Audio converter voltage supply
The cascade control system in the audio converter power supply addresses interference and noise issues by using a current control circuit within the audio frequency range and a voltage regulator outside it, ensuring a stable and noise-free DC supply for audio converters.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- SENNHEISER ELECTRONICS GMBH & CO KG
- Filing Date
- 2025-12-16
- Publication Date
- 2026-06-25
AI Technical Summary
Conventional audio converter power supplies suffer from interference and noise, particularly at high output voltages, which affect the signal being converted, especially in devices like the Neumann U47 condenser microphone.
A cascade control system is implemented, where a current control circuit operates within the audio frequency range (20 Hz - 22 kHz) as an inner loop and a voltage regulator operates below this range as an outer loop, minimizing interference and noise by ensuring the voltage regulator does not affect the audio frequency range.
The solution effectively reduces noise and hum, maintaining a stable DC voltage supply for audio converters without interfering with the audio signal, even under load changes, by isolating the voltage regulation from the audio frequency range.
Smart Images
Figure EP2025087303_25062026_PF_FP_ABST
Abstract
Description
[0001] Sennheiser electronic SE & Co. KG
[0002] Am Labor 1, 30900 Wedemark
[0003] Audio converter power supply
[0004] The present invention relates to an audio converter power supply and in particular a power supply for converters in the acoustic frequency spectrum (20Hz- 22kHz), especially condenser microphones (acoustic-electrical converters) or analog-to-digital and digital-to-analog converters.
[0005] A power supply is required to operate an audio converter.
[0006] It is an object of the present invention to provide an audio converter power supply that is as free from interference as possible. In particular, it is an object of the invention to provide an extremely low-noise and low-hum power supply in order not to affect the signal to be converted.
[0007] This problem is solved by an audio converter power supply according to claim 1.
[0008] Thus, an audio converter power supply is provided. This power supply has an input for receiving an AC voltage as the supply voltage, a rectifier, a current control circuit, a voltage regulator, and an output. The output provides the DC voltage to power an audio converter. The current control circuit is connected to the rectifier and receives a rectified supply voltage from it. The current control circuit generates a current from this current and outputs it to the output, which, when an audio converter is connected to the output, provides the DC voltage to power the audio converter. The voltage regulator is connected to the output and receives the DC voltage present there as a measured value. Depending on the received measured value, the voltage regulator generates a potential that is fed to the current control circuit as a control signal.The current control circuit and the voltage regulator form a cascade control system in that the current control circuit regulates the output current depending on the control signal it receives from the voltage regulator. The current control circuit forms an inner loop of the cascade control system, and the voltage regulator forms an outer loop. Invention.
[0009] *20250666386* As intended, only the current regulation circuit, as the inner loop, operates in the audio frequency range, while the voltage regulator, as an outer loop, only operates below the audio frequency range and essentially does not operate within it. The audio frequency range here lies between 20 Hz and 22 kHz.
[0010] Optionally, the voltage regulator can operate in a frequency range below 10Hz.
[0011] According to one example, the power supply has an auxiliary power supply for providing a plurality of bias voltages.
[0012] According to one example, the auxiliary power supply has a first current source.
[0013] For example, the voltage regulator has a differential stage with two transistors. The time constant of the voltage regulator is defined by a resistor and an output capacitance.
[0014] The supply voltage can be > 40, in particular > 100V.
[0015] The invention also relates to an audio transducer, in particular a condenser microphone, especially a Neumann U47, with a condenser microphone power supply as described above. The Neumann U47 contains a circuit with a tube amplifier, wherein the power supply for the filament voltage of the tube is connected in such a way that the current draw from the power supply is almost constant and any variable portion is caused solely by the audio signal. The Neumann U47 therefore places particular demands on its power supply, which are met by the audio transducer power supply according to the invention.
