JPH06164347A - Switching module - Google Patents

Abstract

PURPOSE:To form a snubber circuit which suppress a surge current generated by the switching operation of an FET by fixing the metallic part of a package to which the drain of a field-effect transistor is connected and a metallic substrate to which the source is connected together across an insulating film and forming a capacitor. CONSTITUTION:The FET 1 is fixed on the metallic part 2 and the drain of the FET 1 is connected to the metallic part 2 of the metallic part of the package 3. Then the metallic substrate 5 has the insulator 4 formed on the top surface of, for example, Al plate like a metal core printed board and further has a copper thin film 9 for forming printed electric conductors on the insulating film 4. Then the metallic part 2 of the package 3 is fixed by soldering onto the copper thin film 9. Then the source of the FET 1 is connected to the substrate 5. The metallic substrate 5 where the package 3 is fixed to a heat radiation substrate 7 across a insulating sheet 6 with a screw 10. Consequently, the switching module is constituted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching module capable of suppressing a switching surge with a simple structure. Field effect transistors are often used as switching elements in switching power supply devices.
Further, since a surge may occur due to switching and the field effect transistor may be damaged, a switching absorber (snubber circuit) is provided to suppress this surge.

[0002]

2. Description of the Related Art In a conventional switching module, for example, as shown in FIG. 3, a field effect transistor 21 sealed in a package is provided with an insulating sheet 2 having a high thermal conductivity.
It has a structure in which it is fixed to the heat radiation fin 23 by aluminum die-casting with a screw 24 via 2, and 25 indicates the lead wire of the source, drain and gate of the field effect transistor 21. Since the drain of the field effect transistor 21 is connected to the metal part of the package, the insulating sheet 22 is interposed between the drain and the heat radiation fin 23 so that the drain is not grounded.

The switching power supply device has, for example, the configuration shown in FIG. 4, and 31 is a gate G, a source S,
A field effect transistor having a drain D, 32 is a transformer, 33 is a DC power supply, 34 and 35 are diodes, 36
Is a choke coil, 37 is a capacitor, 38 is a control circuit, 39 is a capacitor, 40 is a resistor, and the field effect transistor 31 has a radiation fin 23 as shown in FIG.
Is attached to dissipate the heat generated by the switching operation.

The field effect transistor 31 has a drain D.
Is connected to the primary winding of the transformer 32, and the current flowing from the DC power supply 33 to the primary winding of the transformer 32 is supplied to the control circuit 3
ON by applying the control signal from 8 to the gate G,
Turn off the current flowing in the primary winding of the transformer 32,
The voltage induced in the secondary winding by turning off the diode 3
It is rectified and smoothed by a rectifying / smoothing circuit composed of 4, 35, a choke coil 36, and a capacitor 37, and is supplied to a load (not shown) as a DC output voltage. This DC output voltage is detected by the control circuit 38, and compared with a set value to control the ON period of the field effect transistor 31 to stabilize the DC output voltage.

The primary winding of the transformer 32 connected to the drain D of the field effect transistor 31 has a large inductance component and a surge voltage is generated when the field effect transistor 31 is turned on and off.
A snubber circuit (surge absorber) composed of a capacitor 39 and a resistor 40 is connected between and. The capacitor 39 is, for example, 100 to 1000 pF, and the resistor 40 is 1
It is set to 0 to 100Ω.

[0006]

In a field effect transistor as a switching element in a switching power supply device, a surge voltage is generated between a drain D and a source S of the field effect transistor due to switching, and the surge voltage is suppressed. In order to do so, the snubber circuit is provided as described above. This snubber circuit may have only the capacitor, or the capacitor 39 and the resistor 40, or a more complicated circuit configuration as described above, but this has been an obstacle to miniaturization. An object of the present invention is to provide a structure having a function equivalent to that of a snubber circuit for suppressing surge.

[0007]

A switching module of the present invention will be described with reference to FIG. 1. A package 3 in which a drain of a field effect transistor 1 is connected to a metal portion 2 and sealed, and an insulating film 4 are provided. On the formed metal substrate 5, the insulating film 4 between the metal portion 2 and the metal substrate 5 is fixed so that capacitance is formed, and the metal substrate 5 is fixed to the heat dissipation substrate 7 via the insulating sheet 6. In addition, the source of the field effect transistor 1 is connected to the metal substrate 5.

[0008]

The field effect transistor 1 as a switching element is fixed on the metal portion 2 of the package 3 and is molded with, for example, a synthetic resin. Also, the package 3 is fixed on the metal substrate 5 on which the insulating film 4 is formed. At this time, the insulating film 4 of the metal substrate 5 is interposed between the metal substrate 5 and the metal portion 2 of the package 3 to form a capacitance. Since the source of the field effect transistor 1 is connected to the metal substrate 5, the metal portion 2 which is opposed to the drain and source of the field effect transistor 1 with the insulating film 4 interposed therebetween.
A capacitor is formed by the metal substrate 5 and the metal substrate 5, and this capacitor can be used as a snubber circuit.
Further, an insulating sheet 6 similar to the conventional example is interposed between the heat dissipation substrate 7 and the metal substrate 5 to provide a desired insulating structure.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of the essential parts of an embodiment of the present invention.
As described above, the field effect transistor 1 as a switching element is fixed on the metal portion 2, and the drain of the field effect transistor 1 is connected to the metal portion 2 of the package 3. Then, seal it in a metal case,
Alternatively, it is molded with a synthetic resin as shown. Further, lead wires 8 for the gate, source and drain of the field effect transistor 1 are led out from the package 3.

