JP2013005622A - Power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a measure for preventing the explosion-proof valve of a smoothing capacitor from working, even if a voltage greater than a specified value is input in a power supply circuit.SOLUTION: A power supply circuit 1 outputs a predetermined voltage from the secondary coil 52 of a transformer 5 when a second switching element, i.e. a junction transistor 7, is switched between a conduction state and a non-conduction state and thereby a first switching element, i.e. a field effect transistor 6, is switched between a conduction state and a non-conduction state. When a voltage greater than a specified value is input to a rectifier circuit 3, the power supply circuit 1 brings the field effect transistor 6 into conduction state while resisting against an action of the junction transistor 7 to bring the field effect transistor 6 into conduction by the action of a fuse melting circuit 14. Consequently, an overcurrent flows through a fuse 13, and the fuse 13 is blown off before the explosion-proof valve of a smoothing capacitor 4 works.

Description

  The present invention relates to a power supply circuit that is provided in an electric apparatus such as a television receiver or a DVD recorder and generates a predetermined voltage.

  2. Description of the Related Art Conventionally, for example, an electric apparatus such as a television receiver or a DVD recorder is operated by receiving an AC voltage from a commercial AC power source. Such an electric device apparatus includes a power supply circuit, and the power supply circuit operates a predetermined voltage (a load such as a liquid crystal display or a DVD drive included in the electric device apparatus) from an AC voltage supplied from a commercial AC power supply. The voltage necessary for the generation is generated. As such a power supply circuit, one having the configuration shown in FIG. 2 is known.

  The power supply circuit 70 shown in FIG. 2 changes the current flowing through the primary coil 91 of the transformer 72 by switching the field effect transistor 71, which is the first switching element, between the conductive state and the non-conductive state. 72 is a circuit for outputting a predetermined voltage from 72 secondary side coils 92. In the power supply circuit 70, the field effect transistor 71 is switched between the conductive state and the non-conductive state by switching the junction transistor 73 as the second switching element between the conductive state and the non-conductive state. The power supply circuit 70 is an RCC (self-excited oscillation) power supply circuit, and the field effect transistor 71 and the junction transistor 73 are switched between a conductive state and a non-conductive state by self-excited oscillation. .

  When the AC outlet 74 is connected to the commercial AC power source, the AC voltage supplied from the commercial AC power source is input to the rectifier circuit unit 76 from the AC outlet 74 via the fuse 75. The AC voltage input to the rectifier circuit unit 76 is rectified by the rectifier circuit unit 76, and the DC voltage rectified by the rectifier circuit unit 76 is smoothed by the smoothing capacitor 77, and is smoothed by the smoothing capacitor 77. The smoothed DC voltage is input to the primary coil 91 of the transformer 72.

  The power supply circuit 70 operates as follows when a normal voltage (voltage having a rated voltage value to be originally input) is input to the rectifier circuit unit 76.

  First, the voltage smoothed by the smoothing capacitor 77 is input to the first switching capacitor 79 via the starting resistor 78, whereby the first switching capacitor 79 becomes the first switching capacitor 79. Due to the presence of the switching resistor 80, the battery is gradually charged, and accordingly, the voltage input to the base of the field effect transistor 71 rises. When the voltage input to the gate of the field effect transistor 71 reaches a high level, the field effect transistor 71 becomes conductive.

  When the field effect transistor 71 becomes conductive, a current flows from the rectifier circuit section 76 to the primary side coil 91 of the transformer 72 and the drain and source of the field effect transistor 71, thereby causing the second switching capacitor 81 to flow. Due to the presence of the second switching resistor 82, the battery is gradually charged, and accordingly, the voltage input to the base of the junction transistor 73 rises. When the voltage input to the base of the junction transistor 73 reaches a high level, the junction transistor 73 becomes conductive.

  When the junction transistor 73 becomes conductive, a current flows from the start-up resistor 78 between the collector and emitter of the junction transistor 73, and the first switching capacitor 79 is connected between the collector and emitter of the junction transistor 73. As a result, the voltage input to the gate of the field effect transistor 71 is pulled to a low level, and the field effect transistor 71 becomes non-conductive.

