JPH0621728A - Power supply circuit for output amplifier - Google Patents

Abstract

PURPOSE:To provide the power supply circuit for an output amplifier circuit with less distortion at a large output in a short period by adopting the configuration such that a power supply circuit for a long period and a power supply circuit for a short period are provided in parallel for power supply circuits for the output amplifier. CONSTITUTION:An output power of an output amplifier 2 is proportional to a current from power supply circuits 4, 5 supplying power, and the current is supplied from a power supply circuit 4 for a short period supply in the case of small power and a large current for a short period supply. Moreover, the power is supplied from the circuit 4 in the beginning for a large output for a long period supply, and then a voltage across a capacitor 9 is low, a diode 6 is turned on and then the power is supplied from the power supply circuit 5 used usually for a large output for a long period supply succeedingly. Thus, even when a short period output is increased and the circuit 5 is not responsive, a desired current is supplied to the amplifier 2 with good response from the circuit 4 whose time constant is selected and designed by assuming the case. As a result, distortion at a large output for a short period supply is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for an output amplifier used in a power supply circuit of audio equipment.

[0002]

2. Description of the Related Art The output characteristic of an output amplifier is determined by the voltage and current of a power supply circuit supplied to the output amplifier. Conventionally, the power amplifier circuit for output amplifiers, which has reduced distortion at high output for a short time and is capable of reproducing a sound signal close to the input signal, is the power supply for the output amplifier circuit at a high output for a short time. Even if a voltage during no output is applied due to the time constant of the rectifier circuit, the fluctuation rate of the power transformer is increased in order to reduce the distortion due to this.

[0003]

In the above conventional power supply circuit, it is necessary to reduce the wire diameter of the winding of the power supply transformer in order to increase the fluctuation rate of the power supply transformer. As a result, this power supply circuit is used. Although the distortion of the output amplifier at the time of large output for a short time is improved, there is a drawback that the temperature rise of the power transformer becomes large at the time of large output for a long time. Therefore, there is a problem that there is a limit to increase the output value that can reduce the distortion at the time of high output for a short time.

[0004]

In order to solve the above problems, the present invention converts an AC voltage of a first power transformer into a DC voltage through a first rectifier circuit and a first smoothing circuit having a small time constant. A first power supply circuit that converts and uses the direct current voltage as a power supply for an output amplifier; a second power supply circuit that includes a second power supply transformer, a second rectifier circuit, and a second smoothing circuit having a large time constant; When the output voltage of the first power supply circuit falls below a predetermined value, a switching means is provided to use the second power supply circuit instead of the first power supply circuit as the power supply of the output amplifier.

The AC voltage derived from the first secondary winding of the power transformer is converted into a DC voltage through the first rectifier circuit and the first smoothing circuit having a small time constant, and the DC voltage is output. A first power supply circuit for supplying to the amplifier, and a second secondary winding provided in the power supply transformer, and the second secondary winding and the second secondary winding are provided.
Second power supply circuit comprising a rectifier circuit and a second smoothing circuit having a large time constant, and a second power supply circuit instead of the first power supply circuit when the output voltage of the first power supply circuit falls below a predetermined value. The power supply circuit is provided with switching means for using the power supply of the output amplifier.

[0006]

In the power supply circuit for the output amplifier circuit configured as described above, the rectified voltage can be supplied to the output amplifier circuit from the first power supply circuit provided exclusively for a large output for a short time, and the power amplifier circuit for a long time can be supplied. The circuit can be configured to increase the value of the output during a short time without changing the performance of the output during time, and completely independently. Therefore, it is possible to reduce distortion at the time of large output for a short time and obtain a faithful audio signal close to the input signal. Normally, the output for a short time (music output) is limited to about twice as long as the output for a long time (rated output), but when the power supply circuit for the output amplifier circuit configured as described above is adopted, the music output is Can be arbitrarily set to any multiple of the rated output.

[0007]

FIG. 1 is a circuit diagram of an embodiment of the present invention. In FIG. 1, 1 is a signal input terminal, 2 is an output amplifier, 3 is a speaker, 4 is a power supply circuit dedicated for short-time large output, and 5 is an ordinary power supply circuit (for long-time large output). ),
Reference numeral 6 is a backflow prevention diode. The power supply circuit 4 provided exclusively for high power output for a short time is composed of a power supply transformer 7, a rectifying diode 8 and a smoothing capacitor 9 having a small time constant. In addition, the above-mentioned normal power supply circuit 5
Similar to the power supply circuit 4, the (for long time large output) is composed of a power supply transformer 10, a rectifying diode 11 and a smoothing capacitor 12 having a large time constant.

FIG. 2 is a circuit diagram of a second embodiment of the present invention. It is constructed by one power transformer as compared with the embodiment shown in FIG. 1 which uses two independent power transformers. An inexpensive circuit is provided. 2, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and description thereof will be omitted.

