Electricity: electrical systems and devices – Safety and protection of systems and devices – Reverse phase responsive
Patent
1991-12-12
1994-09-20
Pellinen, A. D.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Reverse phase responsive
361 58, 361 88, 320 25, H02H 900
Patent
active
053494890
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a circuit comprising an integrated semiconductor circuit and a protection circuit, which integrated semiconductor circuit comprises a number of components provided on a substrate, which components are each surrounded by a region of a particular conductivity type, and which integrated semiconductor circuit is provided with at least two supply voltage connection terminals and a connection terminal which is coupled to the region of a particular conductivity type.
Integrated semiconductor circuits whose components are manufactured, for example, with the aid of an epitaxial procedure are generally known and are also used on a large scale because the epitaxial procedure is simple, satisfactorily reproducible and cheap.
If the components are epitaxial n-p-n transistors, the region of a particular conductivity type which surrounds an n-p-n transistor is a p-type substrate. An integrated circuit of this type contains a parasitic p-n-p transistor formed by the p-type base, the n-type collector and the p-type substrate. This transistor should always be kept in the off-state in order to be able to guarantee the normal operation of the circuit and because such high currents are otherwise able to flow that one or more p-n junctions break down, which generally means that the integrated circuit has become unusable. For this purpose, it is known to connect the substrate to the most negative voltage in the circuit.
A problem arises, however, if the supply voltage of the integrated circuit is accidentally incorrectly connected, i.e. the positive terminal of the circuit is connected to the negative terminal of the supply source and the negative terminal of the circuit to the positive terminal of the supply source. The substrate is then suddenly connected to the most positive voltage in the circuit and the parasitic p-n-p transistor may be turned on completely, which will result in such high currents that the circuit becomes unserviceable.
Diverse solutions have already been proposed for this problem. Thus, it is possible to include in the integrated circuit a bridge circuit comprising four diodes between the external supply voltage terminals and the internal supply voltage terminals for the circuit, which makes it possible to guarantee at all times a correct polarity for the circuit and therefore also for the substrate regardless of the polarity of the supply voltage connected, with the result that the circuit will function in the correct manner at all times. It is also possible to include, between an external and an internal supply voltage terminals, a single diode which only conducts if the supply voltage is connected in the correct manner, with the result that although the circuit does not function if a supply voltage having an incorrect polarity is connected, it is also unable to become unserviceable.
A drawback of each of these solutions is that a voltage drop of approximately 0.6 V always occurs over a diode in the conducting state. If, therefore, the external supply voltage is relatively low, for example a battery supply of 1.5 to 2 V, said voltage drop is so large that the actual supply voltage for the circuit, 0.9 to 1.4 V, is too low to make satisfactory functioning possible. In particular, this relatively high voltage drop is disadvantageous if a circuit which is supplied is a high-voltage supply circuit in which use is made of, for example, a diode ladder for the voltage multiplication. The practically achievable high voltage will then be lower by the same amount with respect to the maximum possible high voltage than the actual supply voltage with respect to the supply voltage delivered by the supply source, such as a battery.
The object of the invention is to offer a solution for this problem as a result of which, even with relatively low external supply voltages, an incorrect polarity of the supply voltage source connected to an integrated circuit cannot result in said circuit becoming unserviceable, without the value of the external supply voltage and the value of the supply voltage act
REFERENCES:
patent: 3593101 (1971-07-01), Wassink
patent: 3829709 (1974-08-01), Maigret et al.
B.V. Optische Industrie "De Oude Delft"
Jackson S.
Marn Louis E.
Pellinen A. D.
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