[0016] The power supply described in the example can at least partially overcome the disadvantages of conventional linear regulators in power supplies. Conventional linear regulators aim for the highest possible broadband error gain, extending across the audio spectrum and often even beyond. However, the error gain, and thus the suppression of crosstalk between input and output, is limited by capacitive loads, which reduce the bandwidth. Linear regulators only achieve high error gains if the power stages (or output stages) already have very low output impedances to ensure a high bandwidth for the control amplifier and thus high error gain.This design can lead to a very high crosstalk between input and output due to parasitic properties of power transistors and their control. Without an error amplifier, i.e., in the open loop, the circuit can exhibit this parasitic effect.
[0017] Even if a high error amplification can be achieved with a conventional design of the linear regulator, at high output voltages above 100V, as is particularly the case with the Neumann U47 condenser microphone, a multiple of the noise of the reference voltage source is added to the output of the linear regulator, since the error amplifier cannot compensate for this.
[0018] The power supply described in the example should not necessarily cause a corresponding hum current at the input of the power supply to result in a corresponding hum current at the output of the power supply, and very low noise should be achieved.
[0019] As an example, a power supply for an audio converter is provided, featuring cascade control. The inner loop of the cascade control is a current regulator, which is particularly active in the audio frequency range; that is, the current regulator intervenes in the audio frequency range (20 Hz - 22 kHz), but essentially not below it. The outer loop of the cascade control is a voltage regulator, which operates below the audio frequency range, e.g., below 10 Hz; that is, the regulator intervenes, but essentially not in the audio frequency range. One advantage of this power supply is that even with a load change in the audio frequency range, correction by the error amplifier is not necessarily required.
[0020] An audio converter can be a microphone, a condenser microphone, a microphone amplifier with an AD converter.
[0021] Further embodiments of the invention are the subject of the dependent claims.
[0022] The advantages and embodiments of the invention are explained in more detail below with reference to the drawing.
[0023] Fig. 1 shows a block diagram of a power supply for a condenser microphone, Fig. 2 shows a circuit diagram of an auxiliary power supply,
[0024] Fig. 3 shows a circuit diagram of a voltage regulator, and
[0025] Fig. 4 shows a circuit diagram of a current control circuit.
[0026] Fig. 1 shows a block diagram of a power supply for a condenser microphone. The condenser microphone power supply 100 has an input 101, e.g., with an input voltage of approximately 100 V (e.g., 124 V), and an output 102 of approximately 100 V (e.g., 105 V). Furthermore, the power supply 100 includes a rectifier 110, an auxiliary power supply 120, a cascade regulator 130 with a current control circuit 140 as the inner control loop, and a voltage regulator 150 as the outer control loop. The voltage regulator 150 can have a first, second, and third voltage regulator terminal 151, 152, 153. The second voltage regulator terminal 152 is connected to the output 102 of the power supply, at which the constant DC voltage for supplying an audio converter is applied. The voltage to be kept constant is thus provided to the voltage regulator 150 as a measured value via the second voltage regulator connection 152.
[0027] The current control circuit 140 can have a first, second, and third current control terminal 143, 144, and 145, respectively. The current control circuit 140 is connected to the rectifier 110 via its third current control terminal 145 and receives a rectified supply voltage from it. The current control circuit 140 generates a current, which it outputs to the output 102 via its second current mirror terminal 144. When an audio converter is connected to the output 102, this current provides the DC voltage to supply the audio converter. Depending on the measured quantity described above, the voltage regulator 150 generates a potential at its first voltage regulator terminal 151, which is supplied to the current control circuit 140 at its first terminal 143 as a control signal.The current control circuit 140 and the voltage regulator 150 thus form a cascade control in the sense that the current control circuit 140 regulates the current at its second current control terminal 144 depending on the control variable that it receives at its first current control terminal 143 from the voltage regulator 150.
[0028] The rectifier may exhibit a voltage ripple of 2 V. This ripple must be compensated. The rectifier may generate interference during operation, which must then be compensated. Output 102 may be connected to ground via capacitor C5. An AC voltage may be present at input 101, supplied, for example, from the secondary side of a transformer. A rectified supply voltage is available at current control terminal 145 after rectifier 110. The goal is to generate a constant DC voltage at output 102 from the voltage present at current control terminal 145 to power an audio converter. In particular, any interference in the resulting DC voltage at output 102 should ideally contain no components in the audio frequency range.
