JPH064592Y2 - Noise prevention circuit for power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a circuit for preventing noise generated during operation of a semiconductor element that constitutes a power conversion device.

[Conventional technology]

As a power converter, a switching regulator will be taken as an example to explain the noise generated thereby and its prevention circuit.

FIG. 9 is a main circuit connection diagram showing a general configuration of a switching regulator, in which DC power from a DC power supply 1 is supplied to two metal oxide semiconductor field effect transistors (hereinafter abbreviated as MOSFET) 2. After being intermittently connected and rectified by the diode 4 via the transformer 3, the DC power of a desired voltage insulated from the DC power supply 1 is taken out via the filter 5. Note that M1 is the reference potential of the primary side circuit of the transformer 3, and M2 is the reference potential of the secondary side circuit of the transformer 3.

By the way, in order to dissipate the heat generated during the operation of the semiconductor elements constituting the power converter, that is, the two MOSFETs 2 and the diodes 4, when these semiconductor elements are attached to a common cooling fin, the elements and the cooling element are cooled. It is necessary to insulate between the fins.

FIG. 10 is a structural diagram showing a conventional example of noise prevention when a semiconductor element is attached to a cooling fin via an insulator, and the element insulation 11 is provided between the MOSFET 2 and the cooling fin 12.
Is inserted and the fin insulation 13 is inserted between the cooling fin 12 and the case 14 to make the potential of the cooling fin 12 indefinite.
By connecting to the reference potential M1 of T2, the conventional MOSF
The noise released to the outside through the path of ET2 → cooling fin 12 → case 14 is internally processed through the path of MOSFET2 → cooling fin 12 → reference potential M1 to improve the noise prevention effect.

However, when there are many circuits in one device, the number of reference potentials is also many, so that the cooling fin
By connecting 12 to the reference potential M1 via the noise countermeasure capacitor 15, only high frequency noise is returned to the reference potential M1 and low frequency components and direct current components are cut.

[Problems to be solved by the device]

FIG. 11 is an equivalent circuit diagram of the conventional structure shown in FIG.
The noise from the noise source 30 is the capacitance 31 between the element and the fin.
→ Capacitance between fins and case 32 → Noise emitted to the outside through the path between case and ground capacitance 33, and capacitance between the element and fins 31 → Noise countermeasure Noise that is internally processed through the path of capacitor 15 Becomes Here, the point A is the potential of the cooling fin 12, and the point B is the potential of the case 14.

However, due to the inductance 16 present in the lead of the noise countermeasure capacitor 15 and the inductance 17 present in the wiring to the reference potential M1, it is difficult for spike noises having a particularly high frequency to return to the reference potential M1. Such a noise is inconveniently emitted to the outside through the case 14 without being internally processed.

Therefore, an object of the present invention is to enable even noise with a high frequency to be returned to the reference potential of the circuit and effectively prevent noise.

[Means for Solving the Problems]

In order to achieve the above object, the noise prevention circuit of the present invention is a power conversion device in which an insulator is interposed between a semiconductor element and a cooling fin for dissipating heat generated by the semiconductor element. A shield conductor insulated from the semiconductor element and the cooling fin is inserted between the element and the cooling fin, and the shield conductor is connected to the reference potential of the semiconductor element.

[Action]

In this invention, a shield conductor having a structure insulated from the semiconductor element and the cooling fin is inserted between the semiconductor element and the cooling fin, and the shield conductor is connected to the reference potential of the semiconductor element. With such a configuration, the conventional noise countermeasure capacitor becomes unnecessary, and the risk that noise is emitted to the outside due to the frequency characteristic of this capacitor and the inductance of the lead wire can be reduced.

〔Example〕

FIG. 1 is a structural view showing a first embodiment of the present invention.

The noise sources are the MOSFET 2 and the diode 4 as semiconductor elements in the switching regulator shown in FIG. 9, but these semiconductor elements are MOSFE on the metal surface attached to the cooling fin 12 due to their structure.
Since the drain is directly connected to T2 and the cathode is connected to the diode 4, noise is easily emitted to the cooling fin 12.

Therefore, in the first embodiment shown in FIG. 1, the first insulating sheet 21 and the second insulating sheet 22 are inserted between the MOSFET 2 and the cooling fin 12, and the first insulating sheet 21 and the second insulating sheet 22 are further connected. A shield plate 23 connected to the reference potential M1 of the MOSFET 2 is inserted between the two. A fin insulation 13 is provided between the case 14 and the cooling fin 12.

FIG. 2 is an equivalent circuit diagram of the first embodiment shown in FIG. 1, where point A is the potential of the cooling fin 12, point B is the potential of the case 14, and point C is the shield plate 23 of the present invention. It is a potential.

