JP2000032653A - Power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To elongate the life time of a heat generating part and reduce its size, by providing a protective element in its vicinity. SOLUTION: When a diode 2 is overheated and, e.g. the temperature of the diode 2 becomes a first predetermined value of it having the possibility of its heat destruction, examining the temperature distribution surrounding the diode 2 on a printed board, a protective element 1 is mounted in a position B wherein the temperature of the protective element 1 becomes the temperature value coinciding with a second predetermined temperature value whereat its resistance value increases remarkably. In this case, the position B becomes the vicinity of a position A of the diode 2. Doing in this way, the temperature of protective element 1 becomes the temperature value whereat its resistance value increases remarkably, when the temperature of the diode 2 becomes the temperature value of it having the possibility of its heat destruction. Since the protective element 1 is connected in series with the load-power feeding route of a power supply unit, the current flowing in the load-power feeding route is also limited to a very small current value. Therefore, the current flowing in the diode 2 of a heat generating part is restricted to make preventable its heat destruction. Also, the provision of any radiation part is made unnecessary to make reducible the size of the power supply unit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device having a protection element for protecting a heating element on a power supply circuit from overheating.

[0002]

2. Description of the Related Art Generally, when the amount of current flowing through a power supply circuit such as a switching power supply increases, thermal stress on electronic components constituting the power supply circuit increases. So usually
This problem was avoided by incorporating an overcurrent protection circuit as shown in Japanese Utility Model Laid-Open No. 3-94038. But,
In this configuration, a current flowing in the power supply circuit is detected to prevent an overcurrent of the power supply circuit regardless of the temperature of the electronic component. Therefore, depending on the ambient temperature and the protection characteristics, the temperature of electronic components, especially heat-generating components such as diodes, increases, and thermal stress is applied to the heat-generating components. There was a problem that.

[0003]

Therefore, in order to enhance the heat radiation effect of these heat generating components, it is necessary to limit the mounting density of electronic components on a printed circuit board on which a circuit is mounted, or to provide a heat radiating plate. Was. However, these have been major problems in miniaturizing the power supply device.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a power supply device which has a long life of a heat-generating component and is downsized.

[0005]

According to the present invention, in order to achieve the above-mentioned object, the resistance value is steeply increased due to heat generation while being inserted in series in a load power supply path for supplying power to the load. A power supply device comprising: a protection element that becomes the increase point when a current flowing through a power supply path exceeds a rated value and restricts power supply to a load; and a heat-generating component provided in the load power supply path, The protection element and the heat-generating component are provided in the vicinity.

Further, the temperature of the protection element and the heat-generating component are such that when the temperature of the heat-generating component exceeds a first predetermined value, the temperature of the protection element sharply increases the resistance value of the protection element due to radiant heat of the heat-generating component. Is provided so as to have a positional relationship exceeding a second predetermined value. Further, the heat generating component is a diode provided in a load power supply path for supplying a voltage generated through a transformer to a load.

[0007]

(Embodiment 1) FIG. 1 is a circuit diagram showing a configuration of a power supply circuit of a power supply device according to an embodiment of the present invention. In the power supply device of the present embodiment, the AC input unit 7
DC voltage rectified and smoothed by the diode bridge DB and the capacitor C1 from the AC voltage input from the switching element 5 that is turned on and off in response to the signal of the control IC 6 to supply an intermittent current to the primary winding n1 of the transformer T. An AC voltage determined by the turns ratio is generated from the T secondary winding n2. This AC voltage is rectified by the diode 2,
Smoothing is performed by the capacitors C2 and C3, and the smoothed DC voltage is output from the DC output unit 8 to an external load.

The diode 2 is a heat-generating component, and is provided in a load power supply path for supplying a voltage generated by the transformer T to an external load (not shown). Here, the diode 2 is connected in series with a protection element 1 that sharply increases its resistance value under a predetermined condition described later, that is, the protection element 1 is also connected in series to the load power supply path.

The voltage appearing on the winding n3 of the transformer T is rectified by the diode 12, and
4. A constant DC voltage is applied to the VCC terminal of the control IC 6 by the Zener diode ZD.

