JP4529987B2 - Television and power circuit - Google Patents

Description

  The present invention relates to a television and a power supply circuit, and more particularly to a power supply circuit capable of detecting a reduced power state of an AC power supply and a television using the power supply circuit.

  For example, in a television device, a power source that supplies operating power to each part of the television device by converting a primary side voltage based on an AC power source voltage into a plurality of types of predetermined voltages via a transformer and outputting the voltage on the secondary side. A circuit is provided.

  FIG. 4 is a schematic configuration diagram showing an example of the power supply circuit. In FIG. 4, a power supply circuit 1 is a partial resonance power supply circuit, and a rectifier circuit 2 that outputs a primary side voltage by rectifying an external commercial AC power supply, for example, full-wave rectified by a rectifier bridge 2a and smoothed by a capacitor 2b The primary voltage input to the 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, and the operation power supply voltages Vb and Vc of each part of the television apparatus are converted. , Vd from the secondary side, a feedback circuit 4 that feeds back the secondary side voltage to the primary side, and a switching circuit 5 that PWM-controls the primary side voltage using a feedback signal from the feedback circuit 4.

  The feedback circuit 4 is connected to, for example, the output line Lvb of the output voltage Vb of the secondary coil 3b. When the output voltage Vb of the secondary coil 3b exceeds a predetermined voltage, the transistor 4a is turned on via the photocoupler 4b. A feedback signal is output to the switching circuit 5. The switching circuit 5 includes an oscillation circuit. When a feedback signal from the feedback circuit 4 is input, the switching circuit 5 performs feedback control by PWM control and appropriately adjusts the output voltage Vb of the secondary coil 3b to be an appropriate voltage. A drive voltage is output to the primary coil 3a.

  Here, it is well known that the power supply circuit 1 as described above is provided with a power reduction detection circuit or the like in order to protect the circuit from voltage abnormality. For example, Patent Document 1 describes that a power supply circuit includes a power reduction detection circuit 1b as shown in FIG.

  The deenergization detection circuit 1b has one terminal connected to the output line Lvb of the output voltage Vb of the secondary coil 3b and the other terminal grounded, and the divided resistors 6a and 6b and the divided resistors 6a and 6b divided. The diode 7 is connected to the cathode side at the point, and the microcomputer 8 is connected to the anode side of the diode 7 and the voltage reduction detection terminal 8a.

  In the voltage reduction detection circuit 1b configured as described above, the output voltage Vb is divided by the dividing resistors 6a and 6b and reduced to the voltage at the dividing point 6c, and then input to the cathode side of the diode 7. The diode 7 transmits the voltage at the dividing point 6 c to the reduced voltage detection terminal 8 a of the microcomputer 8. For example, when the power supply circuit 1a is operating normally, the voltage at the dividing point 6c is preset to 3.3V, and 3.3V is also applied to the power reduction detection terminal 8a. . On the other hand, when the operation of the power supply circuit 1a becomes abnormal and the output voltage Vb decreases, the voltage at the dividing point 6c also decreases, and the voltage applied to the power reduction detection terminal 8a also decreases.

  Hereinafter, processing when the microcomputer 8 detects a reduced state of the output voltage Vb will be described with reference to the flowchart of FIG. In this process, the microcomputer 8 monitors the output line Lvb of the output voltage Vb via the power reduction detection terminal 8a, and detects that when the voltage input to the power reduction detection terminal 8a is less than 1.0 V, the power supply This process determines whether or not the power supply circuit 1a is in a reduced power state due to an abnormality, and is repeatedly executed while the power is on.

  In FIG. 5, when the process is started, the counter k is set to 0 in step S1. Next, in step S2, the voltage applied to the reduced voltage detection terminal 8a is acquired. In step S3, it is determined whether or not the voltage acquired in step S2 is 1.0 V or less. If the voltage is not below 1.0 V and the determination in step S3 is negative, this routine is terminated.

  On the other hand, if the voltage is 1.0 V or less and the determination in step S3 is affirmative, the counter k is incremented in step S4. Next, in step S5, it is determined whether or not the counter k is 4 or more. If the counter k is less than 4 and the determination in step S5 is negative, it is determined in step S6 whether 50 ms has elapsed. That is, in step S6, it is determined whether 50 ms has elapsed since the voltage became 1.0 V or less and the determination in step S3 was affirmed. Since the determination in step S6 is initially denied, it is repeatedly executed. When 50 ms elapses thereafter and the determination in step S6 is affirmed, the process returns to step S2 and the subsequent processing is repeated.

  On the other hand, if the counter k is 4 or more and the determination in step S5 is affirmative, that is, if 200 ms has elapsed since the voltage was initially 1.0 V or less and the determination in step S3 was affirmed, the process proceeds to step S7. Thus, an off signal Poff is output to the power supply circuit 1a as a signal for commanding on / off of the power supply circuit 1a instead of the on signal Pon. As described above, when the reduced voltage detection circuit 1b detects the reduced voltage state of the output voltage Vb, the power supply circuit 1a is turned off, and the output of the operation power supply voltages Vb, Vc, and Vd is stopped.

