JP2011004551A - Electric apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric apparatus that suspends a power circuit 10 before a smoothing capacitor 15 opens its pressure valve or is destroyed.SOLUTION: The electric apparatus includes a fuse 12 interposed in series on an AC line L1, a startup resistor 18 connecting a DC line L3 to the gate of an FET 17, and a Zener diode 30 having a cathode connected to the DC line L3 and an anode connected to a self-excitation oscillation control circuit 19. When the Zener diode 30 yields, the self-excitation oscillation control circuit 19 stops on-off control over the FET 17 to keep it on. A short-circuit breakdown occurs between the gate and source or between the drain and the source of the FET 17. The short-circuit breakdown causes excess current in the power circuit 10 to fuse the fuse 12.

Description

  The present invention relates to electrical equipment, and in particular, full-wave rectification of alternating current input through a first transmission line connected to a plug for connection to an outlet by a rectifier circuit and smoothing a pulsating current with a smoothing capacitor. The generated direct current is input to the primary winding of the transformer through the second transmission line, and the gate of the field effect transistor having the source-drain inserted in the low voltage side line of the second transmission line is fed back to the transformer. The present invention relates to an electric device including a power supply circuit that generates a desired voltage in a secondary winding of the transformer by performing on / off control with a self-excited oscillation type control circuit based on a current generated in the winding.

Conventionally, a power supply circuit used for electrical equipment has been provided with a fuse. When a current exceeding a predetermined value flows through the fuse, the fuse is blown to shut off the power supply, thereby protecting the power supply circuit from overcurrent. ing.
FIG. 5 is a principal circuit diagram for explaining the outline of a conventional power supply circuit. In the figure, the power supply circuit is roughly divided into an AC portion and a DC portion.

  The AC portion is inserted on the AC line L1 and the plug 1 having the input terminals IN1 and IN2 for connecting to the socket of the AC power source, the AC lines L1 and L2 connected to the input terminals IN1 and IN2, respectively. Fuse 2, filter circuit 3 for removing common mode noise and normal mode noise from AC lines L 1 and L 2, and full-wave rectification of alternating current input from AC lines L 1 and L 2 via AC input terminals 4 a and 4 b. And a diode bridge circuit 4. The diode bridge circuit 4 outputs direct current (pulsating flow) to the DC portion.

  The DC portion includes DC lines L3 and L4 and a transformer 6, and the DC line L3 connects the positive DC output terminal 4c of the diode bridge circuit 4 to one pole of the primary winding 6a of the transformer 6. The DC line L4 connects the negative DC output terminal 4d of the diode bridge circuit 4 via the FET 7 to the other pole of the primary winding 6a. Note that a desired voltage corresponding to the current flowing through the primary winding 6a is generated in the secondary winding 6b of the transformer 6 by appropriately adjusting the number of turns.

  The DC portion is connected between the DC lines L3 and L4 and connected to the smoothing capacitor 5 for smoothing the pulsating current after full-wave rectification so that the source and drain are arranged in series on the DC line L4. A start-up resistor that applies a start-up voltage to the FET 7 by connecting a field-effect transistor (FET) 7 that can connect and disconnect the cage DC line L4 and a portion of the DC line L3 through which the direct current after smoothing flows and the base of the FET 7 8 and a control circuit 9 for controlling on / off of the FET 7 by outputting a gate drive signal for controlling the gate voltage of the FET 7 based on the current flowing through the feedback winding 6c.

  In the power supply circuit of FIG. 5 configured as described above, when an excessive current (overcurrent) flows due to an alternating current input from the plug 1, the fuse 2 is blown and an excessive load is not applied to the power supply circuit. It is configured as follows. However, even if an overcurrent does not flow, an excessive voltage (overvoltage) may be applied to each element, and a high load is applied to each element of the power supply circuit in the time lag from when an excessive alternating current is input until the fuse 2 is blown. May take.

