Electricity: electrical systems and devices – Safety and protection of systems and devices – Circuit interruption by thermal sensing
Reexamination Certificate
1997-11-14
2001-03-20
Sherry, Michael J. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Circuit interruption by thermal sensing
C361S101000, C327S512000, C307S117000
Reexamination Certificate
active
06205010
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a switching apparatus having an overcurrent or overheating protection function, using an electric power semiconductor element which controls the ON-OFF switching operation of a load, and also detects an overload and moves to an automatic interruption mode. More particularly the invention relates to a switch circuit having a protection function, which is suited to control turning a lamp or motor of a car ON or OFF.
A conventional switch circuit with a protection function, having a system for detecting an over-current supplied to a load and automatically interrupting it is generally known. Examples in which the system is applied using a MOS-FET switch circuit are described in, for example, Japanese Patent Application Laid-open 61261920, Japanese Patent Application Laid-open 62-11916, Japanese Patent Application Laid-open 62-143450, and Japanese Patent Application Laid-Open 63-87128, and Japanese Patent Application Laid-Open 63-170145.
However, if a lamp using a tungsten or other filament as a load is used, when the switch circuit is turned on so as to light the lamp, a sharp surge of starting current flows. The reason is that before the lamp lights, the resistance of the filament (at a comparatively low temperature) is low; therefore, when the lamp lights, current rises sharply, and decreases thereafter, due to an increase in the resistance. Thus, in the conventional switch system with over-current protection, the protection function is triggered by the starting current, and a normal lighting operation cannot be performed. Even if a motor is used as a load, when power is supplied to the motor, a large current surge occurs, so that the protection function of the switch circuit is activated and a normal motor driving operation cannot be performed.
In another system, the temperature of an electric power element (switch circuit) is detected, and when the power element is overheated more than the predetermined temperature, the protection function is performed. A switch circuit having such a protection function is described in, for example, Japanese Patent Application Laid-open 2-135818t Japanese Patent Application Laid-Open 1-181474, and Japanese Patent Application Laid-open 7-221261. In these switch circuits, even in the case of a current surge when the lamp lights or the motor starts , no unnecessary protection function is performed, because the time response for temperature rise is slow; thus, a normal lamp lighting operation or a motor starting operation can be performed. By contrast, if a malfunction involving a locking of the motor occurs, the temperature rises and the switch circuit is interrupted.
However, in a conventional overcurrent protected switch circuit which uses a temperature detection system, even if overheating is detected when an error occurs, and the switch circuit is therefore properly interrupted, there is a problem that an ON-OFF cycle occurs, in which the protection function is recovered due to a reduction in the temperature, and thereafter the temperature rises again, so that the cycle is repeated.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a switch circuit having a protection function in which the unnecessary ON-OFF cycle is not repeated.
To accomplish the above object, the switch circuit comprises an electric power element for receiving an input control signal via a switch, energizing according to the control signal, and supplying power to a load; a temperature detecting means for detecting the temperature in the neighborhood of this electric power element; and a control means for opening the aforementioned switch and interrupting input of the control signal to the electric power element when the temperature detected by this temperature detecting means is higher than the predetermined temperature. The switch circuit has an interruption status retaining means, for maintaining the interruption of the control signal to the electric power element, so that repetition of the unnecessary ON-OFF cycle can be eliminated.
In one embodiment of the aforementioned switch circuit, the interruption status retaining means is provided in the control means and has a retaining means for retaining an interruption signal outputted to the switch by the control means, so that repetition of the unnecessary ON-OFF cycle can be eliminated.
In another embodiment of the aforementioned switch circuit, the interruption status retaining means is provided in the temperature detecting means and has a retaining means for retaining the maximum temperature detected by the temperature detecting means, so that repetition of the unnecessary ON-OFF cycle can be eliminated.
According to another feature of the invention, the switch circuit has a resetting means for canceling the interruption status of the interruption status retaining means, so that current supply to the load can be restarted. This may be done on the basis of the control signal.
According to another embodiment, the resetting means cancels the interruption status of the interruption status retaining means when the temperature detected by the temperature detecting means reaches a predetermined interruption canceling temperature, so that an unnecessary over-current can be prevented from flowing to the load.
According to another feature of the invention, the switch circuit may have a reset stopping means for preventing the reset of the resetting means when a predetermined time elapses after the control signal inputted to the electric power element enters the interruption state, so that the power consumption can be reduced
According to still another feature of the invention, the switch circuit has an input controller for superposing a reset signal on a signal inputted to the electric power element in a predetermined timing, and sends an output signal of the input controller means to the electric power element. In this manner, even an instantaneous short-circuit of a load can be reset.
In another embodiment of the invention, the input controller superposes the reset signal only during the time when the control signal energizes the electric power element. Alternatively, the input controller means may superpose the reset signal during the whole term of the control signal.
According to yet another feature of the invention, the reset signal may be superposed on the aforementioned signal according to a timing whose interval increases gradually. In this manner, damage by heat generated due to a rush current at the time of short-circuit can be reduced.
In still another embodiment of the invention, the switch changes over the path through which the control signal is supplied to the electric power element and the path for setting the control terminal of the electric power element at the grounding potential, so that the time required to turn the electric power element off can be shortened.
Finally, in yet another embodiment of the invention, the switch changes over the path through which the control signal is supplied to the electric power element, and the path for connecting to the current source for pulling out terminal of the electric power element. In this way, the time required to turn the electric power element off can be shortened.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
REFERENCES:
patent: 4719531 (1988-01-01), Okado et al.
patent: 5162669 (1992-11-01), Hobelsberger
patent: 5485341 (1996-01-01), Okado et al.
patent: 5563759 (1996-10-01), Nadd
patent: 5638021 (1997-06-01), Kaifler et al.
patent: 61-261920 (1986-11-01), None
patent: 62-11916 (1987-01-01), None
patent: 62-143450 (1987-06-01), None
patent: 63-87128 (1988-04-01), None
patent: 63-170145 (1988-07-01), None
patent: 1-181474 (1989-07-01), None
patent: 2-135818 (1990-05-01), None
patent: 7-221261 (1995-08-01), None
Kon'i Mitsuru
Ohsaka Ichiro
Okamoto Kaneyuki
Watanabe Mitsuhiko
Yoshida Tatsuya
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Hitachi , Ltd.
Huynh Kim
Sherry Michael J.
LandOfFree
Switch circuit having protection function to interrupt input... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Switch circuit having protection function to interrupt input..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Switch circuit having protection function to interrupt input... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2465699