  When the field effect transistor 71 becomes non-conductive, no current flows from the rectifier circuit section 76 to the primary side coil 91 of the transformer 72 and the drain and source of the field effect transistor 71, thereby the second switching capacitor. 81 is discharged via the second switching resistor 82, whereby the voltage input to the base of the junction transistor 73 becomes low level, and the junction transistor 73 becomes non-conductive.

  When the junction transistor 73 becomes non-conductive, the first switching capacitor 79 is again charged by the voltage input via the starting resistor 78, and thereafter the same operation as described above is repeated. It is.

  That is, the field effect transistor 71 becomes conductive, current flows from the rectifier circuit unit 76 to the primary coil 91 of the transformer 72 and the drain and source of the field effect transistor 71, and the junction transistor 73 becomes conductive. As a result, the field effect transistor 71 becomes non-conductive, and no current flows from the rectifier circuit section 76 to the primary side coil 91 of the transformer 72 and the drain and source of the field effect transistor 71, and the junction transistor 73 is The operation of becoming a non-conductive state is repeated.

  That is, the field effect transistor 71 and the junction transistor 73 are repeatedly switched between the conductive state and the non-conductive state, and are repeatedly switched between the state where the current flows through the primary coil 91 of the transformer 72 and the state where the current does not flow. The current flowing through the primary side coil 91 is repeatedly changed, and a predetermined voltage is output from the secondary side coil 92 of the transformer 72. A voltage is also output from the auxiliary coil 93 of the transformer 72. The power supply circuit 70 operates in this way when a normal voltage is input to the rectifier circuit unit 76.

  Further, the power supply circuit 70 receives from the auxiliary coil 93 of the transformer 72 when a voltage equal to or higher than a specified value (for example, a voltage having a voltage value more than twice the rated voltage value to be originally input) is input to the rectifier circuit unit 76. The output voltage rises, and the voltage is input to the base of the junction transistor 73 via the Zener diode 83 and the resistor 84. Accordingly, the voltage input to the base of the junction transistor 73 becomes high level. The junction transistor 73 is turned on, and the field effect transistor 71 is turned off.

  On the other hand, a power supply circuit is known in which a fuse is blown before a smoothing capacitor is opened or destroyed when excessive AC power is input to a rectifier circuit (for example, Patent Document 1). reference). In the power circuit of Patent Document 1, the cathode includes a Zener diode connected between the rectifier circuit unit and the primary side coil, and the anode of the Zener diode when the excessive AC power is input to the rectifier circuit unit. The self-oscillation control circuit detects excessive AC power input and self-oscillates based on the voltage output from the rectifier (ie, based on the voltage input to the primary coil from the rectifier circuit). The control circuit stops the on / off control for the FET and maintains the FET in the on state, thereby causing the short-circuit breakdown of the FET and blowing the fuse.

  There is also known a power supply circuit in which a fuse is blown so as not to cause an operation of an explosion-proof valve of a smoothing capacitor when an output voltage of a secondary side coil increases (see, for example, Patent Document 2). The power supply circuit disclosed in Patent Document 2 includes a protection circuit (a circuit including a photocoupler 12, a Zener diode 25, a photocoupler 26, and the like) that operates according to the output voltage of the secondary coil, and increases the output voltage of the secondary coil. Sometimes the fuse is blown by the operation of the protection circuit (that is, by using the output voltage of the secondary coil) and by making the transistor inactive and shorting the drain-source of the MOSFET. It has become.

JP 2011-4551 A JP 2004-32936 A

  By the way, in the above-described conventional power supply circuit 70, a voltage exceeding a specified value (for example, a voltage having a voltage value more than double the rated voltage value to be originally input) is input due to incomplete indoor wiring or lightning surge. Sometimes. When a voltage exceeding the specified value is input in this way, the explosion-proof valve of the smoothing capacitor 77 works (opens), and there are cases where the user misunderstands this as smoke due to ignition and causes a problem.

