JP2000259264A - Ac adapter for power supply for acoustic equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To fast respond to a load fluctuation and also to reduce output noise by controlling saturation time by controlling a reset current to a saturable reactor. SOLUTION: When a switching part 30 switches a direct current voltage smoothed in a fixed interval to drive a pulse transformer 32, a voltage is generated on an output side of the transformer 32 when the part 30 is ON and the voltage is applied to a saturable reactor 34. When the reactor 34 reaches its saturation, current is fed to a rectification side diode 36 and a load while energy is stored in an output smoothing choke 38. Then, an output voltage is detected directly by a Zener diode 40 and its resistance 42 for a bias current, and a reset current I is made to flow through a transistor 46 for reset current control with it as a reference voltage. Then, the current I is fed to the reactor 34 for control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC adapter, and more particularly to a power supply adapter for audio equipment.

[0002]

2. Description of the Related Art As a conventional AC adapter, FIGS.
4 and the like are known. The AC adapter converts power from an AC commercial power supply to DC and supplies the converted power to a load. As a simple adapter, there is an AC adapter 01 shown in FIG. That is, after the input from the AC outlet 02 and the AC code 03 is added to the transformer T, it is converted into direct current by the rectifying and smoothing circuit 04 and smoothed, and then the stabilized power supply 05 passes through the DC output code 06, Connector 0
7 is output. However, this adapter 01 uses a transformer for commercial frequency as the transformer T,
Since the transformer itself is large and the DC stabilized power supply 05 employs a dropper method, there is a disadvantage that the efficiency is extremely poor.

In order to solve this problem, in the AC adapter 08 shown in FIG. 12, first, a rectifying and smoothing circuit 09 converts an alternating current into a direct current. The switching unit 10 is provided, and the switching unit 10 is controlled by the primary voltage of the output voltage detection unit 11 to drive the transformer T. Thereafter, it is further smoothed and output by the rectifying and smoothing circuit 12. But this adapter 0
8 is not suitable for use in precision equipment such as audio equipment because load fluctuation is large and response to the fluctuation is poor.

In the AC adapter 13 shown in FIG. 13, the detected value of the output voltage detected by the output voltage detecting section 14 is used as a control signal of the switching section 10 and transmitted to the primary side via a photocoupler 15. The output voltage control unit 16 uses the transmitted detection value as a negative feedback control signal to the switching unit 10. However, an adapter using a photocoupler has disadvantages in that the response of the photocoupler is poor, high-speed response is not possible, and output noise is large.

[0005] Instead of using a photocoupler, the voltage may be controlled by a chopper-type constant voltage controller 18 after DC / DC conversion and output as in an AC adapter 17 shown in FIG. There is a problem that the outer shape becomes large and impractical, the number of parts is large, the cost is high, and furthermore, it is difficult to take measures against output noise.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a power supply for audio equipment which responds quickly to load fluctuations and reduces output noise.
An object of the present invention is to provide a C adapter so that sound from a low range to a high range can be reproduced accurately and with a wide dynamic range.

[0007]

An AC adapter for a power supply for audio equipment according to the present invention is a stabilized DC power supply for converting an AC voltage from an AC outlet into a DC voltage, wherein a saturable reactor is connected to an output side of a pulse transformer. The output from this pulse transformer is saturated by the voltage-time product of the saturable reactor, the current is supplied to the load while accumulating energy in the output smoothing choke, and the reset current to the saturable reactor is controlled to saturate. In addition to controlling the time, the reset current obtained based on the reference voltage is fed back to the saturable reactor via the semiconductor switch.

The AC adapter for a power supply for audio equipment according to the present invention is a DC stabilized power supply for converting an AC voltage from an AC outlet into a DC voltage, wherein a saturable reactor is connected to an output side of a pulse transformer. The output from the pulse transformer is saturated by the voltage-time product of the saturable reactor, the energy is stored in the output smoothing choke, the current is supplied to the load, and the reset current to the saturable reactor is controlled to control the saturation time. And a reference voltage generating means as control means for the reset current, amplifies the difference between the reference voltage and the output voltage by error, adjusts the reset current by the error voltage, and saturates by the reset current. It is characterized by controlling the saturation of the reactor.

