JP2011166909A - Switching power supply device and display apparatus with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To save energy in a switching power supply device, and suppress the manufacture cost of a display apparatus with the same. <P>SOLUTION: In the switching power supply device 2, the voltage application to the primary winding T11 of a transformer T1 is switched by a switching element Q1, and an output circuit 4 outputs a flyback voltage induced hereby in a secondary winding T12 to a monitor 3. A control circuit 5 measures a differential voltage between its output voltage and a rated output voltage, and controls the switching operation. When a power switch SW1 sets the voltage output to the monitor 3 to OFF, a forced input circuit 6 inputs a forward voltage into the control circuit 5 for misreading the voltage as the differential voltage. Hereby, the duty ratio of the switching operation is made small, and an energy loss in the transformer T1 is reduced. Moreover, the output voltage of the output circuit 4 is made roughly zero, accordingly the monitor 3 need not be provided with a switch for break of current application linked with the power switch SW1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a switching power supply device that performs switching control of power supply to a primary winding of a transformer and obtains an output from a secondary winding by electromagnetic induction, and an image display device including the same.

  Conventionally, AC voltage is rectified and smoothed, applied to the primary winding of the transformer, and the voltage application is turned on / off using a switching element to generate electromagnetic induction. There is known a switching power supply device (hereinafter referred to as a power supply device) that induces a voltage in a line, rectifies and smoothes the voltage in an output circuit, and outputs the voltage to a load (refer to Patent Documents 1 to 3, for example).

  This power supply device includes a control circuit that measures an output voltage of the output circuit and feedback-controls the duty ratio of the switching operation of the switching element so that the measured voltage matches the rated output voltage. The control circuit includes a photocoupler for electrically insulating the signal transmission path of the circuit, and the photocoupler includes a light emitting element that emits light according to a differential voltage between the output voltage and the rated output voltage. And a light receiving element that receives light from the light emitting element. The control circuit performs the duty ratio control based on the output of the light receiving element. The power supply device configured as described above is mounted on a video display device such as a television receiver, and an output voltage from the device is supplied to a monitor or the like.

  FIG. 2 shows the configuration of a video display device on which the power supply device is mounted. The video display device 101 includes a power supply device 102 and a monitor 103 that is driven by an output voltage from the power supply device 102 and displays a video. The power supply apparatus 102 includes a rectifier circuit BD1 that rectifies an AC voltage from the commercial power supply CP1, a capacitor C1 that smoothes the pulsating voltage rectified by the rectifier circuit BD1, the transformer T1, the switching element Q1, and the output circuit 104 described above. And a control circuit 105 and a photocoupler P1, and further includes a power switch SW1 for turning on / off the voltage output from the output circuit 104 (putting the video display device 101 into a driving state / standby state). The power switch SW1 turns on / off the voltage output when in the on / off state.

  As will be described later, even if the power switch SW1 is turned off, the power supply apparatus 102 is configured so that the output voltage of the output circuit 104 does not become zero and becomes a predetermined standby voltage. For this reason, each of the various circuits in the monitor 103 is provided with various switches for interrupting energization in conjunction with the power switch SW1 (not shown). When the power switch SW1 is in an off state, these switches cut off the supply of standby voltage from the output circuit 104 to each circuit of the monitor 103, and stop the operation of those circuits.

  The output circuit 104 includes a diode D1 for rectifying the voltage induced in the secondary winding of the transformer T1, and a capacitor C2 for smoothing the rectified pulsating current. Output to the monitor 103.

  The control circuit 105 measures the difference between the output voltage from the output circuit 104 and the rated output voltage, and the PWM control circuit performs PWM control of the switching operation of the switching element Q1 based on the measurement result by the difference measurement circuit 106. 107. The difference measurement circuit 106 is arranged on the secondary side of the transformer T1, and the PWM control circuit 107 is arranged on the primary side of the transformer T1, and information transmission between them is performed by the photocoupler P1.

  The difference measurement circuit 106 includes an output measurement line L1 branched from the output circuit 104, and further includes a resistor R1, a light emitting element P11 of the photocoupler P1, and a comparison circuit 108 between the branch point and the ground point. .

