High-performance audio amplifier

Abstract

The present invention relates to a high-performance audio amplifier (102) intended to control at least one loudspeaker (R44), the amplifier comprising a preamplifier stage (301) receiving an input signal (S1), a power amplifier stage (302) connected to the preamplifier stage (301), and a negative feedback loop delivering an image of an output signal (3) to the preamplifier stage (301), the power amplifier stage (302) comprising two power supply circuits (155a, 155b), the two power supply circuits comprising MOSFET transistors (M1, M2). The present invention is characterized in that it comprises: a subcircuit for assisting charging, a subcircuit for assisting discharging of the MOSFET transistors (M1, M2), and a voltage shifting subcircuit.

Description

Technical Field

[0001] The present invention relates to the field of amplifiers and in particular to a high-power audio amplifier intended to control at least one loudspeaker.

[0002] High-power amplifiers have specific applications in providing sound in recording studios or concert halls. They are particularly used to power electrodynamic loudspeakers.

[0003] The invention advantageously makes it possible to obtain a high-power audio amplifier having better efficiency than amplifiers of the prior art while ensuring low distortion. Background Art

[0004] Conventionally, a high power amplifier comprises at least one active component, such as a transistor or a tube, making it possible to amplify the power of a signal received as input while maintaining the shape of the input signal.

[0005] The circuitry of a high-power amplifier typically includes a preamplifier stage followed by a power amplifier stage. More precisely, the output of the power amplifier stage is fed back to the preamplifier stage, so that the preamplifier stage detects the difference between the output signal and the input signal over time, for example, using a differential pair. This difference detected in the preamplifier stage is then amplified in the power amplifier stage to form an output signal, which is conventionally sent to at least one loudspeaker.

[0006] Thus, by way of example, Figure 1 illustrates a high power amplifier 100 with an input signal applied at point S1. The output of the high power amplifier 100 powers a loudspeaker connected between point 3 and ground, the loudspeaker being represented by resistor R44.

[0007] The diagram of the high power amplifier 100 is symmetrical; it also comprises an upper portion 140a which amplifies the positive half-wave of the input signal S1 and a lower portion 140b which amplifies the negative half-wave of the input signal S1.

[0008] In the example of FIG. 1 , the high power amplifier 100 is powered by a single voltage level of + / - 65V.

[0009] The preamplifier stage 201 includes two differential pairs 110a, 110b, each of which includes two transistors Q1, Q2 and Q3, Q4 that are mirror images of each other. Thus, the emitters of the transistors Q1, Q2 are connected to the -65V power bus via resistors R2, R3 and a first constant current source I, while the emitters of the transistors Q3, Q4 are connected to the +65V power bus via resistors R4, R5 and a second current source of the same value I.

[0010] The collectors of transistors Q2 and Q4 are connected to the +65V and -65V power buses, respectively, while the collectors of transistors Q1 and Q3 are connected to the +65V and -65V power buses via resistors R1 and R11, respectively. Without feedback, the gain of preamplifier stage 201 depends on the resistor ratios R1 / R2 and R11 / R4.

[0011] The bases of transistors Q1 and Q3, as well as the bases of transistors Q2 and Q4, are connected to one another. The bases of transistors Q1 and Q3 are also powered by input signal S1. The bases of transistors Q2 and Q4 are connected to speaker R44 via resistor R18 to form feedback for the preamplifier stage. The collectors of transistors Q1 and Q3 ensure coupling between preamplifier stage 201 and power amplifier stage 202.

[0012] The power amplifier stage 202 includes two transistors Q8 and Q9, whose respective bases are connected to the preamplifier stage 201 via resistors R23 and R57. A voltage source T1 is also placed between resistors R23 and R57 to bias the class AB transistors Q8 and Q9. This voltage source T1 is capable of providing a voltage equal to the sum of the voltages required to turn on transistors Q8 and Q9.

[0013] Transistors Q8 and Q9 are also connected to the +65V and -65V power busses, respectively, via their collectors. The emitters of transistors Q8 and Q9 are connected to speaker R44 via resistors R16 and R17. Resistors R16 and R17 are added to control quiescent current, that is, the amount of current conducted by the amplifier when no input signal is being applied. Without resistors R16 and R17, the quiescent current would depend on the characteristics of transistors Q8 and Q9, as well as temperature, which is prohibitive.

[0014] Furthermore, the circuit of FIG. 1 exhibits a peculiarity in the bases of transistors Q2 and Q4. The latter is connected to a protection line 403 comprising a resistor R28 connected in series with a capacitor C4 connected to ground. This component forms a voltage divider, such that the voltage at point S2 is equal to R28 / (R18+R28) multiplied by the voltage of the output signal 3 in AC. In practice, when the voltage across the circuit is alternating, capacitor C4 behaves like a short circuit. On the other hand, when the voltage across the circuit is DC, capacitor C4 behaves like an open circuit. In this case, the output signal 3 of the high-power amplifier 100 is directly connected to point S2. The voltage gain of the high-power amplifier 100 is thus equal to 1, which makes it possible to limit any potentially undesirable DC components in the voltage applied to the terminals of the loudspeaker R44.

[0015] In this type of amplifier, the voltage measured at point S1 relative to ground and the voltage measured at point S2 relative to ground are equal. In other words, the gain of the high power amplifier 100 is equal to the ratio of the resistor values ​​(R18+R28) / R28.

[0016] Thus, a high power voltage amplifier is illustrated in Figure 1. There is another class of high power current amplifiers, as shown in Figure 2.

[0017] This type of high power current amplifier 101 has the same topology as the high power voltage amplifier 100 , namely a pre-amplification stage 201 coupled to an amplifier stage 203 .

[0018] 1, a current measuring resistor R6 is inserted between the speaker R44 and the ground. In addition, the current amplifier 101 does not have a protection line 403. The bases of the transistors Q2 and Q4 are connected to an interconnection point P1 between the resistor R6 and the speaker R44.

[0019] In this configuration, the image of the current applied at point S2 in FIG3 thus passes through the loudspeaker R44. It follows that the transconductance (i.e., the ratio between the output current through the loudspeaker R44 and the input voltage applied at point S1 of the amplifier 101) is equal to 1 / R6 A / V. For a loudspeaker with an impedance of Z, the voltage gain is Z / R6.

[0020] Therefore, the voltage or current amplification components are similar, especially with respect to the preamplification stage and the power amplifier stage. They differ only in terms of the speaker connections and feedback.

[0021] In the following prior art, other types of amplifiers will be described with reference to voltage amplifiers, although the present invention is not limited to this type of amplifier.