  Accordingly, the applicant of the present application has taken measures to connect a Zener diode in parallel with the smoothing capacitor 77 as a measure to prevent the explosion-proof valve of the smoothing capacitor 77 from operating even when a voltage exceeding a specified value is input. Carried out. However, with this measure, the Zener diode will be short-circuited and destroyed when the voltage exceeds the specified value due to lightning surge, and the explosion-proof valve of the smoothing capacitor 77 will work. Further, as a measure for preventing the explosion-proof valve of the smoothing capacitor 77 from operating even when a voltage exceeding a specified value is input, a measure that can be realized at low cost is desired. Even if the contents disclosed in Patent Document 1 and Patent Document 2 described above are applied, the above problem cannot be solved.

  The present invention has been made in order to solve the above-described problem, and can implement a measure for preventing the explosion-proof valve of the smoothing capacitor from operating even when a voltage exceeding a specified value is input. An object is to provide a power supply circuit.

  In order to achieve the above object, according to the first aspect of the present invention, when an AC voltage is input, a rectification circuit unit that rectifies the AC voltage into a DC voltage, and a DC voltage rectified by the rectification circuit unit is smoothed. The smoothing capacitor, the transformer that receives the DC voltage smoothed by the smoothing capacitor, is input to the primary coil, and switched between the conductive state and the non-conductive state. A first switching element that switches between a state in which the smoothed DC voltage is input to a primary coil of the transformer and a state in which the smoothed DC voltage is not input, and a switching state between a conduction state and a non-conduction state. A second switching element that switches between a conducting state and a non-conducting state, and a fuse that cuts off the input of an AC voltage to the rectifier circuit section by being blown The second switching element is switched between the conductive state and the non-conductive state, and the first switching element is switched between the conductive state and the non-conductive state, whereby a predetermined voltage is output from the secondary coil of the transformer. The power supply circuit includes a fuse blown circuit that brings the first switching element into a conductive state in order to blow the fuse when a voltage exceeding a specified value is input to the rectifier circuit unit. Based on the voltage output from the coil, it detects that a voltage exceeding the specified value has been input to the rectifier circuit, and uses the voltage output from the auxiliary coil of the transformer to turn on the first switching element. It is to make.

  According to a second aspect of the present invention, in the power supply circuit according to the first aspect, the fuse blowing circuit is configured such that when the voltage higher than the specified value is input to the rectifier circuit portion, the second switching element is the first switching element. The first switching element is brought into a conducting state against an action to be brought into a non-conducting state.

  According to a third aspect of the present invention, in the power supply circuit according to the second aspect, the fuse blowing circuit has a Zener diode, the cathode being connected to the auxiliary winding side of the transformer, and the anode being the first The first switching element is connected to the switching element side, and the first switching element is turned on by the voltage output from the anode of the Zener diode.

  According to a fourth aspect of the present invention, in the power supply circuit according to the first aspect, the first switching element is a field effect transistor, the gate is connected to the positive voltage side of the rectifier circuit section, and the drain is the primary side of the transformer. Connected to the coil, the source is connected to the ground or the negative voltage side of the rectifier circuit unit, the second switching element is a junction transistor, the base is connected to the source side of the first switching element, the collector Is connected to the gate of the first switching element, the emitter is connected to the ground or the negative voltage side of the rectifier circuit section, and the Zener diode of the fuse blowing circuit has the anode connected to the gate side of the first switching element. It is what.

  According to the first to fourth aspects of the present invention, when a voltage exceeding a specified value is inputted, the first switching element is turned on by the action of the fuse blowing circuit, whereby an overcurrent is generated in the fuse. The fuse is blown before the explosion-proof valve of the smoothing capacitor works. Therefore, even if a voltage exceeding the specified value is input, the explosion-proof valve of the smoothing capacitor does not work (does not open), preventing the user from mistaking smoke from the explosion-proof valve as smoke from ignition. it can. In addition, the fuse blowing circuit detects that a voltage exceeding the specified value is input to the rectifier circuit based on the voltage output from the transformer auxiliary coil, and uses the voltage output from the transformer auxiliary coil. Thus, since the first switching element is configured to be in a conductive state, a measure for preventing the explosion-proof valve of the smoothing capacitor from operating even when a voltage exceeding a specified value is input can be realized at low cost. .

