JPH1051242A - Amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the working efficiency of an amplifier part by inputting the signal which varies in response to the level change of every half cycle of the output signal that is produced by a secondary switch, prepared at the secondary side of a power transformer as the voltage of the amplifier part. SOLUTION: The amplifier input voice signals AMP1 and AMP2 of the CH1 and CH2 are supplied to a PWM(pulse width modulation) generation part 1. The output signals +A, -A, +C, -C and D of the part 1 are supplied to a power supply part 2, together with the commercial AC power voltage, inputted via a plug 4. The DC power voltage +B1, -B1, +B2 and -B2 are applied to an amplifier 3 from the part 2, and the amplifier 3 amplifies the electric power of both signals AMP1 and AMP2. The output voice signals of the part 3 are outputted in voices, via the speakers 5 and 6 respectively. A pulse transformer is used as a floating transformer at the part 2, and also a switching regulator is placed at the primary side of the transformer. Then a fixed repetitive frequency PWM wave is outputted to the secondary side of the floating transformer, based on the signal that is produced at the part 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier, and more particularly to a high-efficiency amplifier for amplifying power of a voice signal.

[0002]

2. Description of the Related Art Heretofore, as a power amplifier for voice signals with higher efficiency than a class A amplifier or a class B amplifier, a signal obtained by switching based on an output signal of a pulse width modulation (PWM) circuit is amplified. An amplifier configured to supply the power supply voltage as a power supply voltage is known (Japanese Utility Model Laid-Open No. 55-179415, Japanese Patent Laid-Open No. 60-51305).

The amplifier disclosed in Japanese Utility Model Laid-Open Publication No. 55-179415 PWM-modulates an input audio signal by a PWM modulation circuit, uses the PWM modulation wave to switch a DC power supply by a switching regulator, and outputs an output signal of the switching regulator. By rectifying and smoothing
A positive / negative voltage proportional to the input audio signal is obtained, and the positive / negative voltage is applied as a positive / negative power supply to a power amplifier for driving a load. With this configuration, an amplifier with a high efficiency and a low distortion factor is to be realized. Is what you do.

The amplifier described in Japanese Patent Application Laid-Open No. Sho 60-51305 supplies an input audio signal delayed by a first delay element to a first amplifier circuit, and supplies an input audio signal to an absolute value circuit. Then, the absolute value signal is compared with the absolute value signal passed through the second delay element by a detection circuit, and the higher (or lower) voltage is taken out of the detection signal and sent to the PWM modulation circuit. Then, the output PWM modulated wave of the PWM modulation circuit is supplied to a second amplifier circuit to generate positive and negative voltages by switching the DC power supply and rectifying and smoothing the switching output. Is supplied as a power supply voltage to the amplifying circuit, and an amplifier with high efficiency and low distortion is realized by such a configuration.

[0005]

However, in the former amplifier of the above-mentioned conventional amplifiers, a pulse transformer is used as a floating transformer (power supply transformer), and a switching operation is performed by a switching regulator provided on the primary side of the pulse transformer. As shown in FIG. 6, the rectifier / smoothing circuit provided on the secondary side of the pulse transformer supplies the power supply voltage + B (curve
II) and -B (shown by curve III),
Possibility to follow. Although the loss of the transformer itself is small, the power (product) of the power supply voltage to the power transistor of the amplifying unit and the current flowing through the power transistor, which is indicated by IV and V in FIG. 6, becomes a loss (heat generation). There is a problem of large efficiency.

Further, the latter of the above-mentioned conventional amplifiers has a configuration in which a commercial transformer is used as a floating transformer (power transformer) and a switching operation is performed on the secondary side of the commercial transformer, so that the efficiency is high. However, there is a problem that the commercial transformer is large and heavy, and the self loss (heat generation) of the transformer itself is large.

[0007] The present invention has been made in view of the above points,
It is an object of the present invention to provide a light-weight, low-loss, high-efficiency amplifier.

[0008]

In order to achieve the above-mentioned object, the present invention provides a method for generating first and second pulse width modulated wave signals corresponding to the levels of positive and negative half cycles of an input signal. A generator for generating a third pulse width modulated wave signal according to the level of the entire input signal, and a pulse transformer as a power transformer, and an input AC voltage provided on the primary side of the pulse transformer. The primary side switch to which the converted DC voltage is applied is switching-controlled by the third pulse width modulation wave signal, and the secondary side switch provided on the secondary side of the pulse transformer has the first and second pulse width modulation waves. A power supply unit that outputs a power supply voltage under switching control of a signal; and an amplification unit that receives a power supply voltage output from a secondary switch of the power supply unit, amplifies an input signal, and outputs the amplified signal. It is obtained by the configuration that.

