JP2004320903A - Power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply unit capable of preventing a malfunction of a switch due to leak current, which is parallel connected to a rush current limiting resistor provided for prevention of the rush current at power supply start. <P>SOLUTION: This power supply unit includes a current detection means for detecting AC current on both hot and cold sides of an AC power supply respectively. The outputs of the two current detection means are supplied to an AND circuit and, by the output of the AND circuit, a relay is operated to open the switch parallel connected to the rush current limiting resistor, thus activating the relay completely. The addition of the AND circuit prevents malfunctions due to the leak current. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power supply device, and more particularly, to a power supply device provided with an inrush current prevention circuit for limiting an inrush current generated at the time of starting up a power supply to prevent a relay malfunction due to a leak current.
[0002]
[Prior art]
When power is supplied from an external AC power supply to external equipment, especially in order to reduce the inrush current when the power is turned on, a device that inserts a resistive element to prevent inrush current into the power supply line or output line only at the time of power supply startup It is known (for example, refer to Patent Document 1 for insertion into a power supply line and refer to Patent Document 2 for insertion into an output line).
[0003]
That is, in Patent Document 1, a resistance element for limiting an inrush current at the time of power supply startup is inserted in series into one of two power supply lines of a commercial power supply connected to a full-wave rectifier circuit, A mechanism for preventing inrush current by arranging a switch for short-circuiting both ends in parallel with a resistance element is shown. In the power supply device described in Patent Document 1, the switch inserted in parallel with the resistance element is turned off when the power is turned on, and the resistance element is inserted in series with the power supply line when the AC power is turned on. The inrush current at the time is limited. Then, after a predetermined time has elapsed after the start of the power supply, the control circuit operates a relay to turn on a switch connected in parallel with the resistance element, thereby bypassing the resistance element connected in series to the power supply line. I have.
[0004]
In the power supply device described in Patent Literature 2, an inrush current limiting resistor for limiting an inrush current generated at the time of power activation is inserted into an output line of a bridge rectifier circuit. That is, an inrush current limiting resistor is inserted into one of the two output lines of the bridge rectifier circuit, and a switch connected in parallel with this is turned on after the power is turned on, so that the inrush current limiting resistor is turned on only when the power is turned on. To be inserted into the output line.
[0005]
However, none of the power supply devices described in Patent Literature 1 and Patent Literature 2 includes a bypass capacitor for noise suppression. Generally, in the case of a switching power supply, a bypass capacitor for absorbing noise generated from the switching converter and releasing the noise to the ground is generally inserted between one end of the rectifier circuit and the ground. FIG. 2 shows an example of a conventional power supply device provided with a bypass capacitor for noise suppression. Hereinafter, this power supply device will be described.
[0006]
In the conventional power supply device shown in FIG. 2, a power supply line 2 to which a current from a commercial AC power supply 1 is supplied is classified into a hot side and a cold side. The power line 2 on the Hot side is connected to one end of the inrush current limiting resistor 4, and the other end of the inrush current limiting resistor 4 is connected to a first input terminal of the bridge rectifier circuit 5. A power line 2 on the Cold side of the commercial AC power supply 1 is connected to one end of a power switch (single-cut switch) 3, and the other end of the power switch 3 is connected to a second input terminal of the bridge rectifier circuit 5. I have.
[0007]
A first output terminal of the bridge rectifier circuit 5 is supplied to one end of a smoothing capacitor 6 for removing a ripple component, and supplied to a switching converter circuit (not shown). The second output terminal of the bridge rectifier circuit 5 is connected to the other end of the smoothing capacitor 6 and connected to the Cold side of the commercial AC power supply 1 via the bypass capacitor 16 and grounded.
[0008]
Anodes of diodes 9 and 10 are connected to a first input terminal and a second input terminal of the bridge rectifier circuit 5, respectively, and their cathodes are connected to each other through a series circuit of resistors 11 and 12 to connect a capacitor. 13 and a resistor 14 connected to a smoothing circuit. One end of this smoothing circuit is connected to the gate electrode of the field effect transistor 15, and the other end is connected to a connection point between the smoothing capacitor 6 and the bypass capacitor 16.
[0009]
Hereinafter, the operation of this conventional power supply device will be described, and its problems will be described.
In FIG. 2, when the power switch 3 is turned on, AC power is supplied from the commercial AC power supply 1 to the bridge rectification circuit 5 via the power supply line 2 and rectified from the first output terminal of the bridge rectification circuit 5. The signal is supplied to a switching converter circuit (not shown) via the smoothing capacitor 6.
[0010]
A switch 7 that is on / off controlled by a relay 8 is connected in parallel to both ends of the inrush current limiting resistor element 4. Since the switch 7 is off when the power is turned on, the power switch is turned off. For a while after the switch 3 is turned on, the inrush current limiting resistance element 4 is connected in series to the power supply line 2. Therefore, it is possible to prevent an extremely large current (rush current) from flowing through the bridge rectifier circuit 5 when the power is turned on.