[0029] Fig. 2 shows a circuit diagram of an auxiliary power supply. The auxiliary power supply 120 has an input 121 and a first current source 122. The input 121 is connected to the output of the rectifier 110 and terminal 145. The current source 122 serves to provide a constant current. The first current source 122 can include a resistor R21, a transistor Q10, a diode D6, and a resistor R20.
[0030] Furthermore, the auxiliary power supply 120 can have a plurality of diodes D41–D49 connected in series. A first low-pass filter TP1 (with a resistor R41 and a capacitor C42) can be provided between the first power source 122 and diode D41. A first bias voltage V1, for example 75 V, can be provided at the output of the first low-pass filter TP1. A second low-pass filter TP2, with a resistor R42 and a capacitor C43, can be provided between diode D44 and diode D45. A second bias voltage V2, for example 40 V, can be provided at the output of this second low-pass filter TP2.
[0031] A third low-pass filter T3, consisting of a resistor R43 and a capacitor C44, can be installed between diode D45 and diode D46. This third low-pass filter T3 can provide a third bias voltage V3 of +35 V.
[0032] A fourth low-pass filter, TP4, with a resistor R44 and a capacitor C45, can be provided between diode D48 and diode D49. A fourth bias voltage, V4, of +5 V can be applied to the output of the fourth low-pass filter, TP4.
[0033] Thus, the auxiliary power supply 120 can generate four bias voltages V1, V2, V3, V4 (75 V, 40 V, 30 V and 5 V). These auxiliary voltages can be used as inputs in other parts of the circuit.
[0034] Fig. 3 shows a circuit diagram of a voltage regulator. The voltage regulator 150 can have a first, second, and third terminal 151, 152, 153. The second terminal 152 is connected to the output 102, at which the constant DC voltage to supply an audio converter is applied. The voltage regulator 150 can have four transistors Q4, Q5, Q6, Q7. Transistor Q7 can have a second bias voltage V2 of, for example, 40 V at its base. Transistor Q4 can have a third bias voltage V3 of, for example, 35 V at its base. A resistor R9 is connected in series with the first terminal 151. The fourth transistor Q7 and the first transistor Q4 are connected in series with resistor R9. A resistor R15 is connected in series with transistor Q4. A resistor R4 and a resistor R3 are connected in series with the second terminal 152, with resistor R3 being coupled to ground.A base terminal of transistor Q5 is coupled to a junction between resistors R3 and R4. This supplies the voltage regulator 150 with the quantity to be regulated. A capacitor C1 and a resistor R14 are coupled in parallel to the base and collector terminals of transistor Q5. The time constant of the voltage regulator, and thus the frequency range in which the voltage regulator 150 operates, can be set via capacitor C1 and resistor R14. A resistor R6 is coupled to a first bias voltage V1 of, for example, 75 V. A junction between resistors R15 and R16 is coupled to the third transistor Q6. A third terminal 153 is coupled to a diode D1 and a base terminal of transistor Q6. Transistor Q6 is coupled to ground via resistor R8.
[0035] Fig. 4 shows a circuit diagram of a current control circuit. The current control circuit 140 has three current control terminals 143, 144, 145, a second current mirror 141, and a cascade 142. The second current mirror 141 has a current control terminal 145, which is coupled to the output of the rectifier 110. The second current mirror 141 has two resistors R5, R2, two transistors Q3 and Q8, and a capacitor C3. The second current mirror 141 has three terminals 141a, 141b, and 141c. A series connection consisting of resistor R5 and transistor Q3 is provided between the first and second current mirror terminals 141a, 141b. A series connection consisting of resistor R2 and transistor Q8 is provided between the first and third terminals 141a, 141c. Capacitor C3 is connected in parallel to this series connection.
[0036] The cascade 142 comprises a constant voltage unit 146 and a third current source 147. The constant voltage unit 146 has a parallel connection of a resistor R11 and a capacitor C4. The third current source 147 has a series connection of a transistor Q9 and a resistor R18, which is in turn coupled to ground. Transistor Q9 has a first bias voltage V1 of, for example, 75 V at its base terminal. Furthermore, the cascade 142 has a transistor Q1, a transistor Q2, and a resistor R10. The cascade 142 has a first terminal 148, a second terminal 144, and a third terminal 149. The third terminal 149 is coupled to terminal 145. The first terminal 148 is coupled to terminal 141b.
