Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
1999-06-22
2001-01-30
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S543000, C327S538000, C327S427000, C361S093500
Reexamination Certificate
active
06181186
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device in which a protection circuit is added to power semiconductor elements such as power MOSFET, IGBT, and so forth.
DESCRIPTION OF THE PRIOR ART
Formerly, for instance, a protection circuit of the semiconductor device disclosed in the Japanese Patent Application Laid-Open No. HEI 3-238869 is known, and a circuit diagram of the protection circuit is shown in FIG.
1
. In this circuit, when a potential of a drain of both of a MOSFET Q
1
and a MOSFET Q
2
is increased while short-circuiting a load connected in between a drain terminal D and a power terminal which is not illustrated, a voltage to be larger than a voltage generated normally is generated in the resistors R
20
and R
30
which are connected to the MOSFET Q
2
. When this voltage value reaches a threshold voltage value of the MOSFET Q
3
, the MOSFET Q
3
turns on to decrease a gate voltage of the MOSFET Q
1
, and the MOSFET Q
2
, thus it is capable of controlling a current of the MOSFET Q
1
.
However, in this semiconductor device, since the gate of both of the MOSFET Q
1
and the MOSFET Q
2
is common, in case where the load is short-circuited, the voltage generated in the resistor is increased, thus a gate voltage of both of the MOSFET Q
1
and the MOSFET Q
2
is decreased. Then, also the drain current of the MOSFET Q
2
is reduced, thus the voltage generated in the resistor is decreased, with the result that this causes the gate voltage of the MOSFET Q
1
and the MOSFET Q
2
to increase again to render the drain current large again. This operation is repeated to the state where the drain current converges on a certain fixed value.
There was the problem that the semiconductor device is destroyed caused by the large current flowing therethrough until the drain current converges according to an operation condition of the semiconductor device or a condition of a short circuit of the load.
Further, since there is scarcely voltage drop due to the load at the time of a short circuit of the load, so a power voltage is directory applied between drain/source of the MOSFET Q
1
, even though the drain current is restricted, at the time point, the electric power consumed by the semiconductor device is large, therefore there was the problem that the semiconductor device is destroyed by heat if the heat resistance is not reduced by increase of the chip size or substituting the large type package therefor.
As the method for achieving such defect, the feedback circuit is added in such a way that it detects state of the load and state of input voltage, causing gate voltage to be reset in connection with the first MOSFET Q
1
and the second MOSFET Q
2
. Such method is disclosed in NIKKEI ELECTRONICS (1986, 7, 28 P. 144, 145). However, there was the problem that in order to newly form the feedback circuit which consists of latch, an operation amplifier, a reference voltage, it becomes necessary to re-investigate the manufacturing process of the semiconductor, and space for layout increases, and cost up occurs.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention, in order to overcome the above-mentioned problems, to provide a semiconductor device in which it becomes unnecessary to re-investigate the manufacturing process of the semiconductor, and space for layout does not increase, and cost up does not occur, in such a way that the semiconductor device causes semiconductor element to be turned off at the time of short circuit of the load to protect the semiconductor element from the short circuit of the load.
According to a first aspect of the present invention in order to achieve the above mentioned object, there is provided a semiconductor device which comprises a first switching means for turning on/off a current flowing into a load, a current detector for detecting the current flowing into the load, a second switching means for switching on/off a connection between the current detector and the load, and a controller for controlling the second switching means and the first switching means, wherein the controller, at a time when the load starts driving, turns on the first switching means, before turns on the second switching means, and the current detector turns off only the first switching means when detecting an excess current.
According to a second aspect of the present invention, in the first aspect, there is provided a semiconductor device, wherein the first switching means and the second switching means are transistors, the current detector is a resistor provided in between the second switching means and a ground point, and the controller consists of a control terminal provided at an input line of the first switching means, resistors connected to the control terminal, and latch for inputting a signal from an intermediate point of said resistors and outputting a control signal to an input line of the second switching means.
According to a third aspect of the present invention, in the second aspect, there is provided a semiconductor device, wherein the first switching means and the second switching means are MOSFETs.
According to a fourth aspect of the present invention, in the second aspect, there is provided a semiconductor device, wherein the first switching means and the second switching means are IGBTs.
According to a fifth aspect of the present invention, in the third aspect, there is provided a semiconductor device, wherein the current detector is depletion type MOSFET whose gate and source are short-circuited.
According to a sixth aspect of the present invention, in any one of the first aspect to the fifth aspect, there is provided a semiconductor device, wherein the semiconductor device is formed within an identical semiconductor.
According to a seventh aspect of the present invention, in any one of the first aspect to the sixth aspect, there is provided a semiconductor device, wherein serially connected in between an input terminal and an output terminal of the first switching means are a clamping diode for clamping a potential of the output terminal of the first switching means, and a reverse-current prevention diode for preventing a current flowing from the input terminal of the switching means towards the output terminal of the same.
According to an eighth aspect of the present invention, in the seventh aspect, there is provided a semiconductor device, wherein the clamping diode is a voltage regulation diode with guard ring structure.
According to a ninth aspect of the present invention, in the seventh aspect or in the eighth aspect, wherein the reverse-current prevention diode is formed by a polycrystal semiconductor over an insulating film.
According to a tenth aspect of the present invention, in any one of the first aspect to the sixth aspect, there is provided a semiconductor device, wherein a bidirectional voltage regulation diode is connected in between the input terminal and the output terminal of the first switching means.
According to an eleventh aspect of the present invention, in the tenth aspect, there is provided a semiconductor device as claimed in claim
32
, wherein the bidirectional voltage regulation diode is formed by a polycrystal semiconductor over an insulating film.
REFERENCES:
patent: 5008586 (1991-04-01), Miyazaki et al.
patent: 5369308 (1994-11-01), Schoofs et al.
patent: 5422593 (1995-06-01), Fujihara
patent: 5541799 (1996-07-01), Schmidt et al.
patent: 5621601 (1997-04-01), Fujihara et al.
patent: 5789971 (1998-08-01), Colletti et al.
patent: 5796278 (1998-08-01), Osborn et al.
patent: 5801573 (1998-09-01), Kelly et al.
patent: 3-238869 (1991-10-01), None
Nikkei Electronics, “MOSFET”, (Jul. 28, 1986), pp. 144-145.
Arai Takao
Itoh Yukio
Callahan Timothy P.
NEC Corporation
Nguyen Hai L.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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