[0022] Different high power amplifier topologies can be characterized using a class system that assigns letters based on the relationship between the shape of the input signal and the shape of the output signal, and the duration that the active components are used during amplification of the input signal.

[0023] Among existing amplifier classes, Class A amplifiers have a topology that causes the active components to conduct a high current, approximately 50% of the maximum output current, in the absence of an input signal. This current is known as the quiescent current. During modulation, this current is superimposed on the output current. This type of amplifier can provide excellent sound quality, but it has the disadvantage of generating significant heat. Consequently, the energy efficiency of this type of amplifier, defined as the ratio between effective output power and absorbed power, is approximately 10%.

[0024] Class B amplifiers are characterized by a topology that causes the active components to conduct for 50% of the input signal cycle when a sinusoidal input signal is applied. For this type of amplifier, the quiescent current is zero. This type of amplifier has higher efficiency than a Class A amplifier, but the output signal's distortion characteristics are significantly degraded compared to Class A amplifiers. Consequently, Class B amplifiers produce lower-quality sound. Manufacturers rarely use this type of amplifier today.

[0025] Class AB amplifiers are characterized by a topology that keeps the active components conducting for 100% of the input signal cycle, but with a low quiescent current of approximately 1% of the maximum output current. This type of amplifier has higher energy efficiency than Class A amplifiers, typically between 30% and 50%, but with lower sound quality. Therefore, Class AB amplifiers offer a good compromise between performance and energy efficiency.

[0026] Class D amplifiers use technology in which active components act like switches. Pulse-width modulation is then used to convert the signal. This system increases energy efficiency to approximately 70%. However, the output signal contains more noise and distortion, making it difficult to reproduce high frequencies with this type of amplifier.

[0027] Class G amplifiers have several power supply buses that can be switched from one to another depending on the power output requirements. This allows for improved energy efficiency by reducing the power dissipated in the active components.

[0028] Class H amplifiers use a power bus whose supply voltage "follows" or is modulated by the input signal. Typically, they have two supply buses, like those in Class G, but only the highest supply voltage is modulated. Modulated power is often implemented using Class D amplifiers.

[0029] The subject matter of the present invention relates in particular to these last two types of amplifiers.

[0030] FIG3 illustrates the upper portion of the power amplifier stage 204. The latter is connected to the power supply circuit 150. Of course, the power amplifier stage also includes a lower portion (not shown) that mirrors the upper portion using an equivalent power supply circuit. Similarly, the circuit also includes a preamplifier stage, which is connected to an independent power supply or to a strong power bus that is also connected to the power supply circuit 150.

[0031] The power supply circuit 150 allows the power level of the power amplifier stage 204 to be selected to suit the amplifier power requirements. Thus, when the amplifier voltage is greater than a threshold, a first, stronger power bus must be used, while when the amplifier voltage is below the threshold, a second, weaker power bus can be used. This lower power bus usage improves the overall efficiency of the amplifier compared to class A, B, and AB amplifiers.

[0032] Furthermore, power supply circuit 150 has a structure independent of preamplifier stage 201 and power amplifier stage 204. In the example of FIG3 , power amplifier stage 204 includes transistor Q10, whose base is connected to the emitter of transistor Q8. This so-called "Darlington" configuration increases current gain. The emitters of transistors Q8 and Q10 are coupled to speaker R44 via their respective resistors R16 and R19. These emitters have respective quiescent currents of, for example, 6 mA for transistor Q8 and 75 mA for transistor Q10.

[0033] The power amplifier stage 204 is connected to a power supply circuit 150 at the collectors of transistors Q8 and Q10. This power supply circuit 150 is connected to two voltage buses having different levels V+ and V++. Thus, the power supply circuit 150 allows one or the other of these voltage levels to be selected depending on the amplification requirements. Typically, the first power supply bus delivers 65V and the second power supply bus delivers 35V. The second power supply bus is intended to be used to power the power amplifier stage 204 when the output signal to be generated does not have a very high voltage (typically less than 32V).

[0034] Since the current through transistor Q8 is relatively low, typically less than 10% of the current through transistor Q10, the collector of transistor Q8 can be directly connected to the first power bus V++ without incurring significant additional power consumption. This embodiment can improve the stability of the amplifier, which is easily damaged when operating as a current amplifier.

[0035] To select the appropriate voltage level, MOSFET transistor M1 is connected directly to the first power bus V++ via its drain and to the second power bus V+ via its source via a fourth diode D3. MOSFET transistor M1 normally switches to a threshold of 27V and then operates linearly above this threshold. When a control voltage greater than the threshold is applied to MOSFET transistor M1, MOSFET transistor M1 turns on the first power bus V++. This voltage is controlled by the relationship between first diodes D8 and D10 connected between the gate of MOSFET transistor M1 and speaker R44, and second resistors R8 and R27 connected between the drain and gate of MOSFET transistor M1.

[0036] A diode D15 is connected between the collector of the transistor Q10 and the speaker R44, with the cathode of the diode being connected to the collector of the transistor Q10.

[0037] FIG4 illustrates the different signals obtained using this assembly.

[0038] Thus, the signal numbered 1 in Figures 3 and 4 represents the gate signal of MOSFET transistor M1. The output signal numbered 3 in Figures 3 and 4 represents the output signal of the amplifier, that is, the signal at the terminals of loudspeaker R44. The output signal numbered 2 in Figures 3 and 4 represents the output signal of power supply circuit 150. We thus notice that output signal 3 is distorted. In fact, the peak of the sinusoidal curve is flattened and shifted around 27 μs. This saturation of output signal 3 is explained by the fact that the supply voltage of MOSFET transistor M1 is insufficient for the amplifier to correctly deliver the output voltage.

[0039] Likewise, Signal 2 has an abnormal voltage peak between 40 and 47 μs, corresponding to an overvoltage at the gate of MOSFET transistor M1. This results in power loss and degradation of amplifier efficiency.

[0040] The technical problem proposed by the present invention is therefore to obtain a high-power audio amplifier which makes it possible to limit the distortions discernible on the signal and thus to increase the efficiency and reduce the saturation of the amplifier. Summary of the Invention

[0041] To solve this problem, the present invention proposes a power supply circuit including a MOSFET transistor controlled by a subcircuit for auxiliary charging, a subcircuit for auxiliary discharging, and a voltage shifting subcircuit, thereby achieving better efficiency of the amplifier while limiting saturation and distortion of the amplifier output signal.

