Electric power supply

Abstract

To provide an electric power supply capable of improving a sound quality of an analog audio device USB-connected to a digital device.SOLUTION: An electric power supply that supplies a power source to an along audio device that receives a digital data from a digital device USB-connected to a digital device, includes: a first resistor and a second resistor that are serially connected to between a GND of a digital device and a GND of the along audio device, and include a resistance value of which a potential difference of the GND of the digital device and the GND of the along audio device is set to a predetermined value or less; and a capacitor that is a capacitor to be connected to the second resistance in parallel, and in which an RC circuit to be formed by the first resistance and the capacitor is a capacitance satisfying a condition of a predetermined cutoff frequency.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a power supply device that supplies power to an analog audio device connected to a digital device via USB.

Background Art

[0002] Conventionally, as shown in FIG. 1, an analog audio device 7 having an analog signal circuit and connected to a digital device 8 via USB is known. When BUS POWER is used to supply power from the digital device 8, it is known that noise on the digital device 8 side leaks into the analog audio device 7 side and degrades the sound quality.

[0003] As a solution to this problem, a method of avoiding sound quality degradation by preventing the analog audio device 7 from being supplied with power from VBUS is known (for example, Non-Patent Document 1).

[0004] For example, as shown in FIG. 2, by supplying power to the analog audio device 7 side from a power supply device 9 and not connecting it to the power supply on the digital device 8 side, a certain degree of sound quality improvement can be achieved.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when the ground lines on the analog side and the digital side are connected as shown in the figure, there is a problem that noise leaks from the ground line and deteriorates the sound quality.

[0007] Therefore, an object of the present disclosure is to provide a power supply device that improves the sound quality of an analog audio device connected to a digital device via USB.

Means for Solving the Problem

[0008] The power supply device of the present disclosure is a device that supplies power to an analog audio device that is USB-connected to a digital device and receives digital data from the digital device, and includes a first resistor, a second resistor, and a capacitor.

[0009] The first resistor and the second resistor are connected in series between the GND of the digital device and the GND of the analog audio device, and have a resistance value that makes the potential difference between the GND of the digital device and the GND of the analog audio device equal to or less than a predetermined value.

[0010] The capacitor is connected in parallel to the second resistor, and the RC circuit composed of the first resistor and the capacitor has a capacitance that satisfies the condition of a predetermined cut-off frequency.

Effect of the Invention

[0011] According to the power supply device of the present disclosure, the sound quality of an analog audio device connected to a digital device via USB can be improved.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present disclosure will be described in detail. Note that components having the same function are denoted by the same reference numerals, and redundant descriptions are omitted.

Example

[0014] Fig. 3 shows an outline of the power supply device of Example 1. As shown in the figure, the power supply device 1 includes a filter circuit 11 and a power supply circuit 12. The filter circuit 11 connects the GND of the digital device 8 and the GND of the analog audio device 7, and improves the sound quality of the analog audio device 7 by reducing noise through the filter circuit 11. The filter circuit 11 is preferably configured to have a small resistance value and a large capacitance of the capacitor in order to improve the sound quality of the analog audio device 7. By reducing the resistance value, the potential difference between the GNDs can be reduced. By increasing the capacitance of the capacitor, the cut-off frequency can be lowered, which contributes to the improvement of the sound quality.

[0015] Note that the power supply device 1 may be realized as an external power supply device outside the analog audio device 7 and the digital device 8, or may be realized as an internal power supply device built in the analog audio device 7 or the digital device 8.

[0016] Note that the analog audio device 7 is, for example, a headphone amplifier, a DAC (Digital Analog Converter), an audio interface, etc., and the digital device 8 is, for example, a computer.

[0017] Fig. 4 shows an outline of the filter circuit 11 of the power supply device 1 of the present embodiment. As shown in the figure, the filter circuit 11 of the power supply device 1 of Embodiment 1 includes a first resistor RA, a second resistor RB, a first capacitor CA, and preferably a second capacitor CB.

[0018] The first resistor RA and the second resistor RB are connected in series between the GND of the digital device 8 and the GND of the analog audio device 7, and have a resistance value that makes the potential difference between the GND of the digital device 8 and the GND of the analog audio device 7 equal to or less than a predetermined value.

[0019] The first capacitor CA is connected in parallel with the second resistor RB, and the RC circuit composed of the first resistor RA and the first capacitor CA has a capacitance that satisfies the condition of a predetermined cut-off frequency.

[0020] The second capacitor CB is connected between the VBUS of the digital device 8 and the GND of the digital device 8.

[0021] Fig. 5 shows a design example of the filter circuit 11 of the power supply device 1 of the present embodiment. The first terminal (VBUS) of the analog audio device 7 is connected to the power supply circuit 12. Although the power supply circuit 12 actually continues at the end of the dotted line in the figure, it is omitted in this figure. The second terminal (-D) and the third terminal (+D) of the analog audio device 7 are respectively connected to the second terminal (-D) and the third terminal (+D) of the digital device 8.

[0022] The digital device 8 and the analog audio device 7 are respectively connected by a USB cable via the power supply device 1, but the signal lines (+D, -D) in the USB cable pass through the power supply device 1 as they are (thru).

[0023] The fourth terminal (GND), the fifth terminal (FG1), and the sixth terminal (FG2) of the analog audio device 7 are respectively grounded (indicated by downward white triangles in the figure).