As a phenomenon that occurs when a high load is applied to the power supply circuit, for example, Patent Document 4 includes the following three. In describing these phenomena, it is assumed that the phenomenon indicated in Patent Document 4 occurs in the power supply circuit in FIG. 5, taking the circuit element names in FIG. 5 as an example.
(1) Before the smoothing capacitor 5 is opened due to breakdown of the breakdown voltage, the field effect transistor (FET) 7 is destroyed in the short mode due to overcurrent, and the fuse 2 is blown by overcurrent flowing through the AC line L1 due to this destruction. The alternating current input from the plug 1 is interrupted.
(2) The valve opening of the smoothing capacitor 5 and the short-circuit breakdown of the FET 7 occur almost simultaneously, whereby the fuse 2 is blown by the overcurrent flowing through the AC line L1, and the alternating current input from the plug 1 is cut off.
(3) Even if only the smoothing capacitor 5 is opened and the electrolyte is ejected, the fuse 2 is not blown and other circuits continue to operate.

In order to prevent the situation corresponding to (1) to (3), the cited document 4 is provided with an AC overvoltage protection circuit for monitoring a DC voltage rectified and smoothed by a rectifier circuit and a smoothing capacitor. . This AC overvoltage protection circuit generates a voltage that is the same as or higher than the gate drive voltage of the FET when the AC power input to the power supply circuit is not excessive, and applies it to the gate of the FET. Circuit.
Therefore, when the AC overvoltage protection circuit of the cited document 4 is applied to the circuit of FIG. 5, when the AC power input to the power supply circuit becomes excessive, the drain-source state of the FET 7 continues to be conductive. . As a result, the fuse is blown before the smoothing capacitor is opened, and the input of the AC power supply is stopped.

In addition, Patent Documents 1 to 3 and 5 disclose techniques for safely stopping the power supply circuit.
First, in Cited Document 1, when the applied voltage of the smoothing capacitor that smoothes the pulsating flow after rectifying alternating current exceeds the rated voltage, for example, the anode is connected to the negative electrode while the cathode is connected to the positive electrode of the smoothing capacitor via a resistor. It is disclosed that the connected Zener diode breaks down to generate an overcurrent, and this overcurrent also causes an overcurrent to occur in the AC circuit in the previous stage of the rectifier circuit, so that the fuse arranged in this AC circuit is blown. Yes.

  Next, in Patent Document 2, when an overvoltage detection circuit detects an overvoltage of a power supply line, a fuse inserted in a line for transmitting a switch operation signal of a switch circuit inserted between the power supply line and the load circuit is provided. It is disclosed that the fuse blown circuit is blown to turn off the switch circuit.

  In Patent Document 3, the voltage in the AC line before rectification is detected, and when the voltage exceeds the Zener voltage of the Zener diode, the Zener diode is turned on, and the resistor with temperature fuse inserted in the AC line Is described, and the power supply circuit is cut off by blowing the temperature fuse.

  Further, in Patent Document 5, when the output voltage of the DC / DC converter circuit increases, a circuit combining a Zener diode and a thyristor blows a fuse inserted between the input terminal IN + and the DC / DC converter. Disabling the DC / DC converter circuit is disclosed.

Japanese Patent Laid-Open No. 7-236276 Japanese Patent Laid-Open No. 10-4624 JP 2004-88857 A JP 2006-288155 A JP 2007-43822 A

However, as described in paragraphs 0035 to 0041 of the cited document 4, the relationship of [time until the AC overvoltage protection circuit operates and the fuse blows] <[opening time of the smoothing capacitor] is satisfied. Therefore, various restrictions are imposed on circuit constants and component selection of each element. For example, in the cited document 4, it is pointed out that the electric field capacitor used for the smoothing capacitor has a different valve opening time and valve opening voltage even if the rating is the same.
Further, the technique of the cited document 1 does not consider the oscillation circuit. Therefore, when the technique of the cited reference 1 is applied to the power supply circuit shown in FIG. 5, the control by the oscillation circuit is continued until the fuse is blown after the Zener diode breaks down, and the smoothing capacitor is charged. May continue to rise and the smoothing capacitor may be damaged.
Further, in the techniques of the cited documents 2 and 5, a fuse is separately provided on the DC line separately from the AC line, and an additional cost is required.
Further, the technique of the cited document 3 is a technique for monitoring the AC line, the monitoring circuit is complicated, and a circuit using a large number of elements is required. Therefore, cost performance is bad.