  The comparison circuit 108 includes resistors R2 to R4 for dividing the output voltage of the output circuit 104, and a shunt regulator S1. The resistors R2 to R4 are connected in series with each other. The comparison circuit 108 compares the voltage applied to the resistor R4 with the reference voltage inside the shunt regulator S1, and changes the supply current to the light emitting element P11 of the photocoupler P1 according to the difference. This change is transmitted to the light receiving element P12 of the photocoupler P1, and the PWM control circuit 107 performs PWM control according to the output of the light receiving element P12. By this series of feedback control, the output voltage of the output circuit 104 becomes the rated output voltage, that is, the predetermined output voltage at the normal time.

  In addition, the difference measurement circuit 106 includes an output voltage change circuit 109 that changes the output voltage of the output circuit 104 by changing the voltage applied to the resistor R4 in accordance with the operation of the power switch SW1. The output voltage changing circuit 109 includes resistors R5 and R6 connected in parallel with the resistors R2 and R3, a power switch SW1 connected in parallel with the resistor R4, and a diode D2. The resistors R5 and R6 are connected in series with each other, and the diode D2 is disposed so as to connect between the resistors R3 and R4 and between the resistor R6 and the power switch SW1, and flows through the resistors R2 and R3. It is a diode that restricts current from flowing in the direction of the power switch SW1.

  In the output voltage changing circuit 109, when the power switch SW1 is turned off, the resistors R5 and R6 are simply connected in parallel with the resistors R2 and R3. Since these combined resistances are smaller than the combined resistance of the resistors R2 and R3, the voltage applied to the resistor R4 becomes high. Therefore, the output voltage of the shunt regulator S1 decreases due to its characteristics, and the supply current to the light emitting element P11 increases. As a result, due to feedback control, the output voltage of the output circuit 104 falls below the rated output voltage and becomes a standby voltage. This standby voltage is not zero. When the power switch SW1 is turned on, the point a in the figure becomes the ground potential, so that the current flowing through the resistors R5 and R6 does not flow through the resistor R4, and the voltage applied to the resistor R4 becomes low. The output voltage is the rated output voltage.

  By the way, in the switching power supply 102, the output voltage when the power switch SW1 is OFF is set to substantially zero, so that the switch in the monitor 103 can be eliminated, thereby reducing the number of switches and the video display device 101. There is a desire to reduce the manufacturing cost of

  Therefore, it is conceivable to insert a power switch in the output line 104a of the output circuit 104. If the power switch is arranged in this manner, the output voltage from the output line 104a when the power switch is in the OFF state can be made substantially zero.

  However, even if the power switch provided on the output line 104a is turned off, the voltage applied to the primary winding of the transformer T1 does not change, so that energy is accumulated in the iron core of the transformer T1, and thus energy is wasted. As a result, energy loss occurs.

Japanese Patent Laid-Open No. 11-215819 JP-A-9-215331 JP-A-1-259754

  The present invention has been made in order to solve the above-described conventional problems, and can reduce the manufacturing cost of electrical equipment and can save energy when the voltage output of the apparatus is set to OFF. And it aims at providing the video display apparatus provided with this.

  In order to achieve the above object, a first aspect of the present invention is a flyback transformer in which a power supply voltage is applied to a primary winding, a switching element for switching power supply voltage application to the primary winding, and the switching element. An output circuit for smoothing the flyback voltage induced in the secondary winding of the flyback transformer by the switching operation and outputting it to the load, and measuring a differential voltage between the output voltage by the output circuit and a predetermined voltage, Based on the measured differential voltage, a control circuit for feedback controlling the duty ratio of the switching operation of the switching element so as to keep the output voltage at a predetermined voltage, and a power switch for turning on / off the voltage output from the output circuit A voltage output from the output circuit by the power switch. A forcible input circuit that forcibly inputs a forward voltage induced in the secondary winding of the flyback transformer by the switching operation of the switching element to the control circuit in the state set to The circuit reduces the flyback voltage by reducing the duty ratio based on the input from the forced input circuit, and brings the output voltage of the output circuit close to zero.