The electric circuit diagram which shows the structure of the power supply circuit which concerns on one Embodiment of this invention. The electric circuit diagram which shows the structure of the conventional power supply circuit.

  Hereinafter, a power supply circuit according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of the power supply circuit according to the present embodiment. The power supply circuit 1 is provided in an electric device such as a television receiver or a DVD recorder, for example. A predetermined voltage (for example, a liquid crystal display or a DVD drive provided in the electric device is provided from an AC voltage supplied from a commercial AC power supply). This circuit generates a voltage necessary for operating the load of the power source.

  The power supply circuit 1 includes an AC outlet 2, a rectifier circuit unit 3, a smoothing capacitor 4, a transformer 5, a field effect transistor 6 that is a first switching element, and a junction type that is a second switching element. A transistor 7, a starting resistor 8, a first switching capacitor 9, a first switching resistor 10, a second switching resistor 11, and a second switching capacitor 12; And a fuse 13 and a fuse fusing circuit 14.

  The power supply circuit 1 is configured such that the junction transistor 7 is switched between a conductive state and a non-conductive state, and the field effect transistor 6 is switched between a conductive state and a non-conductive state. Is a circuit that outputs a predetermined voltage from the secondary coil 52 of the transformer 5. The power supply circuit 1 is an RCC (self-excited oscillation) power supply circuit, and the field effect transistor 6 and the junction transistor 7 are switched between a conductive state and a non-conductive state by self-excited oscillation. .

  In addition, the power supply circuit 1 is configured such that when a voltage higher than a specified value (for example, a voltage having a voltage value more than twice the rated voltage value to be originally input) is input to the rectifier circuit unit 3, By operation, before the explosion-proof valve of the smoothing capacitor 4 is activated (opened), the field effect transistor 6 is turned on to blow the fuse 13. In other words, the power supply circuit 1 prevents the explosion-proof valve of the smoothing capacitor 4 from acting by the action of the fuse fusing circuit 14 even when a voltage exceeding the specified value is input to the rectifying circuit unit 3.

  The AC outlet 2 is for inputting an AC voltage supplied from a commercial AC power source. The AC outlet 2 is connected to a commercial AC power source, and thereby inputs an AC voltage supplied from the commercial AC power source to the rectifier circuit unit 3 via the fuse 13.

  The rectifier circuit unit 3 is for rectifying an AC voltage (that is, an AC voltage supplied from a commercial AC power supply) input from an AC outlet through the fuse 13. The rectifier circuit unit 3 is a diode bridge circuit, and rectifies the AC voltage into a DC voltage when an AC voltage is input from the AC outlet 2 via the fuse 13. The positive voltage side of the rectifier circuit unit 3 is connected to one end side of the primary side coil 51 of the transformer 5, and the negative voltage side of the rectifier circuit unit 3 is connected to the ground.

  The smoothing capacitor 4 is for smoothing the DC voltage rectified by the rectifier circuit unit 3. One end of the smoothing capacitor 4 is connected to the positive voltage side of the rectifier circuit unit 3 (that is, between the positive voltage side of the rectifier circuit unit 3 and one end side of the primary side coil 51 of the transformer 5). The other end is connected to the ground. The smoothing capacitor 4 is charged and discharged according to the voltage value of the DC voltage rectified by the rectifier circuit unit 3, thereby smoothing the DC voltage rectified by the rectifier circuit unit 3.

  The transformer 5 is for transforming voltage. The transformer 5 includes a primary side coil 51, a secondary side coil 52, and an auxiliary coil 53. The primary coil 51 has one end connected to the positive voltage side of the rectifier circuit unit 3 (that is, between the positive voltage side of the rectifier circuit unit 3 and one end side of the smoothing capacitor 4), and the other end. The side is connected between the drain and source of the field effect transistor 6 and the ground via the resistor 41. Therefore, in the transformer 5, a DC voltage rectified by the rectifier circuit unit 3 and smoothed by the smoothing capacitor 4 is input to the primary coil 51. When the current flowing through the primary side coil 51 changes, the transformer 5 changes the current flowing from the secondary side coil 52 and the auxiliary coil 53 to the primary side coil 51 and the primary side coil 51 and the coil 52 described above. , 53 is output in accordance with the coil turns ratio. The secondary coil 52 is connected to a load (not shown) (for example, a liquid crystal display or a DVD drive). One end of the auxiliary coil 53 is connected to the gate of the field effect transistor 6 via the first switching resistor 10 and the first switching capacitor 9, and the other end is connected to the ground.

