DE102007063344A1 - Audio output stage for electrostatic flat surface loudspeaker in motor vehicle, has matching circuit including transformer and arranged between audio output stage for electrodynamic loudspeaker and electrostatic flat surface loudspeaker - Google Patents

Abstract

The output stage (1) has an audio output stage (2) for an electrodynamic loudspeaker, and a matching circuit arranged between the stage (2) and an electrostatic flat surface loudspeaker (20). The matching circuit has a transformer (3) including a center tap (4) connected to an input of a direct current to direct current converter (5), where a bias voltage of the loudspeaker (20) is applied at an output of the converter. An impedance matching circuit is arranged between the stage (2) and the transformer.

Description

The The invention relates to an audio output stage for an electrostatic Area loudspeaker and a suitable matching circuit, in particular for use in a motor vehicle.

From the WO 99/56498 For example, an acoustic element is known comprising at least two porous layers that are electrically conductive or metallized on one side. Between the two porous layers, an insulated plastic layer is arranged, which is preferably formed in two layers, wherein between the two layers is a metallic coating, via which the plastic layer can be charged to a certain electrical potential (bias voltage). At certain points, the plastic layer is connected to the porous layers. Between two such interfaces is an air gap between the porous layers and the plastic layer. By applying a signal to at least one porous layer, the plastic layer is then caused to vibrate, wherein preferably also the other porous layer is subjected to the antiphase signal. This arrangement represents an electrostatic surface speaker.

These need electrostatic flat panel speakers new audio power amps, as these have much higher output voltages at the audio power amp. So is the Bias voltage, for example -320 V and the voltage between the two porous layers are in the range of 500 V. Conventional audio power amplifiers for electrodynamic speakers in a motor vehicle, however, typically have output voltages of a maximum of 40 Vss (peak-to-peak).

Of the The invention is therefore based on the technical problem, a suitable Audio power amplifier for an electrostatic flat speaker and to provide a matching circuit suitable for this purpose, that are simple in construction.

The Solution of the technical problem results from the objects with the features of claims 1 and 5. Further advantageous Embodiments of the invention will become apparent from the dependent claims.

For this includes the audio power amplifier for an electrostatic Area speaker an audio power amplifier for a electrodynamic speakers and a matching circuit, the between the audio power amplifier for an electrodynamic loudspeaker and the electrostatic area speaker is, wherein the matching circuit at least one transformer includes. This will cause the output voltages of the audio power amp for an electrodynamic speaker to the necessary High voltages for an electrostatic flat loudspeaker stepped up.

Preferably the transformer has a center tap on an input a DC / DC converter is connected, wherein at the output of the DC / DC converter the bias voltage of the electrostatic surface speaker is arranged. At the upper tap of the secondary coil is then the first signal voltage for the first electrode of the electrostatic Area loudspeaker tapped. At the bottom tap of the Secondary coil then becomes the second, by 180 ° to first signal voltage out of phase signal voltage tapped, then the second electrode of the electrostatic surface speaker is supplied. The DC / DC converter converts a nearly constant Input voltage at a further input of the DC / DC converter, for example the 12 V of a motor vehicle electrical system to the constant bias voltage from, for example, +300 V -380 V at the output of the DC / DC converter. By the consideration of the voltage at the center tap over the other input can be unbalanced in the output voltage the audio output stage of an electrodynamic speaker balanced become. But there are also possible designs, where the Center tap not routed to an input of the DC / DC converter is.

In Another preferred embodiment is between the audio power amplifier for an electrodynamic loudspeaker and the transformer, an impedance matching circuit arranged preferably from a parallel circuit of a resistor and a capacitor, to which in series another resistor is arranged. In addition to the adaptation of the transformer to the audio power amplifier The impedance matching is for the audio power amplifier and the transformer the capacitive load of the electrostatic Can drive surface speaker without distortion, preferably even at frequencies greater than 20 kHz. This decreases the harmonic distortion and the sound quality increase.

The Invention will be described below with reference to a preferred embodiment explained in more detail. The only figure shows one Schematic structure of an audio power amplifier for an electrostatic flat-panel loudspeaker.

The audio power amplifier 1 for an electrostatic flat speaker 20 includes an audio power amplifier 2 for an electrodynamic loudspeaker, a transformer 3 with center tap 4 and a DC / DC converter 5 , Between the audio power amplifier 2 and the transformer 3 is an im arranged pedanzanpassungsschaltung, which consists of a parallel connection of an ohmic resistance R1 and a capacitor C1, to which a further ohmic resistance R2 is connected in series. Between a primary coil 6 and a secondary coil 7 with the center tap 4 is a transformer sheet 8th arranged to increase the coupling. The upper tap of the secondary coil 7 is with a first electrode 21 of the electrostatic surface speaker 20 connected. The lower tap of the secondary coil 7 is with a second electrode 22 of the electrostatic surface speaker 20 connected. Between the two electrodes 21 . 22 is a plastic layer 23 arranged, which is rechargeable to a certain electrical potential, namely the bias voltage. This is the plastic layer 23 formed, for example, two-ply, wherein between the two plastic layers, a metal coating is arranged, which is connected to the output of the DC / DC converter 5 connected is. The input voltage of the DC / DC converter 5 is, for example, the 12 V vehicle electrical system voltage of a motor vehicle, which is then set to 300-380 V. In addition, there is an input of the DC / DC converter 5 with the center tap 4 of the transformer 3 connected. Its voltage is taken into account when boosting, so that the bias voltage on the plastic layer 23 Unbalances of the audio power amplifier 2 and / or the transformer 3 balances. Through the transformer 3 In this case, for example, the output voltage of 40 Vpp at the output of the audio power amplifier 2 up to 600 Vpp at the output of the audio power amplifier 1 stepped up.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• WO 99/56498 [0002]

Claims (6)

Audio power amplifier ( 1 ) for an electrostatic flat loudspeaker ( 20 ), comprising an audio power amplifier ( 2 ) for an electrodynamic loudspeaker and a matching circuit connected between the audio power amplifier ( 2 ) for an electrodynamic loudspeaker and the electrostatic surface loudspeaker ( 20 ), wherein the matching circuit comprises at least one transformer ( 3 ). Audio power amplifier according to claim 1, characterized in that the transformer ( 3 ) a center tap ( 4 ) connected to an input of a DC / DC converter ( 5 ), wherein at the output of the DC / DC converter ( 5 ) the bias voltage of the electrostatic surface speaker ( 20 ) is present. Audio power amplifier according to claim 1 or 2, characterized in that between the audio output stage ( 2 ) for an electrodynamic loudspeaker and the transformer ( 3 ) An impedance matching circuit is arranged. Audio power amplifier according to claim 3, characterized that the impedance circuit of a parallel circuit of a Resistor (R1) and a capacitor (C1), to which in Row another resistor (R2) is arranged. Adjustment circuit for an electrostatic flat-panel loudspeaker ( 20 ), comprising a transformer ( 3 ) with center tap ( 4 ) and a DC / DC converter ( 5 ), whereby the middle tap ( 4 ) to an input of the DC / DC converter ( 5 ) and at the output of the DC / DC converter ( 5 ) the bias voltage is applied. Matching circuit according to claim 5, characterized in that in front of the transformer ( 3 ) An impedance matching circuit is connected.