JP2002142457A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power supply in structure for preventing the temperature of a land for mounting a thermistor for preventing an inrush current from excessively increasing due to the heat of the thermistor. SOLUTION: Leads 35 and 36 of the thermistor 3 are electrically connected to the lands 23 and 24 being provided on a printed circuit board 20 for fixation. Radiators 21 and 22 are thermally connected to the lands 23 and 24 where the leads 35 and 36 of the thermistor 3 are fixed for mounting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field 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 on which a thermistor for preventing an inrush current is mounted.

[0002]

2. Description of the Related Art In a switching power supply, a large rush current flows when the power is turned on because a large-capacity capacitor is provided in a rectifying / smoothing circuit. If this rush current becomes excessive, it propagates as noise to peripheral devices, etc., so it is necessary to prevent the rush current from becoming excessive,
As a simple means, an NTC thermistor is used.
That is, when the power is turned off, the thermistor has a relatively high resistance value because it is at room temperature. When the power is turned on in this state, the rush current is suppressed. When the power supply is turned on and a steady state is reached, 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. Therefore, the thermistor is kept at a high temperature while the device is operating.

[0003]

In such a switching power supply, the heat of the thermistor is transmitted to the lands of the printed circuit board, and the lands become high heat, which may adversely affect the printed circuit board. In order to prevent the thermistor from transferring heat to the land and to maintain the thermistor itself at a high temperature, the thermistor leads are conventionally made longer so that thermistor's heat is less likely to be transferred to the land. In this configuration, the thermistor is likely to fall down, and may come into contact with peripheral electronic components to cause an electrical trouble.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has an object to provide a radiating structure for a rush current preventing thermistor in a switching power supply, which can prevent the temperature of a land on which the thermistor is mounted from excessively rising due to heat of the thermistor. Aim.

It is another object of the present invention to provide a radiating structure for a rush current preventing thermistor having a structure capable of preventing the thermistor from falling down.

[0006]

According to the first aspect of the present invention, an inrush current preventing thermistor lead is electrically connected to a land provided on a printed circuit board on which electronic components constituting a switching power supply are mounted. A radiator is thermally connected to and fixed to the land to which the leads of the thermistor are fixed.

As described above, by providing the radiator on the land on which the thermistor is mounted, the heat of the land is radiated through the radiator, the temperature of the land is suppressed, and the heat applied to the printed circuit board due to the excessive rise in temperature of the land. Adverse effects are prevented.

According to a second aspect of the present invention, in the first aspect, the radiator has a shape surrounding the lead.

As described above, by setting the shape of the radiator to a shape surrounding the lead, it is possible to prevent the thermistor from falling down due to a hand touching the thermistor, etc.
It is possible to prevent the occurrence of troubles such as a short circuit and a thermal adverse effect due to the thermistor coming into contact with another peripheral device.

[0010]

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 supply, 2 is a rectifier circuit, 3 is an inrush current prevention thermistor, 4 is a transformer that is turned on and off by a switching element 5, 6 is a primary-side smoothing capacitor,
7, 8 are secondary-side rectifying diodes, 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,
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.

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 shown in FIG. 2 has a control unit 14 for improving the power factor and a switching element 15, and further includes a diode 16 for preventing a current from the capacitor 6 from flowing to the switching element 15 when the switching element 15 is turned on. And a choke coil 17 is further provided. This power factor improvement 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 becomes as sinusoidal as possible to prevent generation of harmonics and to generate noise. It is to prevent.

As described above, the structure of the present invention is adopted for the thermistor illustrated in FIGS.

FIG. 3 is an exploded perspective view showing an embodiment of the present invention with respect to the switching power supply shown in FIG. 3, reference numeral 19 denotes a case or L-shaped frame of a switching power supply, 20 denotes 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 a printed circuit board 2
0 is mounted together with the radiators 21 and 22.

FIG. 4 is a perspective view showing an embodiment of the heat radiation structure of the thermistor 3 of the present invention. FIG. 5A is a plan view showing a mounting structure of the thermistor 3 on the printed circuit board 20, and FIGS. 5B and 5C are cross-sectional views showing a structure for fixing a radiator and the lead of the thermistor to the printed circuit board 20, respectively. FIG. 5D is a side view showing the relationship between the thermistor and the height of the radiator.

As shown in FIGS. 4 and 5, the thermistor 3 of this embodiment shows an example in which two thermistor elements 3a and 3b are connected in series.
In some cases, a single thermistor element is used.

The lands 23 and 24 for attaching the thermistor 3 are formed on the printed circuit board 20.
3 and 24 are through holes 2 with conductors plated on the inner wall.
5 and 26 are formed, and the land 2 on the front surface is formed on the back surface of the printed circuit board 20 through these through holes 25 and 26.
Conductor patterns 27, 28 electrically connected to 3, 24
Are formed.

