JPH11168326A - Output amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a heat loss in an output amplifier circuit. SOLUTION: This output amplifier circuit is provided with a pulse width modulation, means 30, a switching means 50 and a DC power source means 17 for supplying DC signals to the switching means 50. Voice frequency band input signals are converted to pulse width modulated signals in the pulse width modulation means 30, the switching means 50 is switched by the pulse width modulation signals and the DC signals are turned to pulse width modulated signals. The signals present in a voice frequency band are extracted from the pulse width modulated signals and the signals for which the voice frequency band input signals are amplified are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an output amplifier circuit for an audio frequency band signal.

[0002]

2. Description of the Related Art Conventionally, a circuit shown in FIG. 2 has been known as an output amplifier circuit for an audio frequency band signal.

In FIG. 2, reference numeral 1 denotes a preamplifier, 10 denotes a power amplifier, and the preamplifier 1 includes a signal input terminal 3 and an integrated circuit 5. The power amplifier 10 includes a power transistor 11 and an emitter. It comprises a resistor 13, a coupling capacitor 15, a DC power supply terminal 17, and a power supply line 19 connected to the DC power supply terminal 17. Reference numeral 21 denotes a dynamic speaker that is a load of the power amplification unit 10. Although not shown, power is supplied to the integrated circuit 5 from the power supply line 19.

The input side of the integrated circuit 5 is connected to the signal input terminal 3, the base of the power transistor 11 is connected to the output side of the integrated circuit 5, the collector is connected to the power supply line 19,
The emitter is grounded through the emitter resistor 13, the connection midpoint between the emitter and the emitter resistor 13 is connected to one end of the voice coil 23 through the coupling capacitor 15, and the other end of the voice coil 23 is grounded.

[0005] The audio frequency band signal input to the signal input terminal 3 is amplified to a predetermined signal level by the integrated circuit 5 and supplied to the base of the power transistor 11. Is supplied to the voice coil 23 of the dynamic speaker 21 through the coupling capacitor 15 to reproduce an audio signal from the dynamic speaker 21.

[0006]

In such a conventional output amplifying circuit, since the drive current Isp of the voice coil 23 passes between the collector and the emitter of the power transistor 11, the difference between the power supply voltage Vcc and the emitter voltage Ve is obtained. The power generated by the voltage and the driving current Isp is consumed by the power transistor 11 to generate heat.

Because of this heat generation, heat radiating members such as heat radiating fins and heat radiating fans of the power transistor 11 are indispensable. There has been an inconvenience that may hinder extending the battery usage time in a device serving as a power supply.

In view of the foregoing, it is an object of the present invention to reduce heat generation of an output amplifier circuit for an audio frequency band signal and to save power of the output amplifier circuit.

[0009]

According to the present invention, in an output amplifier circuit for an audio frequency band input signal, a pulse width modulation means 30, a switching means 50, and a DC power supply means 17 for supplying a DC signal to the switching means are provided. The voice frequency band input signal is converted by the pulse width modulation means 30 into a pulse width modulation signal, and the switching means 50 is switched by the pulse width modulation signal to convert the DC signal into a pulse width modulation signal. A signal in the audio frequency band is extracted from the pulse width modulation signal to obtain a signal obtained by amplifying the audio frequency band input signal.

Further, in the present invention, in a circuit for amplifying an audio frequency band input signal, a DC signal is supplied to the pulse width modulation means 30, the switching means 50, the high cut filter means 60, the signal feedback means 70 and 33, and the switching means. DC power supply means 17 is provided, and this audio frequency band input signal is supplied to the modulation means 30 to be converted into a pulse width modulation signal, and the switching means 5 is switched by the pulse width modulation signal.
The DC signal is converted to a pulse width modulated signal by switching 0, and the pulse width modulated signal is extracted from the pulse width modulated signal through the high cut filter means 60 to extract a signal in this audio frequency band. A signal output obtained by amplifying the frequency band input signal is obtained, and the output is fed back to the modulation means 30 by the signal feedback means 70 and 33.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an output amplifier circuit according to the present invention will be described below with reference to FIG.

FIG. 1 shows the configuration of an output amplifier circuit. The same components as those shown in FIG. 2 are given the same reference numerals and will not be described in detail.

Reference numeral 30 denotes a pulse width modulation unit. The pulse width modulation unit 30 includes a signal input terminal 3 for an audio frequency band signal, an operational amplifier 31, and a pulse width modulator 36. The operational amplifier 31 includes a feedback resistor 35 connected between the non-inverting input 32, the inverting input 33, the output 34, the output 34, and the inverting input 33.
And The pulse width modulator 36 receives the signal input 3
7 and a pulse width modulated signal output 38. 3E is a ground terminal for signal input.

Reference numeral 50 denotes a switching unit, and a switching element of the switching unit 50 is a P-channel MOSFET 51.
(Hereinafter referred to as FET 51). 6
0 is a first high cut filter unit, the first high cut filter unit 60 is a flywheel diode 61,
It comprises a reactance coil 62 and a smoothing capacitor 63. Reference numeral 70 denotes an output detection circuit. The output detection circuit 70 includes two resistors 71 and 72 and a resistor 71 connected in series.
And output detection signal output unit 73 provided at the midpoint of connection between
It consists of. Reference numeral 80 denotes a second high cut filter unit. The second high cut filter unit 80 includes a reactance coil 81 and a smoothing capacitor 82.