  The field effect transistor 6 is for switching between a state where the DC voltage smoothed by the smoothing capacitor 4 is input to the primary side coil 51 of the transformer 5 and a state where it is not input. In the field effect transistor 6, the gate is connected to the positive voltage side of the rectifier circuit unit 3 via the starting resistor 8 (between one end side of the smoothing capacitor 4 and one end side of the primary side coil 51 of the transformer 5). The drain is connected to the other end of the primary side coil 51 of the transformer 5, and the source is connected to the ground via the resistor 41. A capacitor 42 is connected between the drain and source of the field effect transistor 6. The field effect transistor 6 is conductive when the gate voltage, which is the voltage between the gate and the source, is high (the drain-source is conductive), and is non-conductive (the drain / source when the gate voltage is low). The source is not conducting). The field effect transistor 6 is switched between a conducting state and a non-conducting state, so that the DC voltage smoothed by the smoothing capacitor 4 is input to the primary coil 51 of the transformer 5 and is not input. Switch to.

  The junction transistor 7 is for switching the field effect transistor 6 between a conductive state and a non-conductive state. The junction transistor 7 has a base connected to the source side of the field effect transistor 6 via a diode 43, a collector connected to the gate side of the field effect transistor 6, and an emitter connected to the ground. The diode 43 has a cathode connected to the base of the junction transistor 7 and an anode connected to the source of the field effect transistor 6. The junction transistor 7 becomes conductive when the base voltage, which is the voltage between the base and emitter, is high (conductor is connected between the collector and emitter), and is non-conductive when the base voltage is low (collector-collector). The emitter is in a non-conductive state). Junction transistor 7 switches field effect transistor 6 between a non-conductive state and a conductive state by switching between conductive state and non-conductive state.

  One end side of the starting resistor 8 is connected to the positive voltage side of the rectifier circuit unit 3 (between one end side of the smoothing capacitor 4 and one end side of the primary coil 51 of the transformer 5). The end side is connected to the gate side of the field effect transistor 6.

  The first switching capacitor 9 has one end connected to the gate of the field effect transistor 6 and the other end connected to the first switching resistor 10. The first switching resistor 10 has one end connected to the first switching capacitor 9 and the other end connected to one end of the auxiliary coil 53 of the transformer 5.

  The second switching resistor 11 and the second switching capacitor 12 are each connected to the base side of the junction transistor 7, and the other end side is connected to the ground.

  A Zener diode 44 and a resistor 45 are connected between one end of the auxiliary coil 53 of the transformer 5 and the base of the junction transistor 7. The Zener diode 44 has a cathode connected to one end of the auxiliary coil 53 and an anode connected to the resistor 45. The resistor 45 has one end connected to the anode of the Zener diode 44 and the other end connected to the base of the junction transistor 7.

  The fuse 13 is for protecting the power supply circuit 1 from an overcurrent. The fuse 13 is connected between the AC outlet 2 and the rectifier circuit unit 3. The fuse 13 cuts off the input of the AC voltage to the rectifier circuit unit 3 by being blown. The fuse 13 is blown by the overcurrent when an overcurrent flows.

  The fuse fusing circuit 14 is used for fusing the fuse 13 when a voltage higher than a specified value (for example, a voltage having a voltage value more than twice the rated voltage value to be originally input) is input to the rectifier circuit unit 3. This is for making the field effect transistor 6 conductive. The fuse blowing circuit 14 is connected between one end side of the auxiliary coil 53 of the transformer 5 and the gate side of the field effect transistor 6, and includes Zener diodes 61 and 62, a resistor 63, and a diode 64.

