JPS58127415A - Power amplifier - Google Patents

Abstract

PURPOSE:To attain miniaturization, good power efficiency and reduced ripple voltage, by driving a speaker directly with an output voltage of a DC-DC conversion circuit and giving an error signal between said output voltage and an input signal in the opposite phase with said output voltage. CONSTITUTION:A control signal pulse-width-modulating the input signal ei from an input signal source 1 on/off-controls chopper control switches 17, 18 for the chopper control of a DC voltage rectifying a commercial AC power supply 8 to change an output voltage of two DC-DC conversion circuits consisting of high frequency transformers 11, 12, diodes 13, 14 and capacitors 15, 16 and to apply the result to a speaker 5 differentially. Said output voltage is detected at a detection circuit 22 and an inverted phase signal eR of the error voltage applied to an error amplifier 27 together with the signal ei. A signal obtained from the signal eR applied to output voltage correcting devices 29, 30 is given to a capacitor 15 to cancel ripple voltages.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a power amplifier for use in audio playback devices, etc.
In particular, the present invention relates to a power amplifier with improved power efficiency and distortion characteristics.

In general, power amplifiers used in audio playback devices, etc. are required to have a relatively large output because the dynamic range of the signals handled is wide, and the efficiency of speakers connected as loads is low. . For this reason, power amplifiers used in audio playback devices, etc.
Class B amplifiers are often used because they have less power loss and less heat generation problems, although their distortion characteristics are inferior to class B amplifiers.

Hereinafter, such a conventional class B operation power amplifier will be explained with reference to the drawings.

FIG. 1 is a circuit diagram showing an example of a conventional B stitch operation power amplifier,
FIG. 2 is a characteristic diagram showing the power efficiency of FIG. 1. In FIG. 1, 1 is an input signal source, 2 is a preamplifier, 3 and 4 are
5 is a power amplification transistor, 5 is a speaker, and 6 and 7 are power supplies.

In FIG. 1, an input signal to be amplified from an input signal source l is applied to a preamplifier 2, amplified to a predetermined level, and then applied to the base of the preamplifier 2 in order to drive power amplifying transistors 3 and 4. applied. The power amplifying transistors 3 and 4 are NPN and PNP transistors with different polarities, respectively. In the case of an amplifier operating in class B, as is well known, transistors 3 and 4 are such that one transistor is in an active state and the other transistor is in a cut-off state, depending on the polarity of the drive signal applied to the transistors. The output signals of the power amplifying transistors 3 and 4 are combined under alternating voltage control to drive the speaker 5. The power efficiency of the power amplifier shown in FIG. 1 changes depending on its output level P, and becomes K as shown in FIG. 2.

In FIG. 2, the horizontal axis indicates the normalized output P o / Po--- with the maximum output P6 wa a m being 1,
The vertical axis indicates the power efficiency 6. As can be understood from Figure 2, a power amplifier operating in class B has a relatively good power efficiency of about 78% at its maximum output.
As the output becomes smaller, the power efficiency decreases sharply, and when the input signal is 5K, such as a music signal, and the difference between the peak signal level and the average signal level is large, the power efficiency can be as high as 30-. It is normal for it to fall short. Therefore, the first
The class B operation power amplifier shown in the figure not only generates more heat as the output of the amplifier increases, making heat dissipation design difficult. The disadvantage was that it was very large.

As a method to eliminate the above-mentioned drawbacks of class B operation power amplifiers, the power efficiency is improved by configuring the amplifier using a pulse width control method, and the power supply is made smaller by using a switching method for the power supply circuit. Conventionally, methods such as the following are generally known. However, even if these methods are effective individually, no further effects can be obtained, and the overall power consumption including the power supply circuit of the power amplifier is quite large.

The present inventors previously proposed a power amplifier that eliminates the drawbacks of the above-mentioned class B operation power amplifier and pulse width control type power amplifier, in Japanese Patent Application No. 55-44632 (%
(Refer to Publication No. 1611) Proposed at the bank. This conventional power amplifier performs chopper control on a DC voltage obtained by directly rectifying and smoothing an AC power supply using an input signal such as a pulse-width modulated music signal to be amplified, and outputs the DC voltage through a high-frequency transformer and a rectifier and smoothing circuit. The output directly drives the speaker load, improving power efficiency and downsizing the power supply circuit.