  According to a second aspect of the present invention, in the switching power supply device according to the first aspect, the control circuit includes a photocoupler that is turned on / off according to a differential voltage between an output voltage of the output circuit and a predetermined voltage. The duty ratio is reduced when the photocoupler is in a conductive state, and the forced input circuit forcibly supplies a current to the light emitting element of the photocoupler.

  A third aspect of the invention includes the switching power supply device according to the first or second aspect and the load, and the load is driven by an output voltage from an output circuit of the switching power supply device to display an image. It is a video display device which is a display means.

According to the invention of claim 1, when the voltage output from the output circuit is set to OFF by the operation of the power switch, the output voltage from the output circuit does not become a predetermined standby voltage as in the prior art, Since it becomes substantially zero, it is not necessary to provide a switch for cutting off standby voltage on the load. Therefore, the number of switches can be reduced in an electric device including the switching power supply device and the load, and the manufacturing cost of the electric device can be reduced. be able to.
In addition, since the duty ratio of the switching operation of the switching element is reduced when the voltage output is set to OFF, the amount of energy supplied to the primary winding of the flyback transformer is reduced, and therefore the voltage output is set from ON to OFF. Even if this is done, it is possible to prevent the same amount of energy from being accumulated in the iron core of the flyback transformer. For this reason, the energy loss of the flyback transformer when the voltage output is set to OFF can be reduced, and energy saving can be achieved.

  According to the invention of claim 2, the duty ratio of the switching operation of the switching element can be reduced with a simple configuration.

  According to invention of Claim 3, the number of switches can be reduced and manufacturing cost can be held down.

1 is a circuit diagram of a video display device according to an embodiment of the present invention. The circuit diagram of the conventional video display apparatus.

  Hereinafter, a video display device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of a video display device of the present embodiment. The video display device 1 includes a switching power supply device (hereinafter referred to as a power supply device) 2 and a monitor 3 (load, display means) that is driven by an output voltage from the power supply device 2 to display an image.

  The power supply device 2 includes a rectifier circuit BD1 that rectifies an AC voltage from a commercial power supply CP1, a capacitor C1 that smoothes a pulsating voltage rectified by the rectifier circuit BD1, and a flyback to which the smoothed voltage is applied. A transformer (hereinafter referred to as a transformer) T1. The voltage is applied to the primary winding T11 of the transformer T1. The power supply device 2 includes a switching element Q1 that switches application of a power supply voltage to the primary winding T11, and energy is stored in the iron core of the transformer T1 when the switching element Q1 is on. The energy is transmitted from the iron core to the secondary winding T12 of the transformer T1 when the switching element Q1 is off, and a voltage is induced in the secondary winding T12. This voltage is called a flyback voltage. A voltage is also induced in the secondary winding T12 even when the switching element Q1 is on, and this voltage is called a forward voltage. The polarities of the flyback voltage and the forward voltage are opposite.

  Further, the power supply device 2 smoothes the flyback voltage induced in the secondary winding T12 and outputs it to the monitor 3 (load), and outputs the output voltage from the output circuit 4 to a rated output voltage (predetermined voltage). The control circuit 5 for feedback control of the duty ratio of the switching operation of the switching element Q1, the power switch SW1 for turning on / off the voltage output from the output circuit 4, and the output from the output circuit 4 by the power switch SW1. And a forcible input circuit 6 for forcibly inputting a forward voltage induced in the secondary winding T12 to the control circuit 5 in a state where the voltage output is set to OFF. The control circuit 5 measures the differential voltage between the output voltage from the output circuit 4 and the rated output voltage, and performs feedback control based on the measured differential voltage. The forced input circuit 6 inputs the forward voltage as a measurement input to the control circuit 5.

  The output circuit 4 includes a diode D1 for supplying only the flyback voltage to the monitor 3, and a capacitor C2 for smoothing the flyback voltage supplied to the monitor 3. In FIG. 1, only one circuit of the output circuit 4 is shown, but a plurality of output circuits 4 may be provided, and a remote control receiving circuit or the like may be connected as a load to their output terminals.

