JP3319072B2 - Power amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power amplifier for driving a load such as a speaker in audio equipment.

[0002]

2. Description of the Related Art A power amplifier in an audio device modulates a DC voltage supplied from a DC power supply based on an input signal.
Usually, a waveform similar to an input signal is supplied to a speaker as a load. In such power amplifiers, those that minimize power loss and improve power conversion efficiency have been developed.
It is known that power amplifiers include class D power amplifiers.

[0003] By the way, the combination of the switching regulator and the class D power amplifier can improve the power exchange efficiency, but has problems such as an increase in circuit scale and cost.

In view of the above, Japanese Patent Laid-Open No. 57-87218 discloses a conventional method.
There has been a load drive circuit as described in Japanese Patent Application Laid-Open No. H10-209,873.

Hereinafter, a conventional load driving circuit will be described. FIG. 10 shows a conventional load drive circuit.
1001 is a pulse voltage generator for generating a pulsed AC voltage composed of 1002, 1003 and 1004;
Is a rectifier-smoothing device that rectifies and smoothes an AC voltage supplied from a commercial AC power supply and converts it to a DC voltage; 1003 is an inverter that converts the DC voltage generated by the rectifier-smoothing device 1002 into an AC voltage; 1004 controls the inverter 1003 A controller; 1005, a pulse width modulator including 1006 and 1007; 1006, a modulation signal generator for generating a pulse width modulation signal having a pulse width corresponding to the analog input signal;
A switch 1007 modulates the pulse width of the output signal of the pulse voltage generator 1001 in accordance with the output of the modulation signal generator 1006, and a filter 1008 integrates the output of the pulse width modulator 1005.

FIG. 11 is an explanatory diagram for explaining the operation of the conventional load driving device. FIG. 12 is an explanatory diagram for explaining the operation of the conventional load driving device.

Hereinafter, the entire operation will be described with reference to FIGS. In FIG. 10, an AC voltage V21 of a commercial AC power supply is applied to a pulse voltage generator 1001.
In the pulse voltage generator 1001, the AC voltage V21 is supplied to a rectifier / smoothing device 10 comprising a rectifier D1 and a smoothing capacitor C1.
02 is converted to a DC voltage V22. And the DC voltage V
22 is applied to the inverter 1003.

By the way, in the inverter 1003,
The collectors of the transistors Q1 and Q2 are connected in series to both ends of the primary winding L1 of the high-frequency transformer T1. A DC voltage V22 is applied between the common emitter connection point of the transistors Q1 and Q2 and the middle point of the primary winding L1.
The output of the controller 1004 is supplied to the bases of the transistors Q1 and Q2. The controller 1004 includes, for example, an oscillator that generates a square wave signal of a predetermined frequency and an inverted signal thereof, and alternately switches the transistors Q1 and Q2 by supplying a square wave signal of opposite phase to each base of the transistors Q1 and Q2. On and off.

Therefore, the current on the primary side of the transformer T ₁ is interrupted by the on / off operation of the transistors Q ₁ and Q ₂ . Thus, the DC voltage V ₂₂ is developed across the secondary winding as a square-wave-shape AC voltage V ₂₃ having a voltage value corresponding to the winding ratio of the primary winding L ₁ and the secondary winding L _2. Pulsed AC voltage V ₂₃ is the output signal of the pulse voltage generator 1001.

[0010] Next, the analog input signal v _i is input to the pulse width modulator 1005. And the modulation signal generator 1
At 006, it is changed to a pulse signal. This operation will be described with reference to FIGS.

In FIGS. 11 and 12, (a) shows the AC voltage V ₂₃ output from the pulse voltage generator 1001,
(B) the input signal v _i and the triangular wave signal S, (c) the output of modulation signal generator 1006, (d) a pulse width modulator 1
(E) is the waveform of the output of the filter 1008.

First, the input signal v_iWhen there is no signal
This will be described with reference to FIG. As shown in FIG.
Pulse AC voltage V_{twenty three}Have the same positive and negative
It is a pulse-like AC voltage having a duty ratio of 50%. Ma
Further, the modulation signal generator 1006 is provided as shown in FIG.
Generate a triangular wave signal S_iSampling
I do. The output of the modulation signal generator 1006 is shown in FIG.
Input signal v as shown in _iPulse corresponding to the signal level of
It becomes a pulse width signal having a width. Switch 1007 is modulated
It opens and closes according to the output of the signal generator 1006, that is, a modulated signal.
AC voltage V at the output of signal generator 1006_{twenty three}The pulse width of
To adjust the filter, the filter 1008 is shown in FIG.
Such a waveform is input. The filter 1008 is shown in FIG.
Coil L as shown in_Three, L_Four, Capacitor C_Two, C_ThreeFrom
Is a low-pass filter for the pulse width modulator 1005.
The output is integrated to obtain a waveform as shown in FIG.
In FIG. 11D, since the positive and negative pulse widths are equal,
The output of filter 1008 will be zero.

[0013] Then, the input signal v _i is described with reference to FIG. 12 the operation when the such waveform shown in FIG. 12 (b). Modulation signal generator 1006, the input signal v _i and the triangular wave signal S
Compared to the pulse positive greater than the amplitude value amplitude value of the triangular wave signal S of the input signal v _i, for generating a negative pulse is smaller. FIG. 12C shows this, and the output of the pulse width modulator 1005 is shown in FIG.
(E) next to FIG. 12 when integrating this signal with a filter 1008, the input signal v _i is power amplification, to drive the load R _L.