In FIG. 2, reference numeral 20 denotes a power transformer, and a rectifier used for a long-time high-power power circuit 5 between _one terminal T ₁ and an intermediate terminal T _{3 of a} secondary winding of the power transformer 20. circuit 11 is connected, between one terminal T ₁ and the other terminal T ₂ of the said secondary winding rectifier circuit 8 used in the power supply circuit 21 for a large output of the short time is connected. Reference numeral 22 is a current limiting circuit provided between the power supply circuit 21 and the output amplifier 2.

The audio signal input from the signal input terminal 1 is amplified by the output amplifier 2 and is output from the speaker 3 as an audio output. In this case, the power supply to the output amplifier 2 is connected in parallel via the backflow prevention diode 6 and is provided in a dedicated power supply circuit 4 or 21 for a large output for a short time.
Then, the power is supplied from the normal power supply circuit 5 provided for a large output for a long time.

The magnitude of the output of the output amplifier 2 is proportional to the current from the power supply circuit to be supplied. This current is supplied to the power supply circuit 4 for high power for a short time at low power and high power for a short time. Alternatively, it is supplied from 21 and is initially supplied from the power supply circuit 4 at the time of large output for a long time, but thereafter, the voltage across the capacitor 9 becomes low and the diode 6 becomes O.
N, and thereafter, it is properly used so as to be supplied from the normal power supply circuit 5 provided for a large output for a long time.

Therefore, even when the output for a short time becomes large and the normal power supply circuit 5 provided for a large output for a long time does not respond due to the time constant of the circuit, a circuit constant is selected and designed assuming such a case. A desired current is responsively output from the power amplifier circuit 4 or 21 for large output for a short time.
To reduce the distortion at the time of high output for a short time, and even in such a case, a high fidelity audio output close to the input signal can be derived.

FIG. 3 shows a power supply transformer 7 or 20 of a power supply circuit 4 or 21 exclusively provided for a large output for a short time and a power supply transformer 1 of a normal power supply circuit 5 (for a large output for a long time).
An example of the variation rate of 0 or 20 is shown. The vertical axis represents the voltage supplied from the power supply circuit to the output amplifier 2 (proportional to the output of the output amplifier 2), and the horizontal axis represents the power supply circuit to the output amplifier 2.
Current (which is proportional to the time of the output from the output amplifier 2). In FIG. 3, the portion a is a small output, the portion b is a large output for a short time, and the portion c is a large output.

Note that the capacity of the smoothing capacitor 9 and the power supply transformer 7 or the power supply transformer 2 are effective when the power supply circuit 4 or 21 provided exclusively for a large output for a short time is effective.
It is determined by the capacity of 0 (winding wire diameter). Further, the magnitude of the peak of the output for a short time is determined by the voltage of the power transformer 7 or 20 when there is no signal. Further, since the wire diameter of the winding of the power transformer 4 or 20 provided exclusively for a large output for a short time can be made thin, the cost increase of this power transformer can be reduced.

In the second embodiment of the present invention shown in FIG. 2, an extended portion of the winding used in the normal power supply circuit 5 is used as the winding of the power transformer 20 used for a large output for a short time. Alternatively, two independent secondary windings for short time and long time may be provided in the same power transformer, and these secondary windings may be used separately.

[0016]

As described above, the present invention provides a power supply circuit of an output amplifier which can obtain a faithful audio output close to an input signal by reducing distortion at a high output for a short time with a simple circuit configuration. be able to.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of another embodiment of the present invention.

FIG. 3 is an operation explanatory diagram of the present invention.

[Explanation of symbols]

 2 Output amplifier 4, 5, 21 Power supply circuit 7, 10, 20 Power supply transformer 8, 11 Rectifier circuit 9, 12 Smoothing capacitor

Claims (2)

[Claims] 1. A first alternating current voltage of a first power transformer is converted into a direct current voltage through a first rectifying circuit and a first smoothing circuit having a small time constant, and the direct current voltage is used as a power source of an output amplifier.
Of the second power supply circuit, the second power supply transformer, the second rectifier circuit, and the second smoothing circuit having a large time constant, and the output voltage of the first power supply circuit falls below a predetermined value. And a switching unit that uses the second power supply circuit as the power supply for the output amplifier in place of the first power supply circuit. 2. An AC voltage derived from a first secondary winding of a power supply transformer and a first rectifier circuit which has a small time constant.
A first power supply circuit for converting the direct current voltage to the output amplifier and converting the direct current voltage to the output amplifier through the smoothing circuit, and a second secondary winding for the power supply transformer. A second power supply circuit including a second rectifier circuit and a second smoothing circuit having a large time constant; and a first power supply circuit instead of the first power supply circuit when the output voltage of the first power supply circuit falls below a predetermined value. 2. A power supply circuit for an output amplifier, comprising: switching means configured to use the second power supply circuit as a power supply for the output amplifier.