[0009]

The signal waveforms of the audio equipment have almost no repetitive output of the same signal, and have special transient waveforms with severe transient characteristics. For example, the sound of a musical instrument is determined not only by the slow repetition of a sine wave such as a sine wave, but also by a waveform in which a low-level noise-like component is added to the gradual waveform of this transient characteristic. .
Moreover, orchestras and the like are composed of many musical instruments, each of which has a fine sound nuance. The most important factor that determines the performance of an audio device is the speed of response that can follow a signal having a special waveform having such a severe transient characteristic. Further, the signal of the commercial power supply contains a high frequency component and a ripple, and deteriorates sound quality as noise. Noise reduction is essential for improving the performance of audio equipment. Note that, in this specification, an audio device refers to a device having a low-frequency signal amplifier in a circuit, for example, a sound preamplifier, a power amplifier, a CD player, a tuner, and the like. Also, the present invention corresponds to a case of a device for audio using digital signals such as a CD transporter.

According to the present invention, in order to enable high-speed response of an AC adapter for audio equipment and reduce noise,
A saturable reactor is used as a DC stabilized power supply for the C adapter, and mag amp control is performed. That is, the saturable reactor is inserted into the output winding of the output transformer of the AC adapter, and a circuit for supplying a reset current to the saturable reactor is provided. The reset current obtained by directly detecting the output voltage is used for resetting the saturable reactor. Since the saturation time of the saturable reactor is determined by the total reset current, the reset current is controlled to directly control the saturation time and control the output voltage. If the reset current is obtained from the output voltage, the response can follow the voltage fluctuation, so that a high-speed response is possible.

In addition, since a gradual change in current is obtained by the inductance component of the saturable reactor itself after saturation, the change in current to the output rectifier diode is reduced, and the recovery current of the output rectifier diode is reduced. Also, output noise is reduced.

Further, the AC adapter can be made compact with a small number of parts. Therefore, it is possible to provide a low-cost, high-performance audio equipment adapter. Further, since no photocoupler is used, it is easy to comply with safety standards.

[0013]

1 to 5 show an embodiment and a modified example thereof. FIG. 1 shows an AC adapter and its accessories in the embodiment, and FIG. 2 shows a circuit configuration thereof. Reference numeral 20 denotes an AC adapter, and reference numeral 22 denotes an AC adapter case, which contains an AC / DC converter. 02 is an AC outlet, 03 is an AC input cord, 06 is a DC output cord, and 07 is a connector for connecting to a load audio device. Reference numeral 24 denotes a light emitting means such as a neon tube or an LED provided outside the case 22, and R denotes a light emitting means 24.
Reference numeral 26 denotes an external contact portion of the case 22. When the AC outlet 02 is connected to the outlet with the correct polarity, if the contact portion 26 is touched, the light emitting means 22 is turned on, and it is possible to know that the polarity is correct. Of course, on the contrary, when the polarity is not correct due to leakage current or the like, the light may be turned on. The AC adapter 20 of the embodiment
Is not built into audio equipment that requires power,
The reason is that the mag-amp type switching power supply circuit as in the embodiment generates high-frequency electromagnetic noise and affects the signal of the low-frequency amplifier circuit.

FIG. 3 is a circuit diagram of the AC adapter 20 according to the first embodiment. 28 is a rectifying and smoothing circuit for rectifying and smoothing the AC current from the AC code 03, 30 is a switching unit for switching the smoothed DC current,
The pulse transformer 32 is directly driven. Numeral 34 denotes a saturable reactor, which is a saturable choke coil manufactured using a saturable core. The saturated choke coil is called a saturable reactor. This saturable reactor 34
Into the output winding of the transformer 32 to stabilize the DC current. Here, the number of outputs of the pulse transformer 32 is arbitrary, and the duty ratio is controlled by the saturable reactor. 36 is a rectifier-side diode, 38 is an output smoothing choke, which is connected in series with the reactor 34, and when the saturable reactor 34 is saturated, a current flows through the diode 36.
To the choke 38 through which energy is stored. The saturation time of the reactor 34 is determined by the switching unit 30.
Is determined by the total amount of the reset current I supplied to the reactor 34 during the off period. Therefore, by controlling the reset current I, the saturation time of the reactor 34 can be controlled, and the output voltage of the adapter 20 can be controlled.