[0014]

However, in the above-mentioned conventional configuration, since the frequency of the pulse AC voltage is not synchronized with the triangular wave signal which is the sampling clock of the pulse width modulation means, even if the input signal is zero, the output can be reduced. There has been a problem that the generation of an offset voltage at which a signal is generated, or the occurrence of waveform distortion occurs because a pulse corresponding to the signal of the modulation signal generator cannot be input to the filter when an input signal is present.

Further, since the controller for controlling the generation of the pulsed AC voltage generates only a clock signal having a predetermined frequency with a duty ratio of 50%, the fluctuation of the input AC voltage, the impedance of the transformer, the switch and the filter, and the impedance of the load. Cannot cope with the voltage fluctuation caused by the above, there is a problem that the voltage value of the pulse AC voltage fluctuates and waveform distortion occurs in the output waveform.

Further, since the filter is connected to both ends of the coil on the secondary side of the high frequency transformer, the signal demodulated into a low frequency signal by the filter flows to the secondary side of the high frequency transformer. However, the high-frequency transformer has a problem that the signal waveform supplied to the load is largely distorted because the high-frequency transformer does not have a sufficient ability to pass a low-frequency signal.

The present invention solves the above-mentioned conventional problems. By synchronizing the frequency of the pulse AC voltage with the sampling clock of the pulse density modulation means, the pulse width distortion of the amplified pulse can be removed and the output signal of the output signal can be eliminated. It is possible to reduce the occurrence of waveform distortion and to control the pulse AC voltage generation means so that the voltage value generated in the coil provided on the primary side of the high-frequency transformer becomes constant, thereby enabling the input AC voltage to be reduced. And the impedance of the transformer, switch, filter, and load by controlling the pulse voltage generation means so that the voltage value of the voltage generated on the secondary side of the high-frequency transformer becomes constant. To eliminate the effect of the low frequency signal generated by the filter by providing switches at both ends of the secondary coil of the high frequency transformer And to provide a power amplifier which allows the waveform distortion is reduced by a configuration that does not flow to the secondary side of the high-frequency transformer.

[0018]

To achieve this object, a power amplifier according to the present invention comprises a pulse voltage generating means for generating a pulsed AC voltage, and a pulsed AC voltage output from the pulse voltage generating means. Pulse density modulating means for modulating the pulse density of the pulse signal according to the input signal, and filter means for limiting the frequency band of the output signal of the pulse density modulating means. It has a configuration that is synchronized with the clock.

Further, the power amplifier of the present invention has a configuration in which the voltage generated in the winding provided on the primary side of the high frequency transformer in the pulse voltage generating means is constant.

Further, the power amplifier of the present invention has a configuration in which the voltage value of the pulsed AC voltage generated on the secondary side of the high-frequency transformer in the pulse voltage generating means is constant.

[0021]

According to the present invention, the following operations are performed by the above configuration. That is, the pulse voltage generating means applies a DC voltage supplied from a DC power supply to the primary side of the high frequency transformer in synchronization with the sampling clock of the pulse density modulation means, and generates a pulsed AC voltage on the secondary side. Further, the pulse density modulating means samples the input signal in synchronization with the sampling clock and converts it into a pulse signal. Based on this signal, the pulse density of the pulsed AC voltage generated on the secondary side of the high frequency transformer is modulated according to the input signal. The filter means limits the frequency band of the output signal of the pulse density modulation means, and drives the load with the output signal obtained by power-amplifying the input signal.

Further, according to the present invention, the following operation is achieved by the above-described configuration. That is, the pulse voltage generating means applies the DC voltage supplied from the DC power supply to the primary side of the high-frequency transformer in synchronization with the sampling clock of the pulse density modulation means.
A pulse-like AC voltage is generated on the secondary side by applying the voltage. Also,
The pulse density modulation means samples the input signal in synchronization with the sampling clock and converts it into a pulse signal.
Based on this signal, the pulse density of the pulsed AC voltage generated on the secondary side of the high frequency transformer is modulated according to the input signal. By the way, there is a separately provided winding on the primary side of the high-frequency transformer, and the sampling clock is controlled so that a voltage obtained by rectifying and smoothing the AC voltage generated in this winding becomes a constant value. The filter means limits the frequency band of the output signal of the pulse density modulation means, and drives the load with the output signal obtained by power-amplifying the input signal.

Further, the present invention has the following operation by the above-mentioned configuration. That is, the pulse voltage generating means applies the DC voltage supplied from the DC power supply to the primary side of the high-frequency transformer in synchronization with the sampling clock of the pulse density modulation means.
A pulse-like AC voltage is generated on the secondary side by applying the voltage. Also,
The pulse density modulation means samples the input signal in synchronization with the sampling clock and converts it into a pulse signal.
Based on this signal, the pulse density of the pulsed AC voltage generated on the secondary side of the high frequency transformer is modulated according to the input signal. By the way, the sampling signal is 2
The voltage generated in the rectifying / smoothing circuit separately provided on the next side is controlled to be constant. The filter means limits the frequency band of the output signal of the pulse density modulation means, and drives the load with the output signal obtained by power-amplifying the input signal.

[0024]

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

FIG. 1 is a block diagram of a power amplifier according to a first embodiment of the present invention. In FIG. 1, reference numeral 101 denotes a pulse voltage generator for generating a pulsed AC voltage;
2, 103 are input terminals of the pulse voltage generator 101, 10
4 is a rectifier and smoother for converting an AC voltage to a DC voltage, 105
Is a full-wave rectifier, 106 is a capacitor, 107 is an inverter that converts a DC voltage into a pulsed AC voltage, 108 is a transistor, 109 is a high-frequency transformer, 110 is a controller that controls the transistor 108, and 111 and 112 are pulse voltage generators. A half-wave rectifier for half-wave rectifying the output of the device 101;
Density modulator 114 for pulse density modulation of the output of
Is an input terminal for inputting an input signal, 115 is a pulse generator for converting the input signal into a pulse signal, 116 is a switch that opens and closes based on the output of the pulse generator 115, 117 is a required band from the output signal of the switch 116 Filters, 118 and 119 are coils forming the filter 117, 120 and 121 are capacitors forming the filter 117, 122 is an output terminal, and 123 is a load.