The lands 23 and 24 are also provided with two through-holes 32 and 33 made of conductor plating for inserting the mounting legs 30 and 31 of the radiators 21 and 22 respectively. The holes 32 and 33 are also connected to the conductor patterns 27 and 28 on the back surface.

The radiators 21 and 22 of the present embodiment are in the shape of a letter in a plan view and are made of an aluminum alloy, and are provided with grooves 21a and 22a at their two lower sides, respectively, and can be soldered to the grooves. The leg portions 30 and 31 are configured by fitting eyelets made of brass or the like.

The thermistor 3, as shown in FIG. 5 (C), inserts two leads 35, 36 of the thermistor 3 into the through holes 25, 26, and connects the conductor patterns 27, 28 with solder 37 from the back surface. Electrically connect and mechanically secure.

The leads 3a and 3b of the thermistor 3 are set long so as to prevent the heat of the thermistor from being transmitted to the conductor patterns 27 and 28. In order to set such height, the leads 35 and 36 are formed with bent portions 35a and 36a protruding laterally at predetermined height portions, and the bent portions 35a and 36a are formed in the through holes 25 and 26. Locked and soldered.

Further, as shown in FIG.
1 and 22, the two legs 30, 31 are inserted into the through holes 32, 33, respectively, fixed by solder 38, and thermally coupled.

As described above, the thermistor 3 and the heaters 21 and 22
5A, the height H2 of the radiators 21 and 22 to the thermistor elements 3a and 3b is higher than the height H1 of the radiators 21 and 22 from the printed circuit board 20 as shown in FIG. It is desirable to configure. With this configuration, even when the thermistor 3 falls down, contact between the thermistor elements 3a and 3b and the radiators 21 and 22 is more reliably prevented, and the heat of the thermistor elements 3a and 3b is directly transferred to the radiators 21 and 22. Can be prevented from being transmitted to the

By providing the radiators 21 and 22 on the lands 23 and 24 where the thermistor 3 is mounted,
The heat of the lands 23 and 24 is dissipated through the radiators 21 and 22, thereby suppressing the temperature of the lands 23 and 24.
An adverse thermal effect on the printed circuit board 20 due to an excessive rise in the land temperature is prevented.

Further, as shown in FIG.
Since the first and the second 22 have a shape surrounding the leads 35 and 36, even if the thermistor 3 tries to fall down by touching the thermistor 3, the leads 35 and 36 are connected to the radiator 2.
The fall of the thermistor 3 can be prevented by preventing the thermistor 3 from falling down, and the occurrence of troubles such as short-circuit and adverse thermal effects due to the thermistor coming into contact with other peripheral devices can be prevented. 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 the 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.

FIG. 3 is an exploded perspective view showing one embodiment of a heat radiation structure of the thermistor of the present invention for the switching power supply of FIG. 2;

FIG. 4 is a perspective view showing one embodiment of a heat dissipation structure of the thermistor of the present invention.

5 (A) is a plan view showing an embodiment of a heat dissipation structure of a thermistor according to the present invention, and FIGS. 5 (B) and 5 (C) are cross-sections showing attachment structures of the radiator and thermistor leads to a printed board, respectively. FIG. 4D is a side view showing the relative height of the thermistor body and the radiator.

[Explanation of symbols]

1: AC power supply, 2: Rectifier circuit, 3: Thermistor, 3a,
3b: Thermistor element, 4: Transformer, 5: Switching element, 6, 10: Smoothing capacitor, 7, 8: Rectifying diode, 9, 17: Choke coil, 14: Power factor improving control section, 15: Switching element , 20; printed circuit board, 21, 22: radiator, 23, 24: land, 2
5, 26, 32, 33: through hole, 27, 28: conductor pattern, 30, 31: leg, 35, 36: lead,
37, 38: Solder

Continued on front page F term (reference) 5E322 AA01 AB02 EA11 5H006 AA05 CA07 CB01 CB03 CC02 CC08 DA04 DC05 FA02 HA05 HA08 HA42 5H730 BB14 BB23 BB57 CC01 CC04 DD02 EE02 EE08 EE10 FD01 FF19 XC09 ZZ01 ZZ11 ZZ12

Claims (2)

[Claims] An inrush current prevention thermistor lead is electrically connected and fixed to a land provided on a printed circuit board on which electronic components constituting a switching power supply are mounted, and the thermistor lead is fixed to the land. A switching power supply characterized in that a radiator is thermally coupled and mounted. 2. The switching power supply according to claim 1, wherein said radiator has a shape surrounding said lead.