The resistors R1, R2 and R3 are connected in series between the point F between the protection element 1 and the DC output section 8 and the ground, and appear at a point G between the resistors R2 and R3. The voltage, that is, the voltage obtained by dividing the voltage at the point F is applied to the control terminal of the element 4. When the applied voltage exceeds a predetermined voltage, the element 4 conducts and a current flows toward the ground,
A current flows through the light emitting diode 9 of the photocoupler connected in series with the element 4 to emit light.

When the light emitting diode 9 emits light, the phototransistor 11 of the photocoupler conducts, and the control IC 6 which detects this from the FB terminal outputs the switching element so that the secondary output voltage of the transformer T becomes a predetermined voltage from the OUT terminal. A signal for duty-controlling the switching of No. 5 is generated. That is, when the voltage appearing at the point F increases, the switching of the switching element 5 is controlled so as to reduce the voltage, and the output voltage of the power supply circuit becomes constant. Normally, the protection element 1 has a low resistance value and does not affect the output voltage.

When a current equal to or more than the reference value flows through the protection element 1, the temperature of the polymer inside the element increases due to self-heating, and the resistance value increases. In addition, the protection element 1 also has a property that when the temperature of the protection element 1 is heated by a rise in the ambient temperature and the temperature becomes equal to or higher than a predetermined temperature, the resistance value significantly increases.
This is a so-called overcurrent overheat protection element (Polyswitch: manufactured by Raychem).

FIG. 2 shows the resistance-temperature characteristics of the protection element 1, wherein the horizontal axis represents temperature (° C.) and the vertical axis represents the resistance value (Ω). The value has increased significantly.

By the way, in the circuit configured as shown in FIG. 1, when the current flowing through the protection element 1 via the diode 2 becomes a current value equal to or larger than the reference value, the resistance value of the protection element 1 sharply increases remarkably, The current flowing through the protection element 1 is limited to a small value. Since the protection element 1 is connected in series to the load power supply path, the current flowing in the load power supply path is also limited.

That is, by selecting a current value at an increase point at which the resistance value of the protection element 1 is significantly increased to a value that maintains the rating of the power supply device, an overcurrent exceeding the rated value is supplied to the load power supply path. It can be prevented from flowing, and the thermal stress of the electronic components such as the diode 2 which is the heat generating component and the load can be prevented.

By the way, as described above, the operation of the protection element 1 can limit the current not exceeding the rated value to flow through the load power supply path. There is a case where the temperature of a certain diode 2 becomes considerably high due to the influence of the ambient temperature or the like. Therefore, as described above, when the temperature of the protection element 1 becomes equal to or higher than the predetermined temperature, the protection element 1 is arranged at an appropriate position on the printed circuit board by utilizing the property of increasing the resistance value, so that the heating component Overheating can be prevented.

The positional relationship when the protection element 1 and the heat-generating diode 2 in the load power supply path are mounted on a printed circuit board will be described. FIG. 3 is a top view showing the mounting of the load power supply path on the printed circuit board 10, and the same components as those in FIG. 1 are denoted by the same reference numerals. Reference numeral 1 denotes a protection element provided in series with a load power supply path of the power supply device and mounted at a position B on the printed circuit board 10. Reference numeral 2 denotes a protection element also provided on a power supply circuit of the power supply device.
A diode which is a heat-generating component mounted at a position A on 0. Reference numeral 3 denotes another electronic component such as a capacitor mounted on the printed circuit board 10.

At this time, the radiant heat from the diode 2, which is a heat-generating component disposed at the position A on the printed circuit board 10, changes the temperature of the surrounding area on the printed circuit board 10. Therefore, the temperature distribution around the diode 2 on the printed circuit board 10 at the time of overheating when the temperature of the diode 2 reaches the first predetermined value which is a temperature at which the protection element 1 is likely to be destroyed by heat is examined. The protection element 1 is mounted at a position B at which the temperature coincides with a second predetermined value (for example, 120 ° C.) which is a temperature at which the resistance value is significantly increased. At this time, the position B is near the position A.

