JP3804057B2 - Inrush current suppression circuit for power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inrush current suppression circuit for a power supply device including a thermistor having a negative characteristic.
[0002]
[Problems to be solved by the invention]
In general, the input unit of this type of power supply device rectifies an AC input voltage applied via an input terminal by a rectifier, and smoothes the rectified output from the rectifier by a smoothing capacitor. A thermistor having a negative characteristic for suppressing an inrush current flowing through the output line is inserted and connected to one side of the line. This thermistor has a resistance value that decreases as the temperature rises. Normally, two or more of the thermistors having the same characteristics are connected in series. When the resistance value is high immediately after the power is turned on, the inrush current of the output line of the rectifier is suppressed, and in the steady state, the current flowing through the output line is self-heated to reduce its resistance value, thereby reducing the loss caused by the thermistor as much as possible. I try to reduce it.
[0003]
However, when the power supply device is started at full load when the AC input voltage is low (for example, AC 100 V or less) at a low temperature of about −10 ° C., for example, the resistance value of the thermistor is relatively high. The starting current flows in, and the voltage drop of the thermistor increases. Therefore, the voltage across the smoothing capacitor, that is, the supply voltage to the load is in an unregulated state where the rated voltage is lower than the rated value, causing a problem that the power supply device does not start up normally.
[0004]
In order to avoid such a situation, if a thermistor with a small heat dissipation constant that is difficult to dissipate heat is used, the internal temperature rises quickly when current flows, and the resistance value immediately decreases, so the voltage drop of the thermistor Becomes smaller, and the voltage across the smoothing capacitor, which is the output side voltage of the inrush current suppression circuit, is less likely to be in an unregulated state. However, if the entire thermistor is replaced with one having a small heat dissipation constant, the temperature of the element increases remarkably, so that the temperature of the substrate on which the thermistor is mounted rises, making it impossible to increase the mounting density of the substrate. In addition, there are other known inrush current suppression circuits for power supply devices that use thyristor switches and resistors. In this case, however, a large mounting area must be secured and the number of components increases. Cost.
[0005]
Therefore, in view of the above problems, the present invention provides a rush current suppression circuit for a power supply apparatus that can prevent an output voltage of the circuit from being in an unregulated state at the time of start-up and can suppress a temperature rise as much as possible with a simple circuit configuration. Its purpose is to provide.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention suppresses inrush current at start-up by a negative thermistor in a inrush current suppression circuit of a power supply device configured to suppress inrush current at start-up by a negative thermistor. In the inrush current suppression circuit of the power supply device configured to be used , the two thermistors having different heat dissipation constants are connected in series , and these thermistors are in a state where the resistance value is high immediately after the power is turned on at the start-up. inhibiting the flow of the inrush current, then a small one thermistor dissipation constant by self-heating, rapid resistance value is configured to reduce than larger other thermistor dissipation constant.
[0007]
According to the above configuration, immediately after the power is turned on, none of the thermistors has risen in temperature, so the resistance value is high, and the inrush current at startup is effectively suppressed. After that, as the current flows through the thermistor, the resistance value of each thermistor gradually decreases.However, the more starting current that flows into each thermistor at full load, the sooner the thermistor with a smaller heat dissipation constant rises in temperature. On the contrary, the thermistor's case size is also small, so it is difficult to dissipate heat, and the resistance value decreases rapidly. Therefore, the resistance value of the entire thermistor is not increased, the voltage drop is also reduced to some extent, and an unregulated state in which the output side voltage of the inrush current suppression circuit is below the rating can be avoided.
[0008]
Also, thermistors with small heat dissipation constants are difficult to dissipate and the temperature rises rapidly, but thermistors with large heat dissipation constants tend to dissipate heat and the temperature rises slowly, so the temperature rise of the inrush current suppression circuit as a whole The degree is relaxed compared to the case where all the thermistors are replaced with ones having a small heat dissipation constant. Therefore, even when these thermistors are mounted on a substrate, for example, it is possible to suppress the temperature rise of the substrate as much as possible and increase its mounting density. Furthermore, since it is a simple configuration of only a thermistor that does not use a semiconductor switch such as a thyristor, an increase in the number of parts and an increase in cost do not occur.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a power supply device of the present invention will be described with reference to the accompanying drawings. In FIG. 1 showing the electrical configuration of the input unit of the power supply device, reference numerals 1 and 2 denote input terminals to which an AC voltage is input, reference numeral 3 denotes a ground, that is, a ground terminal, and the input terminals 1 and 2 are provided with a line filter 4. Connected. The line filter 4 includes an across-the-line capacitors 5 and 6 that mainly remove low-frequency normal mode noise, and a line bypass capacitor 7 that mainly removes high-frequency normal mode noise and common mode noise. 8 and common mode choke coils 9 and 10 that mainly remove low-frequency common mode noise. In this embodiment, in order to effectively remove the common mode noise, the two-stage common mode choke coils 9 and 10 are provided. However, this may be a single stage. Further, the internal configuration of the line filter 4 is not limited to that of the present embodiment.