  The present invention has been made in view of the above problems, and when excessive AC power is input to the power supply circuit, without depending on variations in the valve opening characteristics of each component of the electric field capacitor as a smoothing capacitor, It is an object of the present invention to provide an electric device including a power supply circuit capable of stopping the power supply circuit before the electrolytic solution is ejected from the electric field capacitor. At the same time, it is an object to achieve the object while reducing the additional cost required for the change from the conventional circuit as much as possible.

  In order to solve the above-described problems, in the electrical device of the present invention, a plug having two input terminals for connecting to an outlet supplying alternating current, a first transmission line connected to each of the two input terminals, and A second transmission line; a rectifier circuit that full-wave rectifies the alternating current input through the first and second transmission lines; an electrolytic capacitor that smoothes the pulsating current output from the rectifier circuit; A third transmission line that inputs a positive output to one end of the primary winding of the transformer, a fourth transmission line that transmits a negative DC output after smoothing, the fourth transmission line, and the primary winding A field effect transistor having a source-drain interposed between the other end of the transistor and a gate of the field effect transistor on / off controlled based on a current generated in the feedback winding of the transformer, In an electrical apparatus including a power supply circuit including a self-excited oscillation type control circuit that generates a desired voltage in the secondary winding of the transformer, a fuse interposed in series with the first transmission line, A starting resistor connecting a third transmission line and the gate; and a Zener diode having a cathode connected to the third transmission line and an anode connected to the control circuit, the control circuit including the Zener When the diode breaks down, the on / off control is stopped and the field effect transistor is maintained in the on state, thereby causing the field effect transistor to be short-circuit broken, generating an overcurrent due to the short-circuit breakdown, and blowing the fuse. is there.

  In the above configuration, when a plug is connected to an outlet, alternating current is input via two input terminals. The outlet is provided with one or a plurality of outlets, and supplies, for example, commercial AC for home use. When a plug is inserted into the outlet, the AC is supplied to the plug. The outlets may be supplied with different voltage alternating currents in different countries, but the outlets may have the same shape. Here, the middle of the first transmission line is composed of a fuse, and when an overcurrent exceeding the fuse rating flows in the first transmission line, the fuse is blown to electrically connect the first transmission line. It shuts off and the power supply to the electrical equipment is stopped. However, the fuse does not blow unless the current flowing through the first transmission line becomes an overcurrent exceeding the rating of the fuse.

  The alternating current input through the first transmission line and the second transmission line respectively connected to the two input terminals is full-wave rectified by the rectifier circuit, and then the pulsating current is smoothed by the electrolytic capacitor which is a smoothing capacitor. The smoothed direct current is input to the one end of the primary winding of the transformer via the third transmission line, and the negative output is connected to the other end of the transformer via the fourth transmission line and the field effect transistor. Is input. The field effect transistor has a source terminal connected to the fourth transmission line and a drain terminal connected to the other end of the transformer.

  The gate drive voltage generated by the self-excited oscillation type control circuit is input to the gate of the field effect transistor. The gate drive voltage is generated so that the feedback current becomes constant based on the feedback current generated in the feedback winding of the transformer, and is a signal for on / off control of the gate. More specifically, when the feedback current reaches the upper limit set in advance in the control circuit, the gate is turned off to suppress the current generated in the primary winding and generated in the secondary winding of the transformer. The current to be reduced is also reduced. By such control, the current generated in the secondary winding is also suppressed to an amount corresponding to the upper limit of the feedback current. This is because the secondary current generated in the secondary winding and the feedback current are in a proportional relationship and correlated if there is no load connected to the secondary winding.

