JPH10164824A - Power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a reliable power circuit that makes it possible to reduce the size, weight and cost of the circuit as much as possible, and further effectively prevent heating from an inrush current limiting element after power supply is started. SOLUTION: A stop control circuit 2 is installed. The stop control circuit 2 is provided with an integration circuit so that, when the off state of a switch lasts during the operation of a power circuit, a stop control signal S will be outputted with a delay of a certain period after a voltage Vr across an inrush current limiting resistor RLM is first inputted. When a stop control signal S is inputted, a DC-to-DC converter 1 stops its operation, and thereafter current is not passed through the inrush current limiting resistor RLM to prevent heating. The stop control circuit 2 is formed of a small number of small, inexpensive parts, including resistors, capacitors, diodes and a transistor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a power supply circuit,
In particular, the present invention is applied to a power supply circuit having an inrush current limiting resistor for limiting an inrush current generated at the time of power supply startup and a bypass circuit forming a path for bypassing the inrush current limiting resistor except at the time of power supply startup. It is preferred.

[0002]

2. Description of the Related Art A circuit diagram of FIG. 5 schematically shows a configuration example of a conventional switching power supply circuit. In the power supply circuit shown in this figure, first, the AC voltage AC is supplied to the bridge rectifier D _B. Bridge rectifier circuit D
The rectified output of _B is supplied to the smoothing capacitor Ci, so that a rectified smoothed voltage is generated across the smoothing capacitor Ci. The DC-DC converter 1 is configured, for example, to perform a switching operation by a predetermined method by inputting the rectified and smoothed voltage, and to generate a DC output voltage E _O of a predetermined level by DC-converting the switching output. ing.

Meanwhile, in the commercial AC when the power AC of the input for starting the power circuit, but flows excessive rush current to the smoothing capacitor Ci through the bridge rectification circuit D _B from the commercial AC power source AC, the The inrush current causes inconvenience such as giving a load to circuit components. For this reason, in the power supply circuit shown in FIG.
Are provided in such a manner that an inrush current limiting element LM for limiting the inrush current is inserted in series. Note that inrush current limiting element LM are may be provided on the output line side of the bridge rectifier circuit D _B.

At both ends of the rush current limiting element LM, switches SW for bypassing the rush current limiting element LM to the line of the commercial AC power supply AC during normal operation other than when the power supply circuit is started are provided in parallel. ing. This switch SW is a switch built in the relay RL. In this case, the relay RL is provided so as to be inserted between the DC output voltage E _O of the DC-DC converter 1 and the ground.

For example, when the power supply is turned off, the switch SW is turned off. When the power supply is started immediately after the commercial AC power supply AC is turned on, DC-
The operation of the DC converter 1 becomes unstable and the DC output voltage E _O
Is not sufficiently obtained, the power is not supplied to the relay RL, and the switch SW is kept off. As a result, a state is obtained in which the inrush current limiting element LM is inserted into the line of the commercial AC power supply AC, so that the inrush current flowing at startup is limited by the inrush current limiting element LM. When a certain period of time has elapsed from the start of the power supply and the DC output voltage E _O is obtained in a substantially stable state, the relay RL is energized.
Is turned on. As a result, the rush current limiting element LM is bypassed from the commercial AC power supply AC line except when the power supply is started. Assuming that the inrush current limiting element LM is continuously inserted into the commercial AC power supply AC line even after the power supply is started, heat generated by a loss in the inrush current limiting element LM due to a rectified current flowing through the inrush current limiting element LM. Although not negligible, the inrush current limiting element LM is bypassed except at the time of power-on as described above, so that heat generation of the inrush current limiting element LM can be avoided.

[0006]

In the power supply circuit described with reference to FIG. 5, the switch SW is turned off from on by some factor during the operation of the power supply circuit. A rectified current may flow through the LM. For this reason, an inrush current limiting element LM having a rated power of a predetermined value or more is adopted, and excessive heat is generated even if a rectified current flows through the inrush current limiting element LM during operation of the power supply circuit. We are taking measures to prevent this from happening. However, when the inrush current limiting element (resistance) LM having a rated power that can suppress excessive heat generation is used as described above, the size of the inrush current limiting element LM itself becomes large. For this reason, the mounting area on the circuit board is considerably increased, which is not suitable for reducing the size and weight of the power supply circuit.