[0010]
Reference numeral 11 denotes a rectifier composed of a diode bridge that rectifies the AC input voltage between the input terminals 1 and 2, and the input side of the rectifier 11 is connected to the common mode choke coil 10 at the last stage of the line filter 4. Reference numeral 12 denotes a smoothing capacitor for reducing the ripple component contained in the rectified output from the rectifier 11, and the DC voltage smoothed here is applied to the chopper type booster circuit 13 which is a harmonic current suppression circuit. The The rectifier 11 is not limited to the bridge type as in the present embodiment, and various types can be used.
[0011]
One of the output lines of the rectifier 11 is inserted and connected in series with inrush current suppressing thermistors 14A and 14B having the same resistance but different heat dissipation constants. These thermistors 14A and 14B constitute an inrush current suppression circuit 14 that does not have a semiconductor switch such as a thyristor. The meaning that the heat dissipation constants differ here does not indicate the error or variation of thermistors having the same heat dissipation constant in terms of specifications (specifications), but at least thermistors 14A and 14B having different specifications of the heat dissipation constants. Means to choose. Further, the same resistance value means that thermistors 14A and 14B having the same resistance value in terms of specifications are selected, and errors and variations existing individually even within the same specification are within an allowable range. ignore.
[0012]
In this embodiment, one end of a thermistor 14A having a small heat dissipation constant is connected to one end of the output side of the rectifier 11, and one end of a thermistor 14B having a large heat dissipation constant is connected to the other end of the thermistor 14A. Further, these thermistors 14A and 14B have negative characteristics in which the resistance value is high at a low temperature immediately after the power is turned on and the resistance value decreases due to self-heating when a steady-state current flows. The thermistor 14A having a small heat dissipation constant has characteristics that thermistor case size is small and heat is not easily dissipated compared to the thermistor 14B having a large heat dissipation constant, so that it is easy to warm, and once the temperature rises, it is difficult to cool. Therefore, when the thermistors 14A and 14B are connected in series and a current flows, the resistance value of the thermistor 14A decreases more rapidly due to self-heating, and the resistance value of the thermistor 14B decreases more slowly. The thermistors 14A and 14B may be connected in the reverse order. Further, it may be connected to the other output line of the rectifier 11.
[0013]
The booster circuit 13 connects a series circuit of a boosting choke coil 16 and a switching element 17 made of a MOS FET between both ends of the smoothing capacitor 12, and a diode 18 and a capacitor 19 between both ends of the switching element 17. And a series circuit of the primary winding of the main transformer 20 and the main switching element 21 made of a MOS FET is connected between both ends of the capacitor 19. The main transformer 20 and the main switching element 21 constitute a main inverter circuit 22 of a power supply device that converts direct current into alternating current. When the switching element 17 is on, energy is stored in the choke coil 16, and when the switching element 17 is off, the energy stored in the choke coil 16 is superimposed on the voltage across the smoothing capacitor 12, and the output side of the boost circuit 13 The voltage across the capacitor 19, that is, the voltage applied to the main inverter circuit 22 is boosted. At the same time, by the switching operation of the switching element 17, the booster circuit 13 brings the AC input voltage between the input terminals 1 and 2 close to the waveform of the input current, thereby improving the power factor and thus suppressing the harmonic current. ing.
[0014]
Next, the effect | action is demonstrated about the said structure. Immediately after the power is turned on at startup, when an AC input voltage is applied between the input terminals 1 and 2, an inrush current flows into the thermistors 14A and 14B from the line filter 4 through the output line of the rectifier 11. However, these thermistors 14A and 14B are in a state where the temperature is low and the resistance value is high. Immediately after the power is turned on, the inrush current flows into the booster circuit 13 which is an input circuit. Thereafter, as the current flows into each thermistor 14A, 14B, the thermistor 14A, 14B self-heats and the resistance value gradually decreases, but in a full load state where the load connected to the output side of the power supply device is large, At the time of starting, the starting current flowing into each of the thermistors 14A and 14B increases, and accordingly, the thermistor 14A having a small heat dissipation constant causes a temperature rise and becomes difficult to cool. As a result, the resistance value of the thermistor 14A rapidly decreases, the resistance values of the thermistors 14A and 14B including the thermistor 14B having a large heat dissipation constant are also reduced, and the voltage drop therebetween is also reduced to some extent. The voltage drop between the terminals, that is, the drop in the output voltage of the inrush current suppression circuit 14 can be alleviated, and the disadvantage that the power supply device does not start up in a so-called unregulated state is avoided.
