Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific current responsive fault sensor
Patent
1995-10-20
1997-12-09
Gaffin, Jeffrey A.
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific current responsive fault sensor
361111, H02H 322
Patent
active
056966598
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an overcurrent protective circuit and semiconductor for protecting a load circuit from overcurrent, which can be easily connected in series to the load circuit in the same way as a fuse and a breaker and which can also be controlled in a quick or a delayed manner depending on the characteristic of the load circuit.
2. Discussion of the Related Art
Hitherto, as means for protecting the load circuit which is connected in series thereto, a fuse and a breaker have been used. The fuse acts to cut off the overcurrent by a fusing action due to the overcurrent flow, so that on all such occasions changing the fuse is needed. The fusing speed is not sufficient to protect the latest electronic circuit. On the other hand, the breaker has a slow cut-off speed, so that the breaker is not used for a circuit requiring quick action.
Further, the fuse and the breaker have a problem that a rush current on switching flows into the load circuit and an overcurrent flows through the load circuit for a short time, which gives stress and degradation to normal circuit elements, resulting in breakdown of the load circuit.
SUMMARY OF THE INVENTION
Accordingly, a first object of the present invention is to provide an overcurrent protective circuit or semiconductor circuit which can be connected in series to the load circuit in the same easy way as the fuse and the breaker and which need not be changed every time the overcurrent flows and which has a cut-off characteristic or speed that can be adjusted depending on the load circuit to protect the latest electronic circuit.
Further, a second object of the present invention is to provide an overcurrent protective circuit or semiconductor circuit in which in a case that a rush current flows, the rush current is suppressed to approximately 1.5 to 2 times the stationary current until the rush current state from supplying power is terminated and after that, the stationary current can be made to flow. In a case that an overcurrent flows, the overcurrent is suppressed to approximately 1.5 to 2 times of the stationary current for a short permissible time of the load circuit and after that, the stationary current can be made to flow. However, in the case that the state of overcurrent flow is still continuing after that, the overcurrent is made to be cut-off.
Furthermore, a third object of the present invention is to provide an AC-type overcurrent protective circuit or semiconductor circuit designed to cut-off the alternating overcurrent by symmetrical arrangement of the first objective overcurrent protective circuit.
According to a first aspect of the present invention, there is provided an overcurrent protective circuit (hereinafter referred to as a first overcurrent protective current) which comprises a first N-type depletion MOS (hereinafter referred to as N-type DMOS) which drain is a positive outer terminal of the circuit and a first P-type depletion MOS (hereinafter referred to as P-type DMOS) which drain is a negative outer terminal of the circuit. The source of the N-type DMOS is connected to the source of the P-type DMOS, the gate of the N-type DMOS is connected to the drain of the P-type DMOS through a resistor or the like and the gate of the P-type DMOS is connected to the drain of the N-type DMOS through a resistor or the like.
In the first overcurrent protective circuit, when an overcurrent flows in a way that the drain of the first N-type DMOS is positive while the drain of the first P-type DMOS is negative, the overcurrent increases the potential difference of the N-type DMOS and the P-type DMOS, which causes the gate voltage of the N-type DMOS and the P-type DMOS to increase. Further, the increased gate voltage of the N-type DMOS and the P-type DMOS makes the potential difference of the N-type DMOS and the P-type DMOS increase further in a repeat manner, resulting in cut-off of the overcurrent, since the potential difference of the P-type DMOS becomes the gate voltage of the N-type DMOS whi
REFERENCES:
patent: 3916220 (1975-10-01), Roveti
patent: 4533970 (1985-08-01), Brown
patent: 5115369 (1992-05-01), Robb et al.
patent: 5319515 (1994-06-01), Pryor et al.
Gaffin Jeffrey A.
Sherry Michael J.
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