Therefore, it is conceivable to employ a resistor with a built-in thermal fuse as the rush current limiting element LM instead. A resistor with a built-in thermal fuse operates to open the resistor inserted into the rectifying line when the thermal fuse is blown to a predetermined temperature or higher. In this case, the switch SW shown in FIG. 5 can be omitted. Since such a resistor with a built-in thermal fuse does not need to use a resistor having a large rated power, the size of the inrush current limiting element LM can be reduced. If power-on (start-up) is repeated relatively frequently, the temperature of the resistor itself rises due to the rush current flowing through the resistor each time, and the temperature may become higher than a predetermined value and the thermal fuse may be blown. Because
At the time of actual use, attention must be paid to handling, which is not preferable.

Alternatively, as the inrush current limiting element LM,
It is conceivable to use a thermistor (the switch SW can also be omitted in this case). In this case, the power loss after the power is turned on is reduced by utilizing the characteristic that the impedance of the thermistor itself decreases as the thermistor inserted into the rectification output line generates heat. Since there is not a small amount of steady heat generation due to the impedance of the device, it becomes difficult to adopt it in a power supply circuit corresponding to a device that consumes a large amount of power, for example. It will cost.

[0009]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention seeks to reduce the size, weight, and cost of the circuit as much as possible, and to reduce the heat generated by the rush current limiting element after power-on. It is an object of the present invention to obtain a highly reliable power supply circuit capable of effectively preventing the power supply.

Therefore, a rectifying and smoothing circuit for rectifying and smoothing a commercial AC power supply and outputting a rectified and smoothed voltage, and a rectified and smoothed voltage supplied from the rectifying and smoothing circuit are input to generate a DC voltage of a required level. A DC-DC converter to output, an inrush current limiting element for limiting an inrush current flowing into the smoothing capacitor forming the rectifying and smoothing circuit when the commercial AC power is turned on, and a time when the commercial AC power is not turned on. During operation of the power supply circuit, a bypass means provided to form a path for bypassing the rush current limiting element, and a voltage across the rush current limiting element is monitored, and during operation of the power supply circuit, When the voltage between both ends is obtained, the power supply circuit is provided with stop control means for controlling so as to stop the operation of the power supply circuit at a predetermined timing. It decided to. Further, the stop control means includes integrating means for inputting a voltage between both ends of the inrush current limiting element to obtain an integrated output, and when the output voltage of the integrating means becomes equal to or higher than a predetermined level, the operation of the power supply circuit is stopped. Is configured to be able to output a control signal for stopping the operation.

According to the above configuration, for example, the bypass means for bypassing the rush current limiting element inserted into the rectification output line causes a malfunction during the operation of the power supply circuit, and the rush current is supplied to the rush current limiting element. Even in the flowing state, control is performed so that the operation of the power supply circuit is stopped when the voltage across the inrush current limiting element generated at this time is obtained.

[0012]

FIG. 1 is a circuit diagram schematically showing a configuration example of a power supply circuit according to an embodiment of the present invention.
The same parts as those in FIG. 5 are denoted by the same reference numerals. In the power supply circuit shown in FIG.
There is supplied to the bridge rectifier D _B. Rectified output of the bridge rectifier circuit D _B is that supplied to the smoothing capacitor Ci, the rectified smoothed voltage is generated across the smoothing capacitor Ci. The DC-DC converter 1 performs, for example, a switching operation according to a predetermined method by inputting the rectified and smoothed voltage, and generates a DC output voltage E _O of a predetermined level by DC-converting the switching output.

In this power supply circuit, an inrush current limiting resistor _RLM is used as a means for suppressing an inrush current when the power is turned on.
It is inserted in series with the negative line of the output side of the bridge rectifier circuit D _B.

A switch SW is provided in parallel at both ends of the rush current limiting resistor _RLM . This switch SW is a switch built in the relay RL. The relay RL is provided between the DC output voltage E _O of the DC-DC converter 1 and the ground.
The switch SW operates as follows.

