JP2011151988A - Power supply circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply circuit that fuses a fuse circuit, with no smoothing capacitor emitting white smoke, even if an input power supply of a rated voltage or higher is supplied. <P>SOLUTION: The power supply circuit includes the fuse circuit which detects an overvoltage state in an input power supply having been inputted through an input line to cut off electrical continuation of the power supply circuit. It includes a rectification circuit for rectifying the input power supply, a smoothing capacitor for smoothing the power supply after rectification, a first Zener diode which is grounded by a cathode while connected to the input line by an anode at a prestage of the rectification circuit, and a second Zener diode which is connected to the input line at a poststage of the smoothing capacitor. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a power supply circuit, and more particularly to a power supply circuit including a fuse circuit for overvoltage protection.

  2. Description of the Related Art Conventionally, there is known a power supply circuit that converts power supplied from an external power supply to a stabilized power supply and supplies it to each circuit. In such a power supply circuit, various circuits are mounted to protect the overvoltage state in the circuit, and when the circuit is in an overvoltage state, the circuit connected to the power supply circuit and the subsequent stage by the above circuit Is protected (see, for example, Patent Documents 1-5).

  A fuse circuit may be used inside the power supply circuit for the purpose of protecting the overvoltage state inside the circuit. This fuse circuit protects the circuit by cutting off the continuity in the circuit by melting the resistance when the circuit is in an overvoltage state.

JP 2007-325428 A Japanese Patent Application Laid-Open No. 07-231659 Japanese Patent Laid-Open No. 11-041155 Japanese Utility Model Publication No. 05-080129 Japanese Patent Application Laid-Open No. 08-051772

  In recent power supply circuits, a smoothing capacitor is used for the purpose of eliminating the pulsating flow of the input power supply. In such a power supply circuit, when the input power supply becomes higher than the rated voltage and shifts to an overvoltage state, a load may be applied to the smoothing capacitor before the overvoltage protection fuse circuit is blown, and white smoke may be generated. Of course, after the overvoltage state has passed for a certain period, the fuse circuit is blown, so there is no safety problem, but it was desirable to suppress the generation of white smoke.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a power supply circuit in which a smoothing capacitor blows a fuse circuit without raising white smoke even when input power having a rated voltage or higher is supplied.

  In order to solve the above problems, in the present invention, in the power supply circuit including a fuse circuit that detects an overvoltage state of the input power input through the input line and cuts off the power supply circuit, the input power is rectified. A rectifier circuit; a smoothing capacitor that smoothes the power supply after rectification; a first Zener diode that is connected to the input line and the anode at the previous stage of the rectifier circuit and is grounded at the cathode; and the subsequent stage of the smoothing capacitor And a second Zener diode connected to the input line.

  In the invention configured as described above, in the power supply circuit including the fuse circuit, the rectifier circuit, and the smoothing capacitor, the first Zener diode is connected to the input line and the anode in the previous stage of the rectifier circuit, Grounded at the cathode, the second Zener diode is connected in parallel on the output side of the smoothing capacitor.

  Therefore, when the input power source is equal to or higher than the rated voltage, the first Zener diode and the second Zener diode break down and are applied to the smoothing capacitor until the fuse circuit is blown and the driving of the power circuit is stopped. In order to reduce the load, the generation of white smoke from the smoothing condenser can be suppressed.

Further, as an example of a power supply circuit that realizes the present invention, an FET for converting an input power supply to alternating current by an on / off operation, a control IC for controlling on / off of the FET, and driving of the control IC It is also possible to include a third Zener diode connected to the start signal supply line for starting the signal and the anode and grounded at the cathode.
In the invention configured as described above, when the input power source is equal to or higher than the rated voltage, the circuit connected to the power supply circuit is stopped in order to stop the driving of the control IC by causing the third Zener diode to breakdown. By shutting off the power supplied to the circuit, the connected circuit can be protected from overvoltage.