  Patent Document 2 discloses a zero cross detection circuit for detecting a zero cross of an input waveform of a commercial power supply in order to detect an instantaneous interruption or an instantaneous stop of a commercial power supply in a fan motor drive control device, and a power reduction state of the commercial power supply. And a reduced-voltage detection circuit for detection.

Patent Document 3 describes that a video signal processing apparatus includes AC detection means. Patent Document 4 describes that an AC power control device includes an AC detection circuit that detects the vicinity of a zero potential of an AC load power source and outputs a detection signal.
Utility Model Registration No. 3123106 JP 2003-50042 A JP 7-298262 A JP 2004-164432 A

  By the way, a device such as a television device is not limited to cost reduction and space saving, and naturally, further downsizing and a reduction in the number of components are desired even in a circuit including a power supply circuit to be mounted. However, as described above, in order to protect the circuit from voltage abnormality, the power supply circuit needs to be equipped with an abnormality detection circuit such as a power reduction detection circuit or an AC detection circuit, thereby reducing the circuit size and the number of parts. There was a possibility of hindering.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and the object of the present invention is to provide a power supply circuit that can detect an AC power supply and a reduced power state of the power supply, and can reduce the size and the number of components, and its power supply circuit. The object is to provide a television using a power supply circuit.

  In order to achieve the above object, according to a first aspect of the present invention, there is provided a television including a power circuit that converts a primary side voltage based on an AC power source voltage into a plurality of types of predetermined voltages via a transformer and outputs the voltage from the secondary side. In John, the power circuit includes a rectifier circuit that outputs a primary side voltage based on a 120-V commercial AC power source, and converts the primary side voltage into a plurality of types of predetermined voltages to obtain an operating power source voltage for each part of the television. A power supply circuit having a transformer that outputs from the secondary side, a feedback circuit that feeds back the secondary side voltage to the primary side, and a switching circuit that PWM-controls the primary side voltage using a feedback signal from the feedback circuit; A voltage reduction circuit having a voltage detection circuit for detecting a primary side voltage and a voltage reduction signal output circuit for outputting a detection signal for detecting a power reduction state. A first Zener diode having a breakdown voltage of 120 V so that a Zener breakdown occurs when the primary side voltage exceeds a first predetermined value, and one terminal of the voltage detection circuit A first dividing resistor connected to the output line of the primary side voltage and having the other terminal grounded, and wherein the first Zener diode is arranged in series on the same output line side from the dividing point; When the base is connected to the dividing point of the dividing resistor and the emitter is grounded and the primary side voltage exceeds the first predetermined value, it is turned on, while the primary side voltage is below the first predetermined value. A first transistor that is turned off at a time, and the first dividing resistor includes one resistor connected to the output line of the primary side voltage and the other resistor grounded. The first Zener diode is arranged in series so that the anode side of the Zener diode is connected to the dividing point and the cathode side is connected to the one resistor. A first light-emitting diode and a first phototransistor whose anode side is connected to the output line of the primary voltage and whose cathode side is connected to the collector of the first transistor. And a second transistor whose base is grounded via the first phototransistor and whose emitter is connected to a signal voltage source of a reduced voltage detection signal for detecting a reduced voltage state. When the primary voltage exceeds the first predetermined value, the second transistor is turned on as the first transistor is turned on. When the primary side voltage is equal to or lower than the first predetermined value while the high voltage is output as the reduced power state detection signal, the second transistor is turned off as the first transistor is turned off. A television which outputs a low signal as a reduced power state detection signal.

  In the power supply circuit of the present invention configured as described above, when the primary side voltage based on the AC power supply voltage exceeds a first predetermined value, a Zener breakdown occurs in the first Zener diode, and the first transistor The first transistor is turned on by dividing the primary voltage at the dividing point of the first dividing resistor connected to the base of the first dividing resistor. When the first transistor is turned on, the first light emitting diode connected to the collector of the first transistor is energized to turn on the first phototransistor, and the reduced signal output circuit is As the first phototransistor is turned on, the second transistor is turned on and outputs a high signal as a reduced voltage detection signal. Therefore, the reduced voltage detection circuit has a primary value that exceeds the first predetermined value. It can be easily detected that an AC power supply voltage is output as a side voltage.

  On the other hand, if the primary side voltage is equal to or lower than the first predetermined value, no zener breakdown occurs in the first zener diode, and the first divided resistor to which the base of the first transistor is connected is connected. The dividing point becomes zero potential and the first transistor is turned off. When the first transistor is turned off, the first light-emitting diode is not energized, the first phototransistor is turned off, and the power-down signal output circuit is turned off when the first phototransistor is turned off. Since the second transistor is turned off and a low signal is output as a power-down state detection signal, the power-down detection circuit reduces the AC power supply voltage so that the primary side voltage is not more than the first predetermined value. The electric state can be easily detected.