  The control circuit 5 includes a difference measurement circuit 51, a PWM control circuit 52, and a comparison circuit 53 each having the same configuration and function as the difference measurement circuit 106, the PWM control circuit 107, and the comparison circuit 108 of FIG. A photocoupler P1 similar to that shown in FIG. 2 is provided. The difference measuring circuit 51, the PWM control circuit 52, and the comparison circuit 53 are not limited to the illustrated circuit configuration. The photocoupler P1 includes a light-emitting element P11 such as an LED and a light-receiving element P12 such as a phototransistor that receives output light from the light-emitting element P11. The output of the output circuit 4 is lowered by a resistor R1. Depending on the differential voltage between the voltage and the reference voltage, the conductive / non-conductive state is established. The PWM control circuit 52 is configured to reduce the on / off duty ratio of the switching element Q1 in accordance with the output of the light receiving element P12 when the photocoupler P1 is in a conductive state. When the duty ratio decreases, the switching element Q1 is turned on and the period in which energy is stored in the iron core of the transformer T1 is shortened. Therefore, the flyback voltage when the switching element Q1 is subsequently turned off decreases.

  The forcible input circuit 6 forcibly supplies current to the light emitting element P11 by the forward voltage when the power switch SW1 is turned on (when the video display device 1 is in standby) in order to turn off the voltage output from the output circuit 4. Then, the photocoupler P1 is turned on. The power switch SW1 is turned off when the voltage output from the output circuit 4 is set to on.

  The forced input circuit 6 is constituted by a loop circuit from the point b in the figure to the point c through the light emitting element P11, and a power switch SW1 is inserted in the loop circuit. The point b is grounded, and the point c is set to a negative potential when the forward voltage is induced. At that time, a current flows from the point b to the point c (indicated by a broken line arrow). Note that the point b is the same potential as the terminal having the lower potential when the flyback voltage is induced in the secondary winding T12, and the point c is the same potential as the terminal having the higher potential.

  In the loop circuit, a diode D3, a light emitting element P11, a resistor R7, a power switch SW1, a Zener diode ZD1, and a diode D4 are arranged in this order from the point b to the point c. The diode D3 is a diode for taking out a current from the point b toward the point c, and supplies the current to the anode of the light emitting element P11. The resistor R7 is a resistor for controlling the current of the loop circuit. The power switch SW1 is composed of a switch element that is turned on / off according to the operation of the mechanical switch, and the Zener diode ZD1 is for obtaining a voltage necessary for driving the power switch SW1. The diode D4 is a diode for limiting the flyback voltage so that the current does not flow back to the loop circuit when the flyback voltage is induced in the secondary winding T12.

  The forced input circuit 6 has a capacitor C3 that is charged with a forward voltage induced in the secondary winding T12. One end of the capacitor C3 is connected to a location having the same potential as the point b, and the other end is connected to a location having the same potential as the point c via a diode D4. The capacitor C3 discharges and causes a current to flow through the loop circuit, causing the light emitting element P11 to emit light.

  Next, the operation when the power switch SW1 is turned on to turn off the voltage output from the output circuit 4 in the video display device 1 will be described. When the power switch SW1 is turned on, the forced input circuit 6 causes the light emitting element P11 to forcibly emit light by the forward voltage or the discharge current of the capacitor C3. Accordingly, the photocoupler P1 becomes conductive, and the PWM control circuit 52 decreases the duty ratio of the switching operation of the switching element Q1 accordingly. As a result, the flyback voltage induced in the secondary winding T12 decreases, and the output voltage of the output circuit 4 approaches zero and becomes substantially zero.

