JP2009050115A - Power supply circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply circuit that suppresses standby power consumption in standby status without affecting a supply voltage during power-on. <P>SOLUTION: A power supply circuit 19 is provided with a smoothing circuit 34, which smoothes an AC current, transmitted to a secondary side via a transformer 33, by a capacitor Cb so as to output a secondary-side voltage Vb, a feedback circuit 35, which outputs a feedback signal based on the secondary-side voltage Vb to a primary side via a photocoupler 35b having a light-emitting diode LED1 with one end connected to an output line Lvb of the secondary-side voltage Vb and the other end connected to a transistor 35a operating on the basis of the secondary-side voltage Vb, a switching circuit 36, which controls a primary-side voltage Va by executing switching on the basis of the feedback signal so as to obtain a prescribed secondary-side voltage Vb, and a transistor 37 that connects the output line Lvb of the secondary-side voltage Vb to a ground line GND via a resistor R1 only in standby status. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a power supply circuit that obtains a predetermined secondary voltage by controlling a primary voltage based on a feedback signal based on a secondary voltage output to a primary side via a photocoupler.

  2. Description of the Related Art A power supply circuit that obtains a predetermined secondary side voltage by controlling a primary side voltage based on a feedback signal based on a secondary side voltage output to a primary side via a photocoupler is well known.

  For example, FIG. 5 is a diagram illustrating a schematic circuit configuration of a conventional power supply circuit. In FIG. 5, a power supply circuit 1 is a partial resonance power supply circuit, and a rectifier circuit 2 that outputs a primary side voltage Va by full-wave rectifying an external commercial AC power supply, for example, with a rectifier bridge 2a and smoothing with a capacitor 2b; The primary side voltage Va input to the primary coil 3a is converted into a plurality of types of predetermined voltages by the secondary coils 3b, 3c and 3d having a predetermined turn ratio, respectively, and energy (alternating current) is given to the secondary side. The transformer 3 for transmission and the alternating current transmitted to the secondary side are rectified and smoothed by the diodes Db, Dc, Dd and the capacitors Cb, Cc, Cd to output the secondary side voltages Vb, Vc, Vd. For example, a feedback circuit 5 for outputting a feedback signal based on, for example, the secondary side voltage Vb to the primary side via the photocoupler 5b, and a feedback from the feedback circuit 5. The primary voltage Va based on a signal consisting of the switching circuit 6 for PWM control.

The feedback circuit 5 includes, for example, a transistor 5a that is turned on when a divided voltage of the secondary side voltage Vb is input to the base and the secondary side voltage Vb exceeds a predetermined voltage, and one end connected to the output line Lvb of the secondary side voltage Vb. And a photocoupler 5b having a light emitting diode connected at the other end to the collector of the transistor 5a. When the secondary side voltage Vb exceeds a predetermined voltage, the transistor 5a is turned on and switched via the photocoupler 5b. A feedback signal is output to the circuit 6.
The switching circuit 6 includes an oscillation circuit, and performs feedback control by PWM control so that the secondary side voltage Vb becomes an appropriate voltage (predetermined voltage) based on the feedback signal from the feedback circuit 5.

  Here, it is desirable that the power consumption during standby (so-called standby power consumption) be minimized as much as possible in an apparatus that includes the power supply circuit as described above and that supplies voltage to each unit from the power supply circuit. In the standby mode, for example, the main power supply is in an on state, and power is supplied only to a part of the circuits such as the microcomputer and the user is waiting for reception of various operations (for example, power-on operation) or according to a reservation program. It is a waiting state such as waiting. Further, when the power is turned on, it is a normal operation state in which, for example, power is supplied to other circuits necessary for operation to display an image on a screen or output sound from a speaker.

