GB2246013A

GB2246013A - "cooling solid state switches"

Info

Publication number: GB2246013A
Application number: GB9014848A
Authority: GB
Inventors: Malcolm Kirby Addy
Original assignee: SAVAWATT
Current assignee: SAVAWATT
Priority date: 1990-07-04
Filing date: 1990-07-04
Publication date: 1992-01-15
Also published as: WO1992001361A1; GB9014848D0; AU8102691A

Abstract

An electrical circuit within a plug has a solid state switch (5) which generates heat during operation of the circuit. A thermal connection is made between the solid state switch (5) and at least one pin (2, 3) of the plug. Heat generated by the switch (5) is conducted out of the plug housing (1) through the pin (2, 3). There may be a direct connection between the pin (2, 3) and switch (5) or the connection may be made via a heat conducting path (9).

Description

HEAT SINKING SOLID STATE SWITCHES The present invention relates to an electrical circuit, in particular a circuit incorporating a solid state switch and a heat sink.

Solid state switches (e.g. triacs, silicon controlled rectifiers, etc.) produce heat during operation. The generated heat is minimal during intermittent switching but increases with frequency. Such devices when used to control power levels of, say, one ampere upwards on a repetitive basis, for example at 50/60 Hertz on 220/240 volt mains power supplies, produce significant heat. The reliability of such devices is dependent on removing the generated heat quickly and effectively to maintain the device at a temperature well below its break-down temperature. Any breakdown at elevated temperature can lead to safety considerations such as loss of electrical safety, integrity, or conflagration.

Such characteristics are well known and such devices are normally provided with a heat sink to dissipate the heat. Heat sinks are commonly metal plates or extrusions to which the solid state devices are firmly attached, or clip-on heat sinks.

The difficulty occurs in particular in the cases where the controller using the solid state switch is miniaturised and/or is required to meet stringent specifications for safety integrity. This is particularly the case when controllers are miniaturised and enclosed for domestic use which also requires them to meet stringent safety specifications. In such cases the small enclosure makes clip-on or other internal heat sinks ineffective particularly as for safety reasons the enclosure cannot be vented to allow convection or forced draught cooling. External heat sinks, the alternative, are frequently unacceptable for aesthetic reasons as well as the difficulties in ensuring adequate electrical isolation integrity in the event of failure.

It is the object of the present invention to obviate or mitigate the above problems.

According to the present invention there is provided an electrical circuit comprising a solid state switch mounted in a housing from which pins or male contacts extend, the pins being adapted for insertion into an electrical socket or female contacts to make connection with power supply connections connected to the socket, wherein said at least one solid state switch is mounted into the housing in thermal contact with at least one of the pins such that heat generated by the switch is conducted out of the housing through said pin.

Preferably said solid state switch is connected directly to said at least one pin.

Alternatively said solid state switch is connected to said at least one pin via a heat conducting path.

Preferably said solid state switch is connected to an earth pin.

Alternatively said solid state switch is connected to a live or neutral pin.

Specific embodiments of the invention will now be described by way of example with reference to the following drawings in which: Figure 1 is an internal view of a first plug connector embodying the invention; and Figure 2 is an internal view of a second plug connector embodying the invention.

Referring to figure 1 there is shown a plug having an enclosure 1 (shown dotted) and three connecting pins (two only shown) an earth pin 2, a live pin 3 and a neutral pin (not shown). This could be, for example, a B.S.1363 3-pin plug for connection to a power supply socket (not shown). Inside the enclosure 1 each pin 2, 3 is connected to a controller circuit board 4 which could be a printed circuit board or an etched silicon substrate. The circuit board 4 is connected at right angles to the pins 2, 3.

On the reverse face of the circuit board 4 there are mounted a solid state switch 5 and three connector tabs 6, 7, 8. Each connector tab is in electrical connection with one of the pins 2, 3. In the embodiment of figure 1 the solid state switch 5 is connected to connector tab 6 corresponding to the earth pin 2. Connector tab 6 is indirectly attached to the earth pin 2 via an element 9 having three right-angled bends. The element 9 provides for an isolated heat and electrical conduction path from the earth pin 2 to the connector tab 6 thus serving to dissipate heat.

Figure 2 shows an alternative embodiment wherein the solid state switch 5 is connected to the live or neutral pin 3 by an attachment 10. In this case the solid state switch 5 is non-isolated.

Connector tab 6 is connected directly to the circuit board 4. In this case the live or neutral plug pin 3 and the respective connector tab 7 or 8 provide a heat sink.

Depending on the configuration of the solid state switch 5 and the plug and/or socket, the solid state switch 5 may be connected to either the earth pin 2, the live pin 3 or the neutral pin or to a combination of any two, or the three.

In the case of the solid state switch 5 having an isolated heat sink connection, the solid state switch 5 is firmly attached to the earth pin 2. In the case of the solid state switch 5 having a nonisolated heat sink connection, the solid state switch 5 is firmly attached to the live 3 or neutral pin (or via an appropriate conducting path). In certain controller configurations it may be possible to connect a plurality of the solid state switch heat sink connections to different pins, or via appropriate heat conducting paths, for example an etched it is to be appreciated that the solid state switch could be etched, wholly or partly on to a silicon substrate supporting the solid state switches 5.

In the event of failure of the solid state switch 5 or associated components a high degree of electrical safety is provided. In particular when an isolated solid state switch 5 is connected to the earth pin 2 either directly or via a heat and electrical conductive path, any failure of the switch insulation will result in a most direct path to earth, considerably minimising risk of secondary safety hazard such as conflagration.

It is to be appreciated that the heat and/or electrical conducting path can be to an output socket or connections, or to both the input plug or connections and the corresponding output socket or connections.

Claims

1. An electrical circuit comprising a solid state switch mounted in a housing from which pins or male contacts extend, the pins being adapted for insertion into an electrical socket or female contacts to make connection with power supply connections connected to the socket, wherein said at least one solid state switch is mounted into the housing in thermal contact with at least one of the pins such that heat generated by the switch is conducted out of the housing through said pin.

2. An electrical circuit according to claim 1 wherein said solid state switch is connected directly to said at least one pin.

3. An electrical circuit according to claim 1 wherein said solid state switch is connected to said at least one pin via a heat conducting path.

4. An electrical circuit according to claims 2 or 3 wherein said solid state switch is connected to an earth pin.

5. An electrical circuit according to claims 2 or 3 wherein said solid state switch is connected to a live or neutral pin.

6. An electrical circuit as hereinbefore described with reference to the accompanying drawings.