JP4243915B2 - Switching power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a switching power supply, and more particularly to a structure for preventing a temperature rise of a land on a printed circuit board to which a thermistor for preventing an inrush current is attached.
[0002]
[Prior art]
In a switching power supply, since a capacitor having a large capacity is installed in the rectifying and smoothing circuit, a large inrush current flows when the power is turned on. When this inrush current becomes excessive, it propagates as noise to peripheral devices and the like, so it is necessary to prevent the inrush current from becoming excessive, and an NTC thermistor is used as a simple means. That is, when the power supply is turned off, the thermistor has a relatively high resistance value due to the room temperature. When the power supply is turned on in this state, the inrush current is suppressed. When the power supply is turned on and in a steady state, the temperature of the thermistor is kept high by energization, the resistance value of the thermistor decreases, and the power supply operates in a state where the loss due to the thermistor is reduced. For this reason, the thermistor is kept at a high temperature while the device is operating.
[0003]
[Problems to be solved by the invention]
In such a switching power supply, heat of the thermistor is transmitted to the land of the printed circuit board, and the land becomes hot, which may cause a thermal adverse effect on the printed circuit board. Also, in order to prevent heat transfer to the land of this thermistor and maintain the thermistor itself at a high temperature, the thermistor lead has been made longer so that the heat of the thermistor is less likely to be transferred to the land. In such a configuration, the thermistor is likely to fall down, and there is a risk of causing electrical trouble by contacting with surrounding electronic components.
[0004]
In view of the above problems, an object of the present invention is to provide a heat dissipation structure for an inrush current preventing thermistor capable of preventing the temperature of a land to which a thermistor is attached from rising excessively due to the heat of the thermistor. .
[0005]
It is another object of the present invention to provide a heat dissipation structure for an inrush current preventing thermistor having a structure capable of preventing the thermistor from collapsing.
[0006]
[Means, actions and effects for solving the problems]
According to the first aspect of the present invention, two leads of an inrush current preventing thermistor are electrically connected and fixed to a land provided on a printed circuit board on which an electronic component constituting a switching power supply is mounted, and the thermistor lead A switching power supply in which a pair of heatsinks are thermally coupled to a land fixed with
The radiator is a U-shaped, U-shaped or arc shape in plan view,
The lead has a foot length structure that makes it difficult for heat to be transmitted from the thermistor element body to the printed board,
Each of the pair of radiators surrounds the corresponding leads of the thermistor with an interval between the inner surfaces thereof, and is disposed on the printed circuit board with the inner surfaces facing each other.
The height and arrangement of the radiator are adjusted so as to avoid contact between the radiator and the thermistor element body when the thermistor falls due to bending of the thermistor lead. It is characterized by that.
[0007]
In this way, by providing a heatsink on the land to which the thermistor is attached, the heat of the land is dissipated through the heatsink, the temperature of the land is suppressed, and the thermal adverse effect on the printed circuit board due to the excessive temperature rise of the land. Is prevented.
[0008]
In addition, by making the shape of the heat sink surrounding the lead, it is possible to prevent the thermistor from falling due to touching the thermistor, etc., and because the thermistor contacts other peripheral devices, The occurrence of troubles such as adverse effects can be prevented.
[0009]
Also, when the thermistor falls due to bending of the thermistor lead, the radiator and thermistor element body are adjusted so that the radiator and thermistor element body do not come in contact with each other, so even if the thermistor falls down, the thermistor element body Therefore, it is possible to more reliably prevent the heat of the thermistor element body from being directly transferred to the radiator.
[0010]
The invention of claim 2 is the invention according to claim 1,
A bent portion protruding laterally is formed in a predetermined portion of the lead, and the bent portion is locked to a through hole provided in a printed circuit board and soldered to the land .
[0011]
As described above, since the bent portion is provided in the lead, when the lead of the thermistor is inserted into the through hole of the printed board and soldered, the bent portion is locked to the through hole. Setting is easy.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a circuit diagram showing an example of a switching power supply to which the structure of the present invention is applied. In the circuit of FIG. 1, 1 is an AC power source, 2 is a rectifier circuit, 3 is a thermistor for preventing inrush current, 4 is a transformer that is turned on / off by the switching element 5, 6 is a primary side smoothing capacitor, and 7 and 8 are secondary sides. A rectifying diode, 9 is a choke coil provided on the secondary side, and 10 is a secondary side smoothing capacitor. The output voltage on the secondary side is detected by the voltage detection unit 11, and the detection signal is sent to the control unit 13 via the photocoupler 12, and the control unit 13 controls the switching element 5 so that the output voltage becomes constant. .