  The Zener diode 61 has a cathode connected to the cathode of the diode 64 and an anode connected to the cathode of the Zener diode 62. The Zener diode 62 has a cathode connected to the anode of the Zener diode 61 and an anode connected to the resistor 63. One end of the resistor 63 is connected to the anode of the Zener diode 62, and the other end is connected to the gate side of the field effect transistor 6. The diode 64 has a cathode connected to the cathode of the Zener diode 61 and an anode connected to one end of the auxiliary coil 53 of the transformer 5.

  That is, the Zener diode 61 has a cathode connected to one end side of the auxiliary coil 53 of the transformer 5 via the diode 64, and an anode connected to the gate side of the field effect transistor 6 via the Zener diode 62 and the resistor 63. ing. The Zener diode 62 has a cathode connected to one end side of the auxiliary coil 53 of the transformer 5 via the Zener diode 61 and the diode 64, and an anode connected to the gate side of the field effect transistor 6 via the resistor 63. ing.

  The power supply circuit 1 having such a configuration operates as follows when a normal voltage (a voltage having a rated voltage value to be originally input) is input to the rectifier circuit unit 3.

  First, the voltage smoothed by the smoothing capacitor 4 is input to the first switching capacitor 9 via the starting resistor 8, thereby charging the first switching capacitor 9. . At this time, the first switching capacitor 9 is gradually charged by the presence of the first switching resistor 10, and as a result, the voltage input to the base of the field effect transistor 6 increases. Go. When the voltage input to the gate of the field effect transistor 6 reaches a high level, the field effect transistor 6 becomes conductive.

  When the field effect transistor 6 becomes conductive, a current flows from the rectifier circuit unit 3 to the primary coil 51 of the transformer 5 and the drain and source of the field effect transistor 6. Thereby, a voltage is output from the secondary side coil 52 and the auxiliary coil 53 of the transformer 5 due to a change in current when the current flows through the primary side coil 51 of the transformer 5. Further, when a current flows between the drain and source of the field effect transistor 6, the second switching capacitor 12 is charged. At this time, the second switching capacitor 12 is gradually charged due to the presence of the second switching resistor 11, and accordingly, the voltage input to the base of the junction transistor 7 increases. Go. When the voltage input to the base of the junction transistor 7 reaches a high level, the junction transistor 7 becomes conductive.

  When the junction transistor 7 becomes conductive, a current flows from the starting resistor 8 between the collector and emitter of the junction transistor 7, and the first switching capacitor 9 is connected between the collector and emitter of the junction transistor 7. It is discharged via. As a result, the voltage input to the gate of the field effect transistor 6 is pulled to a low level, and the field effect transistor 6 becomes nonconductive.

  When the field effect transistor 6 is turned off, no current flows from the rectifier circuit unit 3 to the primary coil 51 of the transformer 5 and the drain and source of the field effect transistor 6. As a result, a voltage is output from the secondary coil 52 and the auxiliary coil 53 of the transformer 5 due to a change in current when no current flows through the primary coil 51 of the transformer 5. In addition, since the current does not flow between the drain and source of the field effect transistor 6, the second switching capacitor 12 is discharged via the second switching resistor 11, thereby the junction transistor 7. The voltage input to the base of the transistor becomes low level, and the junction transistor 7 becomes nonconductive.

  When the junction transistor 7 is turned off, the first switching capacitor 9 is again charged by the voltage input via the starting resistor 8, and thereafter the same operation as described above is repeated. It is.

  That is, (1) the field effect transistor 6 becomes conductive, and a current flows from the rectifier circuit unit 3 to the primary side coil 51 of the transformer 5 and the drain and source of the field effect transistor 6, and the current change at this time A voltage is output from the secondary coil 52 and the auxiliary coil 53 of the transformer 5, (2) the junction transistor 7 is turned on, and (3) the field effect transistor 6 is turned off. Current stops flowing between the primary side coil 51 of the transformer 5 and the drain and source of the field effect transistor 6, and a voltage is output from the secondary side coil 52 and the auxiliary coil 53 of the transformer 5 due to the current change at this time. 4) The operation that the junction transistor 7 is turned off is repeated.