FIG. 2 shows an example of a specific circuit of the pulse density modulator 113 according to the first embodiment of the present invention.
01 is an adder for adding the input signal input from the input terminal 114 and the output signal of the pulse density modulator 113;
Is an integrator that integrates the output signal of the adder 201, 203 is a comparator that determines the polarity of the output signal of the integrator 202, 204 is a clock generator that generates a clock signal from a control signal generated by the controller 110, and 205 is a clock generator. A D-type flip-flop that latches an output signal of the comparator 203 based on an output clock of the clock generator 204;
Reference numeral 6 denotes a driver for amplifying the output signal of the D-type flip-flop 205, and reference numerals 207 and 208 denote transistors which are turned on / off based on the output of the driver 206.

FIG. 3 is an explanatory diagram for explaining pulse width distortion. 4 and 5 are explanatory diagrams of the operation of the power amplifier according to the first embodiment of the present invention. In FIG. 4, (a) shows the output signal of the half-wave rectifier 111 and (b) shows the output of the half-wave rectifier 112. (C) is an input signal supplied to the input terminal 114, (d) is an output signal of the clock generator 204, (e)
Is the output signal of the pulse generator 115, and (f) is the switch 1
16 (g) is an output signal of the filter 117.

The operation of the thus configured power amplifier of the first embodiment of the present invention will be described below.

The power amplifier according to the first embodiment of the present invention comprises a pulse voltage generator 101, a pulse density modulator 113 and a filter 117. Pulse voltage generator 10
1 converts an AC voltage supplied from a commercial AC power supply into a pulsed AC voltage. Next, the pulse density modulator 113 modulates the pulse AC voltage in accordance with the input signal. Then, the filter 117 obtains a power-amplified audio signal by band-limiting the pulse AC voltage subjected to the pulse density modulation, and drives the load 123 connected to the output terminal 122.

The operation of each section will be described below in detail. The pulse voltage generator 101 has input terminals 102 and 1
03, a rectifying / smoothing device 104 including a full-wave rectifier 105 and a capacitor 106, and an inverter 107 including a transistor 108, a high-frequency transformer 109, and a controller 110.
It is composed of

An AC voltage V1 supplied from a commercial AC power supply is applied between the input terminals 102 and 103. The applied AC voltage V1 is converted into a DC voltage V2 by the rectifier / smoothing device 104. That is, after being full-wave rectified by the full-wave rectifier 105, it is smoothed by the capacitor 106.

Next, the DC voltage V2 is supplied to the inverter 107.
Are converted into pulsed AC voltages V3, V4 and V5.
That is, the controller 110 uses the same frequency as the sampling clock of the pulse density modulator 113 and the duty ratio 50
Generate a% clock. The transistor 108 turns on and off based on the output clock of the controller 110. Accordingly, a DC voltage V2 is intermittently applied to the primary winding of the high-frequency transformer 109, and a pulse-like AC voltage V3 similar to the clock generated by the controller 110 is applied to both ends of the primary winding. Occurs. Accordingly, the secondary winding of the high-frequency transformer 109 whose middle point is grounded has a pulse AC voltage V3 generated in the primary winding proportional to the winding ratio of the primary winding to the secondary winding. The pulse AC voltages V4 and V5, which are similar to each other and are opposite in phase, are generated. These pulse AC voltages V4 and V5 are connected to half-wave rectifiers 111 and 1 respectively.
The half-wave rectification is performed at 12. These waveforms are shown in FIG.
Alternatively, they are shown in FIGS.

The pulse density modulator 113 has an input terminal 11
4. It is composed of a pulse generator 115 and a switch 116.

The input signal v _i supplied to the input terminal 114
Is converted into a pulse signal by the pulse generator 115. That is, the pulse generator 115 generates a sampling clock from the clock generated by the controller 110. Then, the input signal v _i is transformed to the sampled pulse density modulated signal. Next, the switch 116 performs pulse density modulation on the pulse AC voltage supplied from the half-wave rectifiers 111 and 112 based on the output of the pulse generator 115.

Here, a specific circuit example of the pulse generator 115 and the switch 116 will be described with reference to FIG.

The clock output from the controller 110 is
Input to the clock generator 204. Clock generator 2
04 or FIG. 5 synchronized with the input clock.
(D) is generated. The adder 201 calculates the difference between the output signal of the input signal v _i and pulse density modulator 113 which is input from the input terminal 114. The integrator 202 integrates the output of the adder 201. Next, the comparator 203 determines the polarity of the output signal of the integrator 202. The D-type flip-flop 205 samples the output of the comparator 203 based on the sampling clock generated by the clock generator 204. Here, the D-type flip-flop 205
The output of a pulse density modulation signal sampled at the sampling clock generated by the clock generator 204 to the input signal v _i. Next, the driver 206 amplifies the output signal of the D-type flip-flop 205 so that the transistors 207 and 208 can be driven. Then, the transistors 207 and 208 perform on / off operations complementarily according to the output of the driver 206. That is, the half-wave rectifier 11
And pulse density modulation in response to the input signal v _i the pulse AC voltage supplied from 1 and 112.

