JPH05283940A - High efficiency amplifier - Google Patents

Abstract

PURPOSE:To increase the power efficiency of the amplifier. CONSTITUTION:An amplifier 12 amplifying input signals drives push-pull connected transistors 14 and 16, applying the requried amount of current to a load 20. A comparator 34 compares the output signal with the collector signal of the transistor 14. When a comparator 32 compares it with the triangular wave, the PWM control of the switching transistor 22 can be performed. In short, the transistor 22, diode 26 and coil 24 are used as switching regulators, improving the power efficiency of the transistors 14. With a boot strap type capacitor 60, the operational point of the switching transistor 22 can be made high potential, resulting in decreasing the voltage drop of the transistor and improving the power efficiency of the entire unit.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a high efficiency amplifier with reduced power consumption.

[0002]

2. Description of the Related Art Conventionally, an amplifier for signal amplification has been used in various circuits, and in a radio receiver,
It is used for amplification of received signals. In such an amplifier, the larger the dynamic range, the larger the amount of power consumed by the amplifier. On the other hand, in battery-powered devices such as car radios, there is a demand to reduce power consumption as much as possible. Therefore, in a conventional radio receiver, the dynamic range is set in consideration of the dynamic range and the power consumption according to the design.

[0003]

However, if the dynamic range is reduced in order to reduce the power consumption in the conventional radio receiver, the sound quality will be deteriorated. Therefore, while maintaining a sufficient dynamic range,
There has been a demand for an amplifier that can reduce power consumption.

The present invention has been made in view of the above problems, and uses a switching power supply to increase the efficiency of an amplifier.

[0005]

The present invention is an amplifier for applying an input signal to a pair of push-pull connected output transistors and outputting an amplified signal from a connection point of the pair of output transistors. Switching transistor and first coil connected in series between one of the output transistors and the power supply, and second switching transistor and second coil connected in series between the other of the pair of output transistors and ground A means for generating a control signal for ON / OFF controlling the first and second switching transistors, and a control means for controlling the control signal according to the level of the output signal of the amplifier.
It is characterized by having.

[0006]

As described above, according to the present invention, the switching transistor and the coil are arranged in the power supply line, and the switching transistor is controlled according to the level of the output signal. A sufficient dynamic range can be secured, and power can be saved for small-level output signals.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing the overall configuration of the embodiment. A signal input terminal 10 is connected to an amplifier 12, and the output side of this amplifier 12 has output transistors 14 and 16.
Connected to the base of. Where the transistor 14
Is an NPN type transistor, the transistor 16 is a PNP type transistor, the collector of the transistor 14 is connected to the high potential side, and the collector of the transistor 16 is connected to the low potential side. The connection point between the emitters of the transistor 14 and the transistor 16 is connected to the load 20 via the DC cut capacitor 18.

Therefore, the AC input signal input from the input terminal 10 is amplified by the amplifier 12 and also by the transistors 14 and 16. If the output signal of the amplifier 12 is positive, the transistor 14 is turned on to supply (push) the current to the load 20, and if negative, the transistor 16 is turned on and the current from the load 20 is turned on. Inhalation (pull) is performed. For a radio receiver,
The load 20 is a speaker.

The collector of the transistor 14 has a power source V _cc.
The switching transistor 22 and the coil 24 are inserted and arranged in this path. Also,
A flywheel diode 26 is provided at a connection point between the transistor 22 and the coil 24. In order to control the on / off of the transistor 22, a PNP transistor 28 whose emitter is connected to the power supply V _cc is connected to the base of the transistor 22, and the base of the transistor 28 is connected to the ground via the transistor 30. ing. Therefore, by turning on and off the transistor 30, the transistor 28 is turned on and off, and the transistor 22 is turned on and off.

In order to control the on / off of the transistor 30, a comparator 32 is connected to the base of the transistor 30, and the output of the comparator 34 is connected to the non-inverting input terminal of the comparator 32. A triangular wave having a frequency f _sw that determines the switching frequency is supplied to the input terminal. Further, in the comparator 34, the inverting input terminal is connected to the collector of the transistor 14, and the non-inverting input terminal is connected to the intermediate point (output) between the transistors 14 and 16 via the battery 36.

Therefore, the comparator 34 includes the transistor 1
It means that the potentials of the collector and the emitter of 4 are compared,
When a large positive output signal is applied to the load 20, the comparator 3
When the output signal (a) of 4 becomes large and the positive small output signal is applied, the output signal (a) of the comparator 34 becomes small.
Further, the comparator 32 compares the signal output from the comparator 34 with the triangular wave, and outputs an ON / OFF pulse signal for the comparison result.