In the present invention, a pulse transformer is used as a power supply transformer, and a positive or negative output signal generated by a secondary switch provided on a secondary side of the pulse transformer is used.
The first and second pulse width modulated wave signals that change corresponding to the level change in each negative half cycle period can be input as the power supply voltage of the amplifier.

Further, according to the present invention, since the primary side switch provided on the primary side of the pulse transformer is switching-controlled by the third pulse width modulated wave signal corresponding to the level of the entire input signal, amplification of all input signals is performed. All the power required for the power transformer can be generated on the secondary side of the power transformer.

[0011]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows a block diagram of one embodiment of an amplifier according to the present invention. As shown in the figure, this embodiment is based on the amplifier input audio signals AMP1, AM1 of the first channel (CH1) and the second channel (CH2).
A pulse width modulation (PWM) generator 1 to which P2 is supplied;
The output signals + A, -A, + C, and -C of the PWM generator 1
And D, and a power supply unit 2 to which a commercial AC power supply voltage is input via a plug 4, and a DC power supply voltage + B1, -B1, + B2, -B2 applied from the power supply unit 2 to input an audio signal AMP1. AMP2, which amplifies the power of AMP2 and AMP2
The sound signal output from the amplifying unit 3 is generated by the speakers 5 and 6, respectively. In the embodiment of the present invention, a pulse transformer is used as a floating transformer (power transformer) in the power supply unit 2, a switching regulator is provided on the primary side, and the PWM is generated by the PWM generation unit 1 on the secondary side. It is characterized in that a switch circuit (secondary switch) controlled based on a signal is provided.

The PWM generator 1 has, for example, the configuration shown in the block diagram of FIG. In the figure, the input audio signals of CH1 and CH2 input to terminals 10 and 11 are respectively adjusted to desired levels by variable resistors VR1 and VR2, and then are branched into two, and one of the input signals AMP.
1. AMP2 is input to the amplifier 3, and the other is PWM.
It is input to the generation unit 1.

[0013] The PWM generation unit 1, an input audio signal of CH1 is positive half-wave rectifier circuit 12 _1, it is supplied to the negative side half-wave rectifier circuit 13 ₁ and the full-wave rectifier circuit 14 _1, each positive half cycle , The half-wave rectified signal of the negative half cycle and the full-wave rectified signal are output. Each positive half-wave rectifier circuit 12 ₁ and the respective half-wave rectified signal of the negative half-wave rectifier circuit 13 ₁ is supplied to the PWM generator 15 _1, 16 _1. The PWM generators 15 ₁ and 16 ₁ compare the level of the input half-wave rectified signal with the triangular wave of a constant repetition frequency (for example, one hundred and several tens of kilohertz), and based on the comparison result, determine the pulse width according to the level of the input half-wave rectified signal. (Duty ratio), a pulse width modulated wave (PWM) having a constant repetition frequency
Wave).

Therefore, for example, if the input audio signal is as shown in FIG.
In the case shown in the figure, a positive half cycle half-wave rectified signal is input.
PWM generator 15₁Is entered as shown in FIG.
The input level is high only during the positive half cycle of the input audio signal.
The pulse width becomes wider as
In the half cycle period, the minimum width (one
) Is output. This PWM
Waves drive circuit 17 ₁To power supply unit 2 as signal + A via
Is output.

Meanwhile, PWM generator 16 ₁ a half-wave rectified signal of the negative half cycle is inputted, as shown in FIG. 5 (C), the negative half-cycle period only the input level of the input audio signal (absolute Value) increases, the pulse width increases,
During the positive half cycle period of the input audio signal, a PWM wave composed of a pulse having a minimum width (constant) is output regardless of the input level. Signal -A The PWM wave through a driving circuit 18 ₁
Is output to the power supply unit 2.

As described above, in the PWM generation unit 1, CH
2 is a positive half-wave rectifier circuit 12_Two, Negative half-wave
Rectifier circuit 13_TwoAnd full-wave rectifier circuit 14_TwoEach supplied
The positive half cycle of the half-wave rectified signal and the negative half
Output as half-wave rectified signal and full-wave rectified signal of cycle
Is done. Positive half-wave rectifier circuit 12_TwoAnd negative half-wave rectifier 1
3_TwoOf each half-wave rectified signal of the PWM generator 15_Two, 1
6_TwoSupplied to PWM generator 15_Two, 16_TwoIs the input half
5B and 5C according to the level of the wave rectified signal.
Such a PWM wave is output. These PWM waves are driven
Circuit 17 _Two, 18_TwoPower supply as signals + C, -C via
2 is output.