[0042] In other words, the invention relates to a high-power audio amplifier intended to control at least one loudspeaker, said amplifier comprising:

[0043] - a preamplifier stage, which receives an input signal;

[0044] a power amplifier stage connected to the preamplifier stage and providing an output signal intended to power the at least one loudspeaker; the preamplifier stage and the power amplifier stage having upper and lower parts mounted in mirror image;

[0045] - feedback, which provides an image of the output signal to the pre-amplification stage;

[0046] - an upper power supply circuit connected to the upper part of the power amplifier stage and allowing it to be powered by the first or second power bus;

[0047] - a lower power supply circuit connected to the lower part of the power amplifier stage and allowing it to be powered by the first or second power bus;

[0048] - Each power supply circuit includes a MOSFET transistor and a monitoring device, the MOSFET transistor being controlled by the monitoring device so as to switch between one or the other of the two power supply buses, the MOSFET transistor being connected to the second power supply bus via a fourth diode, the first terminal of the fourth diode being connected to the source of the MOSFET transistor, and the drain of the MOSFET transistor being connected to the first power supply bus.

[0049] The present invention is characterized in that each power supply circuit further includes:

[0050] - a subcircuit for assisting in charging the MOSFET transistor, comprising at least a first resistor, a first terminal of the first resistor being connected to the gate of the MOSFET transistor and a second terminal of the first resistor being connected to the interconnection point;

[0051] a subcircuit for assisting in discharging the MOSFET transistor, comprising at least a second resistor and a third resistor and a bipolar transistor; the base of the bipolar transistor being connected to the first terminal of the third resistor, the emitter thereof being connected to the gate of the MOSFET transistor, and the collector thereof being connected to the source of the MOSFET transistor via the second resistor, the second terminal of the third resistor being connected to the interconnection point; and

[0052] - a voltage shifting subcircuit comprising a first diode mounted in parallel with the first capacitor; a first terminal of the first diode and a first terminal of the first capacitor connected to a first interconnection node; a second terminal of the first diode and a second terminal of the first capacitor connected to a second interconnection node.

[0053] In particular, the subcircuit for auxiliary charging allows the MOSFET transistor to charge more quickly. In practice, this subcircuit first includes a first resistor, preferably of a high resistance value, approximately 15 kΩ, so as not to exchange too much energy with the amplifier output and generate more distortion. This first resistor allows only a low current to flow to charge or discharge the gate of the MOSFET transistor. The gate behaves like a capacitor; however, the combination of the MOSFET transistor and the first resistor increases the duration of the charging and discharging times.

[0054] The auxiliary discharge subcircuit allows the MOSFET transistor to discharge faster. The bipolar transistor makes it possible to discharge the gate of the MOSFET transistor in particular when the sinusoidal input signal is in its falling phase.

[0055] The voltage shift subcircuit ensures that the gate potential of the MOSFET transistor is always higher than the potential of the amplifier output. Typically, the gate potential of the MOSFET transistor can be 15V higher than the potential of the amplifier output. The voltage shift subcircuit also compensates for voltage drops in the MOSFET transistor.

[0056] According to a second embodiment, the voltage shifting subcircuit further comprises at least a fourth resistor and a second diode mounted in parallel, wherein a first terminal of the second diode and a terminal of the fourth resistor are connected to the first interconnection node, and a second terminal of the fourth resistor and a second terminal of the second diode are connected to the third interconnection node.

[0057] The addition of these components makes it possible to reduce the distortion observed on the amplifier output signal.This improvement in distortion is effective for sinusoidal input signals if they have a relatively low frequency, ie around 1 kHz.

[0058] Advantageously, according to the third embodiment, the subcircuit for auxiliary charging further comprises a fifth resistor mounted in series with the third diode, the fifth resistor and the third diode being mounted in parallel with the branch of the subcircuit for auxiliary charging comprising the first resistor.

[0059] A third diode, mounted in parallel with the first resistor, allows the flow of current intended to charge the gate of the MOSFET transistor and blocks the flow of current intended to discharge the gate of the MOSFET transistor. The fifth resistor preferably has a low value, i.e., approximately 300Ω. Since the charging time constant is equal to the product of resistance and capacitance, this fifth resistor allows for faster charging of the gate of the MOSFET transistor.

[0060] The addition of these components again improves the distortion of sinusoidal input signals up to a frequency of 20 kHz. Consequently, distortion is improved across the entire frequency spectrum. Consequently, the sound reproduction of loudspeakers connected to the amplifier of the present invention is improved. The listener perceives less distortion than with amplifiers of the prior art.

[0061] According to a fourth embodiment, the voltage shifting subcircuit further comprises a second capacitor and a third capacitor, the second capacitor being arranged in parallel with the first capacitor and the first diode, and the third capacitor being arranged in parallel with the third diode and the fifth resistor. These additional components make it possible to limit interference, i.e., interfering signals superimposed on the desired output signal.

[0062] In practice, each power supply circuit includes a first protection diode having a first terminal connected to the source of the MOSFET transistor and a second terminal connected to the gate of the MOSFET transistor. Similarly, each power supply circuit also includes a second protection diode connected between the source and drain of the MOSFET transistor.

[0063] The first protection diode is added in order to protect the MOSFET transistor from overvoltages on its gate which could damage the MOSFET transistor or even render it unusable by breaking the insulation between the gate and the channel, which can only withstand + / - 20V continuously and + / - 30V momentarily.

[0064] The purpose of the second protection diode is to protect the MOSFET transistor from reverse drain-source voltage, which may occur if the voltage of the first power bus appears only after the voltage of the second power bus. The different power buses each have their own transformer windings and smoothing capacitors and therefore have different time constants.

[0065] According to a fifth embodiment, each power supply circuit further comprises a capacitor mounted in parallel with the fourth diode. This capacitor makes it possible to eliminate interference peaks generated by the diode when the MOSFET transistor switches, the first terminal of the diode being connected to the source of the MOSFET transistor. Harmonic distortion (THD) is also improved. This harmonic distortion is a measure of the linearity of the processing performed. It is calculated by comparing the output signal of the device with a perfect sinusoidal input signal.

[0066] In practice, the preamplifier stage is connected to the first power bus of each power supply circuit via a circuit for damping power variations of the first power bus, the power variation damping circuit comprising at least one capacitor and at least one resistor configured as a low-pass filter. In other words, the resistor is connected in series with the capacitor, which is connected to ground.

[0067] This component provides isolation from noise and voltage drops, which occur particularly when high-voltage amplifiers deliver high currents. The capacitor acts as an energy storage device.

