Load compensation circuit

Abstract

This load compensation circuit provides a way to maintain a constant power supply voltage against load fluctuations that occur in digital audio equipment and other loads, including those that cannot be handled by capacitors. [Solution] The noise detection circuit 10 detects the voltage at the midpoint of the power supply supplied to the load as a reference voltage, detects noise on the positive terminal side of the power supply based on the reference voltage, and amplifies the noise with an amplifier OP and outputs it, and the current control circuit 20 supplies current to the load in accordance with the noise amplified by the amplifier OP of the noise detection circuit 10.

Description

Technical Field

[0001] The present invention relates to a load compensation circuit that guarantees the power supply voltage in response to load fluctuations generated inside a load such as a digital audio device.

Background Art

[0002] Audio devices have various circuits driven inside, and the load fluctuations thereof cause fluctuations in the power supply voltage. Particularly in the case of digital audio devices, a large number of switchings are performed inside, and various frequency noises generated at that time further generate moiré, generating noises from an ultra-low frequency of 0.01 Hz to a GHz band.

[0003] These noises ultimately act on the electric circuit in the form of load fluctuations. Therefore, the load of the digital audio device is affected by the superposition of noises from an ultra-low frequency to a GHz band, and fluctuations at various frequencies are repeated.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Generally, as countermeasures against noises in the digital or audio area, filter circuits, capacitors, etc. are often used, but there are limitations to the frequency bands of noises that can be reduced by these circuits.

[0006] Patent Document 1 discloses a circuit for reducing noise components such as ripple contained in a constant voltage output from a constant voltage power supply, but it cannot reduce noises in a wide frequency band based on switches generated in digital audio devices.

[0007] In view of the above circumstances, the present invention aims to provide a load compensation circuit that can always maintain a constant power supply voltage in response to load fluctuations occurring in loads such as those within digital devices, including bandwidths that cannot be handled by capacitors. [Means for solving the problem]

[0008] The load compensation circuit of the present invention includes a noise detection circuit that detects the voltage at the midpoint of the power supply supplied to the load as a reference voltage, detects noise on the positive terminal side of the power supply based on the reference voltage, and amplifies the noise with an amplifier and outputs it, and a current control circuit that supplies current to the load in accordance with the noise amplified by the amplifier of the noise detection circuit. [Effects of the Invention]

[0009] According to the load compensation circuit of the present invention, the voltage at the midpoint of the power supply supplied to the load is detected as a reference voltage, noise on the positive terminal side of the power supply is detected based on the reference voltage, this noise is amplified by an amplifier, and current is supplied to the load according to the amplified noise. Therefore, the power supply voltage can always be kept constant by rapidly compensating for load fluctuations that occur in loads such as digital equipment, including bandwidths that cannot be handled by capacitors. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows an example of a circuit diagram of one embodiment of the load compensation circuit of the present invention. [Modes for carrying out the invention]

[0011] Hereinafter, an embodiment of the load compensation circuit of the present invention will be described in detail with reference to the drawings. Figure 1 is a diagram showing an example of a circuit diagram of the load compensation circuit of this embodiment.

[0012] The load compensation circuit of this embodiment can guarantee the power supply voltage in response to load fluctuations occurring within the load, such as digital audio equipment, thereby improving sound quality. The load compensation circuit of this embodiment uses a wideband and high-speed operational amplifier, and can maintain a constant power supply voltage at all times by rapidly supplementing the current in response to load fluctuations occurring within the load, such as digital audio equipment, including bandwidths that cannot be handled by capacitors.

[0013] The following describes a specific example of the circuit configuration of the load compensation circuit 1 of this embodiment. The load compensation circuit 1 of this embodiment comprises a noise detection circuit 10 and a current control circuit 20. A power supply is connected to the noise detection circuit 10, and a load such as a digital audio device is connected to the current control circuit 20. The resistive elements ext ESR(+) and ext ESR(-) are the equivalent resistance components of the power supply and the power supply line.

[0014] The noise detection circuit 10 is a circuit that detects noise generated by load fluctuations using the midpoint of the power supply voltage as a reference voltage and amplifies the voltage.

[0015] The noise detection circuit 10 includes two resistors R1 and R2 for detecting a reference voltage. Resistors R1 and R2 are connected in series with the power supply, and the reference voltage is detected at reference point CP, which is the connection point between resistors R1 and R2.

[0016] Resistor elements R1 and R2 have the same resistance value, for example, 1.5kΩ in this embodiment. By making resistor elements R1 and R2 have the same resistance value in this way, a voltage of half the power supply voltage is detected as the reference voltage. In this embodiment, for example, the power supply voltage is 12V, and 6V is detected as the reference voltage. The load compensation circuit 1 of this embodiment performs all operations based on this reference voltage.