Hereinafter, the power amplifier according to the prior art described above will be explained with reference to the drawings.

Figure 3 is a circuit diagram showing another example of a conventional power amplifier;
Figures (a), (b), (C) f (d) and (
e) is a waveform diagram for explaining the operation of the circuit of FIG. 3; In FIG. 3, the input signal source 1, preamplifier 2, and speaker 5 are the same as in FIG.
and 12 are high frequency transformers, 13 and 14 are rectifier diodes, 15 and 16 are smoothing capacitors, 17 and 1
8 is a chopper control switch, 19 is a pulse width modulator,
20 is a carrier signal generator, and 21 is a voltage comparator.

The power amplifier shown in FIG.
2. Consisting of rectifier diodes 13 and 14 and smoothing capacitors 15 and 16, DC voltage obtained by rectifying commercial AC power supply 8 by full-wave rectifier circuit 9 is applied via chopper control switches 17 and 18. Two DC-DC conversion circuits, a carrier signal generator 20 and a voltage comparator 21
and a pulse width modulator 19 that pulse width modulates the input signal e to be amplified, and chopper control switches 17 and 18 tf on/off control by the control signal e which pulse width modulates the input signal e. Then, the output voltages of the two DC-DC conversion circuits mentioned above are changed, and the output voltages of the two DC-DC conversion circuits are differentially applied to the speaker 5, which is a load.

Next, its operation will be explained in detail.

The AC voltage from the commercial AC power supply 8 is rectified by a full-wave rectifier circuit 9 and converted to a DC voltage via a smoothing capacitor 10. This DC voltage is applied to the chopper control switch 17.
and 18, it is applied to the high frequency transformers 11 and 12 that constitute the DC-DC conversion circuit. During the period when the chopper control switch 17 is on, the second winding of the high frequency transformer 11 is controlled by the smoothing capacitor IOK mentioned above.
Although a smoother DC voltage is applied, the rectifier diode 13 is in a cut-off state because the secondary winding is coupled with opposite polarity. Next, when the chopper control switch 17 is turned off, the magnetic energy stored in the secondary winding during the period when the chopper control switch 170 was on is released into the secondary winding. A back electromotive force is induced.

Therefore, the rectifier diode 13 becomes conductive,
The voltage generated in the secondary winding Km of the high frequency transformer 11 is supplied to the speaker 5, which is a load. That is,
In a DC-DC conversion circuit composed of a high-frequency transformer 11, a bridging diode 13, and a smoothing capacitor 15, the rectifier diode 13 operates as a reverse operation switch with respect to the on/off operation of the chopper control switch 17. The output voltage smoothed and rectified by the smoothing capacitor 15 is then supplied to the speaker 5.

The output voltage E0 of the aforementioned DC-DC conversion circuit generated across the smoothing capacitor 15 during the period when the rectifying diode 13 is conductive is Bi! According to the risk analysis, as is generally known, it can be expressed by the following equation.

However, in the above equation, D is the duty ratio at which the switch 17 becomes conductive, N and N are the number of primary windings and the number of secondary windings of the high frequency transformer 11, and E is the voltage across the smoothing capacitor 100. .

As is clear from the above formula (1), in 5, the above-mentioned DC-D
When the C conversion circuit changes the duty ratio that turns the chopper control switch 17 on and off, it has the same effect as changing the turns ratio between the primary winding and the secondary winding of the high frequency transformer 11. As a result, a rectified output voltage E0 proportional to the duty ratio is output across the smoothing capacitor 150. This means that if the chopper control switch 17 is controlled by the control signal e obtained by pulse-width modulating the input signal e such as a music signal to be amplified, the output voltage across the smoothing capacitor 150 will change from the input signal e, l. 'c
This means that the input signal e1 has a similar waveform.
is amplified and output to both ends of the smoothing capacitor 15.