  A starting voltage is input from the third transmission line to the gate of the field effect transistor via the starting resistor. When the start-up voltage is input, the field effect transistor is turned on. Therefore, the control circuit turns off the field effect transistor by pulling the gate to a low voltage and electrically connects the gate and the control circuit. The starting voltage is applied to the gate by blocking. Therefore, the field effect transistor is turned on.

  The control circuit is connected to the third transmission line by a Zener diode. Since this Zener diode has a cathode connected to the third transmission line and an anode connected to the control circuit, it breaks down when the voltage of the third transmission line exceeds the Zener voltage, and the third transmission line The voltage of the transmission line is input to the control circuit. Then, the control circuit stops generating the gate drive signal and maintains the state where the starting voltage is applied to the gate. Therefore, when the voltage of the third transmission line exceeds the Zener voltage, the field effect transistor is kept on.

  When the voltage of the third transmission line rises, at least one of the source-base or the source-drain of the field effect transistor that remains on is short-circuited. Then, an overcurrent is generated through this short-circuited path, and an overcurrent is also generated in the alternating current portion of the previous stage of the rectifier circuit. As a result, the fuse is blown and AC input to the power supply circuit is stopped.

  Here, the Zener voltage of the Zener diode is preferably set lower than the voltage at which the electrolytic capacitor opens and higher than the rating of the input voltage of the power supply circuit. In addition, when the plug is connected to a predetermined AC power source that is higher than the rating of the power supply circuit, it is assumed that the electrolytic capacitor is opened or destroyed after the Zener diode breaks down. The time from the breakdown of the Zener diode to the breakdown of the field-effect transistor after the breakdown of the Zener diode is set to “t2”, and the overcurrent from the rated current starts to flow until the fuse blows. It is preferable that each element of the power supply circuit is determined so that a relationship of t1> t2 + t3 is established, where time is “t3”. If the power supply circuit is configured in this manner, the power supply to the power supply circuit can be reliably stopped before the electrolytic capacitor is opened or destroyed.

  In addition, you may arrange | position suitably elements other than the element mentioned above in the 1st-4th transmission line. As an example, a filter circuit can be disposed on the first and second transmission lines. This filter circuit is a circuit that removes common mode noise from the first and second transmission lines. By disposing the filter circuit, it is possible to prevent a sudden voltage increase due to noise, so that the power supply circuit does not stop due to a sudden voltage increase due to noise.

As described above, according to the present invention, it is possible to provide an electric device including a power supply circuit that can stop power supply to the power supply circuit before the electrolytic capacitor is opened or destroyed.
According to the second aspect of the present invention, the power supply to the power supply circuit can be reliably stopped before the electrolytic capacitor is opened or destroyed.
According to the third aspect of the present invention, since a sudden voltage increase caused by noise can be prevented, the power supply circuit does not stop due to a sudden voltage rise caused by noise.

It is a perspective view of a television. It is a principal part circuit diagram which shows the power supply circuit of a television. This is a control signal output from the self-excited oscillation control circuit to the gate of the FET. It is a graph which shows the relationship with respect to the charge amount of the smoothing capacitor of the proof pressure V3 and the breakdown voltage VD. It is a principal part circuit diagram explaining the outline of the conventional power supply circuit.

Hereinafter, embodiments of the present invention will be described in the following order.
(1) Configuration of electrical equipment:
(2) Configuration of power supply circuit:
(3) Summary:

(1) Configuration of electrical equipment:
FIG. 1 is a perspective view showing a television according to an embodiment of the electric apparatus of the present invention. In the present embodiment, a television is used as an example of an electrical device. However, a power supply circuit that converts alternating current into direct current and a power supply cable that inputs alternating current to the power supply circuit are provided to take electricity from the wiring. A variety of devices can be used as long as the electrical device has a plug for connecting to an insertion port (hereinafter referred to as “outlet”) at the end of the power cable.