And a power supply circuit is good also as a structure characterized by having a surge absorber.
A surge absorber is a circuit that prevents a voltage exceeding the rated voltage from being supplied to the power circuit due to lightning or static electricity. However, in conventional power circuits, the smoothing capacitor emits white smoke if the surge absorber has a low withstand voltage. In some cases, the surge absorber's withstand pressure was set above the standard value, leaving a margin. On the other hand, when the breakdown voltage of the surge absorber is increased, the surge absorber acts to suppress the fusing of the fuse circuit. Furthermore, the higher the breakdown voltage of the surge absorber, the higher the cost.
Therefore, in the invention configured as described above, even when the breakdown voltage of the surge absorber is lowered, the smoothing capacitor can be prevented from raising white smoke, and the cost of the surge absorber can be reduced.

Further, the power supply circuit may have a line filter.
The line filter acts to reduce noise input to the power supply circuit, but on the other hand, it also acts to suppress fusing of the fuse circuit. Therefore, in the invention configured as described above, even when the line filter is provided, it is possible to suppress the smoothing condenser from raising white smoke.

  As another aspect of the present invention, an FET for converting an input power source into alternating current by a switching operation, a control IC for controlling on / off of the FET, and a start signal for starting driving of the control IC And a third Zener diode connected to the supply line of the anode at the anode and grounded at the cathode, a surge absorber connected to the subsequent stage of the fuse circuit, and a line filter connected to the subsequent stage of the fuse circuit It is good.

As described above, according to the present invention, when the input power source is equal to or higher than the rated voltage, the first Zener diode and the second Zener diode are used until the fuse circuit is blown and the driving of the power circuit is stopped. Yields and reduces the load applied to the smoothing capacitor, so that the generation of white smoke from the smoothing capacitor can be suppressed.
According to the second aspect of the present invention, when the input power supply is equal to or higher than the rated voltage, the third Zener diode is broken down to stop the driving of the control IC, so that the power supply circuit is connected. The power supplied to the circuit can be cut off to protect the connected circuit from overvoltage.
According to the invention of claim 3, even when the surge absorber has a low withstand voltage, the smoothing capacitor can be prevented from raising white smoke, and the cost of the surge absorber can be reduced.
Furthermore, according to the invention concerning Claim 4, even when a line filter is provided, it becomes possible to suppress that a smoothing capacitor raises white smoke.

2 is a circuit diagram illustrating a configuration of a power supply circuit 100. FIG.

Embodiments of the present invention will be described below in the following order with reference to the drawings.
1. First embodiment:
2. Other embodiments:

1. First embodiment:
FIG. 1 is a circuit diagram illustrating the configuration of the power supply circuit 100. The power supply circuit 100 receives input power supplied through an outlet (not shown) through the input line 90, converts it to a stabilized power supply, and then supplies it to a circuit connected to the secondary winding T <b> 2 of the transformer 97. The power supply circuit 100 illustrated in FIG. 1 is described as a separately-excited oscillation type power supply circuit, but is not limited thereto, and may be a self-excited oscillation type power supply circuit.

  The main part of the power supply circuit 100 is configured to include at least a fuse circuit 91, a surge absorber 92, a line filter 93, a noise capacitor 94, a rectifier circuit 95, a smoothing capacitor 96, a transformer 97, and a switching circuit 98. .

  Further, the power supply circuit 100 has a first Zener diode D1 connected to the input line 90 at the anode in the previous stage of the rectifier circuit 95 and grounded at the cathode, and a second connected in parallel on the output side of the smoothing capacitor 96. Zener diode D2.

  The fuse circuit 91 is connected in series with a positive side terminal of an outlet (not shown), and when the input power supplied through the outlet is equal to or higher than the rated voltage, the fuse circuit 91 cuts off the continuity of the power supply circuit 100 by blowing a resistor.

  The surge absorber 92 is connected to the input line 90 at the subsequent stage of the fuse circuit 91, and protects the power supply circuit from an overvoltage that occurs instantaneously due to lightning, electrostatic discharge, or the like.

  The line filter 93 is connected in series to the input line 90 and removes noise from the input power supplied to the input line 90. Similarly, the noise capacitor 94 is connected to the input line 90 and removes noise from the input power supplied to the input line.