The filter 117 includes coils 118 and 11
9 and capacitors 120 and 121 as a ladder-type filter. Then, constants of the coils 118 and 119 and the capacitors 120 and 121 are set so as to pass a signal in the audio band.

The pulse density modulator 113 and the filter 11
7 will be described. First, the input signal v _i is the operation when no signal will be described with reference to FIG.

In FIG. 4, (a) and (b) are pulse AC voltages supplied by the half-wave rectifiers 111 and 112, respectively, and are rectangular waves having mutually opposite phases and a duty ratio of 50%. (C) the input signal v _i, (d) a pulse AC voltage (a), a waveform of a sampling clock synchronized with (b). When a pulse density modulation in the pulse generator 115 to the input signal v _i a waveform (e). Next, switch 1
16 shows a waveform (f) when the pulse AC voltages (a) and (b) are subjected to pulse density modulation based on the output of the pulse generator 115.
Becomes In the waveform (f), since the number of positive pulses and the number of negative pulses are equal to each other and the areas are equal, the filter 11
When the processing is performed in step 7, the output becomes no signal as shown in the waveform (g).

Next, will be described with reference to FIG. 5 the operation when the input signal v _i is not no signal. 5, the output waveform of the input signal v _i, such as the waveform (c) is inputted pulse generator 115, a waveform (e). When the switch 116 is driven based on the waveform (e), the pulse AC voltages (a) and (b) are subjected to pulse density modulation to become a waveform (f). Treatment of the waveform (f) in the filter 117, the input signal v _i to the similar power amplified signal as the waveform (g) is obtained.

Incidentally, a pulse width distortion as shown in FIG. 3C is generated in the pulse density modulation signal output from the pulse generator 115. That is, when the pulse generator 115 is in the ideal state, the output waveform of the pulse generator 115 changes as shown in FIG. 3B at the rising edge of the sampling clock shown in FIG. However, in an actual circuit, it is as shown in FIG. It can be seen from the comparison with FIG. 3B that a pulse width distortion as shown occurs. In this state, when a DC voltage is supplied to the switch 116 and the DC voltage is subjected to pulse density modulation, the switch 11
The output 6 is an output signal similar to that of FIG. Thus, the pulse width distortion is amplified as it is.

However, in the power amplifier according to the first embodiment of the present invention, by adopting the above configuration, the pulse train of the pulse generator 115 has a pulse width as shown in FIG. , And the pulse width distortion is removed.

As described above, in the first embodiment of the present invention,
By performing pulse density modulation of a pulsed AC voltage in accordance with an input signal, a power amplifier having high power conversion efficiency without generating pulse width distortion is configured.

FIG. 6 is a block diagram showing a power amplifier according to a second embodiment of the present invention. In FIG. 6, reference numeral 601 denotes a pulse voltage generator for generating a pulsed AC voltage;
2, 603 are input terminals of the pulse voltage generator 601;
Reference numeral 4 denotes a rectifying / smoothing device for converting an AC voltage to a DC voltage,
Is a full-wave rectifier, 606 is a capacitor, 607 is an inverter that converts a DC voltage to a pulsed AC voltage, 608 is a transistor, 609 is a high-frequency transformer, 610 is a winding provided on the primary side of the high-frequency transformer 609, and 611 is A winding provided on the primary side of the high-frequency transformer 609, 612 is a half-wave rectifier for half-wave rectifying the pulse voltage generated in the winding 611, 613 is a capacitor for smoothing the output of the half-wave rectifier 612, and 614 is a transistor 608. 615, 616 are half-wave rectifiers for half-wave rectification of the output of the pulse voltage generator 601; 617, a pulse density modulator for pulse-density-modulating the output of the pulse voltage generator 601 according to the input signal; Is an input terminal for inputting an input signal,
619, a pulse generator for converting an input signal into a pulse signal; 620, a switch that opens and closes based on the output of the pulse generator 619; 621, a filter that passes a required band from an output signal of the switch 620; 622, an output terminal;
23 is a load.

FIGS. 7 and 8 are explanatory diagrams of the operation of the power amplifier according to the second embodiment of the present invention.
(A) is the output signal of the rectifier / smoothing device 604, (b) is the output signal of the half-wave rectifier 615, (c) is the output signal of the half-wave rectifier 616, (d) is the input signal supplied to the input terminal 618, (E) is the output signal of the clock generator 204, (f)
Is the output signal of the pulse generator 619, and (g) is the switch 6
20 is an output signal, and (h) is an output signal of the filter 621.

The operation of the thus configured power amplifier of the second embodiment of the present invention will be described below.

The power amplifier according to the second embodiment of the present invention comprises a pulse voltage generator 601, a pulse density modulator 617, and a filter 621. Pulse voltage generator 60
1 converts an AC voltage supplied from a commercial AC power supply into a pulsed AC voltage. Next, the pulse density modulator 617 performs pulse density modulation on the pulse AC voltage according to the input signal. Then, the filter 621 obtains a power-amplified audio signal by band-limiting the pulse AC voltage subjected to the pulse density modulation, and drives the load 623 connected to the output terminal 622.

The details of the operation of each section will be described below. The pulse voltage generator 601 has input terminals 602 and 6
03, a full-wave rectifier 605 and a capacitor 606, a rectifier / smoothing unit 604, a transistor 608, a high-frequency transformer 609, and a half-wave rectifier for half-wave rectifying a pulse voltage generated in a winding 611 provided on the primary side of the high-frequency transformer 609. 612 and a capacitor 607 for smoothing the half-wave rectified voltage and a controller 614.