[0015]
In the subsequent steady state, the AC input voltage applied between the input terminals 1 and 2 is rectified and smoothed by the rectifier 11 and the smoothing capacitor 12 and supplied to the booster circuit 13. The line filter 4 attenuates and removes normal mode noise generated between the lines and the common mode noise generated between the lines and the ground. The rectified output of the rectifier 11 is boosted by the booster circuit 13 and applied to the main inverter circuit 22. At this time, by switching the switching element 17, the current waveform taken in between the input terminals 1 and 2 via the choke coil 16 is controlled in a sine wave shape. As a result, the power factor of the power supply device is improved, and the input The harmonic component of the current can be suppressed to almost zero. The thermistors 14A and 14B are self-heated by the current passing through the output line of the rectifier 11, and the resistance value decreases. Thereby, the loss by the thermistors 14A and 14B is reduced as much as possible.
[0016]
Thus, in this embodiment, immediately after the power is turned on, none of the thermistors 14A, 14B has a temperature rise, so the resistance value is high, and the inrush current at the start-up is effectively suppressed. Thereafter, as the current flows through the thermistors 14A and 14B, the resistance values of the thermistors 14A and 14B gradually decrease. However, the larger the starting current flowing into the thermistors 14A and 14B in the full load state, the smaller the heat dissipation constant. The thermistor 14A immediately rises in temperature, and on the other hand, it becomes difficult to cool, and the resistance value rapidly decreases. Therefore, the resistance values of the thermistors 14A and 14B as a whole are not increased, and the voltage drop is reduced to some extent, so that an unregi state where the output side voltage of the inrush current suppression circuit 14 is less than the rated value can be avoided.
[0017]
The thermistor 14A having a small heat dissipation constant is difficult to dissipate and the temperature rises rapidly. However, the thermistor 14B having a large heat dissipation constant tends to dissipate heat and the temperature rises slowly. The degree of temperature rise is reduced compared to the case where all the thermistors are replaced with ones having a small heat dissipation constant. Therefore, even when these thermistors 14A and 14B are mounted on, for example, a substrate, it is possible to suppress the temperature rise of the substrate as much as possible and increase its mounting density. Further, since the thermistors 14A and 14B do not use a semiconductor switch such as a thyristor, the number of parts and the cost are not increased.
[0018]
That is, by using two or more of the thermistors 14A and 14B having different heat dissipation constants in the inrush current suppressing circuit 14 of the power supply device configured to suppress the inrush current at the start-up by the thermistors 14A and 14B having negative characteristics. The simple circuit configuration makes it difficult for the output side voltage of the inrush current suppression circuit 14 to enter an unregulated state at the time of start-up, and to suppress the temperature rise as much as possible.
[0019]
In addition, this invention is not limited to the said Example, A various deformation | transformation implementation is possible in the range of the summary of this invention.
[0020]
【The invention's effect】
In the inrush current suppression circuit of the power supply device configured to suppress the inrush current at the start-up by the negative thermistor, the present invention uses two thermistors having different heat dissipation constants connected in series . The thermistor suppresses the flow of the inrush current when the resistance value is high immediately after the power is turned on at the time of start-up, and after that, one thermistor with a small heat dissipation constant is self-heated and the other thermistor with a large heat dissipation constant. An inrush current suppression circuit for a power supply device that is configured so that the resistance value decreases rapidly, and with a simple circuit configuration, the output voltage of the circuit is unlikely to be in an unregulated state at start-up, and the temperature rise can be suppressed as much as possible. Can provide.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an input unit of a power supply device according to an embodiment of the present invention.
[Explanation of symbols]
14 Inrush current suppression circuit
14A, 14B thermistor

Claims (1)

In an inrush current suppression circuit of a power supply device configured to suppress an inrush current at start-up by a negative thermistor, two thermistors having different heat dissipation constants are connected in series , and these thermistors are started In the state where the resistance value is high immediately after the power is turned on, the inrush current is prevented from flowing, and then, due to self-heating, one thermistor having a small heat dissipation constant has a resistance value more rapidly than the other thermistor having a large heat dissipation constant. An inrush current suppressing circuit for a power supply device, wherein the inrush current is reduced .

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