  For example, Patent Document 1 includes a current control IC that controls a full-wave rectifier circuit, a smoothing capacitor, and a switching element on the primary side of a converter transformer, and is supplied from a secondary-side diode of a standby signal feedback photocoupler. The standby signal voltage is received by the primary-side transistor of the photocoupler, and the standby-signal feedback photocoupler from the primary-side full-wave rectifier circuit via the half-wave current limiting resistor and the half-wave rectified voltage limiting Zener diode A switching power supply is disclosed in which the switching loss is reduced by half and the standby power can be reduced by turning off the switching element in synchronization with the half-wave rectified voltage input to the collector of the transistor of the transistor, thereby saving power during standby. ing.

Further, in Patent Document 2, in the switching power supply circuit, in order to keep the switch element in the OFF state, a photocurrent receiving portion of a photocoupler is connected to the connection side of the capacitor and the resistor, and the starting current for turning on the switch element Is absorbed by the light receiving portion of the photocoupler and continues to turn on the switch element. Therefore, the oscillation is surely stopped until the output voltage drops in the secondary side circuit. In the conventional circuit, the capacitor used to stop the oscillation was the cause of increasing the power consumption. On the other hand, the same oscillation can be stopped without using the capacitor. It is disclosed that the amount can be reduced.
JP 2002-049442 A JP 2003-304686 A

  By the way, at the time of light emission of the light emitting element of the photocoupler, a current corresponding to the secondary side voltage flows during standby and when the power is turned on. Naturally, the power consumption increases as the current increases. Therefore, in order to further reduce the standby power consumption, it is conceivable to reduce the current during light emission by changing the constant of the resistance. However, since the secondary voltage must be maintained at an appropriate voltage especially when the power is turned on, there is a limit to combining circuit constants in order to reduce standby power consumption.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a power supply circuit that can suppress standby power consumption during standby without affecting the supply voltage during power-on. It is to provide.

  In order to achieve the above object, the invention according to claim 1 is characterized in that a primary side voltage input to a primary coil is converted into a predetermined voltage by a secondary coil and AC is transmitted to the secondary side, and A smoothing circuit for smoothing alternating current transmitted to the secondary side with a capacitor and outputting a secondary side voltage, one end connected to the output line of the secondary side voltage, and the other end based on the secondary side voltage A feedback circuit for outputting a feedback signal based on the secondary side voltage to the primary side via a photocoupler having a light emitting element connected to a transistor that operates, and the feedback signal so as to obtain a predetermined secondary side voltage A switching circuit that controls the primary side voltage by switching based on the output voltage of the secondary side voltage output line only during standby. To some configured to include a switching element connected to the low pressure line is a voltage lower than the secondary voltage.

  In the power supply circuit of the present invention configured as described above, the output line of the secondary side voltage is connected to the low voltage line having a voltage lower than the secondary side voltage via a resistor by the switch element only during standby. Therefore, a current also flows from the output line of the secondary side voltage to the low voltage line, and the current flowing from the output line of the secondary side voltage to the light emitting element of the photocoupler is suppressed (limited).

  Preferably, the switch element may be operated by a power-on signal that is low during standby and high during power-on. With this configuration, the output line for the secondary voltage is connected to the low-voltage line only during standby by the switch element that is activated by the power-on signal.

  Preferably, the switch element has an emitter connected to the output line of the secondary voltage via the resistor, a collector connected to the low voltage line, and a base to which the power-on signal is input. The transistor may be turned on when the power-on signal is low. With such a configuration, it is possible to suppress (limit) the current flowing from the output line of the secondary side voltage to the light emitting element of the photocoupler only at the time of standby only by adding a transistor on the secondary side.

  Preferably, the low-pressure line may be a ground line. By being configured in this manner, it is possible to appropriately flow current from the output line of the secondary side voltage to the low voltage line.

  Preferably, a power-on signal that is low during standby and high during power-on is output by a microcomputer provided in the thin television device, and the switch element has the emitter through the resistor. It is connected to the output line of the secondary side voltage, the collector is connected to the ground line as the low voltage line, the power on signal is input to the base, and the off state is established when the power on signal is high. On the other hand, it is a transistor that is operated so as to be turned on when the power-on signal is low, and may be provided in the thin television device. With this configuration, in the power supply circuit in the flat-screen television device, a transistor that can be activated by a power-on signal is added to the secondary side, and the output line of the secondary side voltage has a resistance only during standby. And is appropriately connected to the ground line, and the current can be appropriately supplied from the output line of the secondary side voltage to the low voltage line.

