JP4085864B2 - Inrush current suppression circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inrush current suppression circuit that is provided in a current path between a power supply side and a load side and suppresses an excessive inrush current when a power switch is turned on.
[0002]
[Prior art]
For example, referring to FIG. 5, a power source 20, a power switch (which may be a relay or the like) 21 for opening / closing a circuit, an overcurrent limiting fuse 22, and a load 23 so that power can be supplied to the load from a power source such as a DCDC converter. Are connected in series. In this circuit 24, when the load 23 is a very small impedance load such as a lamp, an electric motor, a capacitor, etc., when the power switch 21 is turned on to supply power to the load 23, when the power switch 21 is turned on, As shown in FIG. 6, there is a possibility that an inrush current that is excessively larger than a steady-state current may temporarily flow. For example, in the case of a capacitor, an inrush current flows when charging the current to the capacitor, and in the case of a lamp, the inrush current flows before the filament temperature rises. This inrush current causes problems such as shortening the service life of the device or blowing the fuse.
[0003]
For this reason, in order to suppress a temporary excessive inrush current when the power switch 21 is turned on, conventionally, a relatively high resistance value is provided between the power source 20 and the load 23 with reference to FIG. Proposals are made by connecting a resistor element 25 for suppressing inrush current (see Patent Document 1) or by connecting a negative characteristic thermistor 26 between a power source and a load (see Patent Document 2) with reference to FIG. It had been.
[0004]
[Patent Document 1]
Japanese Patent No. 3269377 (second page, third page, FIG. 1)
[Patent Document 2]
Japanese Utility Model Publication 1-2545 (All pages, Fig. 3)
[0005]
[Problems to be solved by the invention]
However, since the resistance element 25 is connected in series with the load 23 in the case of the above-described conventional former, a voltage drop or a voltage drop by the resistance element 25 even with respect to a steady current when the current supply to the load 23 is stabilized. There is a problem in that wasteful consumption of power occurs, and accordingly, power that can be supplied to the load 23 is reduced. In the latter case, the negative characteristic thermistor 26 whose resistance value decreases due to heat generation due to current flow can suppress an excessive inrush current to the load 23 with a large resistance value against the inrush current. When current flows, the resistance value of the negative characteristic thermistor 26 is reduced due to heat generation, so that useless voltage drop and useless consumption of electric power do not occur. However, in this case, since the resistance value is reduced by using the heat generation of the negative characteristic thermistor 26, the steady current that can be continuously supplied is limited by the element temperature of the negative characteristic thermistor 26. Therefore, since the steady current is limited in this way and a large steady current cannot flow, the use of the load 23 with high power consumption is restricted.
[0006]
As an improvement to solve these problems, a circuit shown in FIG. 9 has been proposed. Referring to FIG. 9, a current limiting resistance element 25 is connected between a power source 20 and a load 23, and a switch circuit of an a-contact of the electromagnetic relay 27 is connected in parallel with the resistance element 25. A control circuit 28 for operating the exciting coil of the electromagnetic relay 27 is provided. In this circuit, the electromagnetic relay 27 is kept in the OFF state from the time when the power switch 21 is turned ON until a predetermined time has elapsed when the steady current is stably supplied to the load 23. The current I from 20 is supplied to the load 23 via the resistance element 25. For this reason, when an excessive inrush current at the time when the power switch 21 is turned on flows, the current is supplied to the load 23 in a state limited by the resistance element 25, and then when the stable steady current is supplied, the resistance element 25 The switch circuit of the electromagnetic relay 27 connected in parallel with the resistance element 25 is turned on so that the voltage drop due to the current is suppressed, and a current is supplied to the load through this highly conductive switch circuit. However, even in this case, it is necessary to separately provide the electromagnetic relay 27 and the control circuit 28 for controlling the electromagnetic relay 27. Therefore, the cost is increased such as an increase in the number of parts, and the circuit board has a higher cost. There is a problem that miniaturization becomes difficult because the occupied area becomes large.
[0007]
SUMMARY OF THE INVENTION Accordingly, the present invention aims to realize a problem to be solved by preventing an excessive inrush current from flowing to a load when power is supplied from a power supply to the load by using an inexpensive and simple structure. It is said.
[0008]
[Means for Solving the Problems]
Rush current suppression circuit according to the present invention is provided in an openable current path from the source to the load, and in suppressing the inrush current suppression circuit inrush current to the load, the inrush current suppression in series with said current path the resistance and the positive temperature coefficient thermistor provided, a semiconductor element for performing the operations of the conduction and interruption of the current path connected in parallel with the current path, the operation of the semiconductor element based on the voltage across the thermistor It is characterized by being controlled.