  That is, the junction transistor 7 is repeatedly switched between the conducting state and the non-conducting state, and the field effect transistor 6 is repeatedly switched between the conducting state and the non-conducting state, whereby the current flowing through the primary coil 51 of the transformer 5 is repeated. As a result, a predetermined voltage is output from the secondary coil 52 of the transformer 5, and a voltage is also output from the auxiliary coil 53 of the transformer 5. The power supply circuit 1 operates in this way when a normal voltage is input to the rectifier circuit unit 3. It should be noted that the Zener diode 44 and the Zener diodes 61 and 62 of the fuse blown circuit 14 are not conducted with the voltage output from the auxiliary coil 53 of the transformer 5 when a normal voltage is input to the rectifier circuit unit 3. It is configured.

  The power supply circuit 1 operates as follows when a voltage higher than a specified value (for example, a voltage having a voltage value more than twice the rated voltage value to be originally input) is input to the rectifier circuit unit 3. To do.

  When a voltage higher than a specified value is input to the rectifier circuit unit 3, the current flowing through the primary side coil 51 of the transformer 5 increases. At this time, the change in the current flowing through the primary side coil 51 causes a change in the The voltage output from the auxiliary coil 53 increases.

  Then, the Zener diode 44 is turned on by the voltage output from the auxiliary coil 53 of the transformer 5, and the voltage output from the auxiliary coil 53 of the transformer 5 is input to the base of the junction transistor 7 via the Zener diode 44 and the resistor 45. Is done. As a result, the voltage input to the base of the junction transistor 7 becomes high level, and the junction transistor 7 becomes conductive.

  In addition, the Zener diode 61 and the Zener diode 62 of the fuse blowing circuit 14 are turned on by the voltage output from the auxiliary coil 53 of the transformer 5, and the voltage output from the auxiliary coil 53 of the transformer 5 is the diode 64 and Zener diodes 61 and 62. And the gate of the field effect transistor 6 through the resistor 63. As a result, the voltage input to the gate of the field effect transistor 6 becomes high level, and the field effect transistor 6 becomes conductive. That is, the fuse blowing circuit 14 detects that a voltage higher than a specified value is input to the rectifier circuit unit 3 based on the voltage output from the auxiliary coil 53 of the transformer 5, and from the anodes of the Zener diodes 61 and 62. The field effect transistor 6 is turned on by the output voltage (that is, using the voltage output from the auxiliary coil 53 of the transformer 5).

  Since the junction transistor 7 is in a conductive state, a current flows between the collector and emitter of the junction transistor 7, and the junction transistor 7 puts the field effect transistor 6 in a non-conductive state (the field effect transistor 6 Trying to bring the gate low). On the other hand, the fuse blowing circuit 14 is configured to have a capability of flowing a current equal to or greater than the current flowing between the collector and the emitter of the junction transistor 7. That is, the fuse blowing circuit 14 brings the field effect transistor 6 into a conductive state against the action of the junction transistor 7 trying to make the field effect transistor 6 nonconductive.

  When the field effect transistor 6 becomes conductive, a current having a voltage equal to or higher than a specified value input to the rectifier circuit unit 3 flows between the drain and source of the field effect transistor 6 and the field effect transistor 6 is short-circuited. As a result, an overcurrent flows through the fuse 13 and the fuse 13 is blown before the explosion-proof valve of the smoothing capacitor 4 operates. The power supply circuit 1 operates in this way when a voltage exceeding a specified value is input to the rectifier circuit unit 3.

  According to the power supply circuit 1 having such a configuration, when a voltage higher than a specified value is input to the rectifier circuit unit 3, the field effect transistor 6 becomes conductive due to the action of the fuse blowing circuit 14, thereby An overcurrent flows through 13 and the fuse 13 is blown before the explosion-proof valve of the smoothing capacitor 4 operates. Therefore, even if a voltage exceeding the specified value is input, the explosion-proof valve of the smoothing capacitor 4 does not work (does not open), preventing the user from mistaking smoke from the explosion-proof valve as smoke from ignition. Can do.

  In addition, the fuse blowing circuit 14 detects that a voltage higher than a specified value is input to the rectifier circuit unit 3 based on the voltage output from the auxiliary coil 53 of the transformer 5, and outputs it from the auxiliary coil 53 of the transformer 5. Since the field effect transistor 6 is made conductive by using the applied voltage, a measure to prevent the explosion-proof valve of the smoothing capacitor 4 from operating even when a voltage exceeding a specified value is input is inexpensive. Can be realized.