The metal substrate 5, like a metal-core printed circuit board, has a structure in which, for example, an insulating film 4 is formed on the upper surface of an aluminum plate, and a copper thin film 9 for forming printed wiring is formed thereon. be able to. Insulating film 4 in that case
For example, an insulator such as polyimide having a thickness of 0.1 mm can be used. Then, the metal portion 2 of the package 3 is fixed onto the copper thin film 9 by soldering or the like. Then, the source of the field effect transistor 1 is connected to the metal substrate 5.

The metal substrate 5 to which the package 3 is fixed is fixed to the heat dissipation substrate 7 with the screw 10 via the insulating sheet 6. This constitutes a switching module. The heat dissipation board 7 may be the heat dissipation fin shown in FIG. The insulating sheet 6 has a thickness of 0.3, for example.
It is possible to use a sheet obtained by impregnating fibers of 0.5 mm with silicon, and it is desirable that the sheet has high thermal conductivity and high pressure resistance.

The metal substrate 5 is, for example, 15 mm × 25 m
m size, 0.1 mm thick polyimide insulation film 4
When the metal is formed, the metal substrate 5 and the metal portion 2 of the package 3 are formed.
The electrostatic capacitance between and can be about 100 to 2000 pF. This capacitance can have any desired value by selecting the thickness of the insulating film 4, the dielectric constant, and the facing area.

Therefore, the capacitor formed by the metal portion 2 and the metal substrate 5 facing each other with the insulating film 4 interposed is connected between the drain and the source of the field effect transistor 1, and the electrostatic capacitance of the capacitor is connected. Capacity is 100-200
Since it can be set to about 0 pF, the surge voltage in the switching operation of the field effect transistor 1 can be sufficiently suppressed. That is, the snubber circuit is configured.

FIG. 2 is an explanatory view of the embodiment of the present invention.
1 is a field effect transistor, 12 is a transformer, 13 is a DC power supply, 14 and 15 are diodes, 16 is a choke coil, 17 is a capacitor, 18 is a control circuit, and 19 is a metal substrate. This metal substrate 19 corresponds to the metal substrate 5 in FIG.

A control signal from the control circuit 18 is applied to the gate G of the field effect transistor 11 so that the source S of the field effect transistor 11 is the DC power supply 13 and the drain D is the DC power supply 13 via the primary winding of the transformer 12. Connect to. Further, the induced voltage in the secondary winding of the transformer 12 is rectified by the diodes 14 and 15 and smoothed by the choke coil 16 and the capacitor 17 to supply a DC output voltage to a load (not shown). The control circuit 18 compares the DC output voltage with the set value, applies a control signal to the gate G of the field effect transistor 11 to control the ON period, and stabilizes the DC output voltage.

The source S of the field effect transistor 11 is connected to the metal substrate 19 (5), and the drain D is package 3
Since it is connected to the metal part 2 of
A capacitor indicated by a dotted line is formed between the and. The capacitance of this capacitor is 100-2000pF
Therefore, the snubber circuit can be configured by this capacitor.

[0017]

As described above, according to the present invention, the insulating film 4 is interposed between the metal portion 2 of the package 3 to which the drain of the field effect transistor 1 is connected and the metal substrate 5 to which the source is connected. The capacitor is fixed, and a capacitor is formed through the insulating film 4, and the capacitor is connected between the drain and the source of the field effect transistor 1. A snubber circuit for suppressing the generated surge voltage can be configured. That is, unlike the conventional example, it is not necessary to connect a new capacitor 39 and a resistor 40, the number of parts can be reduced and the space can be omitted, the miniaturization can be facilitated, and the economy can be achieved. There are advantages.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an example of the present invention.

FIG. 3 is a schematic perspective view of a conventional example.

FIG. 4 is an explanatory diagram of a conventional example.

[Explanation of symbols]

 1 field effect transistor 2 metal part 3 package 4 insulating film 5 metal substrate 6 insulating sheet 7 heat dissipation substrate

Claims (1)

[Claims] 1. A package (3) in which the drain of a field effect transistor (1) is connected to a metal part (2) and sealed.
A capacitance is formed by the insulating film (4) between the metal part (2) and the metal substrate (5) on the metal substrate (5) on which the insulating film (4) is formed. And fixing the metal substrate (5) to the heat dissipation substrate (7) via the insulating sheet (6) and connecting the source of the field effect transistor (1) to the metal substrate (5). Characteristic switching module.