  As described above, according to the first aspect of the present invention, a current also flows from the secondary voltage output line to the low voltage line, and the secondary voltage output line to the light emitting element of the photocoupler. Since the flowing current is suppressed (limited), the power supply voltage of the light emitting element, that is, the secondary side voltage is lowered. As a result, a power supply circuit capable of suppressing standby power consumption during standby without affecting the supply voltage when the power is turned on is provided.

  Further, according to the present invention, since the output line for the secondary side voltage is connected to the low voltage line only during standby by the switch element that is activated by the power-on signal, the photocoupler is connected from the output line for the secondary side voltage only during standby. It is possible to suppress (limit) the current flowing to the light emitting element.

  Further, according to the present invention, it is possible to suppress (limit) the current flowing from the output line of the secondary side voltage to the light emitting element of the photocoupler only at the time of standby only by adding a transistor. With this configuration, standby power consumption during standby can be suppressed without affecting the supply voltage when the power is turned on.

  Further, according to the present invention, it is possible to appropriately flow current from the output line of the secondary side voltage to the low voltage line, and accordingly, the power supply voltage of the light emitting element can be appropriately lowered.

  In addition, according to the present invention, in the power supply circuit in the flat-screen television apparatus, the output line of the secondary side voltage is connected via the resistor only at the time of standby only by adding the transistor operated by the power-on signal to the secondary side. Therefore, the current flowing from the secondary voltage output line to the light emitting element of the photocoupler can be appropriately flown from the secondary voltage output line to the low voltage line. The standby power consumption during standby can be suppressed without affecting the supply voltage when the power is turned on with a relatively inexpensive configuration.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(1) Schematic configuration of a thin television device provided with a power circuit (2) Schematic circuit configuration of a power circuit (3) Summary

(1) Schematic Configuration of Thin Television Device Comprising Power Supply Circuit Hereinafter, a liquid crystal television device 10 which is an example of a thin television device provided with a power supply circuit 19 to which the present invention is applied with reference to FIGS. A schematic configuration will be described. FIG. 1 is a perspective view showing a liquid crystal television device 10, and FIG. 2 is a block configuration diagram of the liquid crystal television device 10.
In this embodiment, a liquid crystal television device is exemplified as a thin television device to which the present invention is applied. However, the present invention is not limited to this embodiment. A thin television device such as a television, rear projection television, or organic EL television, a thin display such as a liquid crystal display or plasma display that does not have a television function, or a projector device that projects an image on a screen departs from the gist of the present invention. Various modifications can be made without departing from the scope. In addition, a power supply circuit that obtains a predetermined secondary side voltage by controlling the primary side voltage based on a feedback signal based on the secondary side voltage output to the primary side via a photocoupler, even if it is not a thin television device. If provided, the present invention can be applied. For example, the present invention can be applied to an audio / visual device including the power supply circuit.

  1 and 2, a liquid crystal television device 10 includes a tuner 11, a front end 12, a decoder 13, an OSD circuit 14, an audio output unit 15, an image display unit 16, a remote control receiving unit 17, A microcomputer 18, a power supply circuit 19, and a storage unit 20 are provided. These units such as the microcomputer 18 are connected by a bus 21.

  The tuner 11 is connected to, for example, the antenna 22, and is set to one channel (for example, a channel selected by the user) from the television broadcast signals received by the antenna 22 in accordance with a control signal input from the microcomputer 18. A corresponding television broadcast signal is acquired and output to the front end 12.

  The front end 12 converts the television broadcast signal output from the tuner 11 into an intermediate frequency signal according to a control signal input from the microcomputer 18, for example, and outputs the intermediate frequency signal to the decoder 13.