Reference numeral 40 denotes a Zener diode for obtaining a reference voltage, and reference numeral 42 denotes a resistor for bias current of the diode 40. A current flows from the output voltage to the Zener diode 40 via the resistor 42 to obtain a reference voltage for controlling the reset current I. The capacitor 44 is connected in parallel with the zener diode 40, absorbs the noise of the diode 40, and reduces fluctuations in the transient response.

Reference numeral 46 denotes a transistor for controlling the reset current of the saturable reactor 34. Although a noncontact relay MOSFET is used in the embodiment, a bipolar transistor, an IGBT or the like may be used. The capacitor 44 is connected to the gate of the control transistor 46 via the resistor 48 for preventing abnormal transistor oscillation. The source side of the control transistor 46 is connected to the output voltage side. Reference numeral 50 denotes a diode for preventing reverse voltage application of the control transistor 46, and reference numeral 52 denotes a current limiting resistor of the transistor 46. The reset current I flows from the drain side of the transistor 46 to the reactor 34 via the resistor 52 and the diode 50. 54 is an output smoothing capacitor, and 56 is a flywheel diode.

Next, the operation of this embodiment will be described. When the pulse transformer 32 is driven by switching the DC voltage smoothed at regular intervals by the switching unit 30, a voltage is generated on the output side of the transformer 32 when the switching unit 30 is turned on, and this voltage is transmitted to the saturable reactor 34. Applied. When the saturable reactor 34 is saturated by the voltage-time product, a current is supplied to the diode 36, and a current is supplied to the load while storing energy in the output smoothing choke 38.

Assuming that the time during which a current flows through the rectifier diode 36 is TON, the switching cycle of the switching unit 30 is T, and the input voltage is VI, the output voltage VO can be obtained by the following equation. 34 can be controlled. VO = VI × TON / T

Here, the saturation of the saturable reactor 34 will be described. The saturation time depends on the saturable reactor 34 during the off period of the switching means of the switching section 30.
Is determined by the total amount of the reset current I. That is, by controlling the reset current I, the saturation time of the saturable reactor 34 can be controlled, that is, the output voltage can be controlled. If the reset current is not applied, the magnetic density of the core of the saturable reactor 34 reaches the saturated magnetic density in one to several pulses. By setting the reset current to an appropriate value, the pulse width passing through the saturable reactor 34 can be controlled, and the output voltage can be controlled.

Reset current I of saturable reactor 34
Is determined using the reference voltage in the embodiment. That is, in the embodiment, the Zener diode 40 and its bias current resistor 4
2, the output voltage is directly detected and used as a reference voltage, and a reset current I flows through a reset control diode 46. Then, the reset current I is supplied to the saturable reactor 34 to control it. In the embodiment, since the reset current I is determined from the output voltage, the response to a load change is improved, a high-speed response is possible, and the reset current I can be used as an adapter for audio equipment.

Further, by using the saturable reactor 34, a ripple or an
Since the high frequency component is reduced, the current change from the saturable reactor 34 to the output rectifier diode 36 is also moderated, and the recovery current of the diode, that is, the extra current other than the DC component is reduced, so that the output noise is also reduced. I do.

The current i flowing through the flywheel diode 56, the output smoothing choke 38, and the capacitor 54 is
This is because the current for saturating the choke 38 is made smooth and the energy is gradually stored.

[0023]

[Modification 1] FIG. 4 shows a circuit of an adapter 60 in which the embodiment is modified. Reference numeral 62 denotes a power factor improving circuit obtained by adding a power factor improving function to a rectifying and smoothing circuit for input current. Reference numeral 340 denotes a saturable reactor, which is connected to the opposite polarity side (− side) of the output winding of the transformer 32 in a modified example. In the modification, two resistors are added to the circuit for supplying the reset current as shown in the figure. That is, a resistor 66 is inserted between the Zener diode 40 for obtaining the reference voltage and the capacitor 44 for absorbing the noise of the diode 40, thereby efficiently attenuating the noise from the diode 40 and the noise from the output. As a result, the stability of the voltage applied to the capacitor 44 is improved. The positive side of the output and the reset control transistor 46
A resistor 64 is also connected between the sources. This lowers the equivalent forward admittance characteristics of transistor 46,
This is because oscillation is prevented and stable operation is performed by reducing the control gain. As in the embodiment, a bipolar transistor, an IGBT, or the like may be used as the reset control transistor 46 in addition to the MOSFET.