The power supply line 19 is connected to the source S of the FET 51, connected to the gate G of the FET 51 through the gate bias resistor 52, and connected to the power supply line (not shown) of the pulse width modulator 30. Pulse width modulation signal output terminal 3
8 is connected to the gate G of the FET 51 and the pulse width modulation unit 3
The internal ground line of 0 (not shown) is grounded. The anode side of the flywheel diode 61 of the first high cut filter unit 60 is grounded, the cathode side of the diode 61 is connected to one end of a reactance coil 62, and the other end of the reactance coil 62 is connected to one end of a smoothing capacitor 63. Then, the other end of the capacitor 63 is grounded. FET51
Is connected to a connection point between the cathode side of the diode 61 and one end of the reactance coil 62.

The signal input terminal 3 is connected to a non-inverting input terminal 32 through a resistor 39, and one ends of resistors 71 and 72 constituting an output detection circuit 70 are connected to a connection point between a reactance coil 62 and a smoothing capacitor 63. The other ends of the two resistors 71 and 72 connected in series are grounded, and an output detection signal terminal 73 provided at the midpoint between the resistors 71 and 72 is connected.
Is connected to the inverting input terminal 33 of the operational amplifier 31. The output terminal 34 is connected to the input terminal 37 of the pulse width modulator 36.

This one end of the two resistors 71 and 72 is connected to the reactance coil 8 of the second high cut filter section 80.
1, one end of the reactance coil 81 is connected to one end of the smoothing capacitor 82, and the other end of the smoothing capacitor 82 is grounded. And the reactance coil 81
Is connected to one end of the coupling capacitor 15, and the other end of the coupling capacitor 15 is connected to the voice coil 2 of the speaker 21.
3 and the other end of the voice coil 23 is grounded.

The audio frequency band input signal input to the signal input terminal 3 is supplied to the non-inverting input terminal 32 through the resistor 39, and the output detection signal output section 73 outputs the inverted input terminal 33.
The output detection signal is fed back. The audio frequency band input signal and the output detection signal are compared by the operational amplifier 31 to correct an error between these signals. Then, an audio frequency band input signal whose error has been corrected is supplied from an output 34 to an input 37 of a pulse width modulator 36, and a pulse width modulated signal modulated by changing a pulse width in accordance with the amplitude of the audio frequency band signal is obtained. Obtained from output 38.

The pulse width modulation signal obtained from the output 38 is supplied to the gate G of the FET 51, the FET 51 is switched according to the pulse width of the pulse width modulation signal, and the DC power supplied from the DC power supply terminal 17 to the source S is supplied. The signal is chopped to obtain a pulse width modulated signal from the drain D side, and the pulse width modulated signal is supplied to the first high cut filter unit 60, and the first high cut filter unit 6
0 attenuates high-frequency components (hereinafter referred to as noise components) other than the frequency band of the audio frequency band signal input to the signal input terminal 3, and a signal (hereinafter referred to as a fundamental wave) in this audio frequency band. Components).

Since the first high-cut filter section 60 includes the flywheel diode 61, the energy charged in the actance coil 62 when the switching operation of the FET 51 according to the pulse width modulation signal is in the ON state is performed by the first high cut filter section 60. When the operation is off, the smoothing capacitor 63 is charged. Therefore, the noise component can be more effectively attenuated.

The fundamental wave component whose noise component has been attenuated by the first high-cut filter section 60 is supplied to an output detection circuit 70, and the signal obtained by dividing the fundamental wave component by resistors 71 and 72 is output as an output detection signal. Inverting input terminal 33 from section 73
Return to.

The fundamental wave component is supplied to the second high-cut filter section 80 to obtain a fundamental wave component in which a noise component is further attenuated. Then, this fundamental wave component is combined with the coupling capacitor 1
5 through the voice coil 2 of the dynamic speaker 21
3 and reproduced by the dynamic speaker 21 as an acoustic signal.

The resistor 83 is a resistor provided for discharging the smoothing capacitors 63 and 82.

According to the embodiment shown in FIG. 1, since the operation of the FET 51 constituting the power amplifier is a switching operation, the power supply voltage Vcc and the driving current Is of the voice coil are obtained.
The power generated by p is not consumed by the FET 51 and does not cause heat loss.

Further, according to the embodiment shown in FIG. 1, the first high-cut filter section 60 and the second high-cut filter section 80 for obtaining the fundamental wave component in which the high frequency component is attenuated are provided with a reactance coil. Since an LC type filter including a capacitor is used, power loss in these filter units can be reduced.

[0026]

According to the present invention, the heat loss in the output amplifier circuit can be reduced, and the efficiency of power supply can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an output amplifier circuit of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a conventional output amplifier circuit.

[Explanation of symbols]

3 input terminal, 30 pulse width modulator, 31 operational amplifier, 36 pulse width modulator, 50 switching unit, 6
0 first high cut filter section, 70 output detection circuit, 80 second high cut filter section

Claims (2)

[Claims] 1. An audio frequency band input signal output amplifying circuit, comprising: a pulse width modulation unit; a switching unit; and a DC power supply unit for supplying a DC signal to the switching unit. An input signal is converted into a pulse width modulation signal, the switching means is switched by the pulse width modulation signal to convert the DC signal into a pulse width modulation signal, and a signal in the audio frequency band from the pulse width modulation signal. And an output amplifier circuit for extracting the audio signal to obtain a signal obtained by amplifying the audio frequency band input signal. 2. An output amplification circuit for an audio frequency band input signal, comprising: a pulse width modulation unit, a switching unit, a high cut filter unit, a signal feedback unit, and a DC power supply unit for supplying a DC signal to the switching unit. An audio frequency band input signal is supplied to the modulation means and converted into a pulse width modulation signal.The switching means is switched with the pulse width modulation signal to convert the DC signal into a pulse width modulation signal. The signal in the audio frequency band is extracted from the pulse width modulated signal by passing the width modulated signal through the high cut filter means to obtain a signal output obtained by amplifying the audio frequency band input signal, and the signal output is obtained by the signal feedback means. An output amplifier circuit configured to feed back to the modulation means.