Overload protection for controllable current consumers

#This application claims priority from German Patent Application No. 10 2006 008 292.3, which was filed on Feb. 22, 2006, and is incorporated herein by reference in its entirety.

#The present invention relates to protecting a controllable current consumer from too high through-currents.

#In order to ensure perfect functioning of electronical devices, it is important to protect them from overload, i.e. from too high through-currents. A frequent consequence of overload is heating of the electronical device. Using a temperature sensor mounted to the electronical device, overload of the electronical device can be determined. A multi-chip solution including overload protection is described in EP 0208970 A1 and U.S. Pat. No. 4,937,646 and is shown in FIG. 7. In this example, the temperature sensor has been mounted in the form of a thyristor 710 on a field-effect transistor (MOSFET) 720 which in turn is located on a leadframe 730 and comprises a source terminal (S), a gate terminal (G) and a drain terminal (D) (not shown). The thyristor is dimensioned such that it switches on before a critical temperature for the MOSFET of 150 to 180° C. is reached. Thus, the gate source capacitance of the MOSFET is short-circuited and the MOSFET switches off.

#Preferred embodiments of the present invention will be detailed subsequently referring to the appended drawings, in which:

#FIG. 1 is a schematic illustration of an embodiment of the present invention;

#FIG. 2 shows a circuit in which the current consumer is an enhancement MOSFET, and represents a combination of the current-sensitive and temperature-sensitive overload protections;

#The present invention is based on the central idea that an overload case can be determined by a direct current measurement detecting the current through the current consumer and that, should the current detected be above a threshold, the control signal will be altered via feedback such that the current through the current consumer decreases and the current consumer is protected.

#According to an embodiment, the controllable current consumer is a power transistor, such as, for example, an enhancement MOSFET. The overcurrent circuit is integrated along with a temperature sensor, wherein both signals, overtemperature and/or overcurrent, cause a low-resistance connection between the gate terminal and the source terminal of the power transistor such that the current through the current consumer is brought back to the normal range.

#A considerable advantage of the inventive concept compared to conventional ones is that no heating of the current consumer and, consequently, the temperature sensor need occur, but that the cause for the overload of the current consumer is detected directly and immediate feedback to the control signal of the current consumer takes place. In contrast to an overload protection only coming into effect after the current consumer has heated up, time delay is avoided, as a result of finite heat capacitances of both the current consumer and the temperature sensor. Thus, the time in which the current consumer operates outside the normal range is reduced considerably and the result is a more efficient protection from destruction for both the current consumer and neighboring devices. This is of particular advantage in modern power transistors in which the current density may increase very quickly within a short time.