  According to a second aspect of the present invention for achieving the above object, there is provided a power supply circuit for converting a primary side voltage based on an AC power source voltage into a plurality of types of predetermined voltages via a transformer and outputting the voltage from the secondary side. A first Zener diode in which Zener breakdown occurs when the primary side voltage exceeds a first predetermined value; one terminal is connected to the output line of the primary side voltage and the other terminal is grounded; The first Zener diode is arranged in series on the same output line side from the dividing point, the base is connected to the dividing point of the first dividing resistor and the emitter is grounded, A first transistor that is turned on when the primary side voltage exceeds the first predetermined value, and is turned off when the primary side voltage is equal to or lower than the first predetermined value; and the first transistor Is connected to the collector of is to comprise a reduced voltage detecting circuit having a reduced voltage signal output circuit for outputting a detection signal for detecting a reduced voltage state based on the first transistor ON / OFF.

In the power supply circuit of the present invention configured as described above, when the primary side voltage based on the AC power supply voltage exceeds a first predetermined value, a Zener breakdown occurs in the first Zener diode, and the first transistor Since the divided voltage of the primary voltage is applied to the dividing point of the first dividing resistor to which the base of the first transistor is connected, the first transistor is turned on and connected to the collector of the first transistor. The power reduction signal output circuit can output a detection signal for detecting that an AC power supply voltage that is a primary voltage exceeding the first predetermined value is output. Therefore, the power reduction detection circuit can detect that the AC power supply voltage that is the primary side voltage exceeding the first predetermined value is output. On the other hand, if the primary side voltage is equal to or lower than the first predetermined value, no zener breakdown occurs in the first zener diode, and the first divided resistor to which the base of the first transistor is connected is connected. Since the dividing point is at zero potential, the first transistor is not turned on, and the power reducing signal output circuit has a reduced state of the AC power supply voltage so that the primary side voltage is lower than the first predetermined value. It becomes possible to output a detection signal for detection. Therefore, the power reduction detection circuit can detect a power reduction state of the AC power supply voltage such that the primary side voltage is equal to or lower than the first predetermined value.
According to a second aspect of the present invention, there is provided a second Zener diode in which a Zener breakdown occurs when the primary voltage exceeds a second predetermined value, and one terminal is connected to the output line of the primary voltage and The other terminal is grounded, the second dividing resistor whose cathode is connected to the second Zener diode at the dividing point, the base is connected to the anode of the second Zener diode, and the emitter is grounded A third transistor that is turned on when the primary side voltage exceeds a second predetermined value, and that is turned off when the primary side voltage is equal to or lower than a second predetermined value; And an overpower signal output circuit connected to the collector of the transistor and outputting a detection signal for detecting an overpower state based on on / off of the third transistor. In further comprising a circuit.
3. The power supply circuit according to claim 2, wherein when the primary side voltage exceeds a second predetermined value, a Zener breakdown occurs in the second Zener diode, and the second Zener diode is Since the divided voltage of the primary side voltage is applied to the base of the third transistor connected to the dividing point of the second dividing resistor, the third transistor is turned on and the third transistor is turned on. The overpower signal output circuit connected to the collector of the transistor can output a detection signal for detecting an overpower state of the AC power supply voltage such that the primary side voltage exceeds the second predetermined value. become. Therefore, the overpower detection circuit can detect an overpower state of the AC power supply voltage such that the primary side voltage exceeds the second predetermined value. On the other hand, if the primary side voltage is less than or equal to the second predetermined value, no zener breakdown occurs in the second Zener diode, and the divided voltage of the primary side voltage is present at the base of the third transistor. Therefore, the third transistor is not turned on, and the overpower signal output circuit detects that an AC power supply voltage that is a primary side voltage lower than a second predetermined value is output. It is possible to output the detection signal. Therefore, the overpower detection circuit can detect that an AC power supply voltage that is a primary side voltage that is equal to or lower than the second predetermined value is output.

  According to a third aspect of the present invention, in the power supply circuit according to the second aspect, the reduced-voltage signal output circuit is configured such that the first transistor is energized when the first transistor is turned on. A first light-emitting diode connected to the collector; a first phototransistor connected to the second transistor so as to turn on the second transistor by being turned on when the first light-emitting diode is energized; And when the primary side voltage exceeds a first predetermined value, the second transistor is turned on and outputs a high signal, while the primary side voltage is Is less than or equal to the first predetermined value, the second transistor is turned off to output a low signal.

  In short, in the power supply circuit according to claim 2, the reduced-voltage signal output circuit includes a first light emission connected to a collector of the first transistor so that the first transistor is energized when the first transistor is turned on. A first photocoupler comprising a diode and a first phototransistor to which the second transistor is connected so as to turn on the second transistor by being turned on when the first light emitting diode is energized have.