[0011]
When the power switch 3 is turned on and a current flows to a switching converter (not shown), a current flows through the diodes 9 and 10 and the resistors 11 and 12, and the capacitor 13 starts charging. When the voltage between both ends of the resistor 14 increases to a predetermined voltage after the charging of the capacitor 13 starts, the field effect transistor 15 is turned on, the relay 8 is operated, and the switch 7 is turned on. As a result, the inrush current limiting resistance element 4 is bypassed from the power supply line 2, and a correspondingly large current flows into the bridge rectifier circuit 5.
[0012]
Here, the second output terminal of the bridge rectifier circuit 5 is connected to a bypass capacitor 16 provided as a measure against noise, thereby connecting the AC power supply 1 from the hot power supply line 2 to the cold power supply line 2. A closed circuit is formed. That is, the hot side power line 2 leads to the rush current limiting resistor element 4, the diode 9, the resistors 11, 12, the parallel circuit of the capacitor 13 and the resistor 14, the bypass capacitor 16, and the Cold side power line 2 (ground). A closed path is formed. Here, the power switch 3 is disposed on the Hot side of the power supply line 2. However, when there is no distinction between the Hot side and the Cold side in a commercial power outlet as in Japan, the power switch 3 depends on the insertion state of the outlet. , The power switch 3 is on the Cold side or on the Hot side. Therefore, as shown in FIG. 1, the probability that the power switch 3 is on the Cold side is 50%. When the power switch 3 is connected to the Hot side of the power line 2, the above closed path is not formed. Note that the inrush current limiting resistance element 4 connected to the power supply line 2 does not necessarily need to be on the Hot side of the power supply line 2 and may be on the Cold side.
[0013]
[Patent Document 1]
JP-A-2002-325452 (particularly, FIG. 1)
[Patent Document 2]
JP-A-10-164824 (FIGS. 1 to 4)
[0014]
[Problems to be solved by the invention]
As described above, in the conventional power supply device as shown in FIG. 2, even when the power switch 3 is in the off state, the inrush current limiting resistance element 4, the diode 9, Since a closed path is formed to reach the resistors 11, 12 and the parallel circuit of the capacitor 13 and the resistor 14, the bypass capacitor 16, and the Cold side power supply line (earth) 2, the leak current Ir flows in the direction of the arrow shown in the figure. Flows. Since the capacitor 13 is charged by the leak current Ir, the field effect transistor 15 erroneously determines that the power switch 3 is turned on by the field effect transistor 15, and the relay 8 repeats the on / off operation. Occurs. Therefore, there is a problem that the relay 8 makes a rattle even though the power switch 3 is off.
[0015]
An object of the present invention is to provide a power supply device in which the above-described relay does not malfunction and generate rattling even when the power switch 3 is connected to the Cold side. .
[0016]
[Means for Solving the Problems]
In order to solve the above problems and achieve the object of the present invention, a power supply device of the present invention includes a rectifying and smoothing unit that rectifies and smoothes a commercial AC power supply to obtain a DC voltage, and an inrush current that flows when the commercial AC power supply is started. Current limiting element for limiting power supply, bypass means for forming a path for bypassing the inrush current limiting element, a power switch connected to a power line on the Cold side of the commercial AC power supply, rectifying and smoothing means, and a commercial AC power supply. A bypass capacitor connected between the ground of the AC power supply, first current detecting means for detecting a current flowing through the hot power supply line of the commercial AC power supply, and a current flowing through the Cold power supply line of the commercial AC power supply And a logical product circuit (AND circuit) to which the outputs of the first and second current detecting devices are supplied, and the output of the logical product circuit Is characterized by forming a path to bypass means actuates the bypass inrush current limiting element.
[0017]
According to the present invention, first and second current detecting means for independently detecting a current are provided on each of a hot side and a cold side of a power supply line, and an AND circuit to which outputs of these two current detecting means are added When the power switch is turned off and no current flows to the Cold side, the relay does not operate, and therefore does not rattle.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be described with reference to FIG. Since the embodiment of the present invention shown in FIG. 1 has all the configurations of the conventional example shown in FIG. 2 in common, the same components are denoted by the same reference numerals and described. The description of the described components is omitted.
[0019]
In the embodiment of the present invention shown in FIG. 2, the power supply line 2 on the Hot side of the commercial AC power supply 1, that is, the first input terminal of the bridge rectifier circuit 5 is connected in series with a rectifying diode 9 and resistors 11 and 12. Via a circuit, it is connected to a smoothing circuit composed of a resistor 13 and a capacitor 14 (a circuit composed of the diode 9 to the capacitor 14 constitutes a first current detecting means). The Cold side power supply line 2 of the commercial AC power supply 1 is connected to a second input terminal of a bridge rectifier circuit 5 via a power switch 3. A smoothing circuit of a resistor 19 and a capacitor 20 via a series circuit of a rectifying diode 10 and resistors 17 and 18 (a circuit formed from the diode 10 to the capacitor 20 is a second current detecting means). .)It is connected to the.
