JP2002270359A - Switching power supply for high frequency heating equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the junction temperature of a semiconductor switching- element below the tolerable temperature for reliability, cheaply, in a switching power supply for high frequency heating equipment. SOLUTION: By constituting an attachment position to a heat radiating fin 9 of a rectifier 2 so that the outside of a rectifier 2 package may project outside from the heat radiating fin 9, a contacting face area of the rectifier 2 and the heat radiating fin 9 decreases, and the quantity of heat conducted from the rectifier 2 to semiconductor switching elements 3 and 4 decreases. Therefore, by using the expensive semiconductor switching element of small loss, or without using many heat radiating fins, the junction temperature of the semiconductor switching elements 3 and 4 can be made below the tolerable temperature for reliability, and can constitute it at a low cost using the one heat radiating fin 9.

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 for a high-frequency heating device such as a microwave oven.

[0002]

2. Description of the Related Art Conventionally, as a switching power supply for a high-frequency heating device of this type, for example, those shown in FIGS. 3 and 4 have been widely used. An AC commercial power supply 1 is converted into a DC voltage by a rectifying element 2, and the DC voltage is turned on and off by semiconductor switching elements 3 and 4, whereby an inverter circuit 5 generates a high-frequency voltage in a primary winding of a high-voltage transformer 6.
The high voltage transformer 6 excites a high frequency high voltage in the secondary winding.
This high-frequency high voltage is rectified into a DC high voltage by the high-voltage rectifier circuit 7 and applied to the magnetron 8. The magnetron 8 is driven by the high DC voltage and generates a radio wave of 2.45 GHz.

[0003] By the above operation, the rectifying element 2 is about 15 to 2
5 W is generated, and the semiconductor switching elements 3 and 4 each generate a loss of about 30 to 50 W. Therefore, the rectifying element 2 and the semiconductor switching elements 3 and 4 are attached to the radiating fins 9 for cooling.

[0004]

However, in the above-described conventional configuration, the semiconductor switching elements 3 and 4 generate approximately twice the loss as compared with the rectifying element 2, so that the semiconductor switching elements 3 and 4 are naturally proportional to the loss. Junction temperatures of 3 and 4 are much higher than that of the rectifying element 2.

Further, since the rectifying element 2 and the semiconductor switching elements 3 and 4 are attached to the same radiating fin 9, the semiconductor switching elements 3 and 4 receive heat from the rectifying element 2 by heat conduction, and 4
Junction temperature becomes higher, and may exceed a temperature that is allowable in terms of reliability. The rectifying element 2 also receives heat from the semiconductor switching elements 3 and 4 by heat conduction, and the junction temperature of the rectifying element 2 also increases. However, since the original loss is small, the temperature becomes lower than the temperature allowable in terms of reliability. Therefore, in order to keep the junction temperature of the semiconductor switching elements 3 and 4 below a temperature that is allowable in terms of reliability, an expensive semiconductor switching element 3 or 4 having a smaller loss is used, or the radiation fin 9 having a higher cooling performance is used. Because it had been used, the cost was high.

In order to solve such a problem, as shown in FIG. 5, a radiating fin 9a for the rectifying element 2 and a radiating fin 9b for the semiconductor switching elements 3 and 4 have been proposed. In this case, since the semiconductor switching elements 3 and 4 do not receive heat from the rectifier element 2 due to heat conduction, the junction temperature does not increase accordingly, which is advantageous. However, in this configuration, since the radiation fins are divided into two, the number of assembling steps in manufacturing the switching power supply for the high-frequency heating device is doubled, and the manufacturing cost is increased.
After all, there was a problem that the cost was high.

The present invention solves the above-mentioned conventional problems, and provides a switching power supply for a high-frequency heating device capable of reducing the junction temperature of a semiconductor switching element to a temperature that is less than an allowable temperature with a simple and inexpensive configuration. The purpose is to do.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned conventional problems, a switching power supply for a high-frequency heating apparatus according to the present invention comprises a rectifying element for rectifying a commercial power supply and a rectifying output rectified by the rectifying element. At least one semiconductor switching element, and a radiating fin for cooling the rectifying element and the semiconductor switching element, and a mounting position of the rectifying element to the radiating fin is an outer shape of the rectifying element package. The heat radiation fin is configured so as to protrude from the outer shape.

As a result, the contact area between the rectifying element and the radiation fin is reduced, and the amount of heat conducted from the rectifying element to the semiconductor switching element is reduced. Therefore, the junction temperature of the semiconductor switching element can be reliably tolerated by using one heat radiation fin without using an expensive semiconductor switching element with lower loss and without using a large number of heat radiation fins. Below the temperature,
An inexpensive switching power supply for a high-frequency heating device can be provided.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a rectifying element for rectifying a commercial power supply, at least one semiconductor switching element for switching a rectified output rectified by the rectifying element, the rectifying element and the semiconductor switching element. A radiating fin for cooling the rectifying element, wherein the mounting position of the rectifying element to the radiating fin is configured such that the outer shape of the rectifying element package is protruded from the outer shape of the radiating fin. The contact area between the rectifier and the radiation fin is reduced, and the amount of heat conducted from the rectifying element to the semiconductor switching element is reduced. Therefore, the junction temperature of the semiconductor switching element can be reliably tolerated by using one heat radiation fin without using a low-loss expensive semiconductor switching element and without using a large number of heat radiation fins. It is possible to provide an inexpensive switching power supply for a high-frequency heating device which can be kept at a temperature or lower.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1, 2 and 3. FIG.