  As shown in FIG. 1, a power cable is led out from the television 100, and this power cable is provided with a plug 11 at the tip for connection to an outlet. When the user of the television 100 supplies power to the television 100, the plug 11 is first connected to an outlet. Then, for example, when the power-on button is pressed down, the power supply circuit 10 creates various power supply voltages based on the AC power input from the plug 11 and supplies the power supply voltages to the circuits constituting the television 100.

  However, even if the outlets have the same shape, the power supply voltage supplied from each outlet may be different. When the plug 11 is mistakenly connected to an outlet supplying a power supply voltage different from the rating, it is necessary to stop the power supply voltage generation operation of the power supply circuit 10 at an appropriate timing. Therefore, the power supply circuit 10 of the television 100 of the present embodiment employs a power supply circuit having the following configuration.

(2) Configuration of power supply circuit:
FIG. 2 is a principal circuit diagram showing the power supply circuit 10 of the television 100. In the power supply circuit 10 shown in the figure, a load device is connected to the secondary side of the transformer 16. The load device referred to here is a television 100, such as a display such as a cathode ray tube, a liquid crystal panel module, or a plasma display panel module, a circuit that receives a broadcast signal and generates a signal for driving the display, A circuit for generating an audio signal based on the signal.
In FIG. 1, only one secondary winding of the transformer is shown, but the number of secondary windings can be appropriately increased or decreased according to the number of load devices. Moreover, it can adjust so that a voltage required for each load apparatus may be output by adjusting the number of turns of a secondary winding.

In FIG. 1, the power supply circuit 10 is roughly divided into an AC portion surrounded by a one-dot chain line and a DC portion surrounded by a two-dot chain line.
The AC portion is composed of AC input terminals IN1, IN2, AC lines L1, L2 connected to the AC input terminals, a fuse 12 inserted in series on the AC line L1, and AC lines L1, L2, respectively. A filter circuit 13 for removing mode noise and normal mode noise, and a diode bridge circuit 14 for converting alternating current supplied from the AC lines L1 and L2 into direct current (pulsating flow) are provided. The AC input terminals IN1 and IN2 correspond to electrical contacts with an outlet in the plug 11 of the television 100. In the present embodiment, the AC line L1 constitutes the first transmission line in the claims, and the AC line L2 constitutes the second transmission line in the claims.

  The filter circuit 13 is composed of a common mode choke coil, a bleeder resistor, an across-the-line capacitor, and the like. Noise generated by the AC input from the AC input terminals IN1 and IN2 on the AC lines L1 and L2 , Common mode noise generated between the AC lines L1 and L2 and the ground is reduced. The alternating current whose noise has been reduced by the filter circuit 13 is input to the diode bridge circuit 14 from the AC input terminals 14a and 14b, and is output from the DC output terminals 14c and 14d to the DC portion as a full-wave rectified pulsating current.

  The DC portion is a smoothing capacitor connected between DC lines L3 and L4 and DC lines L3 and L4 respectively connected between the DC output terminals 14c and 14d of the diode bridge circuit 14 and the primary winding 16a of the transformer 16. 15, a field effect transistor (FET) 17 inserted in the DC line L 4, a starting resistor 18 that connects the gate of the FET 17 to the smoothed L 3, and a self-excited oscillation control circuit 19 that is connected to the gate of the FET 17 The capacitor 17a as a snubber circuit that absorbs a transient high voltage generated by switching of the FET 17 and the Zener diode 30 as an overvoltage protection circuit are provided. In the present embodiment, the DC line L3 constitutes the third transmission line in the claims, and the DC line L4 constitutes the fourth transmission line in the claims.

The smoothing capacitor 15 is an electric field capacitor, and has a positive electrode connected to the DC line L3 and a negative electrode connected to the DC line L4. The smoothing capacitor 15 smoothes the direct current (pulsating flow) output from the diode bridge circuit 14 and converts it to substantially direct current.
In the transformer 16, the DC line L3 is connected to one pole of the primary winding 16a, and the DC line L4 is connected to the other pole. When a current (primary current) flows through the primary winding 16a, an amount of current (secondary current) corresponding to the primary current is generated in the secondary winding 16b. When the primary current flows, an amount of current (feedback current) corresponding to the primary current is also generated in the feedback winding 16c of the transformer 16. This feedback current is input to the self-excited oscillation control circuit 19.