  When the primary voltage exceeds the first predetermined value, the first transistor connected to the collector of the first transistor is energized by turning on the first transistor. The first phototransistor is turned on, and the power reduction signal output circuit outputs a high signal by turning on the second transistor as the first phototransistor is turned on. The detection circuit can easily detect that the AC power supply voltage that is the primary side voltage exceeding the first predetermined value is output. On the other hand, when the primary side voltage is equal to or lower than a first predetermined value, the first transistor is turned off, whereby the first light emitting diode is not energized and the first phototransistor is turned off. The voltage reduction signal output circuit outputs a low signal by turning off the second transistor with the first phototransistor turned off. Therefore, the voltage reduction detection circuit has a primary value that is equal to or lower than a first predetermined value. It is possible to easily detect a reduced power supply state of the AC power supply voltage as a side voltage.

According to a fourth aspect of the present invention, there is provided the power supply circuit according to the second or third aspect , wherein the overpower signal output circuit is energized by turning on the third transistor. A second light-emitting diode connected to the collector of the third transistor, and a second light-emitting diode connected to turn on the fourth transistor by being turned on when the second light-emitting diode is energized. And when the primary side voltage exceeds a second predetermined value, the fourth transistor is turned on and outputs a high signal. When the same-side voltage is equal to or lower than the second predetermined value, the fourth transistor is turned off to output a low signal.

In short, in the power supply circuit according to claim 2 or 3 , the overpower signal output circuit is connected to a collector of the third transistor so as to be energized when the third transistor is turned on. A second light-emitting diode and a second phototransistor connected to the fourth transistor so as to turn on the fourth transistor by being turned on when the second light-emitting diode is energized. 2 photocouplers.

  When the primary voltage exceeds the second predetermined value, the third transistor is turned on to energize the second light emitting diode connected to the collector of the third transistor. The second phototransistor is turned on, and the overpower signal output circuit outputs a high signal by turning on the fourth transistor when the second phototransistor is turned on. The circuit can easily detect an overpowered state of the AC power supply voltage such that the primary side voltage exceeds the second predetermined value. On the other hand, if the primary side voltage is equal to or lower than the second predetermined value, the third transistor is turned off, whereby the second light emitting diode is not energized and the second phototransistor is turned off. The overpower signal output circuit outputs a low signal by turning off the fourth transistor as the second phototransistor is turned off, so that the overpower detection circuit is less than or equal to a second predetermined value. It is possible to easily detect that the AC power supply voltage that is the primary side voltage is output.

As described above, according to the first or second aspect of the invention, by providing the first Zener diode, it is possible to detect the AC power supply voltage and reduce the AC power supply voltage in a single power reduction detection circuit. Detection is possible. As a result, it is not necessary to separately provide an AC detection circuit and a power reduction detection circuit, and the power supply circuit can be reduced in size and the number of components. Further, since the power reduction detection circuit is provided on the primary side, it is not necessary to provide a power reduction detection circuit for each power supply voltage corresponding to the plurality of secondary coils on the secondary side, and the power supply circuit can be further reduced in size. And the number of parts can be reduced.
According to the second aspect of the present invention, by providing the second Zener diode, it is possible to detect the AC power supply voltage and the AC power supply voltage overpower state with a single overpower detection circuit. . As a result, there is no need to separately provide an AC detection circuit and an overpower detection circuit, and the power supply circuit can be reduced in size and the number of components. Further, since this overcurrent detection circuit is provided on the primary side, it is not necessary to provide an overcurrent detection circuit for each power supply voltage corresponding to a plurality of secondary coils on the secondary side, and the power supply circuit can be further reduced in size. And the number of parts can be reduced. Furthermore, by being provided in addition to the above-described power reduction detection circuit, it can be easily detected whether or not the AC power supply voltage is in an appropriate range.

  According to the third aspect of the present invention, the power reduction signal output circuit is simply configured, and the detection of the AC power supply voltage and the power supply voltage reduction state can be easily performed.

According to a fourth aspect of the present invention, the overpower signal output circuit is configured simply and can easily detect an AC power supply voltage and an overpowered state of the AC power supply voltage.

Hereinafter, embodiments of the present invention will be described with reference to the drawings according to the following items.
(1) Configuration of power reduction detection circuit (2) Summary of power reduction detection circuit (3) Configuration of overpower detection circuit (4) Summary of overpower detection circuit

(1) Configuration of Reduced Voltage Detection Circuit FIG. 1 is a block diagram illustrating a configuration of a liquid crystal television device 10 as a television to which the present invention is applied. In FIG. 1, a liquid crystal television apparatus 10 includes a microcomputer 11 that controls the operation of the main body, and a tuner 13 that extracts and outputs a television broadcast signal of a channel selected from a television broadcast signal received by an antenna 12. A video processing unit 15 that displays a video based on the television broadcast signal output from the tuner 13 on the liquid crystal panel 14, and an audio processing unit 17 that outputs audio based on the television broadcast signal output from the tuner 13 from the speaker 16. And a remote control receiving unit 19 that receives an operation command transmitted from the remote controller 18 and a power supply circuit 20 that supplies operating power to each unit.

  The microcomputer 11 outputs a signal for instructing on / off of the power supply circuit 20 to the power supply circuit 20a included in the power supply circuit 20 based on the power reduction state detection signal from the power reduction detection circuit 20b included in the power supply circuit 20. Further, the microcomputer 11 controls channel switching, volume up / down, and the like based on the control command received by the remote control receiver 19.