In FIG. 6, input terminals 602 and 60
3, the full-wave rectifier 605, the capacitor 606, the transistor 608, and the high-frequency transformer 609 are the input terminals 102 and 103, the full-wave rectifier 105, and the capacitor 1 shown in FIG.
06, the transistor 108, and the high-frequency transformer 109 perform exactly the same operation.

First, an AC voltage V6 supplied from a commercial AC power source applied between the input terminals 602 and 603 is converted into a DC voltage V7 by the rectifier / smoothing unit 604.

Next, the DC voltage V7 is supplied to the inverter 607.
Is converted into pulsed AC voltages V8, V9 and V10.
That is, the controller 614 generates a clock having a duty ratio of 50% if the AC voltage V6 does not change at the same frequency as the sampling clock of the pulse density modulator 617, that is, if the DC voltage V7 does not change. Transistor 6
08 turns on / off based on the output clock of the controller 614. Accordingly, a DC voltage V7 is intermittently applied to the primary winding of the high-frequency transformer 609, and a pulse-like AC voltage similar to the clock generated by the controller 614 is applied to both ends of the primary winding 610. V8 occurs. Accordingly, the secondary winding of the high-frequency transformer 609 whose middle point is grounded has a pulse AC generated in the primary winding 610 proportional to the winding ratio of the primary winding 610 and the secondary winding. Voltage V
Pulsed alternating voltages V9 and V similar in phase to each other and similar to 8
10 occurs.

On the other hand, on the primary side of the high-frequency transformer 609,
The pulse AC voltage V₈Proportional to
(The proportionality coefficient is the number of windings of the windings 610 and 611.
AC voltage V)₁₁Occurs. Half wave
The flower 612 has a pulse AC voltage V ₁₁Rectifying the capacitor
613 smoothes the DC voltage V₁₂Convert to here
Then, the controller 614 outputs the DC voltage V₁₂Has a predetermined voltage value.
Reference voltage V₁₃Is determined. Now, the AC voltage V₆
Is constant, the DC voltage V₁₂Is also constant and the reference
Pressure V₁₃be equivalent to. However, the AC voltage V₆Fluctuates
And the DC voltage V₇, Pulse AC voltage V₈, V₉, V_Ten, V
₁₁And DC voltage V₁₂Also fluctuate. Therefore, the DC voltage V
₁₂Is the reference voltage V₁₃And different. However, the controller 614
Is the DC voltage V₁₂And reference voltage V₁₃Control so that
Change the duty ratio of the clock generated by the detector 614.
Let That is, the DC voltage V₁₂> Reference voltage V₁₃Then tiger
The period during which the transistor 608 is on is reduced, and the DC voltage V₁₂
<Reference voltage V₁₃When transistor 608 is on
Of the clock generated by the controller 614 so that the interval becomes longer.
Change the duty ratio. These pulse AC voltages
V₉And V_TenAre half-wave rectifiers 615 and 616, respectively.
And is supplied to the pulse density modulator 617.
You.

The pulse density modulator 617 is connected to the input terminal 61
8, a pulse generator 619 and a switch 620.

The pulse density modulator 617 in FIG.
At all have lines of the same operation as pulse density modulator 113 in FIG. 1, in the second embodiment of the present invention, a pulse density modulator
The clock generator 204 shown in FIG.
Controls the clock output from the modulator in the controller 614.
Roux or something to pass through (although the electrical interface
Signal amplitude matching so that
You.

The input signal v _i supplied to the input terminal 618
Is converted into a pulse signal by the pulse generator 619. Next, the switch 620 performs pulse density modulation on the pulse AC voltage supplied from the half-wave rectifiers 615 and 616 based on the output of the pulse generator 619.

The filter 621 in FIG. 6 performs exactly the same operation as the filter 117 in FIG.

When the AC voltage V ₆ fluctuates, the second
The operation of this embodiment will be described with reference to FIGS. Here, an operation when the input signal v _i shown in (d) of FIG. 7 or FIG. 8 is input.

[0058] Figure 7, when the controller 614 does not control the duty ratio of the output clock of the controller 614 so as to coincide with DC voltage V ₁₂ and the reference voltage V _13, that is, outputs a duty ratio of 50% of the clock Indicates when DC voltage V ₇ by the AC voltage V ₆ is varied to that change as in (a) of FIG. Here, the broken line is a voltage value V _dd0 when the AC voltage V ₆ unchanged. DC voltage V ₇
Change as shown in FIG. 7A, the output voltages of the half-wave rectifiers 615 and 616 become as shown in FIGS. 7B and 7C, respectively. That is, the duty ratio is 50%, the voltage value is changed according to the change of the DC voltage V _7. On the other hand, the input voltage v _i shown in (d) of FIG. 7, the pulse generator 619, a pulse-density modulation, is converted into a pulse signal shown in (f) of FIG. When the switch 620 is turned on / off by this pulse signal, a waveform shown in FIG. 7 (g) is obtained. This is applied to the filter 621.
When the signal is band-limited and demodulated into an audio signal, the waveform shown by the solid line in FIG. The waveform when the input signal vi is ideally amplified is shown by a broken line in FIG.
The difference between the solid line and the broken line is hatched. That is, FIG. 7 is a waveform distortion when the voltage value of the AC voltage V ₆ is changed indicates the occurrence.