[0013]
FIG. 2 is a circuit diagram showing another example of a switching power supply to which the structure of the present invention is applied. The circuit of FIG. 2 includes a control unit 14 and a switching element 15 for power factor improvement, and further a diode 16 that prevents current from the capacitor 6 from flowing to the switching element 15 side when the switching element 15 is turned on. And a choke coil 17 is further provided. This power factor correction circuit controls the on / off of the switching element 15 while detecting the voltage of the capacitor 6 so that the output current of the rectifier circuit 2 is as sinusoidal as possible to prevent the generation of harmonics and generate noise. Is to prevent.
[0014]
As described above, the structure of the present invention is adopted for the thermistor illustrated in FIGS.
[0015]
FIG. 3 is an exploded perspective view showing an embodiment of the present invention when the switching power supply shown in FIG. 2 is implemented. In FIG. 3, 19 is a switching power supply case or L-shaped frame, 20 is a printed circuit board on which electronic components are mounted, and the same reference numerals as those in FIG. 2 denote corresponding electronic components. The thermistor 3 is mounted on the printed circuit board 20 together with a pair of radiators 21 and 22.
[0016]
FIG. 4 is a perspective view showing an embodiment of the heat dissipation structure of the thermistor 3 of the present invention. FIG. 5A is a plan view showing the mounting structure of the thermistor 3 on the printed circuit board 20, and FIGS. 5B and 5C are fixing the two leads of the radiator and the thermistor to the printed circuit board 20, respectively. Sectional drawing which shows a structure, FIG.5 (D) is a side view which shows the relationship between the thermistor and the height of a heat radiator.
[0017]
4, as shown in FIG. 5, the thermistor 3 of this example, two thermistor body 3a, but 3b is an example connected in series, the capacitance of the capacitor 6, one of the thermistor element Sometimes it consists of a body .
[0018]
Lands 23 and 24 for attaching the thermistor 3 are formed in the printed circuit board 20, and through holes 25 and 26 in which conductors are plated on the inner wall are formed in the lands 23 and 24. Conductor patterns 27 and 28 electrically connected to the lands 23 and 24 on the surface through the through holes 25 and 26 are formed.
[0019]
The lands 23, 24 are also provided with two conductor-plated through holes 32, 33 for inserting the mounting legs 30, 31 of the radiators 21, 22, respectively. 33 is also connected to the conductor patterns 27 and 28 on the back surface.
[0020]
The radiators 21 and 22 of this example have a U-shape in plan view and are made of an aluminum alloy, and are provided with grooves 21a and 22a on the two lower sides thereof, such as brass that can be soldered to the grooves. The leg portions 30 and 31 are formed by fitting and crimping the eyelets.
[0021]
As shown in FIG. 5 (C), the thermistor 3 inserts the two leads 35 and 36 of the thermistor 3 into the through-holes 25 and 26 and electrically connects the conductor patterns 27 and 28 with solder 37 from the back surface. Connect and mechanically fix.
[0022]
The two leads 35 1 , 36 of the thermistor 3 are configured to have a foot length structure in order to suppress the heat of the thermistor element bodies 3 a, 3 b from being transferred to the conductor patterns 27, 28. In order to set such height, the leads 35 and 36 are formed with bent portions 35a and 36a protruding sideways at predetermined height portions, and the bent portions 35a and 36a are formed in the through holes 25 and 26. It is locked and soldered to the lands 23 and 24 .
[0023]
Further, as shown in FIG. 5B, the heat radiators 21 and 22 are thermally coupled by inserting the two leg portions 30 and 31 through the through holes 32 and 33, respectively, and fixing them with the solder 38. To do.
[0024]
In the state where the thermistor 3 and the heaters 21 and 22 are attached, as shown in FIG. 5D, the thermistor element bodies 3a and 3b are higher than the height H1 of the radiators 21 and 22 from the printed circuit board 20. The height H2 is adjusted to be high .