Furthermore, the PWM generating unit 1, taken out from each of the full-wave rectifier circuit 14 ₁ and 14 ₂ CH1 and CH
The full-wave rectified signals of the two input audio signals are added and synthesized in the adder circuit 19 and then supplied to the PWM generator 20. P
The WM generator 20 is a PWM generator 15 ₁ , 16 ₁ , 1
5 _2, 16 ₂ PWM wave obtained by performing the same pulse width modulation and outputs through the driving circuit 21 as a signal D to the power supply unit 2.

FIG. 3 shows a circuit diagram of an example of the power supply unit 2 shown in FIG. As shown in FIG.
, A full-wave rectified by a bridge type full-wave rectifier circuit 26 through an AC filter 25, and then smoothed by a smoothing capacitor 27 to be converted into a DC voltage. Input to the drain of a field effect transistor (FET) 28. The source of the FET 28 is connected to one end of a primary winding of a pulse transformer 29 which is a power transformer. The pulse transformer 29 is a switching transformer, and is lighter than a commercial transformer to which a commercial power supply voltage is input.

On the other hand, the signal D is input from the input terminal 30 and is electrically isolated by the isolation transformer 31 and then applied to the gate of the FET via the drive circuit 32 to control the switching of the signal. Due to the switching of the FET 28, energy (power) necessary for amplifying the combined signal of the input audio signals of CH1 and CH2 is generated at both ends of the secondary winding of the pulse transformer 29.

The power generated at both ends of the secondary winding of the pulse transformer 29 is full-wave rectified by a bridge type full-wave rectifier circuit 33. One corner of the bridge full-wave rectifier circuit 33 (the positive output terminal) is connected to the drains of the switching MOS field effect transistor (FET) 34 ₁ and 34 _2, another vertex facing the apex of the (negative Side output terminal) is a switching MOS field effect transistor (FE)
T) 35 ₁ and 35 ₂ are connected to the drains. F
In the ETs 34 ₁ and 35 _1, the PWM signals + A and −A output from the PWM generator 1 are respectively applied to the gates to perform switching control. Similarly, FET 34 ₂ and 35 ₂ are PWM wave signal + C and -C output from the PWM generating unit 1 is applied to the gate respectively switching control.

[0021] Thus, FET 34 is outputted from the _first source further from the coils 36 ₁ and the capacitor 38 by the low-pass filter is filtered only the low-frequency component output terminal 40 ₁ consisting of _1, CH1 of an audio signal output to the speaker 5 , A voltage + B1 that changes according to the level of the positive half cycle period is taken out. Similarly, the signal is output from the source of the FET 35 ₁ , and further, the coil 37 ₁ and the capacitor 3
9 ₁ by the low-pass filter is filtered only the low-frequency component output terminal 41 ₁ consisting of a voltage -B1 is taken that varies according to the level of the negative half cycle of CH1 of an audio signal output to the speaker 5.

The signals are output from the sources of the FETs 34 ₂ and 35 ₂ , and furthermore, the coils 36 ₂ and 37 ₂ and the capacitor 3
By being filtered only low frequency components by 8 _2, 39 ₂ each low-pass filter consisting of the output terminal 40 _2, 41 ₂
, Voltages + B2 and -B2 that change according to the levels of the positive and negative half-cycle periods of the audio signal of CH2 output to the speaker 6 are extracted.

Therefore, for example, when the audio signal output to the speaker 5 (or 6) is shown by the curve VI in FIG. 5D, the signal + output from the output terminal 40 ₁ (or 40 ₂ )
B1 (or + B2) is as shown by VII in FIG. 3D, and the signal − output from the output terminal 41 ₁ (or 41 ₂ )
B1 (or -B2) is as shown by VIII in FIG.

The FETs 34 _{1 to} 35 ₂ and the coil 36 ₁
To 37 _2, capacitors 38 _{1-39 2} constitutes the secondary side switch, thereby the electric power generated at both ends of the secondary winding of the pulse transformer 29 to the audio signal level of each channel of CH1, CH2 It can be output precisely by sorting. The above signals + B1, -B1, + B2 and -B2
Is input to the amplifier 3 shown in FIG. 1 as a power supply voltage.