FIG. 8 shows that the controller 614 controls the DC voltage V₁₂And base
Reference voltage V₁₃Output clock of controller 614 so that
This shows a case where the duty ratio of the clock is controlled. In FIG.
(A) is the AC voltage V₆Indicates fluctuation. Here, the broken line
Current voltage V₆When the voltage does not change_dd0And Controller
The output of the half-wave rectifiers 615 and 616
The force voltages are as shown in FIGS. 8B and 8C, respectively.
That is, the DC voltage V₇Is V_dd0Pal when constant
AC voltage V₉And V_TenThe pulse width changes so that
You can see that it is. This is similar to FIG.
Input voltage v shown in (d) _iIs the pulse density modulator 617
FIG. 8 (g) shows the output waveform when the signal is input to. this
Is band-limited by the filter 621 to return to an audio signal.
FIG. 8 (h) shows the result of adjustment, and is similar to FIG. 8 (d).
Shape and no waveform distortion.

As described above, in the second embodiment of the present invention,
Pulse width modulation of a pulsed AC voltage according to an input signal does not cause pulse width distortion, and further stabilizes a voltage value of a pulse AC voltage generated in a primary winding of a high-frequency transformer. Thus, a power amplifier with high power conversion efficiency that does not cause waveform distortion even when the voltage value of the commercial AC power supply fluctuates is configured.

FIG. 9 is a block diagram showing a power amplifier according to a third embodiment of the present invention. In FIG. 9, reference numeral 901 denotes a pulse voltage generator for generating a pulsed AC voltage;
2, 903 are input terminals of the pulse voltage generator 901;
4 is a rectifier / smoothing device for converting an AC voltage into a DC voltage;
Is a full-wave rectifier, 906 is a capacitor, 907 is an inverter that converts a DC voltage into a pulsed AC voltage, 908 is a transistor, 909 is a high-frequency transformer, and 910 is a half-pulse AC voltage generated on the secondary side of the high-frequency transformer 909. 911 is a capacitor for smoothing the output of the half-wave rectifier 910, and 912 is a transistor 90
8, 913 and 914 are half-wave rectifiers for half-wave rectifying the output of the pulse voltage generator 901, and 915 is a pulse density modulator for pulse-modulating the output of the pulse voltage generator 901 according to the input signal. , 916, an input terminal for inputting an input signal, 917, a pulse generator that converts the input signal into a pulse signal, 918, a switch that opens and closes based on the output of the pulse generator 917, 919, a required band from the output signal of the switch 918 Filter 920
Is an output terminal, and 921 is a load. Here, the high-frequency
The secondary side of the lance 909 has a center tap type structure
That is, the center tap is grounded and used. Where the center
-The structure of the tap type winding is
Configuration, and one end of two independent windings
The same applies to connecting a tap and tapping.

The operation of the thus configured power amplifier of the third embodiment of the present invention will be described below.

The power amplifier according to the third embodiment of the present invention comprises a pulse voltage generator 901, a pulse density modulator 915, and a filter 919. Pulse voltage generator 90
1 converts an AC voltage supplied from a commercial AC power supply into a pulsed AC voltage. Next, the pulse density modulator 915 performs pulse density modulation of the pulse AC voltage according to the input signal. Then, the filter 919 obtains a power-amplified audio signal by band-limiting the pulse AC voltage subjected to the pulse density modulation, and drives the load 921 connected to the output terminal 920.

The details of the operation of each section will be described below. The pulse voltage generator 901 has input terminals 902 and 9
And a rectifying / smoothing device 904 comprising a full-wave rectifier 905 and a capacitor 906; a transistor 908; a high-frequency transformer 909; and a half-wave rectifier 910 for half-wave rectifying the pulse AC voltage V17 generated on the secondary side of the high-frequency transformer 909.
And a capacitor 911 for smoothing the half-wave rectified voltage and an inverter 907 including a controller 912.

In FIG. 9, input terminals 902 and 90
3, the full-wave rectifier 905, the capacitor 906, the transistor 908, and the high-frequency transformer 909 are the input terminals 102 and 103, the full-wave rectifier 105, and the capacitor 1 shown in FIG.
06, the transistor 108, and the high-frequency transformer 109 perform exactly the same operation.

First, the AC voltage V14 supplied from the commercial AC power supply applied between the input terminals 902 and 903 is converted into the DC voltage V15 by the rectifier / smoothing unit 904.

Next, the DC voltage V15 is supplied to the inverter 907.
Are converted into pulsed AC voltages V16, V17 and V18. That is, the controller 912 generates a clock with a duty ratio of 50% unless the pulse AC voltage V17 fluctuates at the same frequency as the sampling clock of the pulse density modulator 915. The transistor 908 is turned on / off based on the output clock of the controller 912. Accordingly, a DC voltage V15 is intermittently applied to the primary winding of the high-frequency transformer 909, and a pulse similar to the clock generated by the controller 912 is applied to both ends of the primary winding of the high-frequency transformer 909. AC voltage V16 is generated. Therefore, the secondary winding of the high-frequency transformer 909 whose middle point is grounded has 1
Pulsed alternating voltages V17 and V18 having opposite phases and being similar to the pulsed AC voltage V16 generated on the primary winding in proportion to the winding ratio of the secondary winding and the secondary winding are generated.

On the other hand, when a tone signal is used as the input signal v _i , the amplitude level changes over time, such as a sharp increase in amplitude. When a speaker is used as a load, the impedance of the load has frequency characteristics. Accordingly, the current supplied to the load 921 changes. However, the winding of the high-frequency transformer 909 has impedance. Then, a voltage drop occurs in the winding of the high-frequency transformer 909. Therefore, the load 921 will not be supplied current corresponding to the input signal v _i, waveform distortion occurs.

Therefore, on the secondary side of the high-frequency transformer 909,
Generated pulse AC voltage V₁₇Rectifier 910
The capacitor 911 smoothes this, and the DC voltage V₁₉To
Convert. Here, the controller 912 outputs the DC voltage V₁₉Place
Reference voltage V having a constant voltage value ₂₀Is determined.