  The decoder 13 performs a process according to a predetermined file format (for example, a well-known MPEG-2 format) on the intermediate frequency signal output from the front end 12 in accordance with, for example, a control signal input from the microcomputer 18. Thus, the intermediate frequency signal is separated into an audio signal and a video signal and decoded. Then, the decoded audio signal is output to the audio output unit 15 and the video signal is output to the image display unit 16.

  The OSD circuit 14 outputs an OSD display signal for causing the image display unit 16 to perform a predetermined OSD display (on-screen display display) from the decoder 13 to the image display unit 16 in accordance with, for example, a control signal input from the microcomputer 18. To the video signal.

  The audio output unit 15 includes, for example, an audio output amplifier IC 15a and a speaker 15b. The audio output unit 15 performs predetermined processing such as power amplification on the audio signal input from the decoder 13 by the audio output amplifier IC 15a, and outputs audio based on the audio signal. Audio corresponding to the data is output from the speaker 15b.

  The image display unit 16 includes, for example, a panel drive circuit 16a, a liquid crystal panel 16b, and the like. An image corresponding to image data based on the video signal output from the decoder 13 or an OSD display output from the decoder 13 by the OSD circuit 14 is provided. An image corresponding to the image data based on the video signal obtained by combining the signals is displayed.

  The remote controller receiving unit 17 receives various signals (control commands) transmitted from the remote controller 23, for example, and outputs various data based on these various signals to the microcomputer 18.

  The remote controller 23 is operated by a user, for example, and transmits various signals corresponding to the operation to the remote control receiver 17 using, for example, infrared rays or radio waves.

The microcomputer 18 includes, for example, a CPU 18a, a RAM 18b, a ROM 18c, and the like, and controls the operation of the liquid crystal television device 10. For example, the microcomputer 18 controls power on / off, channel switching, volume up / down, and the like based on a control command received by the remote control receiver 17. Further, the microcomputer 18 outputs a power-on signal (P-ON signal) that is low during standby and high when the power is on, as a signal for commanding the power circuit 19 to be turned on / off.
In the standby state, for example, the main power supply of the power supply circuit 19 is turned on, and power is supplied only to the microcomputer 18 or the remote control receiving unit 17 to accept various operations (for example, power-on operation) by the user. Waiting state such as waiting or waiting according to a reservation program. The power-on state is a normal operation state in which, for example, power is supplied to the tuner 11 or the like to display an image on the liquid crystal panel 16b or output sound from the speaker 15b.

The CPU 18a performs various control operations in accordance with various processing programs for the liquid crystal television device 10 stored in the ROM 18c.
The RAM 18b includes a program storage area for expanding a processing program executed by the CPU 18a, a data storage area for storing input data, a processing result generated when the processing program is executed, and the like.
The ROM 18c stores a system program that can be executed by the liquid crystal television device 10, various processing programs that can be executed by the system program, data that is used when these various processing programs are executed, and the like. The program is stored in the ROM 18c in the form of a computer readable program code.

  The power supply circuit 19 is, for example, a partial resonance power supply circuit, converts commercial AC power into a plurality of types of predetermined voltages, and outputs an operating power supply voltage to each part of the liquid crystal television device 10.

  The storage unit 20 is configured by a nonvolatile semiconductor memory such as an EEPROM, for example, and stores channel information corresponding to broadcast signals, various adjustment values set by the user, and the like.