[0009]
Here, the inrush current is a current that temporarily flows through the circuit at an excessively larger value than usual when the circuit to which the power source and the load are connected is switched on by a switching means that can be freely opened and closed. . The power source is a DC power source such as a DCDC converter or a battery.
[0010]
According to the present invention, the resistance value of the positive temperature coefficient thermistor is small when the power switch is turned on so as to close the circuit for supplying current from the power source to the load, and the current from the power source is for suppressing the inrush current in series with the positive temperature coefficient thermistor. The current flows through the resistor, and almost no current flows through the semiconductor element. Therefore, when the switch is turned on, the voltage drops due to the resistances of the positive temperature coefficient thermistor and the inrush current suppression resistor, and the value of the current flowing to the load is limited by the relatively large resistance value of the inrush current suppression resistor. Thereafter, when the resistance value of the positive temperature coefficient thermistor rises due to temperature rise due to heat generation, the current flowing to the semiconductor element increases, and the semiconductor element is switched to the ON state. The switching causes the semiconductor element to become conductive, so that the current from the power supply flows through the semiconductor element rather than the positive temperature coefficient thermistor and the inrush current suppression resistor, and there is almost no voltage drop with respect to the load. Will flow. In addition, since a relatively large current can flow through the semiconductor element, the current to the load is not limited to a small value even in a steady state.
[0011]
In the present invention, preferably, a negative characteristic thermistor is used as the inrush current suppressing resistor. In this case, the negative characteristic thermistor has a high resistance value when the power is turned on, so that when the power is turned on, the resistance value of the negative characteristic thermistor and the resistance value of the negative characteristic thermistor restrict the current flow to the load. Therefore, it is possible to prevent a large current from flowing to the load inappropriately.
[0012]
In the present invention, a bipolar transistor is preferably used as the semiconductor element. In this case, the current value that can be supplied to the load can be made relatively large.
In the present invention, the positive temperature coefficient thermistor is preferably connected between the emitter and base of the bipolar transistor.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the details of the present invention will be described based on embodiments shown in the drawings. FIG. 1 is a circuit diagram including an inrush current suppressing circuit according to an embodiment of the present invention.
[0014]
Referring to FIG. 1, the inrush current suppression circuit 1 is connected to a circuit that connects a power source 2 that is a DC power source such as a DCDC converter or a battery and a load 3 such as an electric motor. . This circuit includes a power switch 4, a fuse 5, a load 3, and an inrush current suppression circuit 1 that can be manually operated in a circuit connecting the power source 2 and the load 3. The load 3 is, for example, a lamp, an electric motor, a capacitor, or the like, and has a low impedance at least at the start of power supply.
[0015]
The inrush current suppression circuit 1 is connected between the fuse 5 and the load 3 in the current path 6 from the DC power supply 2 to the load 3. This inrush current suppression circuit 1 is connected in parallel with a transistor 7 as a semiconductor element composed of a bipolar transistor, and a positive characteristic thermistor (PTC thermistor) 8 and an inrush current suppression resistor 9 for limiting the current connected in series. The emitter of the transistor 7 is connected to the load side end of the fuse 5 and one end of the positive characteristic thermistor 8, and the collector is connected to one end of the load 3 and one end of the inrush current suppressing resistor 9. The base of the pnp transistor 7 is connected to the other end of the positive temperature coefficient thermistor 8 and the inrush current suppression resistor 9 through a resistor 10.
[0016]
With this configuration, in order to supply current to the load 3, when the power switch 4 is switched from the off state to the on state, the positive temperature coefficient thermistor 8 has almost no temperature rise due to heat generation and has a resistance to the resistance. Since the value (R _P ) is very small, the current (I) from the power supply 2 flows through the positive temperature coefficient thermistor 8 and the inrush current suppression resistor 9 and hardly flows between the emitter and collector of the transistor 7.