In this modification, the saturable reactance 34
0 is connected to the negative side of the output side of the transformer 32. The operation is the same as that of the embodiment, and the energy is stored in the output smoothing choke 38 when the reactance 340 is saturated by the voltage-time product. Further, the reset control of the saturable reactor 340 can be performed by the reset current I from the transistor 46. It is needless to say that other constant voltage generating means may be used without using the Zener diode 40. Further, the diode 50 for preventing reverse voltage from being applied to the transistor 46 and the current limiting resistor 52 of the transistor 46 may of course be replaced.

[0025]

[Modification 2] FIG. 5 shows an adapter 7 according to another modification of the embodiment.
0 shows a circuit diagram. In this modification, a dedicated circuit for reset control of the saturable reactor 34 is provided. That is, the reference voltage Vref is used, the error between the reference voltage Vref and the output voltage is detected by the error amplifier 72, and the reset current to the saturable reactor 34 is adjusted according to the change in the output voltage. For example, when the output voltage exceeds the reference voltage Vref, the output current (reset current I) of the amplifier 72 increases, and an increase in the output voltage is suppressed. Conversely, if the output voltage fluctuates below the reference voltage Vref, the reset current I decreases. Where 74,76
Numerals are negative feedback impedance elements such as resistors, respectively, for reducing the gain at the resonance frequency of the output choke for smoothing the output of the switching power supply and the output capacitor, thereby preventing abnormal oscillation. The resistor 520 functions as a reset current limiting resistor in this modification.

Signal waveforms in most audio equipment such as amplifiers, tuners, players and the like are special, have extremely severe transient characteristics, and change signals sharply. In addition to the variability, the frequency range of the sound is very wide and may include almost all frequency ranges. The AC adapter in the embodiment is used for audio, and operates as a stabilized DC power supply even with such a special signal waveform. In other words, the output is kept constant even if the frequency bandwidth is very wide and the load fluctuates drastically.

FIG. 6 shows a conventional switching power supply circuit, and FIG. 7 shows a waveform of output fluctuation of the power supply circuit. FIG.
Is a reference voltage, and a differential amplified signal of the reference voltage and the output voltage VO is transmitted to the primary side control unit through the photocoupler 80, and controls the transformer via the MOSFET and the like. The variation of the output voltage VO in this case is shown in FIG.

FIG. 8 shows a mag-amp type switching power supply circuit according to the embodiment. Here, the saturable reactor L
Is connected to the output side of the transformer T to apply a reset current I1 to the saturable reactor L. FIG. 9 shows the variation of the output voltage in FIG. In FIG. 8, D is a constant frequency, constant duty ratio drive circuit. As is clear from FIG. 9, the variation 出力 of the output voltage VO is so small as to be a static load variation as compared with the variation in FIG. In other words, if the AC adapter according to the embodiment is used, the output fluctuation can be reduced and the output fluctuation can be made static at a low frequency.

FIG. 10 shows the output noise of the switching power supply when the pulse transformer is turned on and off.
(C) shows an output waveform of the conventional switching power supply, and (C) shows an output waveform of the switching power supply in the embodiment. As is clear from this figure, the conventional switching power supply does not sufficiently reduce high-frequency noise during frequency conversion, and significantly degrades a signal to be reproduced. In addition, the frequency of the generated noise may change the pulsed acoustic signal. On the other hand, according to the embodiment, the output noise, that is, the voltage ripple ΔV is small. Thus, switching noise (high-frequency ripple noise) can be reduced, and the sound quality is improved. Further, as a noise countermeasure, it is possible to reduce high frequency noise in the commercial power supply from being mixed into the smoothing circuit.

As described above, the use of the AC adapter according to the embodiment makes it possible to maintain a good response to a load change, a small noise, and a small output change. That is, it is possible to provide a stable sound device having good sound quality. According to the inventor's audition, the fineness of sound, the separation of musical instrument sounds, the feeling of dynamism, etc. have been improved, and the sound of violin and viola, which must accurately represent minute differences in waveforms, has been improved. The differences could be clearly separated. In particular, the fine sound of the orchestra composed of many instruments was improved and the nuances of the performers were improved.