[0020]
The output of a current smoothing circuit composed of a capacitor 13 and a resistor 14 to which the hot-side AC current is supplied, and the output of a current smoothing circuit composed of a capacitor 20 and a resistor 19 to which the Cold-side AC current is supplied. Are supplied to an AND (logical product) circuit 21. The output of the AND circuit 21 is connected to the gate electrode of the field-effect transistor 15, the source electrode of the field-effect transistor 15 is connected via a relay 8 to a power supply for driving a relay (not shown), and the drain electrode is connected to a bypass capacitor 16 Is grounded via
[0021]
Hereinafter, the operation of the embodiment of the present invention shown in FIG. 1 will be described.
When the power switch 3 is turned on, the AC from the commercial AC power supply 1 is rectified by the bridge rectifier circuit 4, the ripple component is removed by the smoothing capacitor 6, and then converted into a direct current, such as a switching converter circuit. Supplied to connected equipment. When this alternating current starts flowing, first, a rectified half-wave current flows from the power supply line 2 on the Hot side of the commercial AC power supply 1 via the diode 9 and the resistors 11 and 12, and the charging of the capacitor 14 starts. Is done. When the charging voltage of the capacitor 14 rises, the voltage across the resistor 13 rises, and this output is applied to one input of the AND circuit 21.
[0022]
Also, a rectified half-wave current flows from the power supply line 2 on the Cold side of the commercial AC power supply 1 via the diode 10 and the resistors 17 and 18, and charging of the capacitor 20 is started. As described on the Live side, when the charging voltage of the capacitor 20 increases, the voltage across the resistor 19 increases, and this output is applied to the other input of the AND circuit 21.
[0023]
The AND circuit 21 emits an output when both of the two inputs are at the high level, increases the voltage across the resistor 22, and turns on the field effect transistor 15. As a result, a current flows through the relay 8 and the switch 7 is turned off, so that the inrush current limiting resistance element 4 is bypassed and substantially removed from the circuit.
[0024]
Next, a case where the power switch 3 is turned off will be described. In the case of this example, even when the power switch 3 is off, a closed circuit from the hot power line 2 to the cold power line 2 is formed as in the conventional example of FIG. That is, the hot power supply line 2, the inrush current limiting resistance element 4, the rectifying diode 9, the resistors 11 and 12, the parallel circuit of the capacitors 13 and 14, the bypass capacitor 16, and the cold power supply line 2 (ground) are reached. , A closed path is formed, and a leak current Ir flows. Due to the leak current Ir, charging of the capacitor 13 is started in the same manner as described in the description of FIG. 2, and as a result, one input of the AND circuit 21 is set to a high state.
[0025]
However, in this case, since the power switch 3 is turned off, no AC signal from the commercial AC power supply 1 is input to the second input terminal of the bridge rectifier circuit 5. As a result, no current flows through the rectifying diode 10 and the resistors 17 and 18, and the capacitor 20 is not charged. Therefore, since the other input of the AND circuit 21 to which one end of the capacitor 20 is connected is in the low state, the capacitor 13 is charged by the leak current as described above, and the one input of the AND circuit 21 is in the high state. However, the output of the AND circuit 21 maintains the low state. Therefore, the field effect transistor 15 does not turn on, so that the relay 8 does not operate to turn on the switch 7.
[0026]
【The invention's effect】
As described above, in the present invention, the AND circuit 21 is provided before the field-effect transistor 15 that operates the relay 8, and the relay 8 is operated only when two inputs of the AND circuit 21 are in the High state. Therefore, when the power switch 3 in which the other input of the AND circuit 21 is at the low level is in the off state, the relay does not operate due to the leak current Ir flowing through the bypass capacitor 16 and rattling does not occur.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an example of an embodiment of a power supply device of the present invention.
FIG. 2 is a circuit diagram showing an example of an embodiment of a conventional power supply device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Commercial AC power supply, 2 ... Power supply line, 3 ... Power switch (single-cut switch), 4 ... Inrush current limiting resistance element, 5 ... Bridge rectifier circuit, 6, 13, 20 ... Smoothing capacitor, 7 ... Bypass switch, 8 ... Relay, 9, 10 ... Diode, 16 ... Bypass capacitor, 15 ... Field effect transistor, 21 ... AND ( Logical product) circuit

Claims (2)

Rectifying and smoothing means for rectifying and smoothing a commercial AC power supply to obtain a DC voltage;
An inrush current limiting element for limiting an inrush current flowing when the commercial AC power supply is started;
Bypass means for forming a path for bypassing the inrush current limiting element;
A power switch connected to a power line on the Cold side of the commercial AC power supply, a bypass capacitor connected between the rectifying and smoothing means and the ground of the commercial AC power supply,
First current detecting means for detecting a current flowing in a hot-side power supply line of the commercial AC power supply, second current detecting means for detecting a current flowing in a cold-side power supply line of the commercial AC power supply, An AND circuit to which outputs of the first and second current detecting means are supplied, wherein the output of the AND circuit activates the bypass means to form a path for bypassing the rush current limiting element. And power supply. 2. The power supply device according to claim 1, wherein the bypass unit includes a relay circuit and a switch, and activates the relay circuit to close the switch according to an output of the AND circuit. 3.

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