The DC-DC conversion circuit consisting of the high-frequency transformer 12, the rectifying diode 14, and the smoothing capacitor 16 also operates in exactly the same way as the DC-DC conversion circuit including the high-frequency transformer 11 described above, depending on the on/off operation of the chopper control switch 18. However, it is configured to generate an output voltage across the smoothing capacitor 160 with the same polarity as in the above case.

Next, the operation of the pulse width modulator 19 which generates the control signal e given to the one chopper control switches 17 and 18 will be explained.

The pulse width modulator 19 is composed of a voltage comparator 21 and a carrier signal generator 20, and the input signal e to be amplified from the input signal #1 is kept constant by the preamplifier 2 and amplified to a level shown in FIG. (a) Signal e indicating K.

is applied to one input terminal of the voltage comparator 21.

The carrier signal generator 20 generates a sawtooth carrier signal C1 of constant amplitude as shown in FIG. This carrier signal e is set to a frequency that is sufficiently higher than the highest frequency of the audio signal band, for example, about 200 kHz. The voltage comparator 21 compares the aforementioned carrier signal e and the output signal e of the preamplifier 2, and the voltage level thereof is e, )e.

A positive DC voltage is output when (e), and a negative DC voltage is output when (e).As a result, the output signal of the voltage comparator 21 is as shown in FIG.
b) As shown in K, a rectangular waveform control signal e, which is pulse width modulated from the human input signal e, roars.

The positive voltage of this control signal e turns on the chopper control switch 17, and the negative voltage and pressure controls the switch 18.
is applied to the chopper control switches 17 and 18 so as to turn on the chopper control switches 17 and 18. The two DC-DC conversion circuits including the high frequency transformers 11 and 12 operate as described above, and the secondary windings of the high frequency transformers 11 and 12 are
Output signals e (11 and e□) having waveforms as shown in FIGS. 4(C) and (d) are output, respectively. These output signals e・1 and eot
4. Through the rectifying and smoothing circuit consisting of smoothing capacitors 15 and 16, only the positive voltage component passes through the smoothing capacitor 15.
and 160 are output to both ends. This output signal has a DC voltage component E as shown by the dotted line K in Fig. 4 (C) and (d).
j, , , B, , and output signal components Δe1 . which are similar to the input signal e1 and have mutually opposite phases. Output signal e6 consisting of Δei
1 and e. It is l.

Then, the speaker 5 has a smooth capacitor 15 and a capacitor 16.
A difference signal between the output signals eat at both ends of 0 and eat is applied as the driving output signal C. That is, this driving output signal e0 is expressed as ee: ee1 eat''(E, s+
Δet) (Lt−Δet) (2) If the number of primary windings and the number of secondary windings of the high-frequency transformers 11 and 12 constituting the DC-DC conversion circuit are set equal, the aforementioned DC voltage components Eel and E□ can be made equal to each other, and the output signal component Δe and Δh can be made equal to each other. Therefore, in the above equation (2), B, , = rE, l, Δe, = Δe
, =Δe, and the speaker drive signal ee is
As shown in FIG. 4(e), the output signal has a similar waveform to the input signal e that does not include a DC voltage with an amplitude of ee"2XΔe. In other words, the circuit in FIG. Then, the speaker driving output signal e0 can be output.

As explained above, the power amplifier according to the prior art shown in FIG. Because it is configured to rectify and smooth the signal into a waveform similar to the signal and drive the speaker directly, it not only greatly improves power efficiency compared to the well-known class B amplifier power amplifier, but also enables DC-DC Since it is only necessary to use a high frequency transformer in the conversion circuit, a large commercial frequency power transformer is not required, and the size can be significantly reduced. However, the power amplifier shown in FIG.
Figure 4(e) K as shown by the dotted line.

Pulse the input signal to the speaker drive output signal e6 @vp
It is unavoidable to include a ripple voltage depending on the carrier signal frequency used for il, which has the disadvantage that the distortion rate is worse than that of the well-known BP operation power amplifier.

An object of the present invention is to eliminate the drawbacks of the prior art described above and provide a power amplifier with low distortion and high power efficiency.