As described above, according to the embodiment, the sound quality of the audio equipment can be easily improved by improving only the power supply connected to the audio equipment itself without changing the audio equipment itself.

In these embodiments and modifications, the AC
The code 03 and the output code 06 can be made detachable from the AC adapter body. Further, a switch means for turning on / off the input of the alternating current may be provided inside the AC adapter. The number of output controls in the AC adapter is arbitrary, and the number of DC outputs is also arbitrary.

In the first modification of FIG. 4, a power factor improving circuit is added to the input rectifying / smoothing circuit.
Of course, it is optional.

Further, an output display means for displaying an output voltage or the like on the AC adapter may be provided.

In the case of an AC adapter for audio equipment, it is required for sound quality to connect an AC outlet with a polarity that minimizes leakage current to a DC output cord. Therefore, when the AC outlet of the AC adapter is connected to a power source, if the polarity of the connection can be easily and instantaneously determined, the sound quality can be improved. Therefore, as shown in FIG. 1 and FIG.
As a polarity display function, an external contact portion and a light emitting means are provided on the AC adapter. For example, if the user touches the external contact portion while connected to the outlet with the correct polarity, the light is displayed by the light emitting means. As a result, whether the connection of the AC outlet is correct or not can be easily known at the time of connection.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the appearance of an AC adapter according to an embodiment.

FIG. 2 is an internal configuration diagram of an AC adapter according to an embodiment;

FIG. 3 is a circuit diagram of an AC adapter according to the embodiment.

FIG. 4 is a circuit diagram of a modified AC adapter.

FIG. 5 is a circuit diagram of an AC adapter according to another modification.

FIG. 6 is a circuit diagram of an AC adapter used to check an operation state.

7 is an output waveform diagram of the AC adapter of FIG. 6,
(A) is an input voltage waveform diagram, (b) is a pulse current waveform diagram to the secondary side, and (c) is a secondary side voltage waveform diagram.

FIG. 8 is a circuit diagram of an AC adapter of an embodiment used for checking an operation state.

FIG. 9 is an output waveform diagram of the AC adapter of FIG. 8;
(A) is an input voltage waveform diagram, (b) is a pulse current waveform diagram to the secondary side, and (c) is a secondary side voltage waveform diagram.

FIG. 10 is an operation waveform diagram of a switching voltage when a pulse input is turned on / off.

FIG. 11 is a circuit diagram of a conventional AC adapter.

FIG. 12 is a circuit diagram of a conventional AC adapter.

FIG. 13 is a circuit diagram of a conventional AC adapter.

FIG. 14 is a circuit diagram of a conventional AC adapter.

[Explanation of symbols]

 02 AC outlet 03 AC cord 06 Output cord 07 Connector 20, 60, 70 AC adapter 24 Light emitting means 26 Contact part 28 Rectifying smoothing circuit 30 Switching part 32 Pulse transformer 34,340 Saturable reactor 36 Rectifying side diode 38 Output smoothing choke 40 Zener diode 46 Reset current control transistor 72 Error amplifier

Claims (2)

[Claims] 1. A stabilized DC power supply for converting an AC voltage from an AC outlet into a DC voltage, wherein a saturable reactor is connected to an output side of a pulse transformer.
The output from this pulse transformer is saturated by the voltage-time product of the saturable reactor, the current is supplied to the load while accumulating energy in the output smoothing choke, and the reset current to the saturable reactor is controlled to saturate. An AC adapter for an audio device power supply having an output connector, wherein the AC adapter controls output time and feeds back a reset current obtained based on a reference voltage to a saturable reactor via a semiconductor switch. 2. A stabilized DC power supply for converting an AC voltage from an AC outlet into a DC voltage, wherein a saturable reactor is connected to an output side of a pulse transformer,
The output from this pulse transformer is saturated by the voltage-time product of the saturable reactor, the current is supplied to the load while accumulating energy in the output smoothing choke, and the reset current to the saturable reactor is controlled to saturate. In addition to controlling the time, a reference voltage generating means is provided as control means for the reset current to amplify the difference between the reference voltage and the output voltage with an error, adjust the reset current with the error voltage, and adjust the reset current with the reset current. An AC adapter for a power supply for audio equipment, comprising an output connector, wherein the AC adapter controls the saturation of a saturation reactor.