  The FET 17 is inserted in the DC line L4 with the source facing the diode bridge circuit 14 and the drain facing the primary winding 16a. The starting voltage is input to the gate of the FET 17 via the starting resistor 18. The gate of the FET 17 is also connected to the self-excited oscillation control circuit 19, and the self-excited oscillation control circuit 19 can lower the starting voltage by drawing the gate of the FET 17 into a low voltage line such as ground. That is, the self-excited oscillation control circuit 19 can turn off the FET 17 by setting the voltage applied to the gate lower than the drive voltage that can turn on the gate, or turn on the FET 17 by setting it higher than the drive voltage.

The self-oscillation control circuit 19 turns off the FET 17 to suppress the secondary voltage when the feedback current exceeds a predetermined upper limit value, and turns on the FET 17 to increase the secondary voltage when the feedback current falls below the predetermined lower limit value. Let In this way, the self-excited oscillation control circuit 19 performs control so that the secondary voltage becomes a desired value.
When the user selectively instructs whether to actually supply power to the load circuit with the remote control or the power button after the plug 11 is connected to the outlet, the self-excited oscillation control circuit 19 is self-excited. Self-excited oscillation is started only when a predetermined signal instructing excitation oscillation is input. That is, no current flows through the power supply circuit 10 before the self-excited oscillation starts, and the current flows through the power supply circuit 10 only after a predetermined signal is input.

  The Zener diode 30 is connected to the DC line L3 through which the direct current after smoothing the cathode flows, and the anode is connected to the self-excited oscillation control circuit 19. In FIG. 1, in order to adjust the breakdown voltage to a desired value, two Zener diodes are connected in series to form a Zener diode 30. Of course, one Zener diode or three or more Zener diodes may be used. It may be connected in series. When the voltage of the DC line L4 exceeds the breakdown voltage, the Zener diode 30 breaks down and inputs the voltage of the DC line L4 to the self-excited oscillation control circuit 19.

  When the Zener diode 30 breaks down and the voltage of the DC line L3 is input, the self-excited oscillation control circuit 19 detects the voltage and stops the control operation of the FET 15. That is, regardless of the feedback current, the start-up voltage continues to be applied to the FET 17 so that the FET 17 is kept on. Therefore, when the voltage generated between the DC line L3 and the DC line L4 rises and a short circuit breaks between the source and gate or the drain and source of the FET 17, an overcurrent is generated in the DC portion. Then, an overcurrent also flows in the AC portion and the fuse 12 is blown, so that power supply to the power supply circuit 10 is stopped.

The operation of the power supply circuit 10 configured as described above will be described.
For example, when the input voltage rating of the plug 11 of the power supply circuit 10 is 100 V and the plug 11 is connected to a 100 V rated outlet, the following operation is performed. When a user inputs a predetermined signal instructing self-excited oscillation to the self-excited oscillation control circuit 19 with a remote controller or the like, the FET 17 is turned on and a voltage is applied to the primary winding 16a. Then, an amount of secondary current corresponding to the primary current flowing through the primary winding 16a is generated in the secondary winding 16b, and this secondary current is supplied to the load circuit. At the same time, a feedback current is generated in the feedback winding 16 c, and this feedback current is input to the self-excited oscillation control circuit 19. At this time, the DC voltage V1 corresponding to AC100V is applied to the smoothing capacitor 15, and the voltage V1 is charged to the smoothing capacitor 15 after elapse of time corresponding to the time constant of the smoothing capacitor 15.