[0025]
In this way, by providing the radiators 21 and 22 on the lands 23 and 24 to which the thermistor 3 is attached, the heat of the lands 23 and 24 is dissipated through the radiators 21 and 22, thereby the temperature of the lands 23 and 24 is reduced. It is suppressed, and a thermal adverse effect on the printed circuit board 20 due to an excessive rise in the land temperature is prevented.
[0026]
Further, FIG. 4, as shown in FIG. 5 (A), the radiator 21 and 22, have a shape surrounding the lead 35, are arranged at an interval. In other words, the radiators 21 and 22 are arranged so that the inner surface of the radiator 21 surrounds the lead 35 and the inner surface of the radiator 22 surrounds the lead 36. The radiators 21 and 22 are arranged so that the inner surface of the radiator 21 and the inner surface of the radiator 22 face each other. Therefore, even if the thermistor 3 is about to fall due to a hand touching the thermistor 3, the leads 35 and 36 are prevented from falling by the radiators 21 and 22, and the thermistor 3 can be prevented from falling down. It is possible to prevent the occurrence of troubles such as a short circuit and a thermal adverse effect due to contact with the device.
[0027]
Further, when the thermistor 3 falls down due to bending of the leads 35 and 36 of the thermistor 3, the height of the radiators 21 and 22 is avoided so that contact between the radiators 21 and 22 and the thermistor element bodies 3a and 3b is avoided. Therefore, even when the thermistor 3 falls down, the contact between the thermistor element main bodies 3a and 3b and the radiators 21 and 22 is more reliably prevented, and the heat of the thermistor element main bodies 3a and 3b is directly applied to the radiator 21. , 22 can be prevented.
[0028]
Since the bent portions 35a and 36a are provided on the leads 35 and 36, when the leads 35 and 36 of the thermistor 3 are inserted into the through holes 32 and 33 of the printed circuit board 20 and soldered, the bent portions 35a and 36a are formed. The height of the thermistor element main bodies 3a and 3b is easily set by being locked in the through holes 32 and 33.
[0029]
Note that the radiators 21 and 22 may be formed in a U shape or an arc shape in plan view.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an example of a switching power supply to which a structure of the present invention is applied.
FIG. 2 is a circuit diagram showing another example of a switching power supply to which the structure of the present invention is applied.
3 is an exploded perspective view showing an embodiment of a thermistor heat dissipation structure of the present invention for the switching power supply of FIG. 2; FIG.
FIG. 4 is a perspective view showing an embodiment of a thermistor heat dissipation structure of the present invention.
5A is a plan view showing an embodiment of a heat dissipation structure for the thermistor according to the present invention, and FIGS. 5B and 5C are cross-sectional views showing a structure for mounting the heat radiator and the thermistor lead to a printed circuit board, respectively. FIG. 4D is a side view showing the relative relationship between the thermistor body and the radiator.
[Explanation of symbols]
1: AC power source, 2: rectifier circuit, 3: thermistor, 3a, 3b: thermistor element body , 4: transformer, 5: switching element, 6, 10: smoothing capacitor, 7, 8: rectifier diode, 9, 17 : Choke coil, 14: Power factor improving control unit, 15: Switching element, 20: Printed circuit board, 21, 22: Heat radiator, 23, 24: Land, 25, 26, 32, 33: Through hole, 27, 28 : Conductor pattern, 30, 31: Leg, 35, 36: Lead, 37, 38: Solder

Claims (2)

Two leads of an inrush current prevention thermistor are electrically connected and fixed to a land provided on a printed circuit board on which an electronic component constituting the switching power supply is mounted, and a pair of the thermistor leads is fixed to the land. A switching power supply in which the heatsink
The radiator is a U-shaped, U-shaped or arc shape in plan view,
The lead has a foot length structure that makes it difficult for heat to be transmitted from the thermistor element body to the printed board,
Each of the pair of radiators surrounds the corresponding leads of the thermistor with an interval between the inner surfaces thereof, and is disposed on the printed circuit board with the inner surfaces facing each other.
The height and arrangement of the radiator are adjusted so as to avoid contact between the radiator and the thermistor element body when the thermistor falls due to bending of the thermistor lead. A switching power supply characterized by that. The switching power supply of claim 1,
A switching power supply comprising: a bent portion protruding laterally at a predetermined portion of the lead; and the bent portion is engaged with a through hole provided in a printed circuit board and soldered to the land .

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