[0068] Advantageously, the power variation damping circuit further comprises an additional capacitor mounted in parallel with the at least one capacitor. The capacitor mounted in parallel has a more moderate value, typically 103 times lower. This allows for the suppression of high-frequency interferences.

[0069] According to a specific embodiment of the present invention, feedback applied to the preamplifier stage provides a signal proportional to the current through the speaker. This embodiment enables the realization of a high-power current amplifier. As described with reference to FIG. 2 of the prior art, this type of high-power current amplifier has the same topology as a high-power voltage amplifier, namely, a preamplifier stage coupled to an amplifier stage. However, the feedback applied to the preamplifier stage is different.

[0070] By using the power supply circuit of the present invention in a high-power current amplifier, the power consumption of the high-power current amplifier is very limited.

[0071] In fact, the power supply circuit of the present invention will not operate when the amplifier delivers a low voltage. Therefore, the power provided by the power supply will be equal to the product of the output current and the voltage delivered by the lower power supply bus, rather than the maximum voltage delivered by the single power supply bus for a standard Class AB amplifier. At equal power, and assuming, for example, that the voltage delivered by the lower power supply bus is equal to half the voltage of the higher power supply bus, the power supply will provide only half the power. The transistor that dissipates the difference between the power provided by the power supply and the power supplied to the speaker will generate significantly less heat. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] The specific manner of implementing the invention and the advantages resulting therefrom will become clear from the following description of an embodiment with the support of the accompanying drawings, in which:

[0073] FIG1 is an electrical diagram of a high power voltage amplifier of the prior art;

[0074] FIG2 is an electrical diagram of a high power current amplifier of the prior art;

[0075] FIG3 is an electrical diagram of a prior art high power voltage amplifier including a power supply stage;

[0076] 4 is a graph showing the evolution of the gate voltage of the MOSFET transistor, the output voltage of the amplifier, and the output signal of the power supply circuit of the circuit of FIG. 3 ;

[0077] Figure 5a and Figure 5b is an electrical diagram of a high power voltage amplifier according to one embodiment of the present invention;

[0078] Figure 6 is an electrical diagram of a power supply circuit of a high power amplifier according to a second embodiment;

[0079] Figure 7 is the gate voltage of the MOSFET transistor, the output voltage of the amplifier, and Figure 6 a graph showing the evolution of an output signal of a power supply circuit of a circuit in the case where the input signal has a sinusoidal curve with a frequency of 20 kHz;

[0080] Figure 8 is the gate voltage of the MOSFET transistor, the output voltage of the amplifier, and Figure 6 a graph showing the evolution of an output signal of a power supply circuit of a circuit in a case where the input signal has a sinusoidal curve with a frequency of 1 kHz;

[0081] Figure 9 is an electrical diagram of a power supply circuit of a high power amplifier according to a third embodiment;

[0082] Figure 10is the gate voltage of the MOSFET transistor, the output voltage of the amplifier, and Figure 9 a graph showing the evolution of an output signal of a power supply circuit of a circuit in the case where the input signal has a sinusoidal curve with a frequency of 20 kHz;

[0083] Figure 11 is the gate voltage of the MOSFET transistor, the output voltage of the amplifier, and Figure 9 a graph showing the evolution of an output signal of a power supply circuit of a circuit in a case where the input signal has a sinusoidal curve with a frequency of 1 kHz;

[0084] Figure 12 is an electrical diagram of a power supply circuit of a high power amplifier according to a fourth embodiment;

[0085] Figure 13 is the gate voltage of the MOSFET transistor, the output voltage of the amplifier, and Figure 12 a graph showing the evolution of an output signal of a power supply circuit of a circuit in the case where the input signal has a sinusoidal curve with a frequency of 20 kHz;

[0086] Figure 14 is an electrical diagram of a power supply circuit of a high power amplifier according to a fifth embodiment;

[0087] Figure 15 is the gate voltage of the MOSFET transistor, the output voltage of the amplifier, and Figure 14 a graph showing the evolution of an output signal of a power supply circuit of a circuit in the case where the input signal has a sinusoidal curve with a frequency of 20 kHz;

[0088] Figure 16 is an electrical diagram of a power supply circuit of a high power amplifier according to the first embodiment of FIG. 5 ;

[0089] Figure 17 is the gate voltage of the MOSFET transistor, the output voltage of the amplifier, and Figure 16 a graph showing the evolution of an output signal of a power supply circuit of a circuit in the case where the input signal has a sinusoidal curve with a frequency of 20 kHz;

[0090] Figure 18a and Figure 18b is an electrical diagram of a high power current amplifier according to an embodiment of the present invention; and

[0091] Figure 19 is an electrical diagram of a protection structure of a high power current amplifier according to an embodiment of the present invention. DETAILED DESCRIPTION

[0092] like Figure 5a to Figure 5bFor example, the high power amplifier 102 of the present invention is symmetrical, which includes amplifying the upper portion of the positive half-wave of the input signal S1 and amplifying the lower portion of the negative half-wave of the input signal S1.

[0093] High-power amplifier 102 includes a preamplifier stage that receives input signal S1 and provides signals from the collectors of transistors Q5 and Q6 via a network consisting of resistors R23 and R57 connected in parallel with capacitors C7 and C8. These signals are supplied to power amplifier stage 302 via transistors Q8 and Q9. The latter provides output signal 3, intended to power loudspeaker R44. Feedback provides an image of output signal 3 to preamplifier stage 201.

[0094] The high power amplifier 102 further includes an upper power supply circuit 155 a connected to an upper portion of the power amplification stage 302 and a lower power supply circuit 155 b connected to a lower portion of the power amplification stage 302 .

[0095] The preamplifier stage 301 includes two differential pairs 110a, 110b, each of which includes two transistors Q1, Q2 and Q3, Q4 mounted in mirror image. Thus, the emitters of the transistors Q1, Q2 are connected to the -65V power bus via resistors R2, R3 and a first constant current source I1, while the emitters of the transistors Q3, Q4 are connected to the +65V power bus via resistors R4, R5 and a second current source of the same value I1.

[0096] Current sources I1 and I2 include transistors Q23 and Q24, respectively, whose collectors are connected to resistors R2 and R3, and R4 and R5, respectively. The emitters of transistors Q23 and Q24 are connected to resistors R6 and R10. The second terminal of resistor R6 is connected to the -65V power bus and to ground via a capacitor C11 connected in series with resistor R46. The second terminal of resistor R10 is connected to the +65V power bus and to ground via a capacitor C12 connected in series with resistor R48.

