JP2007166165A - Audio digital amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital amplifier the distortion (ripple) caused between speaker terminals of which is smaller than that of the conventional digital amplifiers and in which sound quality is improved and input/output capacitors are made compact. <P>SOLUTION: The audio digital amplifier provided with: two step-down inverters connected in parallel; a speaker connected between output terminals of the inverters; and capacitors each at least connected between the output terminal of each step-down inverter and a negative terminal or a positive terminal of a DC power supply, is characterized in to include a drive control section that symmetrically turns on/off a pair of series switches SHa and SLa of one of the step-down inverters, symmetrically turns on/off a pair of series switches SHb and SLb of the other of the step-down inverters in an opposite phase to the turning on/off above, and applies two-phase drive to two pairs of the switches with a phase difference between the pairs. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an audio digital amplifier for realizing a low output voltage ripple characteristic.

Since the audio digital amplifier is highly efficient and can be reduced in size and weight, the demand for audio digital amplifiers has been increasing in recent years including portable devices. In general, a full bridge type digital amplifier as shown in Patent Document 1 (Japanese Patent Laid-Open No. 2003-273656) is used as the digital amplifier. This circuit is shown in FIG.
In FIG. 9, a pair of step-down inverters INV1 and INV2 are connected in parallel to the input DC power supply Ei, and the step-down inverter INV1 is provided with a pair of switch elements SHa and SLa, and is intermediate between the switch element SHa and the switch element SLa. And a speaker SP input terminal, an inductor La is provided, a capacitor Ca is provided between the output side of the inductor La and the negative terminal of the input DC power supply Ei, and the step-down inverter INV2 includes a pair of switch elements SHb and SLb. The inductor Lb is provided between the middle of the switch element SHb and the switch element SLb and the speaker SP input terminal, and the capacitor Cb is provided between the output side of the inductor Lb and the negative terminal of the input DC power supply Ei.
In the switching control, among the four switch elements, the switches SHa and SLa are turned on / off symmetrically, and are turned on / off with respect to SHb and SLb in the opposite phase.

Circuit example 2 shown in FIG. 13 is an inverter circuit that is generally used for a motor drive or the like. This circuit is different from FIG. 9 in that one capacitor CSP is provided between the outputs of the inductors La and Lb. As shown in FIG. 14, the switches of this circuit are driven in two phases with a phase difference of 180 degrees. That is, the pair of switches SHb and SLb are switched with a phase difference of 180 ° between the pair of switches SHa and SLa. By doing so, the AC components of the currents iLa and iLb flowing through the inductors La and Lb become smaller as the volume of the speaker is lower, so that the voltage distortion and efficiency of the speaker can be improved. However, since this inverter circuit is in a state where the speaker is floating from the ground (GND), common mode noise cannot be ignored when applied to an audio digital amplifier. It is also difficult to detect the speaker voltage.
JP 2003-273656 A JP 2005-109590 A

An object of the present invention is to reduce distortion caused by a speaker of a digital amplifier.

The digital amplifier according to the present invention has two step-down inverters in parallel, a speaker is connected between the output terminals of these inverters, and at least between the negative terminal and / or the positive terminal and the output terminal of each step-down inverter. In an audio digital amplifier in which a capacitor is provided in a single stage or multiple stages and at most a capacitor is provided between the output terminals of each step-down inverter in addition to the capacitor,
A pair of series switches of one step-down inverter are turned on / off symmetrically, and the pair of series switches of the other step-down inverter are turned on / off symmetrically. An audio digital amplifier, characterized in that a drive control unit for providing a switch with a phase difference for two-phase driving is provided.
That is, the audio digital amplifier of the present invention has the same basic configuration as that of the conventional full-bridge digital amplifier and the main circuit shown in FIG. Instead of operating as a bridge circuit, the two pairs of switch elements are switched at different phases as in the inverter circuit shown in FIG.

The audio digital amplifier of the present invention improves the sound quality because the distortion (ripple) generated between the speaker terminals can be reduced without increasing the number of parts of the main circuit by the above configuration. Furthermore, the input / output capacitor and the inductor can be reduced in size.

The best mode for carrying out the invention will be described with the following examples.

FIG. 1 shows a circuit diagram of Embodiment 1 of an audio digital amplifier according to the present invention. FIG. 2 shows waveforms of switching control of each part of the circuit of FIG. In FIG. 1, the main circuit configuration is the same as in FIG. 9, and the same parts are denoted by the same reference numerals. A pair of step-down inverters INV1 and INV2 are connected in parallel to the input DC power supply Ei, and the step-down inverter INV1 Is provided with a pair of switch elements SHa and SLa, an inductor La is provided between the switch element SHa and the middle of the switch element SLa and the speaker SP input terminal, and between the output side of the inductor La and the negative terminal of the input DC power supply Ei Is provided with a capacitor Ca, and the step-down inverter INV2 is provided with a pair of switch elements SHb, SLb, and an inductor Lb is provided between the switch element SHb and the middle of the switch element SLb and the speaker SP input terminal. A capacitor Cb is provided between the output side and the negative terminal of the input DC power supply Ei.
For the drive control of the switch, the two-phase drive control unit Dri is used to turn on and off the switches SHa and SLa symmetrically, and on the other hand, the SHb and SLb are turned on and off symmetrically. However, these two pairs of switches are driven in two phases with a phase difference of 180 degrees.