  In the video display device 1 configured as described above, only the flyback voltage is output from the output circuit 4 to the monitor 3, and the control circuit 5 measures the differential voltage between the output voltage and the rated output voltage and performs feedback control. However, when the voltage output from the output circuit 4 is set to OFF by the operation of the power switch SW1, the forcible input circuit 6 inputs the forward voltage to the control circuit 5, and the control circuit 5 converts the input into the above difference. Misidentified as a voltage. As a result, the control circuit 5 reduces the duty ratio of the switching operation of the switching element Q1 according to the input, and the output voltage of the output circuit 4 does not become a predetermined standby voltage as in the prior art, but is substantially zero. become. Therefore, it is not necessary to provide the monitor 3 with a standby voltage cutoff switch. For this reason, the number of switches can be reduced, and the manufacturing cost can be suppressed. Further, it is possible to save power of the power supply device 2 when the voltage output is set to OFF.

  Further, when the voltage output is set to OFF, the duty ratio of the switching operation of the switching element Q1 is reduced, so that the amount of energy supplied to the primary winding T11 of the transformer T1 is reduced. For this reason, even if the voltage output is set from on to off, it is possible to prevent an amount of energy that does not change from being accumulated in the iron core of the transformer T1. As a result, the energy loss of the transformer T1 when the voltage output is turned off can be reduced, and energy saving can be achieved.

  The power switch SW1 is inserted in the loop circuit of the forced input circuit 6, and the current flowing in the loop circuit can be made lower than the output line 41 of the output circuit 4 by the current control resistor R7. Accordingly, the power switch SW1 may be a switch having a low current upper limit value that can be handled as compared with the switch when the switch for energization / cutoff is inserted into the output line 41. For this reason, the cost of a switch can be held down and it contributes to the cost reduction of the power supply device 2 as a result.

  In addition, the forced input of the forward voltage to the control circuit 5 only requires a current to flow through the light emitting element P11 by the forward voltage, so that the forced input can be performed with a simple configuration and the duty ratio can be reduced.

  Further, since the switching power supply device is conventionally provided with the photocoupler P1, it is only necessary to additionally install the forced input circuit 6, so that the design change can be reduced. Further, the conventional output voltage changing circuit 109 can be omitted.

  In addition, this invention is not limited to the structure of said embodiment, A various deformation | transformation is possible according to a use purpose. For example, the power switch SW1 may be a mechanical switch operated by a user, and in that case, the Zener diode ZD1 is unnecessary.

DESCRIPTION OF SYMBOLS 1 Video display apparatus 2 Switching power supply device 3 Monitor (load, display means)
4 Output circuit 5 Control circuit 6 Forced input circuit P1 Photocoupler P11 Light emitting element Q1 Switching element SW1 Power switch T1 Transformer (flyback transformer)
T11 Primary winding T12 Secondary winding

Claims (3)

A flyback transformer in which a power supply voltage is applied to the primary winding;
A switching element for switching power supply voltage application to the primary winding;
An output circuit for smoothing a flyback voltage induced in a secondary winding of the flyback transformer by the switching operation of the switching element and outputting the smoothed voltage to a load;
A control circuit that measures a differential voltage between an output voltage by the output circuit and a predetermined voltage, and feedback-controls the duty ratio of the switching operation of the switching element so as to keep the output voltage at the predetermined voltage based on the measured differential voltage When,
In a switching power supply device comprising: a power switch for turning on / off a voltage output from the output circuit;
With the voltage output from the output circuit set to OFF by the power switch, the control circuit is forced to apply a forward voltage induced in the secondary winding of the flyback transformer by the switching operation of the switching element. A forced input circuit for inputting,
The control circuit is configured to reduce the flyback voltage by reducing the duty ratio based on an input from the forced input circuit, thereby bringing the output voltage of the output circuit close to zero. . The control circuit includes a photocoupler that is turned on / off according to a differential voltage between an output voltage of the output circuit and a predetermined voltage, and reduces the duty ratio when the photocoupler is turned on. Is configured as
The switching power supply device according to claim 1, wherein the forcible input circuit forcibly supplies a current to a light emitting element of the photocoupler. The switching power supply device according to claim 1 or 2, and the load,
The video display device, wherein the load is display means that displays video by being driven by an output voltage from an output circuit of the switching power supply device.

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