Now, if the pulse AC voltage V ₁₇ is constant,
DC voltage V ₁₉ is also constant and equal to the reference voltage V _20. Then, a clock having a duty ratio of 50% is output from the controller 912.

[0071] However, when the pulse AC voltage V ₁₇ is varied, also varies the DC voltage V _19. Therefore, the DC voltage V ₁₉
It is different from the reference voltage V _20. However, the controller 912
The controller 9 controls the DC voltage V ₁₉ and the reference voltage V _{20 to} be equal.
12 changes the duty ratio of the clock generated. That is, if the DC voltage V ₁₉ > the reference voltage V ₂₀ , the ON period of the transistor 908 is reduced, and the DC voltage V ₁₉ <
For reference voltage V ₂₀ changes the duty ratio of the clock controller 912 so transistor 908 is the time on the longer occurs. High frequency transformer 909-2
The pulse AC voltages V ₁₇ and V ₁₈ generated on the secondary side are half-wave rectified by half-wave rectifiers 913 and 914, respectively. Then, it is supplied to the pulse density modulator 915.

The pulse density modulator 915 has an input terminal 91
6, a pulse generator 917 and a switch 918.

The pulse density modulator 917 in FIG.
At all have lines of the same operation as pulse density modulator 113 in FIG. 1, in the third embodiment of the present invention, a pulse density modulator
The clock generator 204 shown in FIG.
Controls the clock output by the modulator in the controller 912.
Roux or something to pass through (although the electrical interface
Signal amplitude matching so that
You.

The input signal v _i supplied to the input terminal 916
Is converted into a pulse signal by the pulse generator 917. Next, the switch 918 performs pulse density modulation on the pulse AC voltage supplied from the half-wave rectifiers 913 and 914 based on the output of the pulse generator 917. Pulse density modulator 91
The output of No. 5 is supplied to a filter 919 and band-limited, and an audio signal is supplied to a load 921 via an output terminal 920.

The filter 919 in FIG. 9 performs exactly the same operation as the filter 117 in FIG.

[0076] Here, the operation of the third embodiment of the present invention when the pulse AC voltage V ₁₇ occurs a voltage drop by the impedance of the winding of the high-frequency transformer 909 is varied with reference to FIGS. 7 and 8 described I do. Here, an operation when the input signal v _i shown in (d) of FIG. 7 or FIG. 8 is input.

FIG. 7 shows a case where the controller 912 does not control the duty ratio of the output clock of the controller 912 so that the DC voltage V ₁₉ matches the reference voltage V ₂₀ , that is, outputs a clock having a duty ratio of 50%. Indicates that
Half-wave rectifier by pulse AC voltage V ₁₇ is varied 9
13 and 914 are output from FIGS. 7B and 7C, respectively.
Let's say that it has changed. That is, the duty ratio is 50%
Although, the voltage value is changed in accordance with changes in the pulse AC voltage V _17. On the other hand, the input voltage v _i shown in FIG. 7 (d)
Are subjected to pulse density modulation in a pulse generator 917 and converted into a pulse signal shown in FIG. When the switch 918 is turned on / off by this pulse signal, a waveform shown in FIG. 7 (g) is obtained. When this is band-limited by the filter 919 and demodulated into an audio signal, a waveform shown by a solid line in FIG. In FIG. 7H, the waveform when the input signal vi is ideally amplified is shown by a broken line, and the difference between the solid line and the broken line is hatched.
That is, FIG. 7 shows that the waveform distortion occurs when the voltage value of the pulse AC voltage V ₁₇ is varied.

FIG. 8 shows a case where the controller 912 controls the duty ratio of the output clock of the controller 912 so that it matches the DC voltage V ₁₉ and the reference voltage V ₂₀ . When the pulse AC voltage V ₁₇ is varied similarly to FIG. 7, a half-wave rectifier 913
And 914 change as shown in FIGS. 7B and 7C, respectively. However, by the operation of the controller 912, the output voltages of the half-wave rectifiers 913 and 914 are as shown in FIGS. 8B and 8C, respectively. That is, the pulse AC voltage V
_It can be seen that the pulse width changes so that the voltage value of ₁₇ becomes constant. This similarly to FIG. 7, the input voltage v _i shown in (d) of FIG. 8, the output waveform of the input time to the pulse density modulator 915 is (g) in FIG. 8. This is band-limited by the filter 919 and demodulated to an audio signal as shown in FIG. 8 (h), which is similar to FIG. 8 (d) and has no waveform distortion.

As described above, in the third embodiment of the present invention,
By pulse-modulating the pulsed AC voltage according to the input signal, no pulse width distortion occurs.
By stabilizing the voltage value of the pulse high-current voltage generated in the secondary winding of the high-frequency transformer, the waveform distortion occurs even if the voltage value of the commercial AC voltage fluctuates or a voltage drop occurs due to the impedance of the high-frequency transformer winding. This constitutes a power amplifier with high power conversion efficiency in which no power generation occurs. Incidentally, the present invention
In the third embodiment, the rectifying / smoothing circuits 910 and 911 and the
High-frequency transformer 909 connected to density modulator 915
The secondary winding is shared, but independent.
The same effect can be obtained by using a winding
Needless to say.

[0080]

As described above, according to the present invention, since the occurrence of pulse width distortion can be eliminated by synchronizing the frequency of the pulse AC voltage with the sampling clock of the pulse density modulation means, the occurrence of waveform distortion of the output signal can be eliminated. Can be obtained.