To achieve this objective, the present invention directly drives a speaker with the output voltage of a DC-DC conversion circuit, and the DC-DC converter circuit directly drives a speaker.
By comparing the output voltage of the DC conversion circuit and the input signal to be amplified, and injecting the error signal into the output voltage of the DC-1)C conversion circuit in reverse phase, the output voltage of the DC-DC conversion circuit is obtained. The device is characterized in that the ripple voltage included in the output signal for driving the speaker is reduced.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 5 is a circuit diagram showing an embodiment of the power amplifier according to the present invention, and FIGS. 23
is an output voltage detection circuit, 24 and 25 are DC blocking foundations, 26 is a phase inverter, 27 and 28 are error amplifiers,
29 and 30 are output voltage correction devices, 31, 32, 33,
34, 39 and 40 are resistors, 35 and 36 are amplifiers, 3
7 and 38 are transistors, 41 and 42 are operating voltage supply terminals, and portions corresponding to those in FIG. 3 are given the same reference numerals, and a description thereof will be partially omitted.

In FIG. 5, the output voltage detection circuits 22 and 23 are constituted by resistors 31 and 32, and 33 and 34, respectively, and divide the voltage of the speaker driving output signal supplied to the speaker 5.

The output voltage correction circuits 29 and 30 are connected to the amplifier 3, respectively.
5. Composed of a transistor 37, a resistor 39, an amplifier 36, a transistor 38, and a resistor 40, and converts the correction voltage generated in the resistors 39 and 40 into DC-DC via smoothing capacitors 15 and 16 that constitute a DC-DCC circuit. It acts to inject the output voltage of the circuit. The word difference amplifier 27 compares the detection voltage v1 divided by the output voltage detection circuit 22 and applied via the DC blocking capacitor 24 with the input signal e to the amplifier, and generates an error signal e1 which is the difference. to the voltage correction device 29 and also to the error amplifier 28
are the detection voltage and input signal e which are divided by the output voltage detection circuit 23 and applied via the DC blocking capacitor 24 and the phase inverter 26.

The voltage correction device 30 has a function of comparing the difference signals with the voltage correction device 30 and providing the error signal to the voltage correction device 30.

Next, the operation of this embodiment will be explained.

@ In Figure 5, the output voltage detection circuit 22 divides the output voltage al11 of the DC-DC conversion circuit including the high frequency transformer 11 according to the ratio of the resistance values of the resistors 31 and 32, and outputs the divided voltage. As shown in the waveform diagram in FIG. 4(C), this output voltage e @ has a DC component, but the divided detection signal V has a DC component due to the action of the DC blocking capacitor 24. It is similar to the input signal e shown in FIG. 6(b) to be amplified as shown in FIG. It is applied to one input terminal of the width transducer 27.

The error amplifier 27 is provided with a voltage gain of IK, and compares the input signal e to be increased applied to the other input terminal with the aforementioned detection signal v, and detects only the error thereof. 5 is configured to invert the phase of the error voltage and output it as an error signal C1. That is, the error amplifier 27
is the above-mentioned detection signal V, and input signal e, is v, )
When e, K, the negative voltage corresponding to the error is expressed as v, (
When e, K, the positive voltage corresponding to the error is the error signal e,
Output as . Therefore, the feedback gain (1/β) of the voltage determined by the resistors 31 and 32 of the output voltage detection circuit 22 is expressed as Ie, which is the signal component of the output voltage e*l of the DC-DC conversion circuit with respect to the input signal e, If the gain is set to be the same as the gain of the sixth
As shown in Figure (C) K, only the ripple voltage V component included in the detection signal V is phase inverted.

Furthermore, since the amplifier 35 in the voltage correction circuit 29 amplifies the error signal e1 from the error amplifier 27, its voltage gain G is equal to the feedback gain (1/β) of the output voltage detection circuit 22.
is set equal to .

As a result, the emitter terminal of the transistor 37 has El=
A signal whose peak value is equal to the ripple voltage included in the signal voltage (e, x Q), that is, the output voltage eo of the DC-DC conversion circuit including the high-frequency transformer 11, and whose phase is inverted is obtained. This signal voltage is injected from the ground side of the smoothing capacitor 15 in the DC-DC conversion circuit including the high-frequency transformer 11, and the output voltage e6. The ripple voltage included in the voltage can be canceled out.