[0097] Diodes D1, D2 are installed between the bases of transistors Q23, Q24 and the second terminals of resistors R6, R10, while resistors R45, R47 are installed between the bases of transistors Q23, Q24 and the interconnection point between capacitors C11, C12 and resistors R46, R48.

[0098] The collectors of transistors Q2 and Q4 can be directly connected to the +65V and -65V power buses, respectively. Alternatively, the collectors of transistors Q2 and Q4 can be connected to the +65V and -65V power buses, respectively, via power variation damping circuits 304 and 305 .

[0099] Power variation damping circuits 304 and 305 include resistors R52 and R55 connected in series with capacitors C15 and C19 connected to ground. The second terminals of resistors R52 and R55 are connected to the + / -65V power bus. Advantageously, additional capacitors C16 and C20 can be connected in parallel with capacitors C15 and C19. In practice, capacitors C15 and C19 have values ​​between 150 and 300 μF, while capacitors C16 and C20 have values ​​between 150 and 300 nF.

[0100] The collectors of transistors Q1, Q3 are connected to the +65V and -65V supply buses respectively via resistors R1, R11 and advantageously via power variation damping circuits 304, 305. Without feedback, the gain of the first preamplification stage 102 depends on the resistor ratios R1 / R2 and R11 / R4.

[0101] The bases of transistors Q1 and Q3 are connected to each other and to ground via resistor R7. The bases of transistors Q2 and Q4 are also connected to each other. The bases of transistors Q1 and Q3 are supplied with input signal S1. A voltage source V1 connected between point S1 and ground represents the generator of input signal S1. An intermediate filtering circuit can be inserted between input signal S1 and the bases of transistors Q1 and Q3. This circuit comprises, for example, a bandpass filter including resistor R9, capacitor C10 connected to ground, and two capacitors C1 and C6 connected in parallel.

[0102] The bases of transistors Q2 and Q4 are connected to loudspeaker R44 via resistor R18 in order to form feedback applied to preamplifier stage 301. The collectors of transistors Q1 and Q3 ensure coupling of preamplifier stage 301 with circuits 306, 303, 307 and resistors R12, R13.

[0103] The power amplifier stage 302 comprises two transistors Q8 , Q9 , whose respective bases are connected to the pre-amplifier stage 301 via circuits 306 , 307 .

[0104] Circuits 306 and 307 include transistors Q5 and Q6, whose emitters are connected to the + / -65V voltage bus via resistors R12 and R13, and whose bases are connected to the collectors of transistors Q1 and Q3. Capacitors C2 and C3 are connected between the bases and collectors of transistors Q5 and Q6 to improve amplifier stability. The collectors of transistors Q5 and Q6 are connected, on the one hand, to resistors R57 and R23, which are connected in parallel with capacitors C8 and C7, and, on the other hand, to bias circuit 303. The bias circuit includes transistor Q7, whose emitter is connected to the collector of transistor Q5 and whose collector is connected to the collector of transistor Q6. Resistor R14 is connected between the collector and base of transistor Q7, while another resistor R15 is connected between the emitter and base of transistor Q7. Finally, a capacitor C5, for example, having a value of 1 μF, is connected between the emitter and collector of transistor Q7. Capacitor C5 improves amplifier stability. Alternatively, resistors R13, R12 may be connected to the +65V and -65V power buses via power variation damping circuits 304, 305, respectively.

[0105] Circuits 306 and 307 perform a second voltage amplification. The gain of this amplification is proportional to the ratio of the resistance seen by the collector to the resistance present at the emitters of Q5 and Q6. When one of transistors Q5 and Q6 is on, its counterpart is blocked; therefore, the on-state transistor experiences a very high resistance and, therefore, a very significant voltage gain.

[0106] Power amplifier stage 302 also includes two transistors Q10 and Q11, whose bases are connected to the emitters of transistors Q8 and Q9, respectively. This so-called "Darlington" configuration increases current gain. The emitters of transistors Q8 and Q10 are coupled to speaker R44 via their respective resistors R16 and R19, while the emitters of transistors Q9 and Q11 are coupled to speaker R44 via their respective resistors R17 and R20. For example, they each have a quiescent current of 6 mA for transistors Q8 and Q9 and 75 mA for transistors Q10 and Q11.

[0107] The power amplifier stage 302 is connected to two power supply circuits 155a, 155b at the collectors of transistors Q8-Q11. These power supply circuits 155a, 155b are connected to two voltage buses having different levels V+, V++. Thus, the power supply circuits 155a, 155b make it possible to select one or the other of these voltage levels depending on the amplification requirements. Typically, the first power supply bus delivers + / - 65V and the second power supply bus delivers + / - 35V. The second power supply bus is intended to be used to power the power amplifier stage 302 when the output signal to be generated does not have a very high voltage (typically less than 27V).

[0108] Since the current through transistors Q8 and Q9 is relatively low, typically less than 10% of the current through transistors Q10 and Q11, the collectors of Q8 and Q9 can be directly connected to the first power bus V++ without causing significant additional power consumption. This embodiment improves the stability of the amplifier in terms of its phase margin and its gain margin.

[0109] Furthermore, the bases of transistors Q2 and Q4 are connected to a protective line comprising a resistor R28 connected in series with a capacitor C4 connected to ground. This assembly forms a voltage divider. In effect, when the voltage across the circuit is alternating, capacitor C4 behaves like a short circuit. On the other hand, when the voltage across the circuit is DC, capacitor C4 behaves like an open circuit. In this case, the output of high-power amplifier 100 is directly connected to point S2. The voltage gain of high-power amplifier 100 is thus equal to 1, which limits any potentially undesirable DC components in the voltage applied to the terminals of loudspeaker R44.

[0110] For the power supply circuits 151 - 155 , 155 a , 155 b , several embodiments are possible.

[0111] For all the following embodiments, the signal numbered 1 represents the gate signal of the MOSFET transistors M1 and M2. The output signal numbered 3 represents the output signal of the amplifier, that is, the signal at the terminal of the loudspeaker R44. The output signal numbered 2 represents the output signal of the power supply circuit 151-155, 155a, 155b, that is, the signal present at the collector of the transistors Q8 and Q10.

[0112] In the rest of the description, only the upper power supply circuit is illustrated, but Figure 5a to Figure 5b This allows for understanding the positioning of corresponding components of the lower power circuit.