[0017]
Therefore, immediately after the power switch 4 is turned on, current supply to the load 3 through the transistor 7 is suppressed, and current is supplied to the load 3 through the positive characteristic thermistor 8 and the inrush current suppression resistor 9. At this time, since the voltage drop is relatively large by the inrush current suppression resistor 9, an excessive inrush current is not supplied to the load 3. By supplying a current after the power switch 4 is turned on, the positive temperature coefficient thermistor 8 generates heat so that the temperature rises and its resistance value increases. As the resistance value of the positive temperature coefficient thermistor 8 increases, the voltage between the terminals of the positive temperature coefficient thermistor 8 increases, so that the voltage between the emitter and base of the transistor 7 increases. When the base current (Ib) increases as the voltage between the emitter and the base increases, when the base current value exceeds a predetermined value, the emitter-collector of the transistor 7 is switched to a conductive state, and the current supplied from the power source 2 is changed. (I) is supplied to the load 3 through the transistor 7 with almost no voltage drop. Note that the timing of switching to a state in which current is supplied to the load 3 through the transistor 7 is not when an inrush current corresponding to the impedance of the load 3 flows, but when a stable steady current flows from the state in which the inrush current flows. Set when
[0018]
Next, another embodiment of the present invention will be described with reference to FIG. In addition, about the structure similar to embodiment shown in FIG. 1, while abbreviate | omitting description, the same code | symbol is attached | subjected.
[0019]
Referring to FIG. 2, a negative characteristic thermistor (NTC thermistor) 11 is provided as an inrush current suppressing resistor connected in series with the positive characteristic thermistor 8 instead of a normal resistance element.
[0020]
With this configuration, immediately after the power switch 4 is turned on, current supply to the load 3 via the pnp transistor 7 is suppressed, and current is supplied to the load 3 through the positive characteristic thermistor 8 and the negative characteristic thermistor 11. At this time, the negative characteristic thermistor 11 hardly generates heat, and its resistance value is large, so that the voltage drops relatively large, so that an excessive inrush current is not supplied to the load 3. By supplying a current after the power switch 4 is turned on, the positive temperature coefficient thermistor 8 generates heat so that the temperature rises and its resistance value increases. The resistance value of the negative characteristic thermistor 11 also decreases as the temperature rises due to heat generation, but the resistance decrease rate is set smaller than the resistance increase rate of the positive characteristic thermistor 8. As the resistance value of the positive temperature coefficient thermistor 8 increases, the voltage between the terminals of the positive temperature coefficient thermistor 8 increases, so that the voltage between the emitter and base of the transistor 7 increases. When the base current (Ib) increases as the voltage between the emitter and the base increases, when the base current value exceeds a predetermined value, the emitter-collector of the transistor 7 is switched to a conductive state, and the current supplied from the power source 2 is changed. (I) is supplied to the load 3 through the transistor 7 with almost no voltage drop. Note that the timing of switching to a state in which current is supplied to the load 3 through the transistor 7 is not when an inrush current corresponding to the impedance of the load 3 flows, but when a stable steady current flows from the state in which the inrush current flows. Set when
[0021]
The present invention is not limited to the above-described embodiment, and various modifications can be made.
[0022]
(1) In the inrush current suppression circuit 1 shown in FIG. 1 and FIG. 2, the embodiment using the pnp type transistor is exemplified. However, as shown in FIG. 3 and FIG. 4, the npn type transistor is used. The inrush current suppression circuit 1 may be configured.
[0023]
In the case of FIG. 3, the collector of the transistor 12 as a semiconductor element is connected to the power supply side, and the emitter is connected to the load 3 side. An inrush current suppressing resistor 13 and a resistor 14 are connected between the collector and the base, and a positive characteristic thermistor 15 is connected between the inrush current suppressing resistor 13 and the load 3.
[0024]
According to the configuration of FIG. 3, immediately after the power switch 4 is turned on, the resistance value of the positive temperature coefficient thermistor 15 is small, so the voltage between the base and the emitter of the transistor 12 is small and the base current (Ib) hardly flows. The transistor 12 is not in a conductive state. For this reason, a current is supplied to the load 3 through the inrush current suppressing resistor 12 and the positive temperature coefficient thermistor 15. At this time, since the resistance value of the inrush current suppression resistor 13 is relatively large, the voltage drop due to the inrush current suppression resistor 13 is increased, and the inrush current to the load 3 is suppressed. When the resistance value of the positive temperature coefficient thermistor 15 increases due to the heat generation of the positive temperature coefficient thermistor 15 due to current supply and the temperature rises, the voltage between the base and the emitter of the transistor 12 increases, so that the base current (Ib) Will increase. When the base current (Ib) exceeds a predetermined value, the collector-emitter of the transistor 12 is switched to a conductive state, so that the current from the power source 1 is almost free from voltage drop across the load 3 via the transistor 12. Supplied.