(2) Schematic Circuit Configuration of Power Supply Circuit FIG. 3 is a diagram illustrating a schematic circuit configuration of the power supply circuit 19 provided in the liquid crystal television device 10. In FIG. 3, for example, an external commercial AC power source is rectified by a full-wave rectification by a rectification bridge 32a, smoothed by a capacitor 32b, and outputted to a primary side voltage Va, and input to a primary coil 33a. The transformed primary voltage Va is converted to a predetermined voltage by the secondary coil 33b having a predetermined turns ratio, and the energy is transmitted to the secondary side (alternating current). The transformer 33 is transmitted to the secondary side. A smoothing circuit 34 that rectifies and smoothes alternating current with a diode Db and a capacitor Cb and outputs a secondary side voltage Vb, and a feedback circuit that outputs a feedback signal based on the secondary side voltage Vb to the primary side via a photocoupler 35b. 35 and a switch for controlling the primary side voltage Va by switching based on a feedback signal from the feedback circuit 35 And a transistor as a switching element that connects the output line Lvb of the secondary side voltage Vb to the ground line GND as a low voltage line having a lower voltage than the secondary side voltage Vb through the resistor R1 only at the time of standby, for example. 37.

More specifically, the feedback circuit 35 includes, for example, a divided resistor R2 having one end connected to the output line Lvb of the secondary side voltage Vb and the other end connected to the ground line GND;
The collector and base are connected to the dividing point Ps of the dividing resistor R2, and the emitter is connected to the output line Lvb of the secondary side voltage Vb via the resistor R1 and the ground line GND via the Zener diode ZD1, and the secondary side voltage A transistor 35a that operates based on Vb;
A light emitting element such as a light emitting diode LED1 whose one end is connected to the output line Lvb of the secondary voltage Vb via the resistor R3 and the other end is connected to the collector of the transistor 35a, and a light receiving element such as a photo diode connected to the switching circuit 36 And a photocoupler 35b having a transistor PTR1, and when the secondary voltage Vb exceeds a predetermined voltage, the transistor 35a is turned on and a feedback signal is output to the switching circuit 36 via the photocoupler 35b.
The switching circuit 36 includes, for example, an oscillation circuit, and performs feedback control by PWM control so that a predetermined secondary voltage Vb is obtained based on a feedback signal from the feedback circuit 35.

  For example, the emitter of the transistor 37 is connected to the output line Lvb of the secondary side voltage Vb and the emitter of the transistor 35a via the resistor R1, the collector is connected to the ground line GND, and the base is powered on from, for example, the microcomputer 18 The transistor is connected so that a signal (P-ON signal) is input, and is activated by the power-on signal so that it is turned on when the power-on signal is low. Therefore, at the time of standby, the power-on signal is set low to connect the output line Lvb of the secondary side voltage Vb to the ground line GND via the resistor R1.

By configuring the power supply circuit 19 in this manner, the output line Lvb of the secondary side voltage Vb is only in the standby state by the transistor 37 which is turned on when the power-on signal from the microcomputer 18 is low. Since the current flows from the output line Lvb of the secondary side voltage Vb to the ground line GND, the photocoupler 35b emits light from the output line Lvb of the secondary side voltage Vb. The current flowing to the diode LED1 is suppressed (limited).
Further, only by adding the transistor 37 that is activated by the power-on signal to the secondary side, the output line Lvb of the secondary side voltage Vb is appropriately connected to the ground line GND through the resistor R1 only in the standby state. A current can be appropriately passed from the output line Lvb of the secondary voltage Vb to the ground line GND.

(3) Summary As described above, according to this embodiment, a current also flows from the output line Lvb of the secondary side voltage Vb to the ground line GND, so that the photocoupler is connected from the output line Lvb of the secondary side voltage Vb. Since the current flowing to the light emitting diode LED1 of 35b is suppressed (limited), the power supply voltage of the light emitting diode LED1, that is, the secondary side voltage Vb is lowered. As a result, the power supply circuit 19 is provided that can suppress standby power consumption during standby without affecting the supply voltage when the power is turned on.

  Further, according to the present embodiment, the output line Lvb of the secondary side voltage Vb is connected to the ground line GND via the resistor R1 only at the time of standby only by adding the transistor 37 activated by the power-on signal to the secondary side. Since the current is appropriately connected and the current can also flow from the output line Lvb of the secondary side voltage Vb to the ground line GND, the current flows from the output line Lvb of the secondary side voltage Vb to the light emitting diode LED1 of the photocoupler 35b. It is possible to appropriately suppress (limit) the current and appropriately lower the power supply voltage of the photocoupler 35b. With a relatively inexpensive configuration, the standby voltage is maintained without affecting the supply voltage when the power is turned on. Power consumption can be suppressed.