  FIG. 3 shows control signals output from the self-excited oscillation control circuit 19 to the gate of the FET 17. As shown in the figure, the self-excited oscillation control circuit 19 outputs a low voltage (L) when the feedback current exceeds a predetermined value, and outputs a high voltage (H) when the feedback current is less than the predetermined value. The low voltage (L) is lower than the voltage that can turn on the gate of the FET 17, and the high voltage (H) is higher than the voltage that can turn on the gate of the FET 17. In this manner, the self-excited oscillation control circuit 19 controls the current generated in the secondary winding 16b to approach a predetermined value.

  On the other hand, for example, when the input voltage rating of the plug 11 of the power supply circuit 10 is 100 V, the plug 11 is connected to a 200 V rated outlet as follows. When a user inputs a predetermined signal instructing self-excited oscillation to the self-excited oscillation control circuit 19 with a remote controller or the like, the FET 17 is turned on and a voltage is applied to the primary winding 16a. Then, a secondary current in an amount corresponding to the primary current flowing through the primary winding 16a is generated in the secondary winding 16b, and this secondary current is supplied to the load circuit, and at the same time, a feedback current is generated in the feedback winding 16c. The feedback current is input to the self-excited oscillation control circuit 19 as in the case of the 100V outlet described above.

However, when the FET 17 is turned on, charging of the smoothing capacitor 15 is started. At this time, a DC voltage V <b> 2 corresponding to the AC voltage 200 V is applied across the smoothing capacitor 15.
Note that the smoothing capacitor 15 of the present embodiment has a resistance to charge a voltage V3 not less than V1 and less than V2, and the Zener diode 30 is selected so that the breakdown voltage VD is not less than V1 and less than V3. Shall. Accordingly, the Zener diode 30 breaks down at the voltage VD before the voltage charged in the smoothing capacitor 15 reaches V3. Then, the self-excited oscillation control circuit 19 stops the self-excited oscillation and maintains the gate of the FET 17 at a voltage that can be turned on or higher. As a result, the gate-source or the drain-source of the FET 17 is short-circuited and an overcurrent flows through the DC portion of the power supply circuit 10. In response to this overcurrent, an overcurrent is also generated in the AC portion, so that the fuse 12 is blown and the supply of power to the power supply circuit 10 is stopped.

FIG. 4 is a graph showing the relationship between the withstand voltage V3 of the smoothing capacitor 15 and the breakdown voltage VD of the Zener diode 30 with respect to the charge amount of the smoothing capacitor 15. As shown in the figure, the time from when the voltage of the smoothing capacitor 15 reaches the breakdown voltage VD until it reaches the withstand voltage V3 of the smoothing capacitor 15 is t2, until the Zener diode 30 breakdowns and the FET 17 is short-circuited. If the time required for this is t3 and the time from the time when the FET 17 is short-circuited to the time when the fusing of the fuse 12 is completed is t4, the rating of each element is selected so as to satisfy the following equation (1).
t2> t3 + t4 (1)
Since the rating of each element is determined in this way, the power supply to the power supply circuit 10 can be reliably stopped before the smoothing capacitor 15 is opened or destroyed.

(3) Summary:
As described above, according to the electrical apparatus according to the present embodiment,
Plug 11, AC line L1 and AC line L2, rectifier circuit 14, smoothing capacitor 15, DC line L3 and DC line L4, primary winding 16a, secondary winding 16b, and feedback winding 16c are provided. In the television 100 including the power supply circuit 10 including the transformer 16, the FET 17, and the self-oscillation control circuit 19, the fuse 12 inserted in series on the AC line L1, the DC line L3, and the FET 17 And a zener diode 30 having a cathode connected to the DC line L3 and an anode connected to the self-excited oscillation control circuit 19, and the self-excited oscillation control circuit 19 includes the zener diode 30. When the breakdown occurs, the on / off control for the FET 17 is stopped and the FET 17 is maintained in the on state. The FET17 source - gate or drain - are shorted destroyed between the source, to generate an overcurrent in the power supply circuit 10 to blow the fuse 12 by the short-circuit breaking. Therefore, the power supply circuit 10 can be stopped before the smoothing capacitor 15 is opened or destroyed.