Further, by controlling the pulse voltage generator so that the voltage generated in the coil provided on the primary side of the high-frequency transformer becomes constant, fluctuations in the input AC voltage can be eliminated, so that the output voltage can be reduced. The effect of enabling the occurrence of signal waveform distortion to be reduced can be obtained.

Further, by controlling the pulse voltage generator so that the voltage value of the voltage generated on the secondary side of the high frequency transformer becomes constant, the voltage drop due to the impedance of the high frequency transformer (modulated by the input signal, load impedance, etc.) ) Can be removed, so that the effect of reducing the occurrence of waveform distortion of the output signal can be obtained.

Further, by connecting the midpoint of the winding on the secondary side of the high-frequency transformer to ground and connecting to the switching element via a half-wave rectifier at both ends of the winding, a low-voltage supply to the load demodulated by the filter is achieved. Since a configuration in which the frequency signal is not passed to the secondary side of the high-frequency transformer can be realized, the effect of enabling the occurrence of waveform distortion of the output signal to be reduced can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a power amplifier according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a specific configuration of the pulse density modulator of the first embodiment.

FIG. 3 is an operation explanatory diagram for explaining the operation of the first embodiment;

FIG. 4 is an operation explanatory diagram for explaining the operation of the first embodiment;

FIG. 5 is an operation explanatory diagram for explaining the operation of the first embodiment;

FIG. 6 is a block diagram showing a configuration of a power amplifier according to a second embodiment of the present invention.

FIG. 7 is an operation explanatory diagram for explaining the operation of the second embodiment.

FIG. 8 is an operation explanatory diagram for explaining the operation of the second embodiment.

FIG. 9 is a block diagram showing a configuration of a power amplifier according to a third embodiment of the present invention.

FIG. 10 is a block diagram showing a configuration of a conventional load driving device.

FIG. 11 is an operation explanatory diagram for explaining the operation of the conventional example.

FIG. 12 is an operation explanatory diagram for explaining the operation of the conventional example.

[Explanation of symbols]

 Reference Signs List 101 pulse voltage generator 102, 103, 114 input terminal 104 rectifier smoother 105 full-wave rectifier 106, 120, 121 capacitor 107 inverter 108 transistor 109 high-frequency transformer 110 controller 111, 112 half-wave rectifier 113 pulse density modulator 115 pulse generation Container 116 Switch 117 Filter 118, 119 Coil 122 Output terminal 123 Load

──────────────────────────────────────────────────続 き Continuation of the front page (56) References Japanese Utility Model Showa 54-96135 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) H03F 3/217

Claims (4)

(57) [Claims] 1. A pulse voltage generating means for generating a pulse-like AC voltage, and a pulse-like AC voltage which is not rectified and smoothed from a pulse-like AC voltage output from said pulse voltage generating means .
Pulse density modulation means for performing pulse density modulation of a pulse density of an output voltage of the pulse voltage generation means in accordance with an input signal, and filter means for limiting a frequency band of an output signal of the pulse density modulation means. A power amplifier, characterized in that: 2. A pulse voltage generating means for controlling a high-frequency transformer having a winding 1 on a primary side and a winding 2 on a secondary side, and applying a DC voltage supplied from a DC power supply to the winding 1 The control means applies a DC voltage supplied from a DC power supply to the winding 1 in synchronization with a sampling clock of the pulse density modulation means, and applies a pulse synchronized to the sampling clock to the winding 2 2. The power amplifier according to claim 1, wherein the power amplifier generates a constant AC voltage. 3. A high-frequency transformer having a winding 1 and a winding 2 on a primary side and a winding 3 on a secondary side, and rectifies and smoothes an AC voltage generated in the winding 2 on a primary side. Smoothing means, control means for controlling application of a DC voltage supplied from a DC power supply to the winding 1, and control means for generating a clock having a predetermined frequency.
And a duty cycle of a clock generated by the oscillation means.
Modulating means for modulating an input ratio, and an output signal of the modulating means
A switch for opening and closing in synchronization with the modulation means;
Means that the amplitude value of the output signal of the smoothing means becomes a constant value.
The duty ratio of the clock of the output of the oscillation means is
Modulates, and the switch controls the output clock of the modulating means.
Modulating a duty ratio, wherein the switch is provided with the modulation means
To the winding 1 of the high-frequency transformer in synchronization with the output of
Applying a DC voltage supplied from a power supply;
Generating a pulsed alternating voltage on line 3, the pulse density
The modulating means samples the output signal of the modulating means.
Features pulse density modulation of input signal as lock
The power amplifier according to claim 1, wherein 4. A high-frequency transformer having a winding 1 on a primary side and windings 2 and 3 on a secondary side and rectifying and smoothing an AC voltage generated on the winding 2 on a primary side. Smoothing means, control means for controlling application of a DC voltage supplied from a DC power supply to the winding 1, and control means for generating a clock having a predetermined frequency.
And a duty cycle of a clock generated by the oscillation means.
Modulating means for modulating an input ratio, and an output signal of the modulating means
A switch for opening and closing in synchronization with the modulation means;
Means that the amplitude value of the output signal of the smoothing means becomes a constant value.
The duty ratio of the clock of the output of the oscillation means is
Modulates, and the switch controls the output clock of the modulating means.
Modulating a duty ratio, wherein the switch is provided with the modulation means
DC power supply to winding 1 of high-frequency transformer in synchronization with the output of
DC voltage supplied from the
Generating pulsed AC voltage, pulse density modulation means
The output signal of the modulation means as a sampling clock
A pulse density modulation of the input signal.
The power amplifier according to claim 1.