FIG. 4 is a circuit diagram of an example of the amplifying unit 3 described above. In the figure, the same components as those in FIGS. 1 and 2 are denoted by the same reference numerals. 4, amplifier 3 and the negative feedback amplifier 51 _1, 51 _2, a pre-driver 52 _1, 52 _2, N
It comprises channel transistors Q11, Q21 and P-channel transistors Q21, Q22.

The transistors Q11 and Q12 have their bases connected together and their emitters connected together. The collector of the transistor Q11 has a terminal 53 _1.
The signal + B1 is supplied as a power supply voltage, the collector of the transistor Q12 is the signal -B1 through the terminal 54 ₁ is supplied as a power supply voltage via.

[0027] Similarly, the transistors Q21 and Q22 are emitter connected in common with the base is commonly connected to each other and the signal + B2 to the collector of the transistor Q21 through the terminal 53 ₂ is supplied as a power supply voltage, the collector of the transistor Q22 is the signal -B2 is supplied as a power supply voltage via terminal 54 _2. Additional signal + B1 and -B1 in the pre-driver 52 _1, +
B2 and -B2 is inputted as a power supply voltage to the pre-driver 52 _2.

Next, the operation of the amplifier 3 will be described. The audio signals of CH1 and CH2 extracted from the variable resistors VR1 and VR2
1 _1, 51 ₂ is supplied to the pre-driver 52 _1, 52 ₂ after being amplified is power amplified. Audio signal CH1 that have been subjected to the power amplification by the pre-driver 52 ₁ is amplified is input to the base of the output stage transistors Q11 and Q12, a negative feedback amplifier 51 with the sound is supplied to the speaker 5
Negative feedback to ₁ Similarly, the audio signal of CH2 that have been subjected to the power amplification by the pre-driver 52 ₂ output stage transistor Q
21 and Q22 are input to the bases and amplified, supplied to the speaker 6, and sounded, and the negative feedback amplifier 51 ₂
Negative feedback.

Here, in this embodiment, the signals + B1 and -B1 generated by the secondary switches of the pulse transformer 29 in the power supply unit 2 are used as the collector power supply voltages of the output stage transistors Q11 and Q12. Signal + B2
−B2 is supplied as the collector power supply voltage of the output stage transistors Q21 and Q22.

Here, as described above, for example, the speaker 5
5 or (D), the signal + B1 or + B2 becomes the signal VII in FIG. 5 (D).
As shown by, during the positive half cycle of the audio signal, it changes following the audio signal at a level slightly larger than the audio signal, and
The signal -B1 or -B2 has a constant voltage close to 0V during the positive half cycle of the audio signal, as indicated by VIII in FIG. 3D, during the negative half cycle of the audio signal. In the negative half cycle period of the audio signal, the waveform changes slightly following the audio signal at a level (absolute value) slightly higher than that of the audio signal. Therefore, the amplifier 3 includes only the primary-side switch shown in FIG. When compared with the output audio signal of the conventional amplifier and the waveform of the power supply voltage, the power loss can be clearly reduced and the amplification can be performed, and the efficiency of the amplifier 3 can be improved.

The present invention is not limited to the above embodiment.
Instead of (this is also a pulse transformer), another electrical insulating means such as a photocoupler may be provided.

[0032]

As described above, according to the present invention,
A signal generated by the secondary switch provided on the secondary side of the power transformer, which changes in accordance with the level change in each of the positive and negative half cycle periods of the output signal, is input as the power supply voltage of the amplifier. In addition, the efficiency in the amplifying unit can be improved as compared with the conventional amplifier having only the primary side switch.

Further, according to the present invention, the primary switch provided on the primary side of the power transformer performs a switching operation in accordance with the level of the composite signal of the signals of the plurality of channels to perform all the necessary operations for amplifying all the input signals. This power is generated on the secondary side of the power transformer, so that the efficiency of the power supply unit can be improved as compared with a conventional amplifier using a commercial transformer.

Further, according to the present invention, since the power transformer is a pulse transformer, the weight can be reduced as compared with a conventional amplifier using a commercial transformer.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram illustrating an example of a PWM generation unit in FIG. 1;

FIG. 3 is a circuit diagram of an example of a power supply unit in FIG. 1;

FIG. 4 is a circuit diagram of an example of an amplifier in FIG. 1;

FIG. 5 is a signal waveform diagram for explaining operation according to the embodiment of the present invention.