  In addition, this invention is not restricted to the structure of the said embodiment, A various deformation | transformation is possible. For example, a fuse blowing circuit detects that a voltage exceeding a specified value has been input to the rectifier circuit based on the voltage output from the transformer auxiliary coil, and uses the voltage output from the transformer auxiliary coil. As long as the field effect transistor is in a conductive state, another configuration may be used. In addition, the fuse blown circuit turns the field-effect transistor into a conductive state against the action of the junction transistor trying to turn the field-effect transistor into a non-conductive state when a voltage exceeding a specified value is input to the rectifier circuit section. Any other configuration may be used as long as it is configured as described above. Further, the other end of the smoothing capacitor, the other end of the auxiliary coil, the source of the field effect transistor, the emitter of the junction transistor, the other end of the second switching resistor, and the second switching The other end side of the capacitor may be connected to the negative voltage side of the rectifier circuit unit.

DESCRIPTION OF SYMBOLS 1 Power supply circuit 2 AC outlet 3 Rectifier circuit part 4 Smoothing capacitor 5 Transformer 6 Field effect transistor (1st switching element)
7 Junction transistor (second switching element)
8 Start-up resistor 9 First switching capacitor 10 First switching resistor 11 Second switching resistor 12 Second switching capacitor 13 Fuse 14 Fuse blowing circuit 41 Resistor 42 Capacitor 43 Diode 44 Zener diode 45 Resistance 51 Primary side coil 52 Secondary side coil 53 Auxiliary coil 61 Zener diode 62 Zener diode 63 Resistance 64 Diode

Claims (4)

A rectifier circuit unit that rectifies the AC voltage into a DC voltage by inputting the AC voltage;
A smoothing capacitor for smoothing the DC voltage rectified by the rectifier circuit unit;
A transformer in which a DC voltage smoothed by the smoothing capacitor is input to a primary coil;
By switching between the conducting state and the non-conducting state, the first switching is performed so that the DC voltage smoothed by the smoothing capacitor is switched between a state where the DC voltage is input to the primary coil of the transformer and a state where the DC voltage is not input. Elements,
A second switching element that switches the first switching element between a conductive state and a non-conductive state by switching between a conductive state and a non-conductive state;
A fuse that cuts off the input of AC voltage to the rectifier circuit section by being blown,
The second switching element is switched between a conductive state and a non-conductive state, and the first switching element is switched between a conductive state and a non-conductive state, whereby a predetermined voltage is output from the secondary coil of the transformer. In the power supply circuit
A fuse fusing circuit for bringing the first switching element into a conductive state in order to blow the fuse when a voltage of a specified value or more is input to the rectifier circuit unit;
The fuse blowing circuit detects that a voltage exceeding a specified value is input to the rectifier circuit unit based on a voltage output from the auxiliary coil of the transformer, and outputs a voltage output from the auxiliary coil of the transformer. A power supply circuit using the first switching element in a conductive state by using.   The fuse blowing circuit is against the action that the second switching element attempts to make the first switching element non-conductive when a voltage of a specified value or more is input to the rectifier circuit unit, The power supply circuit according to claim 1, wherein the first switching element is turned on.   The fuse blowing circuit has a Zener diode, and the Zener diode has a cathode connected to the auxiliary winding side of the transformer, an anode connected to the first switching element side, and an anode of the Zener diode The power supply circuit according to claim 2, wherein the first switching element is turned on by a voltage output from the power supply circuit. The first switching element is a field effect transistor, the gate is connected to the positive voltage side of the rectifier circuit unit, the drain is connected to the primary coil of the transformer, and the source is ground or the rectifier circuit unit It is connected to the negative voltage side
The second switching element is a junction transistor, a base is connected to a source side of the first switching element, a collector is connected to a gate of the first switching element, and an emitter is ground or the rectifier circuit Connected to the negative voltage side of the
4. The power supply circuit according to claim 3, wherein the Zener diode of the fuse blowing circuit has an anode connected to a gate side of the first switching element. 5.

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