As Example 2, various examples of connection methods of capacitors and inductors will be introduced.
There are a plurality of connection method examples as described in the above feature, and FIG. 3 to FIG. 7 show connection examples. Further, it is possible to connect a plurality of capacitors and inductors, and an example of a two-stage connection is shown in FIG. In any of these switch drive controls, the ripple reduction effect can be obtained by the switch drive control similar to that shown in FIG.
3 to 8, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted. Only the capacitor arrangement will be introduced next.
The capacitor arrangement in FIG. 3 is such that capacitors CHa, CHb, CLa, and CLb are provided between the negative and positive terminals of the input DC power supply Ei and the output terminals of the inductors La and Lb of each step-down inverter INV1 and INV2. is there.
The capacitor arrangement in FIG. 4 is such that capacitors Ca and CSP are provided between the negative terminal of the input DC power supply Ei and the output terminals of the inductors La and Lb of the step-down inverters INV1 and INV2.
The capacitor arrangement in FIG. 5 is such that capacitors Ca and Cb are provided between the plus terminal of the input DC power supply Ei and the output terminals of the inductors La and Lb of the step-down inverters INV1 and INV2.
The capacitor arrangement in FIG. 6 is such that a capacitor Ca is provided between the positive terminal of the input DC power supply Ei and the output terminal of the inductor La of each step-down inverter INV1, and further the negative terminal of the input DC power supply Ei and the inductor of the step-down inverter INV2. A capacitor Cb is provided between the output terminal of Lb.
In the capacitor arrangement in FIG. 7, a capacitor Ca is provided between the positive terminal of the input DC power supply Ei and the output terminal of the inductor La of the step-down inverter INV1, and further, the output terminal of the inductor La of the step-down inverter INV1 and the step-down inverter INV2. The capacitor CSP is provided between the output terminal of the inductor Lb.
The capacitor arrangement in FIG. 8 is such that the capacitor Ca is placed between the negative terminal and / or positive terminal of the input DC power supply Ei and the output terminals of a pair of series inductors La, Lb and La ′, Lb ′ of the step-down inverters INV1 and INV2. , Ca ′, Cb, and Cb ′.
In addition to this, there are a plurality of examples of capacitor arrangements, but in any case, at least one capacitor is connected to the minus terminal or the plus terminal of the input DC power supply Ei, that is, is grounded.

Audio digital amplifiers are more efficient than analog amplifiers and can be miniaturized, so they are beginning to be used in portable electronic devices where miniaturization and improved battery life are important. It also contributes to miniaturization and low power consumption of flat-screen TVs, 5.1ch theater systems, and car audio.

1 is a circuit diagram of an audio digital amplifier according to Embodiment 1. FIG. FIG. 3 is a voltage / current waveform diagram of each part of the audio digital amplifier circuit according to the first embodiment. FIG. 6 is a circuit diagram illustrating an example of a method for connecting a capacitor and an inductor as Example 2; It is a circuit diagram which introduces two examples of the connection method of a capacitor | condenser and an inductor like FIG. FIG. 4 is a circuit diagram for introducing three examples of a method of connecting a capacitor and an inductor as in FIG. 3. It is a circuit diagram which introduces four examples of the connection method of a capacitor | condenser and an inductor like FIG. FIG. 4 is a circuit diagram for introducing five examples of a method of connecting a capacitor and an inductor as in FIG. 3. FIG. 4 is a circuit diagram for introducing six examples of a method of connecting a capacitor and an inductor as in FIG. 3. It is a circuit diagram which shows the conventional full bridge type digital amplifier example 1. FIG. It is the audio | voice input waveform of the conventional full bridge type digital amplifier example 1, and a speaker both-ends voltage waveform. It is a speaker both-ends voltage waveform when the LC filter of the conventional full bridge type digital amplifier example 1 is made small. 6 is a voltage / current waveform of each part of a circuit of a conventional full-bridge digital amplifier example 1; It is a circuit diagram which shows the conventional full bridge type digital amplifier example 2. FIG. It is a voltage-current waveform of each part of the circuit of the conventional full bridge type digital amplifier example 2.

Explanation of symbols

Ei input DC power supply
SHa, SHb, SLa, SLb Switch element
Ca, Cb, CHa, CHb, CLa, CLb, CSP, Ca ', Cb' capacitors
La, Lb, La ', Lb' inductors
SP speaker

Claims (1)

Two step-down inverters are connected in parallel, a speaker is connected between the output terminals of these inverters, and a capacitor is provided between the negative terminal and / or the positive terminal and the output terminal of each step-down inverter, or the capacitor In other audio digital amplifiers with capacitors between the output terminals of each step-down inverter,
A pair of series switches of one step-down inverter are turned on / off symmetrically, and the pair of series switches of the other step-down inverter are turned on / off symmetrically. An audio digital amplifier comprising a two-phase drive control unit for causing a switch to have a phase difference and two-phase driving.

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