[0025]
In the case of FIG. 4, the collector of the transistor 12 as a semiconductor element is connected to the power supply side, and the emitter is connected to the load 3 side. A negative characteristic thermistor 16 and a resistor 14 are connected between the collector and the base, and a positive characteristic thermistor 15 is connected between the negative characteristic thermistor 16 and the load 3.
[0026]
According to this configuration, immediately after the power switch 4 is turned on, since the resistance value of the positive temperature coefficient thermistor 15 is small, the voltage between the base and the emitter of the transistor 12 is small and the base current hardly flows. For this reason, a current is supplied to the load 3 through the negative characteristic thermistor 16 and the positive characteristic thermistor 15. At that time, since the resistance value of the negative characteristic thermistor 16 is relatively large because the temperature has hardly increased, the voltage drop due to the negative characteristic thermistor 16 becomes large, and the inrush current to the load 3 is suppressed. It will be. When the resistance value of the positive temperature coefficient thermistor 14 increases as the positive temperature coefficient thermistor 15 generates heat and increases in temperature with the supply of current, the voltage between the base and the emitter of the transistor 12 increases, so that the base current (Ib) Will increase. When the base current (Ib) exceeds a predetermined value, the collector-emitter of the transistor 12 is switched to a conductive state, so that the current from the power source 1 is almost free from voltage drop across the load 3 via the transistor 12. Supplied.
[0027]
(2) The semiconductor elements used in the inrush current suppression circuit according to the present invention are not limited to bipolar transistors, and various semiconductor elements such as FETs can be employed.
[0028]
(3) The inrush current suppression circuit according to the present invention may be unitized and configured as a single circuit component.
[0029]
【The invention's effect】
As described above, according to the present invention, the resistance value of the positive temperature coefficient thermistor is small when the power switch is turned on to close the circuit for supplying current from the power source to the load, and the current from the power source is The current flows through the series inrush current suppression resistor, and almost no current flows through the semiconductor element. Therefore, when the switch is turned on, the voltage drops due to the resistances of the positive temperature coefficient thermistor and the inrush current suppression resistor, and the value of the current flowing to the load is limited by the relatively large resistance value of the inrush current suppression resistor. Thereafter, when the resistance value of the positive temperature coefficient thermistor rises due to temperature rise due to heat generation, the current flowing to the semiconductor element increases, and the semiconductor element is switched to the ON state. The switching causes the semiconductor element to become conductive, so that the current from the power supply flows through the semiconductor element rather than the positive temperature coefficient thermistor and the inrush current suppression resistor, and there is almost no voltage drop with respect to the load. Will flow. In addition, since a relatively large current can flow in the semiconductor element, the current to the load is not limited to a small value even in a steady state.
[Brief description of the drawings]
FIG. 1 is a circuit diagram including an inrush current suppressing circuit according to an embodiment of the present invention. FIG. 2 is a circuit diagram including an inrush current suppressing circuit according to another embodiment of the present invention. 4 is a circuit diagram including an inrush current suppressing circuit according to another embodiment of the present invention. FIG. 4 is a circuit diagram including an inrush current suppressing circuit according to another embodiment of the present invention. FIG. 6 is a diagram showing an inrush current after power-on in the circuit shown in FIG. 5. FIG. 7 is a circuit diagram showing an example of a conventional inrush current suppression circuit. FIG. FIG. 9 is a circuit diagram showing another example. FIG. 9 is a circuit diagram showing still another example of a conventional inrush current suppression circuit.
1 Inrush current suppression circuit 2 Power supply 3 Load 6 Current path 7 Semiconductor element (transistor)
8 Positive thermistor 9 Inrush current suppression resistor

Claims (4)

In an inrush current suppression circuit that is provided in a freely openable / closable current path from the power source to the load and suppresses the inrush current to the load,
An inrush current suppression resistor and a positive temperature coefficient thermistor are provided in series with the current path ,
A semiconductor element for performing the operations of the conduction and interruption of the current path connected in parallel with the current path,
An inrush current suppressing circuit, wherein the operation of the semiconductor element is controlled based on a voltage across the positive temperature coefficient thermistor. The inrush current suppression circuit according to claim 1,
An inrush current suppression circuit, wherein a negative characteristic thermistor is used as the inrush current suppression resistor. In the inrush current suppression circuit according to claim 1 or 2,
An inrush current suppressing circuit, wherein a bipolar transistor is used as the semiconductor element. In the inrush current suppression circuit according to claim 3,
The inrush current suppressing circuit, wherein the positive temperature coefficient thermistor is connected between an emitter and a base of the bipolar transistor.

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