The rectifier circuit 95 rectifies and outputs the AC input power supplied to the input line 90.
The smoothing capacitor 96 is connected to the input line 90 and smoothes and outputs the input power source rectified by the rectifier circuit 95. A rush suppression resistor R1 is mounted between the rectifier circuit 95 and the smoothing capacitor 96.

  The transformer 97 is configured to include a primary side winding T1 and a secondary side winding T2 in which the number of turns of the coil is different, and when the AC power generated by the switching circuit 98 is supplied to the primary side winding T1, An AC power source corresponding to the winding ratio is generated in the secondary winding T2. The primary winding T1 is connected to the input line 90 and the switching circuit 98, and the secondary winding T2 is connected to a circuit (not shown). Furthermore, the transformer 97 includes a feedback winding Tf corresponding to the secondary winding T2, and the feedback winding Tf has a winding ratio based on the voltage value of the AC power generated in the secondary winding T2. A feedback voltage corresponding to is generated.

The switching circuit 98 converts the rectified and smoothed power supplied to the input line 90 into an AC power by an oscillation operation. The switching circuit 98 includes a control IC 98a for controlling oscillation and an FET 98b that is turned on / off by a PWM signal output from the control IC 98a.
The control IC 98a is connected to the input line 90 via the start signal supply line 98c at the start terminal, connected to the gate of the FET 98b via the bridge circuit 98d via the PWM terminal, and connected via the feedback winding Tf and the feedback line 98e via the feedback terminal. Has been. Therefore, when a start signal is input to the start terminal, the PWM signal is supplied from the PWM terminal to the gate of the FET 98b through the bridge circuit 98d. The duty ratio of the PWM signal is feedback controlled based on the feedback voltage supplied from the feedback winding Tf.

  In the first Zener diode D1, the anode is connected to the input line 90 and the cathode is grounded in the previous stage of the rectifier circuit 95. The second Zener diode D2 is connected to the input line 90 at the subsequent stage of the smoothing capacitor 96 (before the start signal supply line 98c). For this reason, when the input power supplied to the input line 90 is equal to or higher than the rated voltage, the first and second Zener diodes D1 and D2 pass a breakdown current, and the load applied to the smoothing capacitor 96 is reduced.

  Further, a third Zener diode D3 is connected to the start signal supply line 98c. The third Zener diode D3 is connected to the start signal supply line 98c at the anode and grounded at the cathode. Therefore, when the power supplied to the input line 90 becomes equal to or higher than the rated voltage, the third Zener diode D3 breaks down and interrupts the start signal supplied to the control IC 98a.

  Here, the first Zener diode D1, the second Zener diode D2, and the third Zener diode D3 are set so that the breakdown voltage of breakdown is VD1 <VD2 <VD3 (VD1 is the Zener diode D1). Breakdown voltage, and similarly, VD2 and VD3 are breakdown voltages of Zener diodes D2 and D3). For this reason, when the power supplied to the input line exceeds the rated voltage, the Zener diode D1 breaks down first, and then breaks down in the order of the Zener diode D2 and the Zener diode D3.

=== Operation of the power supply circuit ===
Hereinafter, the operation of the power supply circuit according to the present embodiment will be described.
When power within the rated voltage is supplied to the input line 90 through the outlet, the input power is rectified and smoothed by the rectifier circuit 95 and the smoothing capacitor 96 after passing through the line filter 93 and the noise capacitor 94. Then, the rectified and smoothed power is supplied to the start signal supply line 98c and drives the control IC 98a. Therefore, a PWM signal is output from the control IC 98a to the FET 98b, and the FET 98b is turned on / off according to the duty ratio. As a result, the input voltage supplied to the primary side winding T1 of the transformer 97 is converted into alternating current, and an alternating pressure corresponding to the winding ratio is generated in the secondary side winding T2.
On the other hand, a feedback voltage corresponding to the AC voltage generated in the secondary winding T2 is generated from the feedback winding Tf, and a feedback signal is supplied to the control IC 98a through the feedback line 98e. Therefore, the control IC 98a controls the duty ratio of the PWM signal according to the feedback signal, and keeps the AC voltage generated in the secondary winding T2 at a constant value through the on / off control of the FET 98a.