As is apparent from FIG. 2, the noise generated by the noise source 30 is internally processed by the circuit from the point C to the reference potential M1 via the capacitance 41 between the element and the shield plate. The noise emission to the outside is suppressed to a minimum by the path of the capacitance between fins 42 → the capacitance between fins and the case 32 → the case and capacitance between the ground 33.

FIG. 3 is a structural diagram showing a second embodiment of the present invention, and FIG.
The drawing is an equivalent circuit diagram of the second embodiment shown in FIG. In the second embodiment, the insulation between the cooling fin 12 and the case 14 (fin insulation 13 in FIG. 1) is omitted, but as shown in the present invention, the shield plate 23 is used as the cooling fin 12 and the MOSFET 2. Since the structure is insulated from both of them, the structure can be simplified by eliminating the need for double insulation in this way.

FIG. 5 is a block diagram of the present invention applied to the MOSFET used in the switching regulator of FIG. 9, and FIG. 6 is a block diagram of the present invention applied to the diode used in the switching regulator of FIG. However, in FIG. 6, since one anode of the diode is connected to the reference potential M2, this anode and the shield plate can be directly connected.

FIG. 7 is a diagram showing the formation of capacitance between the element and the shield plate by applying the present invention. A first insulating sheet 21 having a thickness of 0.1 to 0.4 mm is provided between the MOSFET 2 and the shield plate 23. It shows that the capacitance 41 between the element and the shield plate of several tens of picofarads is formed by the insertion.

FIG. 8 is a view showing an embodiment of the present invention in which the semiconductor element used in the switching regulator shown in FIG. 9 is mounted on a common cooling fin. The cooling fin 12 and the first insulating sheet 21 are shown in FIG. And the second insulating sheet 22 is MOSFE
The one common to T2 and diode 4 may be used, but MOS
The shield plate for the FET 2 and the shield plate for the diode 4 may be separate, and the shield plate for the MOSFET 2 may be connected to the reference potential M1 and the shield plate for the diode 4 may be connected to the reference potential M2.

[Effect of device]

According to this invention, when a semiconductor element that generates noise is insulated and attached to a cooling fin, a shield conductor insulated from the cooling fin and the semiconductor element is inserted between the semiconductor element and the cooling fin. By configuring the shield conductor to be connected to the reference potential of the semiconductor element, by internally processing the noise generated during the operation of the power conversion device configured by the semiconductor element, the internal processing is performed. Noise can be effectively prevented. Further, it also has an effect that the insulation between the cooling fin and the case can be omitted.

[Brief description of drawings]

FIG. 1 is a structural diagram showing the first embodiment of the present invention, and FIG.
1 is an equivalent circuit diagram of the first embodiment shown in FIG. 1, FIG. 3 is a structural diagram showing a second embodiment of the present invention, and FIG. 4 is an equivalent circuit diagram of the second embodiment shown in FIG. FIG. 5 is a block diagram of the present invention applied to the MOSFET used in the switching regulator of FIG. 9, and FIG. 6 is a block diagram of the present invention applied to the diode used in the switching regulator of FIG. FIG. 7 is a diagram showing the formation of capacitance between the element and the shield plate by applying the present invention, and FIG. 8 is mounting the semiconductor element used in the switching regulator shown in FIG. 9 on a common cooling fin. FIG. 9 is a diagram showing an embodiment of the present invention in the case of the present invention, FIG. 9 is a main circuit connection diagram showing a general configuration of a switching regulator, and FIG. 10 is a semiconductor element mounted on a cooling fin via an insulator. In case of noise prevention, In structural view, FIG. 11 is an equivalent circuit diagram of a conventional structure shown in Figure 10. 1 ... DC power supply, 2 ... MOSFE as semiconductor element
T, 3 ... Transformer, 4 ... Diode as semiconductor element, 5 ... Filter, 11 ... Element insulation, 12 ... Cooling fin, 13 ... Fin insulation, 14 ... Case, 15 ... Noise countermeasure Capacitors, 16,17 …… Inductance, 21 …… First
Insulation sheet, 22 …… Second insulation sheet, 23 …… Shield plate, 30 …… Noise source, 31 …… Element-fin capacitance,
32 …… Fin-case capacitance, 33 …… Case-community capacitance, 41 …… Element-shield plate capacitance, 42…
… Capacitance between shield plate fins.

Claims (1)

[Scope of utility model registration request] 1. A power converter having a structure in which an insulator is interposed between a semiconductor element and a cooling fin that dissipates heat generated by the semiconductor element. Also, a noise prevention circuit for a power conversion device, wherein a shield conductor insulated from the cooling fin is inserted, and the shield conductor is connected to a reference potential of the semiconductor element.