Needless to say, the present invention is not limited to the above embodiments. It goes without saying for those skilled in the art,
・ Applying mutually interchangeable members and configurations disclosed in the above embodiments by appropriately changing the combination thereof.− Although not disclosed in the above embodiments, it is a publicly known technique and the above embodiments. The members and configurations that can be mutually replaced with the members and configurations disclosed in the above are appropriately replaced, and the combination is changed and applied. It is an embodiment of the present invention that a person skilled in the art can appropriately replace the members and configurations that can be assumed as substitutes for the members and configurations disclosed in the above-described embodiments, and change the combinations and apply them. It is disclosed as.

DESCRIPTION OF SYMBOLS 1 ... Plug, 2 ... Fuse, 3 ... Filter circuit, 4 ... Diode bridge circuit, 4a ... AC input terminal, 4b ... AC input terminal, 4c ... DC output terminal, 4d ... DC output terminal, 5 ... Smoothing capacitor, 6 ... Transformer, 6a ... primary winding, 6b ... secondary winding, 6c ... feedback winding, 7 ... field effect transistor, 8 ... starting resistance, 9 ... control circuit, 10 ... power supply circuit, 11 ... plug, 12 ... fuse, DESCRIPTION OF SYMBOLS 13 ... Filter circuit, 14 ... Diode bridge circuit, 14a ... AC input terminal, 14b ... AC input terminal, 14c ... DC output terminal, 14d ... DC output terminal, 15 ... Smoothing capacitor, 16 ... Transformer, 16a ... Primary winding, 16b ... secondary winding, 16c ... feedback winding, 17 ... field effect transistor, 17a ... capacitor, 18 ... starting resistance, 19 ... self-excited oscillation control circuit 30 ... Zener diode, 100 ... television, IN1 ... AC input terminal, IN2 ... AC input terminals, L1, L2 ... AC line, L3, L4 ... DC line

Claims (3)

A plug having two input terminals for connection to an outlet supplying alternating current, a first transmission line and a second transmission line connected to the two input terminals, respectively, and the first and second transmissions A rectifying circuit for full-wave rectifying the alternating current input through the line; an electrolytic capacitor for smoothing the pulsating current output from the rectifying circuit; and a first positive output of the smoothed direct current input to one end of the primary winding of the transformer. 3 transmission line, a fourth transmission line for transmitting a negative DC output after smoothing, and a source-drain interposed between the fourth transmission line and the other end of the primary winding. Self-excitation for generating a desired voltage in the secondary winding of the transformer by controlling on / off of the field effect transistor and the gate of the field effect transistor based on the current generated in the feedback winding of the transformer In the electric apparatus having a power supply circuit and a control circuit for sustaining oscillating,
A fuse interposed in series on the first transmission line;
A starting resistor for connecting the third transmission line and the gate to supply a starting voltage to the gate;
A Zener diode having a cathode connected to the third transmission line and an anode connected to the control circuit,
When the Zener diode breaks down, the control circuit stops the on-off control and maintains the field-effect transistor in an on state, causing the field-effect transistor to be short-circuited and generating an overcurrent due to the short-circuit breakdown. An electrical apparatus characterized by fusing the fuse. The Zener voltage of the Zener diode is set lower than the voltage at which the electrolytic capacitor opens, and higher than the input voltage rating of the power supply circuit,
When the plug is connected to a predetermined AC power supply that is higher than the rating of the power supply circuit, the time from when the Zener diode breaks down until the electrolytic capacitor is assumed to open or break is defined as t1. Where t2 is the time from when the Zener diode breaks down until the field-effect transistor is short-circuited, and t3 is the time from when an overcurrent greater than the rated value starts to flow to the fuse until it blows. The electric device according to claim 1, wherein each element of the power supply circuit is determined so that a relationship of t2 + t3 is established.   The electrical apparatus according to claim 1, further comprising a filter circuit that removes common mode noise from the first and second transmission lines.

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