For example, when the power is off, the switch SW is turned off. When the power supply is started immediately after the commercial AC power supply AC is turned on, DC-
The operation of the DC converter 1 becomes unstable and the DC output voltage E _O
Is not obtained sufficiently, the relay RL is not energized, and the switch SW is kept off. At this time, the inrush current limiting resistor _RLM is in a state of being inserted into the rectified output line, and therefore, the inrush current flowing at the time of startup is limited by the inrush current limiting resistor _RLM . The relay RL is energized when a certain period of time has elapsed from the start of the power supply and the DC output voltage E _O has become substantially stable. As a result, the switch SW is controlled to be turned on. As a result, the rush current limiting resistor _RLM is bypassed from the rectified output line except when the power is turned on.

That is, as long as the power supply circuit shown in FIG. 1 is operating properly, the inrush current limiting resistor _RLM is inserted into the rectification current path only at the time of starting the power supply to suppress the inrush current. , The inrush current limiting resistor _RLM is bypassed to the rectified current path. As a result, no rectified current flows through the inrush current limiting resistor _RLM during the normal operation after the start of the power supply circuit, and power loss and heat generation in the inrush current limiting resistor _RLM can be avoided.

In the power supply circuit according to the present embodiment, a stop control circuit 2 is provided. The stop control circuit 2 monitors the voltage Vr across the inrush current limiting resistor _RLM during operation of the power supply circuit, for example, and when it is detected that the voltage Vr is generated, there is a certain time difference as described later. It operates to output the stop control signal S. In the DC-DC converter 1, the stop control signal S
Is input, the operation is stopped. Thus, in this embodiment supposed to operation of the power supply circuit itself is stopped, it becomes possible to rectified current does not flow to the rectifying and smoothing circuit comprising a bridge rectifier circuit D _B and the smoothing capacitor Ci. As a result, even if the switch SW is turned off, it is possible to prevent the inrush current limiting resistor _RLM from generating heat. For this reason, in the present embodiment, it is not necessary to employ a resistor having a large rated power as the inrush current limiting resistor _RLM , and it is possible to select a resistor smaller than the conventional one.

The circuit diagram of FIG. 2 specifically shows an example of the internal configuration of the stop control circuit 2 in the power supply circuit shown in FIG. 1, and the same parts as those of FIG. Description is omitted. The stop control circuit 2 shown in FIG.
It comprises an integration circuit 2a and a second integration / control signal output circuit 2b. The first integration circuit 2a includes a diode D ₁ and a resistor R
₁ , R ₂ and a capacitor C ₁ . The anode of the diode D ₁ is rush current limiting resistor R _LM and a smoothing capacitor C
i is connected to the connection point with the negative terminal, and the cathode is connected to a resistor R
₁ is connected to one end. Connected resistors R ₁ and R ₂ are connected in series, the cathode of the diode D _1, and to insert between the end of the negative output terminal side of the bridge rectifier circuit D _B inrush current limiting resistor R _LM Is done. Capacitor C ₁ is connected in parallel with the resistor R _2. Second integration / control signal output circuit 2b, a diode D _2, resistors R _3, R _4, constituted by a capacitor C _2, and a transistor Q. The anode of the diode D ₂ is first
Is connected to the positive terminal of the capacitor C ₁ of the integrating circuit 2a,
The cathode is connected to one end of a resistor R _3. The resistors R ₃ and R ₄ connected in series are connected so as to be inserted between the cathode of the diode D ₂ and the end of the inrush current limiting resistor _RLM (negative electrode terminal side of the smoothing capacitor Ci). Capacitor C ₂ is connected in parallel with the resistor R _4. The base of the transistor Q is a capacitor C ₂
Is connected to the positive terminal, the emitter is connected to the negative terminal of the capacitor C _2. The collector is connected to the DC-DC converter 1, and the output of the collector serves as a stop control signal S.