  FIG. 2 is a schematic configuration diagram illustrating an example of the power supply circuit 20. In FIG. 2, the power supply circuit 20 includes: (a) a rectifier circuit 2 that outputs a primary side voltage Va based on an external commercial AC power source of 120 V, for example, and converts the primary side voltage Va into a plurality of types of predetermined voltages. The transformer 3 that outputs the operating power supply voltages Vb, Vc, and Vd of each part of the television apparatus from the secondary side, the feedback circuit 4 that feeds back the secondary side voltage Vb to the primary side, and the primary side by the feedback signal from the feedback circuit 4 A power supply circuit 20a having a switching circuit 5 for PWM-controlling the voltage Va; (b) a voltage detection circuit 20b1 for detecting the primary side voltage Va; and a power reduction signal for outputting a detection signal for detecting a power reduction state. And a reduced voltage detection circuit 20b having an output circuit 20b2.

  Since the power supply circuit 20a has substantially the same configuration as the power supply circuit 1a shown in FIG. 4, the description thereof is omitted here.

  The voltage detection circuit 20b1 includes a first Zener diode ZD1 that generates a Zener breakdown when the primary side voltage Va exceeds a first predetermined value, one terminal connected to the output line Lva of the primary side voltage Va, and the other terminal. Is grounded and the first Zener diode ZD1 is connected in series to the first dividing resistor R1 arranged in series on the output line Lva side from the dividing point R1c, and the base is connected to the dividing point R1c of the first dividing resistor R1. The emitter is grounded and turned on when the primary side voltage Va exceeds the first predetermined value, while being turned off when the primary side voltage Va is equal to or lower than the first predetermined value. And a transistor Tr1.

  The first dividing resistor R1 includes one resistor R1a connected to the output line Lva of the primary side voltage Va and the other resistor R1b grounded, and the anode side of the first Zener diode ZD1 is connected to the dividing point R1c. The first Zener diode ZD1 is arranged in series so that the cathode side is connected to one resistor 1a.

  The reduced signal output circuit 20b2 includes a first light emitting diode PC1a whose anode side is connected to the output line Lva of the primary side voltage Va via the third resistor R3 and whose cathode side is connected to the collector of the first transistor Tr1. And a first photocoupler PC1b composed of a first phototransistor PC1b, a base of which is grounded via the first phototransistor PC1b, and a deenergized state detection signal DET for detecting a deenergized state. The signal voltage source 21 has a second transistor Tr2 whose emitter is connected. The collector of the second transistor Tr2 is connected to the microcomputer 11.

  That is, the reduced-voltage signal output circuit 20b2 includes the first light-emitting diode PC1a and the first light-emitting diode PC1a connected to the collector of the first transistor Tr1 so that the first transistor Tr1 is energized when the first transistor Tr1 is turned on. The first photocoupler PC1 includes the first phototransistor PC1b to which the second transistor Tr2 is connected so as to turn on the second transistor Tr2 by being turned on when the power is turned on. The power reduction signal output circuit 20b2 outputs a power reduction state detection signal DET to the microcomputer 11 based on the on / off state of the first transistor Tr1. For example, when the second transistor Tr2 is turned on as the first transistor Tr1 is turned on, a high signal is output to the microcomputer 11 as the deenergized state detection signal DET, while the second signal is output as the first transistor Tr1 is turned off. When the transistor Tr2 is turned off, a low signal is output to the microcomputer 11 as the reduced power state detection signal DET.

  In the voltage reduction detection circuit 20b configured as described above, when the primary side voltage Va exceeds the first predetermined value, a Zener breakdown occurs in the first Zener diode ZD1, and the base of the first transistor Tr1 is connected. The dividing point R1c of the first dividing resistor R1 is divided by the primary voltage Va to turn on the first transistor Tr1. When the first transistor Tr1 is turned on, the first light-emitting diode PC1a connected to the collector of the first transistor Tr1 is energized to turn on the first phototransistor PC1b, and the first phototransistor PC1b is turned on. As the transistor PC1b is turned on, the second transistor Tr2 is turned on, and a high signal is output to the microcomputer 11 as the reduced power state detection signal DET. Therefore, the power reduction detection circuit 20b can easily detect that the AC power supply voltage is output such that the primary voltage Va exceeds the first predetermined value. The power reduction state detection signal DET is a detection signal for detecting a power reduction state. When the primary side voltage Va exceeds the first predetermined value, a high signal is output. It is also a detection signal for detecting the output of the AC power supply voltage that makes the primary side voltage Va so as to exceed.

