Electricity: electrical systems and devices – Safety and protection of systems and devices – Circuit interruption by thermal sensing
Patent
1999-08-18
2000-04-18
Sherry, Michael J.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Circuit interruption by thermal sensing
361 938, H02H 504
Patent
active
060522682
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electrical apparatus of the kind including a semiconductor switching device, an arrangement that derives a measure of power dissipated by said device, a sensor that provides a measure of the temperature in the vicinity of the device, and means to restrict flow of current through the device in response to a combination of the measure of power and the measure of temperature.
The usual way of protecting electrical equipment and its wiring from current overloads is by means of an electromagnetic relay switch, thermal wire fuse or electrothermal circuit breaker. These previous arrangements, however, are usually relatively heavy and bulky. They also have a slow response time and can be unreliable in the long term. Because of this, there is a move towards using solid state power controllers (SSPC) employing power semiconductors, to switch electrical energy to a load and to interrupt current flow should an overload be detected.
The advantages of solid state controllers over electromechanical counterparts are well recognised and typically include factors such as reduced weight, reduced time to respond, increased lifetime and increased reliability.
Despite these advantages, using power semiconductors in such a role does require a great deal of care because of the adverse effect of high temperatures on semiconductor devices. The maximum temperature for devices made of silicon is about 175.degree. C. and for semiconductors made of silicon carbide it is about 400.degree. C. In current limiting SSPC's, the power density within each die may exceed 500 W for short periods, resulting in rapid heating of the die and surrounding area.
In U.S. Pat. No. 4,937,697 there is described a circuit for protecting an FET device. The circuit employs a reference circuit to provide an indication of temperature of the device so that increased current can be supplied to the device when it has a low temperature.
It is an object of the present invention to provide apparatus for use in power switching and a method of controlling switching of a circuit protection device.
According to one aspect of the present invention there is provided electrical apparatus of the above-specified kind, characterised in that the apparatus includes a processor that calculates the resultant heat gain and heat loss of the semiconductor device over a period of time at a plurality of different nodes within the device, that the processor calculates the temperature of the device at a plurality of different nodes in the device at the end of that time, and that the apparatus restricts flow of current through the device if the calculated temperature of the node with the highest calculated temperature exceeds a predetermined temperature.
The apparatus preferably restricts current flow through the device by opening the device. The semiconductor switching device preferably comprises a semiconductor die mounted on one side of a substrate, the temperature sensor being mounted on the opposite side of the substrate
According to another aspect of the present invention there is provided a method of protecting a semiconductor circuit protection device comprising the steps of measuring the temperature in the vicinity of the device, determining the power dissipated by the device, determining the temperature of the semiconductor device from the power dissipated by the device and the measured temperature in the vicinity of the device, comparing the determined temperature with a maximum permitted temperature, and restricting current flow through device if the maximum permitted temperature is exceeded, characterised in that the resultant heat gain and heat loss of the semiconductor device is calculated over a period of time at a plurality of different nodes within the device, that the temperature of the device at a plurality of different nodes in the device is calculated at the end of that time, and that the flow of current through the device is restricted if the calculated temperature of the node with the highest calculated temperature exceeds a predetermined
REFERENCES:
patent: 4727450 (1988-02-01), Fachinetti et al.
patent: 5854731 (1998-12-01), Thomas
Sherry Michael J.
Smiths Industries Public Limited Company
LandOfFree
Electrical apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrical apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrical apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2341262