[0037] The cascade controller 130 has a current control circuit 140 as its inner loop and a voltage regulator 150 as its outer loop. The voltage regulation 150 in the outer loop operates well below the audio spectrum.
[0038] The voltage converter has a level converter which adapts a first signal level to a second signal level without affecting the signal shape.
[0039] The inner circuit of the cascade control, namely the current control circuit 140, can be designed such that a phase margin is not consumed by an output filter capacitance C1. This ensures a high internal loop gain. Furthermore, high-quality current control can be achieved without having to consume phase margin.
[0040] The output capacitance C1 can be used to improve the control of the voltage regulation 150 in the audio range in such a way that noise is reduced.
[0041] Preferably, the cutoff frequency of the voltage regulator 150 lies outside the audio frequency range, so that noise from the voltage regulator and noise from a reference voltage diode are not in the audio frequency range. Thus, even the noise relevant in the audio frequency range can be reduced. Furthermore, by providing the current control loop, it is possible to effectively limit the maximum current without additional effort.
[0042] In the current control circuit 140, a current mirror consisting of resistors R5 and R2, as well as transistors Q3 and Q8, can be implemented. In this current mirror 141, the output current of the circuit is set via the voltage across capacitor C3. Since the current mirror 141 is at a potential similar to a humming voltage input at terminal 145, a voltage must be set to achieve the most ideal current regulation possible. This is accomplished by the voltage regulator 150, and in particular by a cascade of transistors Q7, Q4, and Q6. The first terminal 143 of the current control circuit 140 is connected to the first terminal 151 of the voltage regulator 150. Transistor Q6 provides the reference current. Because the charging of capacitor C3 is also carried out by the current control circuit, this results in a degree of noise filtering for the voltage regulator.To achieve the highest possible amplification in the current mirror, small-signal transistors capable of high current gain are used. To reduce the power dissipation of transistors Q7, Q4, and Q6, a transistor Q1 is included in the cascade. Transistor Q1 maintains the potential across the current mirror contact. This is advantageous because it further linearizes the current control circuit.
[0043] Since the control of transistor Q1 is at the level of the self-voltage, control is carried out at high impedance via a current source through transistor Q9.
[0044] Voltage regulation can be achieved via a differential stage, namely transistors Q4 and Q5. The time constant of the voltage regulator is set by R14 and C1. Preferably, the time constant is chosen such that the cutoff frequency of the voltage regulator is less than 0.2 Hz. According to the invention, the cutoff frequency can be selected such that no significant regulation occurs in the audio frequency range by the voltage regulator 150.
[0045] In the setup shown in Fig. 3, the voltage regulator 150 reacts to disturbances in the voltage to be regulated, which is supplied to it via the second terminal 152, according to a frequency-dependent transfer function. With the setup shown and a selected cutoff frequency of 0.2 Hz, the amplitude of this transfer function at 20 Hz (i.e., at the lower end of the audible frequency range) is already more than 30 dB lower than the amplitude of this transfer function at the selected cutoff frequency.
[0046] According to the invention, the voltage regulator 150 should be designed such that it does not essentially interfere in the audio frequency range, which is achieved if the amplitude of the transfer function of the voltage regulator is at least 20 dB lower than the maximum amplitude of this transfer function over the entire audio frequency range from 20 Hz to 22 kHz, with the maximum amplitude occurring below 20 Hz.
[0047] Due to the described interaction of the current control circuit 140 with the voltage regulator 150, which only operates below the audio frequency range, the entire circuit behaves at output 102 almost like an ideal current source, although the current is adjusted depending on the resulting voltage at output 102. This adjustment of the output voltage is performed so slowly that it contains no component in the audio frequency range, so the adjustment has no effect whatsoever on the audio signal received by a connected audio converter.
