Circuit for the protection of IGFETs from overvoltage

Electrical transmission or interconnection systems – Nonlinear reactor systems – Parametrons

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Details

307363, 307550, 307559, 307577, 340662, 361 56, 361 91, 357 2313, H02H 904, H03K 1716, H03K 3353, H03K 17687

Patent

active

045800634

ABSTRACT:
A pair of IGFETs connected in cascade across a d-c power supply form a source/drain junction constituting the output terminal of a self-biasing amplifier to which binary-coded bipolar signals are transmitted by way of a voltage divider effectively inserted between an input terminal and the afore-mentioned junction, a tap of that voltage divider being connected to the gate of a first of these IGFETs whose source is tied to one of the two supply terminals; the drain and the gate of the second IGFET are tied to the opposite supply terminal. A protective diode lies between the input terminal and the supply terminal connected to the source of the first IGFET so as to be reverse-biased by the voltage divider in a quiescent state and to break down in the presence of an abnormally high input voltage of a given polarity (positive in the specific instance described). An ancillary IGFET connected between the input terminal and the opposite supply terminal has its gate biased at a potential so chosen that this IGFET conducts in the presence of an input voltage of the other (negative) polarity approaching the forward-conduction threshold of the protective diode so as to prevent that threshold from being reached. The voltage divider may terminate at a source/drain junction of another pair of cascaded IGFETs that are identical with the IGFETs of the first pair and are connected in parallel therewith across the supply, the gate of the first IGFET of this other pair being tied to the last-mentioned source/drain junction which is also connected to the gate of the ancillary IGFET so as to bias same to the potential of the input and output terminals in the quiescent state in which the voltage divider is not traversed by any current.

REFERENCES:
patent: 3712995 (1973-01-01), Steudel
patent: 4011467 (1977-03-01), Shimada et al.
patent: 4160923 (1979-07-01), Maeda et al.
patent: 4408245 (1983-10-01), Pryor
patent: 4423431 (1983-12-01), Sasaki
patent: 4449158 (1984-05-01), Taira
patent: 4481521 (1984-11-01), Okumura
patent: 4509067 (1985-04-01), Minami et al.

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