[0024] It is preferable that the first terminal (VBUS) of the digital device 8 and the fourth terminal (GND) of the digital device 8 are connected via a second capacitor CB as shown in the figure.

[0025] The fourth terminal (GND) of the digital device 8 is connected to the GND of the analog audio device 7 (indicated by a downward white triangle in the right corner of the figure). A filter circuit 11 is connected between the fourth terminal (GND) of the digital device 8 and the GND of the analog audio device 7.

[0026] <Filter circuit 11> As shown in the figure, the filter circuit 11 includes RA1, RA2, RA3, RA4 connected in parallel on the GND side of the digital device 8, a second resistor RB connected in series to a first resistor RA which is a combined resistor composed of RA1 - RA4, and a first capacitor CA connected in series to a first resistor RA which is a combined resistor composed of RA1 - RA4 and connected in parallel to the second resistor RB. In the example of the figure, the resistance values of RA1 - RA4 are 4.7 [Ω]. Therefore, the resistance value of the first resistor RA which is these combined resistors is 1.2 [Ω]. The resistance value of the second resistor RB is 10 [Ω], the capacitance of the first capacitor CA is 10000 [μF], and the capacitance of the second capacitor CB is 3300 [μF].

[0027] <Measurement results of voltage drop by filter circuit 11> In the filter circuit 11 having the design values shown in FIG. 5, with the GND of the digital device 8 as a reference ("0 [mV]" in the figure), the overall voltage drop (y [mV] in the figure), the voltage drop across the first resistor RA (x [mV] in the figure), and the voltage drop across the second resistor RB (y - x [mV]) were actually measured with actual products A, B, and C connected as the analog audio device 7, and the results are shown in FIG. 6.

[0028] Since the sound quality improvement effect was sufficient in all of products A, B, and C, y may be in the range of minus number [mV] to several tens [mV], and specifically, it is preferable that y is up to about -50 [mV].

[0029] That is, if the potential difference between the GND of the digital device 8 and the GND of the analog audio device 7 is 50 [mV] or less, it is preferable, and if the resistance values of the first resistor RA and the second resistor RB are set to satisfy this condition, it is preferable.

[0030] <Experiment of changing the parameters of the filter circuit 11 and comparing the sound quality> Next, an experiment was conducted in which the second resistor RB was fixed at 10 [Ω] and the capacitance of the first capacitor CA was changed to compare the sound quality of the analog audio device 7.

[0031] [When the capacitance of the first capacitor CA is decreased] There was a lack of three-dimensional sound and it was difficult to distinguish fine sounds. Also, when chords or multiple instruments sounded, the sounds might mix and the afterglow and delicate sounds might be buried.

[0032] [When the capacitance of the first capacitor CA is increased] The resolution improved across the entire sound range, but the resolution in the low-frequency range improved significantly compared to other sound ranges, and as a result, the sounds in other sound ranges tended to be buried.

[0033] Based on the experimental results, the standard value of the combined resistance value of the first resistor RA was set to about 1.2 [Ω], and the standard value of the capacitance of the first capacitor CA was set to about 10,000 [μF]. At this standard value, the cut-off frequency of the RC circuit composed of the first resistor RA and the first capacitor CA is 13 [Hz].

[0034] Based on this standard, suitable conditions are set as follows.

[0035] · The first capacitor CA preferably has a low ESR value and the largest possible capacitance. For example, it is preferable if it is about 8,200 to 22,000 [μF].

[0036] · The preferable cut-off frequency is around 13 [Hz], and it is preferable if it is about 10 to 20 [Hz].

[0037] <Summary> From the results obtained in the above measurements and experiments, a plurality of combinations of capacitors and resistors that satisfy the conditions were considered, and the conditions for suitable parameters were determined.

[0038] · The potential difference between the GND of the digital device 8 and the GND of the analog audio device 7 is 50 [mV] or less · The first capacitor CA has a sufficiently low ESR value and its capacitance is about 8,200 to 22,000 [μF] · The cut-off frequency is about 10 to 20 [Hz] (more preferably around 13 [Hz]) · The resistance value of the second resistor RB is about 4.7 to 15 [Ω] (a reference value obtained from the overall voltage drop)

Claims

1. A power supply device that is connected to a digital device via USB and supplies power to an analog audio device that receives digital data from the digital device, a first resistor and a second resistor that are connected in series between the GND of the digital device and the GND of the analog audio device and have a resistance value that makes the potential difference between the GND of the digital device and the GND of the analog audio device equal to or less than a predetermined value, a capacitor connected in parallel to the second resistor, the capacitor including a capacitor having a capacitance such that the RC circuit composed of the first resistor and the capacitor satisfies the condition of a predetermined cut-off frequency Power supply device.

2. The power supply device according to claim 1, including a second capacitor connected between the VBUS of the digital device and the GND of the digital device Power supply device.

3. The power supply device according to claim 1, wherein the potential difference between the GND of the digital device and the GND of the analog audio device is 50 [mV] or less Power supply device.

4. The power supply device according to claim 1, wherein the capacitance of the first capacitor is 8,200 [μF] or more and 22,000 [μF] or less Power supply device.

5. The power supply device according to claim 1, wherein the condition of the cut-off frequency is 10 [Hz] or more and 20 [Hz] or less Power supply device.

6. The power supply device according to claim 5, wherein the condition of the cut-off frequency is around 13 [Hz] Power supply device.

7. The power supply device according to claim 1, wherein the resistance value of the second resistor is 4.7 [Ω] or more and 15 [Ω] or less Power supply device.

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