The stop control circuit 2 configured as described above operates in the following manner. For example, during the operation after the start-up of the power supply circuit shown in FIG.
It is assumed that the switch SW, which has been on, has been turned off for some reason. This allows
A rectified current flows through the inrush current limiting resistor _RLM at a timing corresponding to the cycle of the commercial AC power supply AC. As a result, as shown in a period t1 to t2 during which the rectified current flows in FIG. across the resistor R _LM voltage Vr will occur. Then, in the period t1 to t2, that is the voltage Vr is applied to the series connection is rectified resistor R ₁ -R ₂ by the diode D _1, a current obtained based on the voltage Vr from the diode D ₁ resistance through R _1, it will be charged in the capacitor C _1. Then, when the operation of charging the said capacitor C ₁ is repeated each time the period of the AC voltage AC is somewhat repeated, the capacitor C _1, the voltage Vr diode D ₁
(Voltage drop) by the resistors R ₁ , R ₂
Thus, charging is gradually performed until the voltage reaches the same potential as a predetermined voltage value obtained by dividing the voltage.

Meanwhile, in the period in which the rectified current, as shown in the period t2~t3 of FIG are not flow example, the voltage Vr across the inrush current limiting resistor R _LM is not generated, the time period, FIG. as referred to 3 negative side of the negative electrode side of the smoothing capacitor Ci of the capacitor C ₁ becomes the same potential. Therefore, in the period t2 to t3, the charge stored in the capacitor C _1, so that the operation can be obtained to charge the capacitor C ₂ from the diode D ₂ via a resistor R _3.

[0021] Such an operation that is repeated every commercial power supply cycle, for example, initially has a certain time lag from the time when the voltage Vr generated across the inrush current limiting resistor R _LM, both ends of the capacitor C ₂ It will be charged until the voltage exceeds the base-emitter voltage V _BE of the transistor Q. When such a state is obtained, the transistor Q conducts and a current flows between the collector and the emitter. That is, the stop control signal S is output. The above time difference is, the resistance R ₁ (and R ₂₎ and the time constant by the integrating circuit composed of the capacitor C _1, resistors R ₃
(And R ₄ ) and the time constant of the integrating circuit composed of the capacitor C ₂ .

As can be seen from the above description, the stop control circuit 2 according to the present embodiment operates a certain amount of time after the voltage Vr is first generated across the inrush current limiting resistor _RLM during the operation of the power supply circuit. Wait for a period and stop control signal S
Is configured to be output. Thus, after the voltage Vr generated across the inrush current limiting resistor R _LM, immediately're to have a time difference so as not to output a stop control signal S is first inrush current limiting resistor R at the power supply startup
_This is to prevent a malfunction such as stopping the operation of the DC-DC converter 1 in response to the voltage Vr generated by the rush current flowing through the _LM . In addition, during the operation of the power supply circuit, the switch SW may be temporarily turned off due to a factor such as noise and may return to the on state again. This is to prevent the operation of the power supply circuit from being stopped unnecessarily so that the stop control circuit 2 can ignore it. Note that the stop control circuit 2 first sets the voltage V
In a time length corresponding to a period from the input of r to the output of the stop control signal S, the temperature generated by the heat generated by the inrush current limiting resistor _RLM is not so great as to affect the reliability of the power supply circuit. .

The stop control circuit 2 shown in FIG. 2 is composed of a small, small and inexpensive component element group composed of diodes, resistors, capacitors, and transistors. The cost and the size of the circuit board do not matter. In addition, in the present embodiment, in addition to this, since a small inrush current limiting resistor _RLM can be used as described above, compared with a case where a resistor or a thermistor with a built-in temperature fuse is provided, for example, Overall, it is possible to reduce the size, weight, and cost of the power supply circuit.

FIG. 4 is a circuit diagram showing a configuration of a power supply circuit according to another embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals and description thereof is omitted. In the power supply circuit shown in this figure, the switch SW ₁ is provided for the AC voltage AC line. The stop control signal S outputted from the stop control circuit 2 that is supplied to the switch SW _1, is adapted to control the on / off switch SW _1. Here, a specific example of the internal configuration of the stop control circuit 2 is not shown, but it may be substantially the same as the circuit configuration shown in FIG. In addition, the switch SW ₁ is considered other various relay, not particularly limited here. In such a configuration, for example, at the time of operation of the power supply circuit startup and subsequent power circuit, the switch SW ₁ is assumed to ON state is maintained. If the switch SW is turned off during the operation of the power supply circuit and the state where the voltage Vr is generated across the inrush current limiting resistor _RLM every time the rectified current flows continues, the stop control circuit 2 stop control signal S waiting period is to be supplied to the switch SW _1. In the switch SW _1, the stop control signal S during the operation of the power supply circuit is inputted, and are adapted to be switched from ON to OFF, thereby is stopped the supply of the commercial AC power supply AC of the power supply circuit The operation will also stop. In this manner, in the present embodiment, the rectified current is prevented from flowing and the inrush current limiting resistor _RLM is prevented from generating heat.