[0048] The Neumann U47 condenser microphone can be described as a condenser microphone with an electron tube as an amplifier (see: https: / / de.wikipedia.org / wiki / Neumann). ).
[0049] List of reference signs
[0050] 100 Condenser microphone power supply
[0051] Entrance 101
[0052] 102 Output 110 Rectifier
[0053] 120 Auxiliary power supply
[0054] Entrance 121
[0055] 122 first power source
[0056] 130 Cascade controller 140 Current control circuit
[0057] 141 Current Mirror
[0058] 141a first current mirror connection
[0059] 141 b second current mirror connection
[0060] 141c third current mirror connection 142 cascade
[0061] 143 first current regulator connection
[0062] 144 second current regulator connection
[0063] 145 Third current regulator connection 146 Constant voltage unit
[0064] 147 Power source
[0065] 148 first power source connection
[0066] 149 third power source connection 150 voltage regulator
[0067] 151 first voltage regulator connection
[0068] 152 second voltage regulator connection
[0069] 153 third voltage regulator connection
[0070] 155 second voltage regulator connection
Claims
Claims 1. Audio converter power supply, comprising an input (101) for receiving an AC voltage as the supply voltage, a rectifier (110), a current control circuit (140) with a first current control terminal (143), a second current control terminal (144) and a third current control terminal (145), a voltage regulator (150) with a first voltage control terminal (151) and a second voltage control terminal (152), and an output (102) at which a DC voltage is output for supplying an audio converter, wherein the current control circuit (140) is connected to the rectifier (110) via its third current control terminal (145) and receives a rectified supply voltage from there, wherein the current control circuit (140) generates a current and outputs it to the output (102) via its second current control terminal (144), which, when an audio converter is connected to the output (102), causes the DC voltage to supply the audio converter.characterized in that the second voltage regulator terminal (152) of the voltage regulator (150) is connected to the output (102) and receives the DC voltage applied to the output (102) as a measured quantity, wherein the voltage regulator (150) generates a potential at its first voltage regulator terminal (151) depending on the received measured quantity, which is supplied to the current control circuit (140) via its first current control terminal (143) as a control quantity, wherein the current control circuit (140) and the voltage regulator (150) form a cascade control in the sense that the current control circuit (140) controls the current at its second current control terminal (144) depending on the control quantity that it receives at its first current control terminal (143) from the voltage regulator (150), wherein the current control circuit (140) acts as an inner loop of the cascade control in the audio frequency range.and wherein the voltage regulator (150) acts as an outer loop of the cascade control only below the audio frequency range and essentially does not act in the audio frequency range, the audio frequency range being between 20Hz and 22kHz.
2. Audio converter power supply according to claim 1, further comprising an auxiliary power supply (120) for providing with a plurality of bias voltages (V1 , V2, V3, V4).
3. Audio converter power supply according to claim 2, wherein the auxiliary power supply (120) comprises a first current source (122).
4. Audio converter power supply according to one of claims 1 to 3, wherein the voltage regulator (150) has a differential stage with two transistors (Q4, Q5), wherein a time constant of the voltage regulator (150) is formed by a resistor (R14) and an output capacitance (C1).
5. Audio converter power supply according to one of claims 1 to 3, with a supply voltage of > 40V, in particular > 100V.
6. Audio converter power supply according to any one of claims 1 to 5, wherein the voltage regulator (150) has a frequency-dependent transfer function that responds to disturbances in the voltage to be regulated, wherein at a cutoff frequency of 0.2 Hz the amplitude of the transfer function at 20 Hz is more than 30 dB lower than the amplitude of this transfer function at this cutoff frequency, wherein the voltage regulator (150) is designed such that it does not substantially affect the audio frequency range by having the amplitude of the transfer function of the voltage regulator (150) in the entire audio frequency range from 20 Hz to 22 kHz at least 20 dB lower than the maximum amplitude of the transfer function of the voltage regulator (150), wherein the maximum amplitude occurs below 20 Hz.
7. Audio converter, comprising an audio converter power supply according to one of claims 1 to 6.
8. Condenser microphone, in particular Neumann U47, with an audio converter power supply according to one of claims 1 to 6.