[0017] A temperature compensation circuit 11 is connected to the reference point CP between resistors R1 and R2 to perform temperature compensation for the reference voltage. The temperature compensation circuit 11 comprises two transistors Q1 and Q2, and two resistors R3 and R4. The current flowing through the two transistors Q1 and Q2 changes in accordance with the temperature fluctuation of the reference voltage, thereby suppressing the temperature fluctuation of the reference voltage. In this embodiment, the resistance values ​​of resistors R3 and R4 are, for example, 3.3 kΩ. The VCP supplied to resistor R4 is the reference voltage.

[0018] The capacitor C1 of the noise detection circuit 10 is a capacitor that guides only the AC component appearing on the positive side of the power supply to the amplifier OP, which will be described later. In this embodiment, the capacitance value of capacitor C1 is set to 1200 μF, and the ESR is set to 7 mΩ.

[0019] The noise detection circuit 10 includes an operational amplifier (OP) as the amplifier OP. The amplifier OP amplifies and outputs the noise generated by load fluctuations. The operating magnification of the amplifier OP is determined by the ratio of the resistors R7 and R8 connected to the amplifier OP. In this embodiment, for example, the resistance value of resistor R7 is set to 150Ω, the resistance value of resistor R8 is set to 1.5kΩ, and the operating magnification is set to 10 times.

[0020] Furthermore, resistors R5 and R6 are connected to the positive input of amplifier OP. In this embodiment, the resistance of resistor R5 is, for example, 220Ω, and the resistance of resistor R6 is, for example, 51Ω. The capacitance of capacitor C1, which is connected to the positive input of amplifier OP, is increased by an amount equivalent to the resistance ratio multiplier of resistor R5, relative to the ESR of capacitor C1, which is 7mΩ. In this embodiment, the capacitance of capacitor C1 becomes 220Ω / 0.007Ω = 30000, meaning that capacitor C1 behaves as if its capacitance has been increased by approximately 30,000 times.

[0021] The capacitor C2, resistor element R9, and resistor element R10 of the noise detection circuit 10 constitute a power supply filter for the amplifier OP. In the present embodiment, the capacitance value of the capacitor C2 is, for example, 1200 μF, and the resistance values of the resistor element R9 and the resistor element R10 are, for example, 1.0 Ω.

[0022] With the configuration of the noise detection circuit 10 of the present embodiment as described above, for the noise on the positive electrode side of the power supply, only the AC component thereof is input to the amplifier OP through the capacitor C1, amplified by a factor of 10, and output from the amplifier OP.

[0023] Next, the current control circuit 20 will be described. The current control circuit 20 supplies current to the load according to the noise output from the amplifier OP of the noise detection circuit 10.

[0024] The current control circuit 20 includes transistors Q3 to Q7 and resistor elements R11 to R29. In the present embodiment, for example, the resistance values of the resistor elements R11 and R12 are 22 Ω, the resistance value of the resistor element R13 is 1 kΩ, the resistance value of the resistor element R14 is 3.3 kΩ, the resistance value of the resistor element R15 is 1.2 kΩ, the resistance value of the resistor element R16 is 470 Ω, the resistance values of the resistor elements R17 to R28 are 120 Ω, and the resistance value of the resistor element R29 is 270 Ω.

[0025] The current from the power supply is always fluctuating according to the operating conditions of the current control circuit 20 composed of the transistors Q3 to Q7 and the resistor elements R11 to R2, and is separated into the directions of arrow A and arrow B shown in FIG. 1.

[0026] When the power supply voltage is 12V and there is no noise, a current of about 120 mA always flows in the direction of arrow A. This current value is the maximum value of the current that can suppress the voltage fluctuation of the power supply. When the power supply voltage is 5V and there is no noise, it is about 80 mA.

[0027] The noise component generated by the load is always observed as noise that swings in the negative direction at the positive terminal of the power supply. Therefore, the voltage amplified by amplifier OP is always amplified as a voltage in the negative direction. This amplified negative voltage wave is input to the base of transistor Q5, causing current to flow through transistors Q5, Q3, and Q4, and the emitter voltages of transistors Q3 and Q4 swing in the negative direction due to the noise. Therefore, the higher the amplitude of the noise component, the smaller the current value flowing in the direction of arrow A, and as a result, the current value in the direction of arrow B increases. The current flowing in the direction of arrow B is then supplied to the load. In other words, the load compensation circuit 1 of this embodiment behaves as if it were a negative resistance element in response to voltage fluctuations of the power supply due to load noise. The cascaded transistors Q6 and Q7 have the functions of temperature compensation and circuit stabilization. Transistor Q6 has the function of a constant voltage source and absorbs the combined current of the parallel connected resistors R17 to R28. The emitter voltage (VE) maintains its set value despite this change in suction current. The emitter voltage of transistor Q6 is 1.85V when the power supply voltage is 12V and 1.20V when the power supply voltage is 5V, indicating a low impedance power supply.