  As mentioned above, although the Example of this invention was described in detail based on drawing, this invention is applied also in another aspect.

  For example, in the above-described embodiment, the switching circuit 36 for controlling the primary side voltage Va is a separately-excited oscillation type switching circuit, but instead of the separately-excited oscillation type switching circuit, for example, a transformer as shown in FIG. The present invention can also be applied to a well-known self-oscillation type switching circuit 36b having a tertiary coil 33c on the primary side of 33.

  In the above-described embodiment, the transistor 37 is used as the switch element. However, the present invention is not limited to this. The switch element can connect the output line Lvb of the secondary side voltage Vb to the ground line GND through the resistor R1 only during standby. If so, the present invention can be applied. For example, a switch element such as a MOSFET may be used.

  In the above-described embodiment, the low-voltage line having a voltage lower than the secondary side voltage Vb is the ground line GND. However, the ground line GND is not necessarily required. For example, a line having a voltage lower than the secondary side voltage Vb may be used as long as the operation of the power supply circuit 19 is not affected. Even if it does in this way, the temporary effect of this invention is acquired.

  The above description is only an embodiment, and the present invention can be implemented in variously modified and improved forms based on the knowledge of those skilled in the art.

It is a perspective view which shows an example of the liquid crystal television apparatus provided with the power supply circuit to which this invention is applied. It is a block diagram which illustrates the composition of a liquid crystal television device. It is a figure which illustrates the schematic circuit structure of the power supply circuit of this invention. It is another figure which illustrates the schematic circuit structure of the power supply circuit of this invention. It is a figure which illustrates the schematic circuit structure of the conventional power supply circuit.

Explanation of symbols

10: Liquid crystal television device (flat-screen television device)
18: microcomputer 19: power supply circuit 33: transformer 33a: primary coil 33b: secondary coil 34: smoothing circuit 35: feedback circuit 35a: transistor 35b: photocoupler 36, 36b: switching circuit 37: transistor (switch element)
Cb: Capacitor LED1: Light emitting diode (light emitting element)
Lvb: output line GND: ground line (low pressure line)

Claims (5)

A transformer that converts the primary side voltage input to the primary coil into a predetermined voltage at the secondary coil and transmits alternating current to the secondary side;
A smoothing circuit for smoothing the alternating current transmitted to the secondary side with a capacitor and outputting a secondary side voltage;
A feedback signal based on the secondary side voltage via a photocoupler having one end connected to the output line of the secondary side voltage and the other end connected to a transistor operating based on the secondary side voltage A feedback circuit that outputs to the primary side,
A switching circuit for controlling the primary side voltage by switching based on the feedback signal so as to obtain a predetermined secondary side voltage;
In a power supply circuit comprising:
A power supply circuit comprising a switch element that connects the output line of the secondary side voltage to a low voltage line having a voltage lower than the secondary side voltage through a resistor only during standby.   2. The power supply circuit according to claim 1, wherein the switch element is actuated by a power-on signal that is low during standby and high during power-on. The switch element is
An emitter is connected to the output line of the secondary side voltage via the resistor,
A collector is connected to the low pressure line,
The above power-on signal is input to the base,
3. The power supply circuit according to claim 2, wherein the power supply circuit is a transistor that is turned on when the power-on signal is low.   4. The power supply circuit according to claim 1, wherein the low-voltage line is a ground line. A power-on signal that is low during standby and high when the power is on is output by a microcomputer provided in the thin television device,
The switch element is
An emitter is connected to the output line of the secondary side voltage via the resistor,
The collector is connected to the ground line as the low-pressure line,
The above power-on signal is input to the base,
A transistor that is turned on when the power on signal is high while being turned on when the power on signal is low;
The power circuit according to claim 1, wherein the power circuit is provided in the thin television device.

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