It should be noted that the present invention is not limited to the configuration shown in each of the above embodiments, and various modifications are possible. For example, the stop control circuit 2 shown in FIG. 2 by providing two integrated circuits, so that the stop control signal S with a time difference from the generation of the voltage Vr at both ends of the first inrush current limiting resistor R _LM is output However, it is also possible to obtain the time difference by one integrating circuit by adjusting the time constant or the like. In addition, the stop control circuit 2 may be variously configured in addition to the configuration including the integration circuit as shown in FIG. 2, and may be configured to include a delay circuit and a timer in some cases.

[0026]

As described above, the present invention includes the stop control circuit to stop the operation of the power supply circuit when a voltage across the inrush current limiting resistor is obtained during the operation of the power supply circuit. By performing the control so as to perform the control, it is possible to provide a highly reliable power supply circuit capable of effectively preventing the inrush current limiting element from generating heat after the power is turned on. In addition, by adopting such a configuration, a large rated power is not required for the inrush current limiting element, so that it is possible to select a small one, so that it is possible to suppress the burden on the cost and the increase in the circuit scale. . Further, the stop control circuit of the present invention can be formed by a small and inexpensive small number of component elements,
As a result, it is possible to promote downsizing / weight reduction and cost reduction of the circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a configuration example of a power supply circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram specifically showing a configuration of a stop control circuit in the power supply circuit of the present embodiment.

FIG. 3 is a waveform diagram showing a voltage across a rush current limiting resistor corresponding to a commercial power supply cycle.

FIG. 4 is a circuit diagram illustrating a configuration example of a power supply circuit according to another embodiment.

FIG. 5 is a circuit diagram showing a configuration example of a power supply circuit as a conventional example.

[Explanation of symbols]

1 DC-DC converter, 2 stop control circuit, 2a
First integration circuit, 2b second integration / control signal output circuit, AC
A commercial AC power supply, D _B bridge rectifier circuit, SW, SW
₁ switch, Ci smoothing capacitor, R _LM inrush current limiting resistor, RL relays, S stop control signals, D _1, D
₂ diode, R ₁ , R ₂ , R ₃ , R ₄ resistance, C
_1, C ₂ capacitor, Q transistor

Claims (4)

[Claims] 1. A rectifying and smoothing circuit for rectifying and smoothing a commercial AC power supply to output a rectified and smoothed voltage, and a rectified and smoothed voltage supplied from the rectifying and smoothing circuit is input to generate and output a DC voltage of a required level. DC-D
A C converter; an inrush current limiting element for limiting an inrush current flowing into the smoothing capacitor forming the rectifying / smoothing circuit when the commercial AC power is turned on; and a power supply that is not used when the commercial AC power is turned on. A bypass means provided to form a path for bypassing the inrush current limiting element during operation of the circuit; and a voltage at both ends of the inrush current limiting element, and monitoring the inrush current during operation of the power supply circuit. A power supply circuit, comprising: a stop control unit that controls so as to stop the operation of the power supply circuit at a predetermined timing when it is detected that a voltage between both ends of the current limiting element is obtained. . 2. The power supply according to claim 1, wherein the stop control means is configured to stop the operation of the power supply circuit by stopping the operation of the DC-DC converter. circuit. 3. The power supply circuit according to claim 1, wherein the stop control means is configured to stop the operation of the power supply circuit by stopping supply of the commercial AC power. . 4. The stop control means includes an integrator for inputting a voltage between both ends of the inrush current limiting element to obtain an integrated output, and when the output voltage of the integrator becomes equal to or higher than a predetermined level, The power supply circuit according to claim 1, wherein the power supply circuit is configured to output a control signal for stopping operation of the power supply circuit.