  On the other hand, when the primary side voltage Va is equal to or lower than the first predetermined value, no zener breakdown occurs in the first Zener diode ZD1, and the first divided resistor R1 to which the base of the first transistor Tr1 is connected is connected. The dividing point R1c becomes zero potential, and the first transistor Tr1 is turned off. When the first transistor Tr1 is turned off, the first light emitting diode PC1a connected to the collector of the first transistor Tr1 is not energized and the first phototransistor PC1b is turned off, and the first phototransistor PC1b is turned off. As the transistor PC1b is turned off, the second transistor Tr2 is turned off, and a low signal is output to the microcomputer 11 as the reduced power state detection signal DET. Therefore, the power reduction detection circuit 20b can easily detect a power reduction state of the AC power supply voltage such that the primary side voltage Va is equal to or lower than the first predetermined value.

  For example, when the microcomputer 11 determines that the reduced power state detection signal DET is a low signal continuously for a predetermined time, the off signal Poff is used instead of the on signal Pon as a signal for commanding the on / off of the power supply circuit 20a. Is output to the power supply circuit 20a, and the power supply circuit 20a is turned off to stop the output of the operating power supply voltages Vb, Vc, and Vd.

  The first predetermined value is a lower limit of a necessary voltage value that is experimentally obtained and determined in advance as a voltage necessary for obtaining appropriate secondary voltages Vb, Vc, and Vd. This is a value corresponding to the lower limit value of the AC power supply voltage necessary for obtaining the secondary side voltages Vb, Vc, Vd. Accordingly, if it is determined that the power supply voltage is reduced when the AC power supply voltage does not exceed about 80V with respect to the 120V AC power supply voltage, the primary voltage Va at that time exceeds about 113V (= 80 × √2). Therefore, it is desirable to use a first Zener diode ZD1 having a breakdown voltage of about 120V.

(2) Summary of Voltage Reduction Detection Circuit As described above, according to the present embodiment, by providing the first Zener diode ZD1, the detection of the AC power supply voltage and the detection of the AC power supply voltage can be performed by one voltage reduction detection circuit 20b. It is possible to detect the reduced power state. As a result, there is no need to separately provide an AC detection circuit and a power reduction detection circuit, and the power supply circuit 20 can be reduced in size and the number of components.

  In particular, since the voltage reduction detection circuit 20b is provided on the primary side, it is necessary to provide a voltage reduction detection circuit for each of the secondary side voltages Vb, Vc, and Vd corresponding to a plurality of secondary coils on the secondary side. Therefore, the power circuit 20 can be further downsized and the number of parts can be reduced.

(3) Configuration of Overpower Detection Circuit Next, another embodiment of the present invention will be described. In the following description, parts common to the embodiments are denoted by the same reference numerals and description thereof is omitted. In addition, a plurality of embodiments described in the present specification can be applied to a common object, unless technically incompatible.

  FIG. 3 is a schematic configuration diagram illustrating an example of the overcurrent detection circuit 20c. The overpower detection circuit 20c is provided in the power supply circuit 20 in addition to the power reduction detection circuit 20b, and is connected to the rectifier circuit 2 in parallel with the power reduction detection circuit 20b.

  In FIG. 3, the overpower detection circuit 20c includes a voltage detection circuit 20c1 that detects the primary voltage Va, and an overpower signal output circuit 20c2 that outputs a detection signal for detecting an overpower state.

  The voltage detection circuit 20c1 includes a second Zener diode ZD2 that generates a Zener breakdown when the primary side voltage Va exceeds a second predetermined value, one terminal connected to the output line Lva of the primary side voltage Va, and the other terminal. Is connected to the dividing point R2c, the second dividing resistor R2 is connected to the cathode side of the second Zener diode ZD2, the base is connected to the anode side of the second Zener diode ZD2, and the emitter is grounded. The third transistor Tr3 is turned on when the primary side voltage Va exceeds the second predetermined value, and turned off when the primary side voltage Va is equal to or lower than the second predetermined value. .

  The second divided resistor R2 includes a resistor R2a connected to the output line Lva of the primary side voltage Va and a resistor R2b grounded.

  The overpower signal output circuit 20c2 includes a second light emitting diode PC2a whose anode side is connected to the output line Lva of the primary side voltage Va via the fourth resistor R4 and whose cathode side is connected to the collector of the third transistor Tr3. And a second phototransistor PC2b, a second photocoupler PC2 and a base that is grounded via the second phototransistor PC2b and an overcurrent state detection signal DET2 for detecting an overcurrent state. The signal voltage source 22 includes a fourth transistor Tr4 whose emitter is connected. The collector of the fourth transistor Tr4 is connected to the microcomputer 11.

  That is, the overpower signal output circuit 20c2 includes the second light emitting diode PC2a and the second light emitting diode PC2a that are connected to the collector of the third transistor Tr3 so that the third transistor Tr3 is energized when the third transistor Tr3 is turned on. The second photocoupler PC2 is composed of the second phototransistor PC2b to which the fourth transistor Tr4 is connected so as to turn on the fourth transistor Tr4 by being turned on at the time of energization. Then, the overpower signal output circuit 20c2 outputs an overpower state detection signal DET2 to the microcomputer 11 based on on / off of the third transistor Tr3. For example, when the fourth transistor Tr4 is turned on as the third transistor Tr3 is turned on, a high signal is output to the microcomputer 11 as the overcurrent detection signal DET2, while the fourth transistor Tr3 is turned off as the fourth transistor Tr3 is turned off. When the transistor Tr4 is turned off, a low signal is output to the microcomputer 11 as the overcurrent detection signal DET2.