FIG. 6 is a waveform diagram showing an output audio signal and a power supply voltage of an example of a conventional amplifier.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Pulse width modulation (PWM) generation part 2 Power supply part 3 Amplification part 5, 6 Speaker ₁₀ , 11, 30 Input terminals 12 ₁ , 12 ₂ Positive half-wave rectification circuit (first generation part) 13 ₁ , 13 ₂ Negative Side half-wave rectifier circuit (second generator) 14 ₁ , 14 ₂ Full-wave rectifier circuit (third generator) 15 ₁ , 15 ₂ Pulse width modulation (PWM) generator (first generator) 16 ₁ , 16 ₂ pulse width modulation (PWM) generator (second generation unit) 17 ₁ , 17 ₂ , 18 ₁ , 18 ₂ , 21, 32 drive circuit 19 addition circuit (third generation unit) 20 pulse width modulation ( PWM) generator (third generator) 28 switching MOS field-effect transistor (FET) (primary switch) 29 pulse transformer 31 isolation transformer 34 ₁ , 34 ₂ , 35 ₁ , 35 ₂ switching MOS type Field effect transistor ( ET) (secondary side switch) 36 _1, 36 _2, 37 _1, 37 ₂ low-pass filter coil (secondary side switch, the filter circuit) 38 _1, 38 _2, 39 _1, 39 ₂ low-pass filter capacitor (secondary 40 ₁ , 40 ₂ , 41 ₁ , 41 ₂ Power supply voltage output terminals 51 ₁ , 51 ₂ Negative feedback amplifiers 52 ₁ , 52 ₂ Predrivers 53 ₁ , 53 ₂ Positive power supply voltage input terminals 54 ₁ , 54 ₂ Negative side power supply voltage input terminal + A, -A, + C, -C, D PWM wave signal + B1, -B1, + B2, -B2 Amplifier unit power supply voltage

Claims (4)

[Claims] 1. A first and a second pulse width modulated wave signal corresponding to the level of each of positive and negative half cycle periods of an input signal, respectively, and a third signal corresponding to a level of the entire input signal. A generating unit that generates a pulse width modulated wave signal; and a primary switch that uses a pulse transformer as a power supply transformer and is applied with a DC voltage converted from an input AC voltage provided on a primary side of the pulse transformer. A power supply unit that is switched by a pulse width modulation signal and a secondary switch provided on a secondary side of the pulse transformer is switching controlled by the first and second pulse width modulation signals and outputs a power supply voltage; And an amplification unit to which the power supply voltage output from the secondary side switch of the power supply unit is input, and amplifies and outputs the input signal. Vessel. 2. The generator according to claim 1, wherein the audio signal of a plurality of channels is input as the input signal, and the pulse width of each of the input audio signals of each channel changes according to the level in a positive half cycle, and In the first half cycle period, a first pulse width modulated wave signal is generated for each channel as a pulse train of a pulse having a minimum width.
And a pulse width of the input audio signal of each channel changes according to the level in the negative half cycle period. A second generation unit that generates a second pulse width modulation signal for each channel, and a third generation unit that generates a signal obtained by pulse width modulation of the combined signal of the plurality of channel signals as the third pulse width modulation signal. The amplifier according to claim 1, further comprising a generation unit. 3. The power supply unit includes a conversion unit that converts the input AC voltage into a DC voltage, the pulse transformer as a power supply transformer, an output terminal of the conversion unit, and one end of a primary winding of the pulse transformer. A first switching element that constitutes the connected primary-side switch; and an electrical insulating unit that electrically insulates the third pulse width modulated wave signal and inputs the third pulse width modulated wave signal to the first switching element as a switching signal. A rectifier circuit for rectifying a signal induced on the secondary side of the pulse transformer, a signal from a positive output terminal of the rectifier circuit being input, and switching controlled by the first pulse width modulated wave signal. 2, and a signal from the negative output terminal of the rectifier circuit is input.
A third switching element that is switching-controlled by the second pulse width modulation signal, and a filter that removes unnecessary frequency components of output signals of the second and third switching elements and outputs the positive and negative power supply voltages 2. The amplifier according to claim 1, comprising a circuit, wherein said second and third switching elements and said filter circuit constitute said secondary-side switch. 4. When an audio signal of a plurality of channels is input as the input signal, the second and third switching elements and the filter circuit are provided for each channel, and the second and third switching elements provided for each channel are provided. The amplifier according to claim 3, wherein the switching of the three switching elements is controlled by the first and second pulse width modulation wave signals generated for each channel.