to the ground potential, the diode D3' is reverse biased. It turns off automatically. Therefore, the load current 12 at this time flows through the path of diode D2, transistor Q3', negative power supply Vcc', positive wake-up source Vcc, output transistor Q1, and load RL, and a large current can be supplied to load RL.

It should be noted that even when the input signal ei is a negative voltage, all the elements on the opposite side operate in the same manner, so a description thereof will be omitted.

As described above, according to the present invention, when the input signal is large, the ground side of the load is connected to the positive side or the negative side of the positive and negative power supplies, and when the input signal is small, it is connected to the midpoint of the positive and negative power supplies. Therefore, it is possible to obtain four times the output of a conventional class B amplifier with the same power supply voltage, and if the maximum output is the same, a high efficiency amplifier with less heat loss can be realized.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional power amplifier, FIG. 2 is a waveform diagram of each part of FIG. 1, and FIG. 3 is a diagram showing the principle of the present invention. 1...Input terminal, 2...Output terminal, Q
,,Q1'...Power amplification transistor, Q2
．． Q2I..., transistor constituting the comparison circuit, Q3. Q3', Q4°94', D2. D2', Da,
D3/... Elements constituting the switch circuit,
RL...Load, VCC...Positive power supply, V
cc' ・・・・・・Negative power supply. Name of agent: Patent attorney Toshio Nakao and 1 other person
Figure 2 (!I Figure 13 Utsubo Figure 5

Claims (1)

[Claims] A push-pull connected power amplification transistor, a positive and negative power supply connected in series, and a ground side of a load connected to the output terminal of the power amplification transistor are connected to the positive side of the positive power supply, the negative side of the negative power supply, and the above. Compare the output voltage of the power amplifying transistor with the reference voltage and the switch circuit connected to the midpoint of the positive and negative power supplies, and if the output voltage does not exceed the reference voltage, connect the ground side of the load to the midpoint of the positive and negative power supplies. a comparison circuit that is connected to the midpoint and switches the switch circuit to connect the ground side of the load to the positive side of the positive power supply or the negative side of the negative power supply when the output voltage exceeds the reference voltage. power amplifier.