  In the overcurrent detection circuit 20c configured as described above, when the primary side voltage Va exceeds the second predetermined value, a zener breakdown occurs in the second zener diode ZD2, and the second zener diode ZD2 causes the first zener breakdown to occur. The base of the third transistor Tr3 connected to the dividing point R2c of the second dividing resistor R2 is divided by the primary side voltage Va to turn on the third transistor Tr3. When the third transistor Tr3 is turned on, the second light-emitting diode PC2a connected to the collector of the third transistor Tr3 is energized to turn on the second phototransistor PC2b, and the second phototransistor PC2b is turned on. When the transistor PC2b is turned on, the fourth transistor Tr4 is turned on, and a high signal is output to the microcomputer 11 as the overcurrent detection signal DET2. Therefore, the overpower detection circuit 20c can easily detect an overpower state of the AC power supply voltage such that the primary side voltage Va exceeds the second predetermined value. The overpower state detection signal DET2 is a detection signal for detecting an overpower state, but when the primary side voltage Va exceeds the second predetermined value, a high signal is output. It is also a detection signal for detecting the output of an AC power supply voltage that is in an overpower state such that the primary side voltage Va exceeds the range.

  On the other hand, if the primary side voltage Va is less than or equal to the second predetermined value, no zener breakdown occurs in the second Zener diode ZD2, and the divided voltage of the primary side voltage Va is present at the base of the third transistor Tr3. As a result, the third transistor Tr3 is turned off. When the third transistor Tr3 is turned off, the second light-emitting diode PC2a connected to the collector of the third transistor Tr3 is not energized, the second phototransistor PC2b is turned off, and the second phototransistor PC2b is turned off. As the transistor PC2b is turned off, the fourth transistor Tr4 is turned off, and a low signal is output to the microcomputer 11 as the overcurrent detection signal DET2. Therefore, the overpower detection circuit 20c can easily detect that the AC power supply voltage that is the primary voltage Va that is equal to or lower than the second predetermined value is output.

  For example, when the microcomputer 11 determines that the overpower state detection signal DET2 is a high signal continuously for a predetermined time, the off signal Poff is used instead of the on signal Pon as a signal for commanding the on / off of the power supply circuit 20a. Is output to the power supply circuit 20a, and the power supply circuit 20a is turned off to stop the output of the operating power supply voltages Vb, Vc, and Vd.

  The second predetermined value is an upper limit of a necessary voltage value that is experimentally obtained and determined in advance as a voltage necessary for obtaining appropriate secondary voltages Vb, Vc, and Vd. This is a value corresponding to the upper limit value of the AC power supply voltage necessary for obtaining the secondary side voltages Vb, Vc, Vd. Therefore, it is desirable to use the second Zener diode ZD2 having a breakdown voltage corresponding to it.

(4) Summary of Overpower Detection Circuit As described above, according to the present embodiment, by providing the second Zener diode ZD2, the detection of the AC power supply voltage and the detection of the AC power supply voltage can be performed by one overpower detection circuit 20c. It is possible to detect an overpower condition. As a result, there is no need to separately provide an AC detection circuit and an overpower detection circuit, and the power supply circuit 20 can be reduced in size and the number of components.

  Further, since the overcurrent detection circuit 20c is provided on the primary side, it is necessary to provide an overcurrent detection circuit for each of the secondary side voltages Vb, Vc, and Vd corresponding to a plurality of secondary coils on the secondary side. Therefore, the power circuit 20 can be further downsized and the number of parts can be reduced.

  In particular, by being provided in addition to the power reduction detection circuit 20b, it can be easily detected whether or not the AC power supply voltage is in an appropriate range.

  As mentioned above, although the Example of this invention was described in detail based on drawing, what was mentioned above is one embodiment to the last, and this invention is implemented in the aspect which added various change and improvement based on the knowledge of those skilled in the art. can do.

It is a block diagram explaining the structure of the liquid crystal television apparatus with which this invention is applied. It is a schematic block diagram which shows an example of a power supply circuit provided with a power reduction detection circuit. It is a schematic block diagram which shows an example of an overpower detection circuit. It is a schematic block diagram which shows an example of the conventional power supply circuit. It is a flowchart which shows the process of the microcomputer of FIG.