[0113] like Figure 6For example, in a first embodiment, power circuit 151 includes MOSFET transistors M1 and M2, whose drains are directly connected to a first power bus V++ and whose sources are connected to a second power bus V+ via fourth diodes D3 and D11. The fourth diodes can be conventional diodes or Schottky diodes. In practice, the anode of fourth diode D3 is connected to the second power bus V+, and its cathode is connected to output signal number 2, representing the output signal of power circuits 151-155, 155a, and 155b. The cathode of fourth diode D11 is connected to the second power bus -V+. MOSFET transistors M1 and M2 are blocked for voltages below a threshold (typically 35V), but switch and operate linearly above this threshold. MOSFET transistors M1 and M2 allow conduction of the first power bus V++ when a control voltage greater than the threshold is applied to them. This voltage is controlled by the association of sub-circuit 131 for auxiliary charging, sub-circuit 141 for auxiliary discharging, and sub-circuit 161 for voltage shifting.

[0114] The sub-circuit 131 for auxiliary charging comprises first resistors R24 , R31 connected between the gates of the MOSFET transistors M1 , M2 and the interconnection points A1 , A2 .

[0115] Subcircuit 141 for auxiliary discharge includes transistors Q12 and Q13, whose emitters are connected to the gates of MOSFET transistors M1 and M2, and to subcircuit 131 for auxiliary charge. The collectors of transistors Q12 and Q13 are connected to output signal 2 of power supply circuit 151 via second resistors R8 and R27. The bases of transistors Q12 and Q13 are connected to interconnection points A1 and A2 via third resistors R21 and R39.

[0116] The voltage shift subcircuit 161 includes first capacitors C18 and C23 mounted in parallel with first diodes D8 and D10. The cathode of the first diode D8 is connected to the first interconnection node N1, and the anode of the first diode D8 is connected to the second interconnection node N2. The diode D10 is reversely connected, that is, its cathode is connected to the interconnection node N3 and its anode is connected to the interconnection node N4, as shown in FIG. Figure 5a to Figure 5b The first interconnection node is connected to the interconnection point A1, and the second interconnection node is connected to the speaker R44.

[0117] The voltage shift subcircuit ensures that the gate potential of the MOSFET transistor M1 is always 15V higher than the potential of the amplifier output.

[0118] Furthermore, the Darlington circuit formed by transistors Q8 and Q10 requires a 5V dropout voltage, that is, a voltage equal to the difference between the input voltage at the collector of transistor Q8 and the output voltage at the emitter of transistor Q10. On the other hand, MOSFET transistor M1 requires a 10V dropout voltage, that is, a voltage equal to the difference between the input voltage at its gate and the output voltage at its source at maximum current and saturation. Therefore, the voltage shifting subcircuit must compensate for the voltage drops across the two bipolar transistors Q8 and Q10, as well as the MOSFET transistor M1: 5 + 10 = 15V.

[0119] Power supply circuit 151 advantageously includes first protection diodes D5 and D13. Diode D5 has its anode connected to output signal 2 of power supply circuit 151, and its cathode connected to the gate of MOSFET transistor M1. Diode D13 has its cathode connected to the output of power supply circuit 155b, and its anode connected to the gate of MOSFET transistor M2. Similarly, power supply circuit 151 includes second protection diodes D4 and D12. Diode D4 has its cathode connected to the source of MOSFET transistor M1, and its anode connected to the source of MOSFET transistor M1. Diode D12 has its cathode connected to the source of MOSFET transistor M2, and its anode connected to the drain of MOSFET transistor M2.

[0120] Using this component, Figure 7 and Figure 8 The different signals obtained are exemplified in .

[0121] Figure 7 The signal illustrated in corresponds to a signal obtained with a sinusoid of frequency 20 kHz provided at the input of the high power amplifier 102 .

[0122] Therefore, we note that Output Signal 3 is distorted at the vertices of the triangular-shaped sinusoidal curve. Therefore, it is impossible to accurately reproduce the 20kHz sinusoidal curve. On the other hand, no abnormal voltage peaks are observed. Therefore, power loss is limited.

[0123] Figure 8 The signal illustrated in corresponds to a signal obtained with a sinusoid of frequency 1 kHz provided at the input of the high power amplifier 102 .

[0124] Therefore, we notice that the output signal 3 is less distorted than at 20 kHz. To the naked eye, the sinusoidal curve of the output signal 3 even appears to be perfectly reproduced. However, the resulting harmonic distortion (THD) is greater than 0.1%.

[0125] like Figure 9For example, in the second embodiment, the voltage shifting subcircuit 162 of the power stage 152 further includes second diodes D6 and D29 installed in parallel with the fourth resistors R22 and R26. The cathode of the second diode D6 is connected to the interconnection point N1, and the anode of the second diode D6 is connected to the third interconnection node N10. The diode D29 is reversely connected, that is, its cathode is connected to the interconnection node N20 and its anode is connected to the interconnection node N4, as shown in FIG. Figure 5a to Figure 5b Example.

[0126] Using this component, Figure 10 and Figure 11 The different signals obtained are exemplified in . Figure 10 The signal illustrated in corresponds to a signal obtained with a sinusoid of frequency 20 kHz provided at the input of the high power amplifier 102 .

[0127] Therefore, we notice that the output signal 3 is distorted at the positions of the vertices of the sine curve having a triangular appearance. Therefore, it is impossible to correctly reproduce the sine curve of 20 kHz.

[0128] Figure 11 The signal illustrated in corresponds to a signal obtained with a sinusoid of frequency 1 kHz provided at the input of the high power amplifier 102 .

[0129] To the naked eye, the sinusoid of the output signal 3 appears perfectly reproduced on the positive half-wave and slightly distorted on the negative half-wave. The harmonic distortion THD is equal to 0.45% because the observed distortion corresponds to the generation of harmonics.

[0130] Therefore, the addition of these components does not help reduce the distortion observed in the amplifier output signal. The addition of the second diodes D6 and D29 and the fourth resistors R22 and R26 degrades the dynamic performance of the circuit. In order to make these components beneficial, that is, to make them improve low-frequency and high-frequency degradation, a more complex circuit is required. To achieve performance gains, other components can be added around transistors Q12 and Q13.

[0131] like Figure 12 For example, in a third embodiment, the subcircuit for charging 132 of the auxiliary power stage 153 further includes a circuit branch comprising a third diode D9, D14 connected in series with a fifth resistor R29, R30, which is arranged in parallel with the first resistors R24, R31. The cathode of the third diode D9 is connected, for example, to the gate of the MOSFET transistor M1. The anode of the third diode D14 is connected to the gate of the MOSFET transistor M2. Alternatively, the components D9, R29 and D14, R30 can be reversed, such that the third diodes D9, D14 are connected to the gates of the MOSFET transistors M1, M2 via the resistors R29, R30.