That is, as shown in FIG.
When the input signal to the non-inverting input terminal of is a, the input signal to the inverting input terminal is b, and the output signal is c, a triangular wave b
A signal c that becomes H is obtained for a portion where is lower than the signal a. Further, the higher the level of the control signal to the transistor 14 is, the longer the signal c is at the H level. Therefore, if the output signal is at a high level, the signal c becomes H for a long time (a large duty ratio). Therefore, by controlling the transistor 30 with this signal c, the transistor 2
2 is turned on / off at the frequency of f _{sw, and} the higher the duty ratio is, the higher the level of the output signal is, the longer the ON period is.

Since the coil 24 is connected to the emitter of the switch 22, this circuit functions as a switching regulator, the output signal is kept in a waveform corresponding to the input signal, and the potential of the collector of the transistor 14 is changed. , An AC waveform with a frequency f _sw that fluctuates between the power supply potential and the potential of the output waveform. Therefore, while maintaining a sufficiently large dynamic range, it is possible to prevent wasteful current from being sent when the signal is small, and it is possible to increase power efficiency.

The battery 36 is for compensating the forward bias voltage of the transistor 14 (usually 0.7).
The flywheel diode 26 is for collecting a current from the ground side to the coil 24.

Next, a switching regulator similar to that described above is provided between the collector of the transistor 16 and the ground. That is, the switching transistor 42, the coil 44, and the flywheel diode 46 are provided.

Then, in order to control the switching transistor 42, it has comparators 50 and 52, the inverting input terminal of which is connected to the collector of the transistor 16 and the non-inverting input terminal of which is connected to the battery 54. It is connected to the output terminal. Further, a triangular wave is supplied to the non-inverting input terminal of the comparator 50. Therefore, the comparator 52 outputs the output corresponding to the input signal supplied to the transistor 16 to the comparator 50.
To the transistor 42 and the comparator 50 outputs a pulse signal having a duty ratio corresponding to the input signal level.
Supply to the base of. Therefore, as in the case described above, the switching transistor 42 is turned on / off at the duty ratio according to the input signal.

In this embodiment, one end of the bootstrap capacitor 60 is connected to the output point, and the other end of the bootstrap capacitor 60 is connected to the base of the transistor 28. A power supply _Vcc is connected to the base of the transistor 28 via a resistor 62 and a diode 64. Therefore, the base voltage of the transistor 28 can be increased by the bootstrap capacitor when the voltage at the output point is large, and the potential here can be equal to or higher than the power supply voltage V _cc . Therefore,
The operating point of the transistor 28 by turning on / off the transistor 30 can be set to a high potential, and the saturation voltage of the transistor 22 can be set to the minimum (1V _BE ). Therefore, also here, the efficiency of the circuit can be improved. Immediately after the start of operation, etc., the resistor 62 and the diode 64 from the _Vcc side.
Via, the potential of the base of the transistor 28 is raised to V _cc .

As described above, in this embodiment, the transistor 2 is connected by the bootstrap capacitor 60.
Since the base potential of 8 is set to a high potential, the operation of the switching transistor 22 can be efficiently performed, and the power efficiency can be increased as a whole.

[0019]

As described above, according to the high-efficiency amplifier of the present invention, by using the switching regulator, it is possible to store unnecessary power in the output transistor in the coil and suppress unnecessary power consumption. be able to. Since the switching regulator operates according to the input signal, there is no adverse effect on the output signal.

Further, by providing the bootstrap capacitor, the efficiency of the switching transistor can be increased and the power efficiency as a whole can be further increased.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an overall configuration of an embodiment.

FIG. 2 is a waveform diagram for explaining the operation of the switching transistor.

[Explanation of symbols]

 12 Amplifiers 14, 16 Output Transistors 20 Loads 22, 42 Switching Transistors 24, 44 Coils 60 Bootstrap Capacitors

Claims (2)

[Claims] 1. An amplifier which applies an input signal to a pair of push-pull connected output transistors and outputs an amplified signal from a connection point of the pair of output transistors, wherein one of the pair of output transistors and a power supply A first switching transistor and a first coil connected in series between the first and second coils, a second switching transistor and a second coil connected in series between the other of the pair of output transistors and ground, and the first and second coils A high-efficiency amplifier comprising: a means for generating a control signal for on / off controlling a switching transistor; and a control means for controlling the control signal according to the level of an output signal of the amplifier. 2. The amplifier according to claim 1, further comprising a bootstrap capacitor having one end connected to a signal output end and obtaining a high voltage at the other end, wherein the first switching is performed by the high voltage obtained by the bootstrap capacitor. High-efficiency amplifier characterized by driving a transistor.