Explanation of symbols

2: Rectifier circuit 3: Transformer 4: Feedback circuit 5: Switching circuit 10: Liquid crystal television apparatus (television)
20: Power supply circuit 20a: Power supply circuit 20b: Reduced voltage detection circuit 20b1: Voltage detection circuit 20b2: Reduced voltage signal output circuit 21: Signal voltage source Lva: Primary voltage output line PC1: First photocoupler PC1a: First 1 light emitting diode PC1b: first phototransistor R1: first dividing resistor R1a: one resistor R1b: other resistor R1c: dividing point R3: third resistor Tr1: first transistor Tr2: second transistor ZD1: first Zener diode

Claims (4)

In a television including a power supply circuit that converts a primary side voltage based on an AC power supply voltage into a plurality of types of predetermined voltages via a transformer and outputs the voltage from the secondary side.
The power circuit is
A rectifier circuit that outputs a primary side voltage based on a commercial AC power supply voltage of 120 V, and a transformer that converts the primary side voltage into a plurality of types of predetermined voltages and outputs operating power supply voltages of the above-mentioned parts of the television from the secondary side. A power supply circuit having a feedback circuit that feeds back the secondary side voltage to the primary side, and a switching circuit that PWM-controls the primary side voltage using a feedback signal from the feedback circuit;
A power reduction detection circuit having a voltage detection circuit for detecting the primary side voltage and a power reduction signal output circuit for outputting a detection signal for detecting a power reduction state;
The voltage detection circuit is
A first Zener diode having a breakdown voltage of 120 V so that a Zener breakdown occurs when the primary voltage exceeds a first predetermined value; one terminal connected to the output line of the primary voltage; and the other And a base connected to the dividing point of the first dividing resistor and the first dividing resistor arranged in series on the output line side of the dividing point. And a first transistor that is turned on when the primary side voltage exceeds a first predetermined value while the emitter is grounded, and turned off when the primary side voltage is equal to or lower than the first predetermined value. Have
The first dividing resistor is
One resistor connected to the output line of the primary side voltage and the other resistor grounded. The anode side of the first Zener diode is connected to the dividing point and the cathode side is connected to the one resistor. The first Zener diode is arranged in series so that
The power reducing signal output circuit is
A first light-emitting diode and a first phototransistor, whose anode side is connected to the output line of the primary voltage via a third resistor and whose cathode side is connected to the collector of the first transistor, are configured. A first photocoupler, a second transistor whose base is grounded via the first phototransistor, and whose emitter is connected to a signal voltage source of a deenergized state detection signal for detecting a deenergized state; Have
When the primary voltage exceeds a first predetermined value, the second transistor is turned on as the first transistor is turned on, and a high signal is output as a power-reduction state detection signal. When the primary side voltage is equal to or lower than a first predetermined value, the second transistor is turned off as the first transistor is turned off, and a low signal is output as a reduced power state detection signal. John. In a power supply circuit for converting a primary side voltage based on an AC power supply voltage into a plurality of types of predetermined voltages via a transformer and outputting from the secondary side,
A first Zener diode in which Zener breakdown occurs when the primary side voltage exceeds a first predetermined value;
A first dividing resistor in which one terminal is connected to the output line of the primary voltage and the other terminal is grounded, and the first Zener diode is arranged in series on the output line side from the dividing point. When,
The base is connected to the dividing point of the first dividing resistor and the emitter is grounded, and is turned on when the primary side voltage exceeds the first predetermined value, while the primary side voltage is the first side voltage. A first transistor that is turned off when less than a predetermined value of
A power reduction signal output circuit connected to the collector of the first transistor and outputting a detection signal for detecting a power reduction state based on on / off of the first transistor;
A reduced voltage detecting circuit having,
A second Zener diode in which Zener breakdown occurs when the primary side voltage exceeds a second predetermined value;
A second dividing resistor in which one terminal is connected to the output line of the primary voltage and the other terminal is grounded, and the cathode side of the second Zener diode is connected to the dividing point;
The base is connected to the anode side of the second Zener diode and the emitter is grounded, and is turned on when the primary voltage exceeds a second predetermined value, while the primary voltage is the second voltage. A third transistor that is turned off when less than a predetermined value of
An overpower signal output circuit connected to the collector of the third transistor and outputting a detection signal for detecting an overpower state based on on / off of the third transistor;
A power supply circuit comprising an overpower detection circuit having The power reducing signal output circuit is
The first light emitting diode connected to the collector of the first transistor so that the first transistor is energized when turned on, and the second light emitting diode when turned on when the first light emitting diode is energized. A first photocoupler configured with a first phototransistor to which the second transistor is connected so as to turn on the transistor;
When the primary side voltage exceeds the first predetermined value, the second transistor is turned on and outputs a high signal, while when the primary side voltage is equal to or lower than the first predetermined value, the second transistor is turned on. The power supply circuit according to claim 2, wherein the transistor is turned off to output a low signal. The overpower signal output circuit is
The second light emitting diode connected to the collector of the third transistor so that the third transistor is turned on when turned on, and the fourth light emitting diode when turned on when the second light emitting diode is turned on A second photocoupler configured with a second phototransistor to which the fourth transistor is connected so as to turn on the transistor;
When the primary side voltage exceeds the second predetermined value, the fourth transistor is turned on and outputs a high signal, while when the primary side voltage is equal to or lower than the second predetermined value, the fourth transistor is turned on. 4. The power supply circuit according to claim 2 , wherein the transistor is turned off to output a low signal. 5.

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