[0132] Using this component, Figure 13 The different signals obtained are illustrated in . These signals correspond to signals obtained with a sinusoid of frequency 20 kHz provided at the input of the high power amplifier 102 .

[0133] We observe that the output sinusoid corresponding to output signal number 3 is well restored. On the other hand, output signal 2, representing the output voltage of power supply circuit 153, exhibits distortion between 0 and 5 μs and between 18 and 20 μs. Its THD is 0.26%. The addition of these components improves the distortion of sinusoidal input signals up to a frequency of 20 kHz.

[0134] like Figure 14 For example, in the fourth embodiment, the voltage shifting sub-circuit of the power supply stage 154 further includes third capacitors C21 and C24 installed in parallel with the fourth resistors R22 and R26 and the second diodes D6 and D29, and second capacitors C17 and C22 installed in parallel with the first diodes D8 and D10 and the first capacitors C18 and C23.

[0135] Figure 15 Different signals obtained with such an assembly are illustrated in . These signals correspond to signals obtained with a sinusoidal curve having a frequency of 20 kHz provided at the input of the high power amplifier 102 .

[0136] Therefore, we observe that signal 2 is less disturbed, but the switching of the fourth diode D3 still generates disturbances, in particular between 45 and 50 μs.

[0137] In practice, the second capacitors C17, C22, for example using electrochemical technology, typically have an effective value of between 5 and 15 μF and form an energy reservoir, while the first capacitors C18, C23, for example using electrochemical plastic film technology, typically have a lower value of between 50 and 150 nF and make it possible to smooth out high-frequency interference. The THD is reduced to 0.21%.

[0138] This correlation allows circuits to be more efficient during transient phases, when signals grow and decay.

[0139] like Figure 5a to Figure 5b and Figure 16 For example, in the fifth embodiment, the power stage 155 , 155 a , 155 b further includes a fourth capacitor C14 , C25 installed in parallel with the fourth diode D3 , D11 .

[0140] Figure 17Different signals obtained with such an assembly are illustrated in . These signals correspond to signals obtained with a sinusoidal curve having a frequency of 20 kHz provided at the input of the high power amplifier 102 .

[0141] We observe that the interference generated by the fourth diode D3, D11 disappears between 45 and 50 μs. This results in a slight drop in THD from 0.21% to 0.2%.

[0142] Although reference has been made previously to the high power audio amplifier 102 for enabling the supply of voltage to the loudspeaker R44 Figure 5a to Figure 5b arrive Figure 17 The invention has been described, but it is also possible to use the power supply circuit of the invention for a high power current audio amplifier, ie to provide current to a loudspeaker.

[0143] To achieve this, Figures 18a to 18b In this example, a current measuring resistor R61 is inserted between the speaker R44 and ground. Furthermore, the current amplifier 103 does not include a protection line 403. The bases of the transistors Q2 and Q4 are connected to the interconnection point between the resistor R61 and the speaker R44 via a capacitor C40. Therefore, this capacitor C40 allows only the AC component of the signal to pass.

[0144] In this configuration, the loudspeaker R44 is therefore traversed by an alternating current, the image of which is applied to the point S2. It follows that, for an alternating signal, the transconductance of the amplifier is equal to 1 / R61.

[0145] Alternatively, to protect the speaker R44 and the amplifier itself, a resistor can be added to the feedback between point S2 and the output of amplifier 3. In the event of a DC component at the terminals of speaker R44, this DC component is applied to the bases of transistors Q2 and Q4 via resistor R18. The feedback will tend to cancel this DC component. Furthermore, resistor R18 helps limit the amplifier's gain in the absence of speaker R44, also preventing it from oscillating.

[0146] When the current is alternating, capacitor C40 has a negligible impedance compared to the value of resistor R18. In normal operation, that is, when there is no DC component and when speaker R44 is actually present at the amplifier output, resistor R18 has little effect. On the other hand, if speaker R44 is not present at the amplifier output, we can consider point S2 connected to the amplifier output via resistor R18, on the one hand, and to ground via resistor R61, on the other hand, because capacitor C40 behaves like an AC short circuit. Consequently, voltage amplification will be limited to (R18 + R61) / R61, because the amplifier's output voltage, multiplied by R61 / (R18 + R61), is compared to the input voltage applied at point S1 via the differential pair formed by transistors Q1 / Q2 and Q3 / Q4. The amplifier will then not deliver its maximum output voltage, which could be dangerous. Similarly, if a DC component is present and speaker R44 is present or absent at the amplifier output, the capacitor behaves like an open circuit, and the DC component is thus re-injected at point S2 via resistor R18. Therefore, for DC voltages the voltage gain is limited to 1, which does not risk damaging the speaker R44.

[0147] In another variant, a current amplifier protection circuit can be added. To this end, Figure 19 For example, the interconnection point P1 between resistor R61 and speaker R44 is connected to the first terminal of resistor R70. In this embodiment, the second terminal of resistor R70 is connected to the collector of transistor Q16. The collector of transistor Q16 is also connected to the base of a second transistor Q15. A voltage divider consisting of resistors R71 and R72 allows the current threshold at which the protection circuit activates to be adjusted. The first terminal of resistor R71 is connected to the second power bus V+, which has a value of 32V. The second terminal of resistor R71 is connected to the base of transistor Q15 and the collector of transistor Q16. The first terminal of resistor R72 is connected to the second terminal of resistor R70, and the second terminal of resistor R72 is grounded. The turn-on threshold voltage of transistor Q15 is thus shifted by: V+*R72 / (R71+R72). This improves sensitivity, that is, lowers the current threshold at which the protection circuit activates.

[0148] Transistor Q15 is preferably a Darlington transistor. This allows for limiting the distortion caused by the circuit by drawing a lower current at the terminals of measuring resistor R61, while maintaining sufficient sensitivity due to the voltage divider network R71 / R72. Another voltage divider bridge, consisting of resistors R73 and R74, is inserted between point 3 and ground. The first terminal of resistor R73 is connected to point 3. The second terminal of resistor R73 is connected to the base of transistor Q16 and to the first terminal of resistor R74. The second terminal of resistor R74 is grounded. This adapts the voltage threshold at which neutralizing current protection begins. The emitters of transistors Q16 and Q15 are connected together and to ground, and the collector of transistor Q15 is connected to the base of transistor Q8 via diode D21, the cathode of which is connected to the collector of transistor Q15.