  Next, when the input power supplied to the input line exceeds the rated voltage, a voltage higher than the standardized input voltage is applied to the smoothing capacitor 96 even if the fuse circuit 91 is not immediately blown. At this time, the load applied to the smoothing capacitor 96 is reduced by the breakdown of the first Zener diode D1 and the breakdown of the second Zener diode D2. Therefore, before the white smoke is generated by the load applied to the smoothing capacitor 96, the fuse circuit 91 is melted and the driving of the power supply circuit 100 is shut off.

  Further, when the input power source exceeds the breakdown voltage D3, the Zener diode D3 breaks down, and the start signal supplied to the control IC 98a is cut off. Therefore, the oscillation of the switching circuit 98 is stopped and the power supply from the transformer 97 is interrupted.

  As described above, in the power supply circuit 100, when the input power supply is equal to or higher than the rated voltage, the first Zener diode D1 and the second Zener diode D1 and second Since the Zener diode D2 of this type yields and the load applied to the smoothing capacitor is reduced, the generation of white smoke from the smoothing capacitor can be suppressed.

  Further, in the power supply circuit 100 including the surge absorber 92, the fuse circuit 91 is not easily blown, but by using the present invention, the first Zener diode D1 and the second Zener diode D1 and the second Zener diode D1 are used until the fuse circuit 91 is blown. The Zener diode D2 can reduce the load applied to the smoothing capacitor 96, and the smoothing capacitor 96 can be prevented from generating smoke. Therefore, even if the breakdown voltage of the surge absorber 92 is lowered, the smoothing capacitor 96 can be prevented from raising white smoke, and the cost of the surge absorber 92 can be reduced.

  Further, the line filter acts to reduce noise input to the power supply circuit 100, but on the other hand, it also acts to suppress fusing of the fuse circuit. Therefore, in the power supply circuit 100 according to the present embodiment, it is possible to suppress the smoothing capacitor from raising white smoke even when the line filter is provided.

2. Other embodiments:
Various embodiments of the power supply circuit according to the present invention exist.
The drive method of the power supply circuit is an example of the separately excited oscillation method, and may be a self-excited oscillation method.
Moreover, the number of each diode shown in the figure is an example, and a plurality of diodes may be used as one set.

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.

90 ... input line, 91 ... fuse circuit, 92 ... surge absorber, 93 ... line filter, 94 ... noise capacitor, 95 ... rectifier circuit, 96 ... smoothing capacitor, 97 ... transformer, 98 ... switching circuit, 98a ... control IC 98b, FET, 98c, start signal supply line, 98d, bridge circuit, 98e, feedback line, 100, power supply circuit

Claims (5)

In a power supply circuit having a fuse circuit that detects an overvoltage state of an input power supply input through an input line and cuts off the conduction of the power supply circuit,
A rectifier circuit for rectifying the input power supply;
A smoothing capacitor for smoothing the power supply after rectification;
A first Zener diode connected to the input line at the anode in the previous stage of the rectifier circuit and grounded at the cathode;
A power supply circuit comprising: a second Zener diode connected to the input line at a subsequent stage of the smoothing capacitor. FET for converting the input power to AC by on / off operation,
A control IC for controlling on / off of the FET;
2. The power supply circuit according to claim 1, further comprising: a third Zener diode connected to a start signal supply line for starting driving of the control IC by an anode and grounded by a cathode. 3.   The power supply circuit according to claim 1, further comprising a surge absorber.   The power supply circuit according to any one of claims 1 to 3, further comprising a line filter. FET for converting the input power to AC by on / off operation,
A control IC for controlling on / off of the FET;
A third Zener diode connected to the start signal supply line for starting the driving of the control IC at the anode and grounded at the cathode;
A surge absorber connected to a subsequent stage of the fuse circuit;
The power supply circuit according to claim 1, further comprising: a line filter connected to a subsequent stage of the fuse circuit.

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