[0028] Specifically, the noise on the load side will be reduced by the reciprocal of the noise amplification factor of the amplifier OP. In other words, if the noise amplification is 10 times, the noise on the load side will be reduced to 1 / 10. This means that both external noise and noise generated by load fluctuations will be reduced. As described above, the load compensation circuit 1 of this embodiment can produce a noise reduction effect by the reciprocal of the amplification factor of the noise by amplifying the noise with the amplifier OP.

[0029] Through the operation of the load compensation circuit 1 of this embodiment as described above, fluctuations in the current value caused by the load can be compensated for.

[0030] The capacitors C3 to C8 connected in parallel immediately before the load are Os-Con (conductive polymer aluminum solid electrolytic capacitors), and are installed to handle the high-frequency range that cannot be fully covered by the load compensation circuit 1 described above.

[0031] According to the load compensation circuit 1 of the above embodiment, the voltage at the midpoint of the power supply supplied to the load is detected as a reference voltage, noise on the positive terminal side of the power supply is detected based on the reference voltage, the noise is amplified by an amplifier, and current is supplied to the load according to the amplified noise. Therefore, the power supply voltage can always be kept constant by rapidly compensating for load fluctuations that occur in loads such as digital audio equipment, including bandwidths that cannot be handled by capacitors.

[0032] Furthermore, since the noise cancellation reference point CP is set to the midpoint of the voltage between the positive and negative terminals of the power supply, load fluctuations can be detected as noise on the positive terminal side, and a more appropriate current can be supplied to the load in response to these fluctuations.

[0033] Furthermore, the load compensation circuit 1 of the above embodiment is equipped with a temperature compensation circuit that performs temperature compensation for the reference voltage, thereby improving the stability of the reference voltage and enabling the provision of a more appropriate current in response to load fluctuations.

[0034] Furthermore, in the load compensation circuit 1 of the above embodiment, the reference voltage is generated by two resistors R1 and R2, so the reference voltage can be generated with a simpler configuration.

[0035] Furthermore, in the load compensation circuit 1 of the above embodiment, since an operational amplifier is used as the amplifier OP, noise can be amplified with a simpler configuration, and noise countermeasures can be implemented over a wider bandwidth.

[0036] Furthermore, by combining the load compensation circuit 1 of the above embodiment with high-capacitance capacitors C3 to C8 having low ESR characteristics, such as polymer aluminum solid electrolytic capacitors, it is possible to further improve sound quality. In the above description of the embodiment, an example was given in which a digital audio device was connected as the load. However, the load compensation circuit of the present invention is not limited to audio devices and can be used (connected) to other digital devices as the load. For example, when used with a digital device that has Wi-Fi functionality, the range over which stable wireless communication is possible can be greatly extended by noise cancellation.

[0037] The following further notes are disclosed regarding the present invention.

[0038] (Note 1) The load compensation circuit of the present invention includes a noise detection circuit that detects the voltage at the midpoint of the power supply supplied to the load as a reference voltage, detects noise on the positive terminal side of the power supply based on the reference voltage, and amplifies the noise with an amplifier and outputs it, and a current control circuit that supplies current to the load in accordance with the noise amplified by the amplifier of the noise detection circuit.

[0039] (Note 2) The load compensation circuit described in Appendix 1 may include a temperature compensation circuit that performs temperature compensation for the reference voltage.

[0040] (Note 3) In the load compensation circuit described in Appendix 1 or 2, the noise detection circuit can generate a reference voltage using two resistive elements.

[0041] (Note 4) In the load compensation circuit described in any one of the appendices 1 to 3, the amplifier may be an operational amplifier. [Explanation of symbols]

[0042] 1 Load compensation circuit 10. Noise detection circuit 11 Temperature compensation circuit 20 Current control circuit CP reference point OP amp

Claims

1. A noise detection circuit that detects the voltage at the midpoint of the power supply supplied to the load as a reference voltage, detects noise on the positive terminal side of the power supply based on the reference voltage, and amplifies the noise using an amplifier and outputs it, The noise detection circuit comprises a current control circuit that supplies current to the load in accordance with the noise amplified by the amplifier of the noise detection circuit, The noise detection circuit includes a capacitor for guiding only the AC component of the noise appearing on the positive side of the power supply to the non-inverting input of the amplifier, and the amplifier amplifies and outputs the AC component of the noise detected by the capacitor. An audio load compensation circuit having a transistor circuit in which the current limiting circuit increases the current supplied to the load as the noise output from the amplifier of the noise detection circuit increases, and decreases the current supplied to the load as the noise decreases.

2. The audio load compensation circuit according to claim 1, further comprising a temperature compensation circuit that performs temperature compensation for the aforementioned reference voltage.

3. The audio load compensation circuit according to claim 1, wherein the noise detection circuit generates the reference voltage using two resistive elements.

4. The audio load compensation circuit according to claim 1, wherein the amplifier is an operational amplifier.

5. The audio compensation circuit according to claim 1, wherein the current control circuit controls the current to the load using a plurality of transistors.

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