[0149] The circuit must be mirrored to manage current protection during the negative half-wave, and then the NPN transistor must be replaced with a PNP transistor.

[0150] This circuit makes it possible to limit the risk of power failure of the current amplifier, in particular when it is overloaded or when its output is short-circuited. In fact, in these cases, the product of the output current and the voltage of the power bus will be completely dissipated by the transistors, and they may be damaged.

[0151] use Figure 19 In this circuit, if the current in current-measuring resistor R61 is sufficient to turn on transistor Q15, the latter can divert the signal from the base of transistor Q8 to ground via diode D21, thereby blocking it. On the other hand, if the voltage at the terminals of speaker R44 is sufficient to turn on transistor Q16, the signal from the base of transistor Q15 will be diverted to ground, and the latter transistor will be blocked. Thus, in the presence of sufficient voltage at the amplifier output, the protective circuit is neutralized.

[0152] In summary, the invention makes it possible to obtain a high-power audio amplifier which makes it possible to limit the distortions recognized on the signal and thus to increase the efficiency and reduce the saturation of the amplifier.

Claims

1. A high-power audio amplifier (102) intended to control at least one loudspeaker (R44), said amplifier comprising: - a preamplifier stage (201, 301), receiving an input signal (S1); - a power amplifier stage (202-203, 302) connected to the preamplifier stage (201, 301) and providing an output signal (3) intended to power the at least one loudspeaker (R44); the preamplifier stage (201, 301) and the power amplifier stage (202-203, 302) comprising an upper part and a lower part mounted mirror-image to each other; - a feedback providing an image of the output signal (3) to the preamplifier stage (201, 301); - an upper power supply circuit (151-155, 155a) connected to the upper part of the power amplifier stage (202-203, 302) and enabling it to be powered by the first power bus (V++) or the second power bus (V+); - a lower power supply circuit (155b) connected to the lower part of the power amplifier stage (202-203, 302) and enabling it to be powered by the first or second power bus; - Each power supply circuit (151-155, 155a, 155b) comprises a MOSFET transistor (M1, M2) and a monitoring device, wherein the MOSFET transistor (M1, M2) is controlled by the monitoring device so as to switch between one or the other of two power supply buses (V++, V+), the MOSFET transistor (M1, M2) being connected to the second power supply bus (V+) via a fourth diode (D3, D11), the first terminal of the fourth diode being connected to the source of the MOSFET transistor (M1, M2), and the drain of the MOSFET transistor (M1, M2) being connected to the first power supply bus (V++), characterised in that each power supply circuit (151-155, 155a, 155b) further comprises: - a subcircuit (131-133) for assisting in charging the MOSFET transistors (M1, M2), comprising at least a first resistor (R24, R31), a first terminal of the first resistor (R24, R31) being connected to the gates of the MOSFET transistors (M1, M2) and a second terminal of the first resistor (R24, R31) being connected to the interconnection point (A1); - a subcircuit (141) for assisting in discharging the MOSFET transistors (M1, M2), comprising at least a second resistor (R8, R27) and a third resistor (R21, R39) and a bipolar transistor (Q12, Q13); the base of the bipolar transistor (Q12, Q13) being connected to the first terminal of the third resistor (R21, R39), the emitter thereof being connected to the gate of the MOSFET transistors (M1, M2), and the collector thereof being connected to the source of the MOSFET transistors (M1, M2) via the second resistor (R8, R27), the second terminal of the third resistor (R21, R39) being connected to the interconnection point (A1, A2); and - a voltage shifting subcircuit (161-163) comprising a first diode (D8, D10) mounted in parallel with a first capacitor (C18, C23); a first terminal of the first diode (D8, D10) and a first terminal of the first capacitor (C18, C23) being connected to a first interconnection node (N1, N4), which is itself connected to the interconnection point (A1, A2) of the subcircuit (141) for auxiliary discharge; a second terminal of the first diode (D8, D10) and a second terminal of the first capacitor (C18, C23) being connected to a second interconnection node (N2, N3), which is itself connected to the output signal (3).

2. The amplifier according to claim 1, wherein The voltage shifting subcircuit (161-163) further comprises at least a fourth resistor (R22, R26) and a second diode (D6, D29) mounted in parallel, a first terminal of the second diode (D6, D29) and a terminal of the fourth resistor (R22, R26) being connected to the interconnection point (A1, A2), and a second terminal of the fourth resistor (R22, R26) and a second terminal of the second diode (D6, D29) being connected to a third interconnection node (N10).

3. The amplifier according to claim 1 or 2, characterized in that The subcircuit (131-133) for auxiliary charging further includes a fifth resistor (R29, R30) installed in series with a third diode (D9, D14); the fifth resistor (R29, R30) and the third diode (D9, D14) are installed in parallel with a branch of the subcircuit (131-133) for auxiliary charging including the first resistor (R24, R31).

4. The amplifier according to claim 2, wherein: The voltage shift subcircuit (161-163) further includes a second capacitor (C17, C22) and a third capacitor (C21, C24), wherein the second capacitor (C17, C22) is installed in parallel with the first capacitor (C18, C23) and the first diode (D8, D10), and the third capacitor (C21, C24) is installed in parallel with the second diode (D6, D29) and the fourth resistor (R22, R26).

5. The amplifier according to claim 1, wherein Each power supply circuit (151-155, 155a, 155b) includes a first protection diode (D5, D13) having a first terminal connected to the source of the MOSFET transistor (M1, M2) and a second terminal connected to the gate of the MOSFET transistor (M1, M2).

6. The amplifier according to claim 1, wherein: Each power supply circuit (151-155, 155a, 155b) further includes a second protection diode (D4, D12) connected between the source and the drain of the MOSFET transistor (M1, M2).

7. The amplifier according to claim 1, wherein Each power supply circuit (151-155, 155a, 155b) further includes a fourth capacitor (C14, C25) installed in parallel with the fourth diode (D3, D11).

8. The amplifier according to claim 1, wherein The preamplifier stage (201, 301) is connected to the first power bus (V++) of the respective power supply circuit (151-155, 155a, 155b) by means of a power variation damping circuit (304, 305) of the first power bus (V++), the power variation damping circuit (304, 305) comprising at least one capacitor (C15, C19) and at least one resistor (R52, R55) arranged as a low-pass filter.

9. The amplifier according to claim 8, characterized in that The power variation damping circuit (304, 305) further comprises an additional capacitor mounted in parallel with the at least one capacitor (C16, C20).

10. The amplifier according to claim 1, wherein The feedback applied to the preamplifier stage provides a signal proportional to the current through the speaker.

Images