By doing so, when the diode 2 reaches a temperature at which there is a risk of thermal destruction, the protection element 1 reaches a temperature at which the resistance value is significantly increased, and the protection element 1 is connected in series to the load power supply path. Therefore, the current flowing through the load power supply path is also limited to a small value. Therefore, the current flowing through the diode 2, which is a heat-generating component provided in the load power supply path, is limited, and thermal destruction of the diode 2 can be prevented. At this time, even if the current flowing through the load power supply path exceeds the rated value even before the temperature at which the diode 2 is likely to be thermally damaged, the current flowing through the protection element 1 is limited to a minute value.

Therefore, whether a current that significantly increases the resistance value flows through the protection element 1, or whether the temperature of the protection element 1 rises to a temperature at which the resistance value of the protection element 1 increases significantly due to an increase in the ambient temperature. When either of the conditions is satisfied, the current flowing through the load power supply path is limited.

Therefore, it is possible not only to prevent the overcurrent from flowing through the load power supply path, but also to reduce the thermal stress due to the overheating of the heat-generating component, and to keep the life of the heat-generating component long. Further, there is no need to provide a heat radiating component, and the power supply device can be downsized.

In the present embodiment, the protection element 1 is configured to protect the heat of the diode 2 shown in FIG. 1, but is configured to protect the switching element 5 and the diode 12 from overheating of other heating elements. You may.

[0023]

As described above, according to the first aspect of the present invention, the resistance is sharply increased due to heat generation and is inserted in series in the load power supply path for supplying power to the load. When the flowing current exceeds the rated value, the protection element that becomes the increase point and limits the power supply to the load and the heat-generating component provided in the load power supply path are provided in the vicinity, so that the load power supply path Overheating can be prevented, and when the heat-generating component is overheated, the temperature of the protection element provided in the vicinity of the heat-generating component also increases, thereby increasing the resistance value of the protection element due to heat generation. Thus, the current flowing through the load power supply path is limited. Therefore, it is possible to limit the current flowing to the heat-generating component provided in the load power supply path, prevent the heat-generating component from being thermally destroyed, and maintain the life of the heat-generating component for a long time. Also,
There is no need to provide a heat radiating component, and the power supply device can be downsized.

According to the second aspect of the present invention, when the temperature of the heat-generating component exceeds, for example, a first predetermined value in an overheated state, the protection element and the heat-generating component provided in the load power supply path are A second step in which the temperature of the protection element sharply increases the resistance value of the protection element due to radiant heat of the heat generating component;
Are provided so as to have a positional relationship exceeding the predetermined value, the resistance value of the protection element increases when the heating component is overheated, and the current flowing through the load power supply path is limited. Therefore, the current flowing through the heat-generating component in the load power supply path is limited, so that thermal destruction of the heat-generating component can be prevented, and the life of the heat-generating component can be kept long. Further, there is no need to provide a heat radiating component, and the power supply device can be downsized.

According to the third aspect of the present invention, since the heat-generating component is a diode provided in a load power supply path for supplying a voltage generated through a transformer to a load, when the diode is overheated, the protection element is activated. The resistance value increases, and the current flowing through the load power supply path is limited. Therefore, the current flowing through the diode provided in the load power supply path is limited, so that the diode can be prevented from thermal destruction and the life can be maintained long. Also, there is no need to provide heat dissipation components,
The size of the power supply device can be reduced.

[Brief description of the drawings]

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

FIG. 2 is a characteristic diagram showing resistance-temperature characteristics of the protection element of the present invention.

FIG. 3 is a top view showing a state where the power supply circuit is mounted on a printed circuit board.

[Explanation of symbols]

 1 protection element 2 diode

Claims (3)

[Claims] 1. A load power supply line for supplying electric power to a load, which is inserted in series, generates a steep resistance due to heat generation, and increases the current when the current flowing through the load power supply line exceeds a rated value. A power supply device comprising: a protection element for restricting power supply to a load; and a heat-generating component provided in the load power supply path, wherein the protection element and the heat-generating component are provided in the vicinity. And power supply. 2. The protection element and the heat-generating component, wherein when the temperature of the heat-generating component exceeds a first predetermined value, the temperature of the protection element sharply increases the resistance value of the protection element due to radiant heat of the heat-generating component. 2. The power supply device according to claim 1, wherein the power supply device is provided so as to have a positional relationship exceeding a second predetermined value. 3. The device according to claim 1, wherein the heat-generating component is a diode provided in a load power supply path for supplying a voltage generated through a transformer to a load. Power supply.