FIG. 3 described in the conventional example is also a circuit diagram showing a switching power supply for a high-frequency heating device in an embodiment of the present invention. A commercial power supply 1 which is an alternating current is converted into a DC voltage by a rectifying element 2, and the DC voltage is turned on and off by a semiconductor switching element 3, 4, whereby an inverter circuit 5 generates a high frequency voltage in a primary winding of a high voltage transformer 6. The transformer 6 excites a high frequency high voltage to the secondary winding. This high-frequency high voltage is rectified into a DC high voltage by the high-voltage rectifier circuit 7,
Applied to the magnetron 8. The magnetron 8 is driven by the high DC voltage and generates a radio wave of 2.45 GHz.

FIG. 1 is a diagram showing a configuration in which the rectifying element 2 and the semiconductor switching elements 3 and 4 are attached to the radiation fin 9.
By the above operation, the rectifying element 2 generates a loss of about 15 to 25 W, and the semiconductor switching elements 3 and 4 each have a loss of about 30 to 25 W.
Generates 50W loss. Therefore, the rectifying element 2 and the semiconductor switching elements 3 and 4 are attached to the radiating fin 9 for cooling. However, unlike the conventional example, the package outer shape of the rectifying element 2 protrudes from the radiating fin 9 and is attached. I have.

The operation and operation of the switching power supply for a high-frequency heating device configured as described above will be described below.

First, since the semiconductor switching elements 3 and 4 generate approximately twice the loss as compared with the rectifying element 2, the junction temperature of the semiconductor switching elements 3 and 4 is naturally larger than that of the rectifying element 2 in proportion to the loss. Will also be quite high. Further, since the rectifying element 2 and the semiconductor switching elements 3 and 4 are attached to the same radiating fin 9, the semiconductor switching elements 3 and 4 receive heat from the rectifying element 2 by heat conduction, and the junction of the semiconductor switching elements 3 and 4 is performed. The temperature will be even higher. However, in the present embodiment, since the package outer shape of the rectifier element 2 is mounted so as to protrude beyond the outer shape of the heat radiation fin 9, the contact area between the rectifier element 2 and the heat radiation fin 9 is reduced, and the semiconductor switching element is thermally conductive. The amount of heat applied to 3, 4 also decreases in proportion.
Therefore, the junction temperature of the semiconductor switching elements 3 and 4 can be made lower than the temperature that is allowable in terms of reliability. On the other hand, since the contact area between the rectifying element 2 and the radiating fins 9 is reduced, the heat radiating effect of the rectifying element 2 is deteriorated.
Although the junction temperature rises, the original loss is small, so that the temperature can be lowered below the temperature that is allowable in terms of reliability.

FIG. 2 is also a diagram showing a configuration in which the rectifying element 2 and the semiconductor switching elements 3 and 4 are attached to the radiation fins 9.
As shown in this figure, by changing the mounting position of the rectifying element 2 to the radiating fins 9, it is possible to change the dimension of the package of the rectifying element 2 protruding from the outer shape of the radiating fins 9. The contact area with the fin 9 can be changed. Thereby, for example, when the junction temperature of the rectifying element 2 exceeds the temperature allowable in reliability and the junction temperature of each of the semiconductor switching elements 3 and 4 becomes lower than the temperature allowable in reliability, the rectifying element 2 and the radiation fin The junction temperature of the rectifying element 2 and the semiconductor switching elements 3 and 4 can be made lower than the allowable temperature for reliability by changing the mounting position in the direction in which the area of contact with the element 9 increases. As described above, by optimizing the contact area between the rectifying element 2 and the radiating fin 9, the junction temperature of each of the rectifying element 2 and the semiconductor switching elements 3 and 4 can be made lower than the temperature allowable in terms of reliability. .

As described above, in this embodiment, the mounting position of the rectifying element 2 to the radiating fins 9 is configured such that the outer shape of the package of the rectifying element 2 protrudes from the outer shape of the radiating fins 9. Accordingly, the contact area between the rectifying element 2 and the radiation fins 9 is reduced, and the amount of heat due to heat conduction from the rectifying element 2 to the semiconductor switching elements 3 and 4 is reduced. Therefore, the junction temperature of the semiconductor switching elements 3 and 4 can be relied on by using one heat radiation fin 9 without using a low-loss expensive semiconductor switching element and without using a large number of heat radiation fins. It is possible to provide an inexpensive switching power supply for a high-frequency heating device, which can be kept at a temperature not higher than an acceptable temperature.

[0018]

As described above, according to the first aspect of the present invention, the switching of the high-frequency heating device can be performed with a simple and inexpensive configuration so that the temperature of the semiconductor switching element can be kept below the temperature allowable in terms of reliability. Power can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a rectifying element and a semiconductor switching element of a switching power supply for a high-frequency heating device mounted on a radiation fin according to an embodiment of the present invention.

FIG. 2 is another configuration diagram of a rectifying element and a semiconductor switching element of a switching power supply for the high-frequency heating device, which are attached to a radiation fin.

FIG. 3 is a circuit diagram of a switching power supply for a high-frequency heating device according to an embodiment of the present invention and a conventional example.

FIG. 4 is a diagram showing a conventional rectifying element and a semiconductor switching element of a switching power supply for a high-frequency heating device, which are mounted on a radiation fin.

FIG. 5 is another mounting configuration diagram of a rectifying element and a semiconductor switching element of a conventional switching power supply for a high-frequency heating device to a radiation fin.

[Description of Signs] 2 Rectifying element 3 Semiconductor switching element 4 Semiconductor switching element 9 Heat radiation fin

Claims (1)

[Claims] 1. A rectifying element for rectifying a commercial power supply, at least one semiconductor switching element for switching a rectified output rectified by the rectifying element, and a heat radiation for cooling the rectifying element and the semiconductor switching element. A switching power supply for a high-frequency heating device, comprising: a fin; and a mounting position of the rectifying element to the radiating fin is such that an outer shape of the rectifying element package protrudes from an outer shape of the radiating fin.