The configuration and operation for canceling out the ripple voltage included in the output voltage of the DC-DC conversion circuit including the high frequency transformer 11 have been described above. The DC-DC conversion circuit including the high frequency transformer 12 on the other hand is connected to the fi 5 as shown in FIG.
I) Signal component output Δe of the output voltage of the C-DC conversion circuit,
and input signal e are in opposite phase to each other. Therefore, the configuration for canceling out the ripple voltage included in the output voltage includes the above-mentioned high frequency transformer 11 in that it requires the phase inverter 26 between the output voltage detection circuit 23 and the error amplifier 28. Although this is different from the case of canceling out the ripple voltage included in the output voltage of the DC-DC conversion circuit, the other configurations and operations are the same as in the above case.

As explained above, the embodiment of the present invention shown in FIG.
A ripple voltage included in the output voltage of a DC-DC conversion circuit whose output voltage is variably controlled by a control signal obtained by pulse width modulating the input signal to be amplified is detected, and a signal having an opposite phase to the ripple voltage is detected. Since it is injected into the output voltage of the DC-DC conversion circuit, the ripple voltage included in the output voltage of the DC-DC conversion circuit is canceled out, and therefore, the output voltage of the DC-DC conversion circuit applied to the speaker is The signal distortion rate in the output signal for driving the speaker is significantly reduced.

FIG. 7 is a circuit diagram showing another embodiment of the power amplifier according to the present invention.

The power amplifier shown in FIG. 7 is different from the power amplifier shown in FIG. The only difference is that a is provided, and the other configuration and operation are the same as in the case of FIG. The high frequency transformers 43 and 44 have one winding connected in series between the DC-DC conversion circuit and the load speaker 5, and the other winding receiving the error correction signal E.

is applied to cancel out the ripple voltage included in the output voltage of the KDC-DC conversion circuit, as in the case of FIG.

In the embodiment of the power amplifier according to the present invention explained with reference to FIG. 5 and FIG. Not only rectified commercial AC power sources, but also DC power sources such as car batteries and dry batteries can be used in the same way.

As explained above, according to the present invention, the output voltage of the DC-DC conversion circuit, that is, the ripple voltage included in the speaker driving output signal is extracted by comparing it with the input signal to be amplified. By injecting the error signal into the output voltage of the DC-DC conversion circuit in an opposite phase, it is possible to eliminate the ripple voltage of the output signal for driving the speaker. can be provided.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an example of a conventional power amplifier, Fig. 2 is a characteristic diagram showing its power efficiency, Fig. 3 is a circuit diagram showing another example of a conventional power amplifier, Fig. 4 (a) . (b), (C)? (d) and (e) are waveform diagrams for explaining its operation, FIG. 5 is a circuit diagram showing one embodiment of the power amplifier according to the present invention, and FIGS. 6(a) and (b).
) and (c) are waveform diagrams for explaining the operation, No. 7
The figure is a circuit diagram showing another embodiment of the power amplifier according to the present invention. 1... Input signal source, 8... Commercial AC power supply, 9... Full wave rectifier circuit, 10, 15.16.
... Smoothing capacitor, 11, 12, 43, 44
...High frequency transformer, 13,14...
Rectifier diode, 17° 18...Chopper control switch, 19...Pulse width modulator, 20
...Carrier signal generator, 21...1
Voltage comparator, 22, 23...output voltage detection circuit,
24.25...DC blocking capacitor, 26.
... Phase inverter, 27.28 ... Error amplifier, 29.30 ... Output voltage correction device, 41
, 42... Operating voltage supply terminal. ′ □″Go

Claims (1)

[Claims] In a voltage amplifier that chopper-controls a DC voltage using a control signal obtained by pulse-width modulating an input signal to be amplified, and drives a load directly by an output signal of a DC-DC conversion circuit that variably controls the output voltage, the DC-DC converter a first means for detecting a difference between the voltage of the output signal of the circuit and the voltage of the input signal; and a second means for applying the differential output signal from the first means to the output signal of the DC-DC conversion circuit. 1. A power amplifier comprising means for removing a ripple component contained in an output signal of the DC-DC conversion circuit that drives the load.