Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Utilizing three or more electrode solid-state device
Reexamination Certificate
1999-08-17
2001-06-26
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Utilizing three or more electrode solid-state device
Reexamination Certificate
active
06252451
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to the field of switches, and more specifically to the making of switches adapted to switching a circuit connected to the mains in a way compatible with present standards relative to electromagnetic disturbances.
2. Discussion of the Related Art
To switch a high mains voltage, thyristor-type switches which are normally off (which have to be controlled to be turned on) or assemblies which are normally on (which have to be controlled to be turned off) are currently used. The turn-on or turn-off control of these switches creates a strong current variation during a very short time interval. This abrupt variation is likely to cause electromagnetic disturbances in neighboring equipment.
FIG. 1
illustrates an example of normally-on switch assembly. It is desired herein to control the supply of a load
1
intended for receiving part of the power that an A.C. supply voltage source Vac, for example the mains voltage, applied between two terminals
2
,
3
, can provide. The power provided to load
1
is controlled by a switching circuit
4
. Circuit
4
includes a switch
5
and a control circuit
6
. Switch
5
is a gate turn-off thyristor (GTO), provided with anode and cathode gates which are interconnected by a resistor R
1
.
FIG. 2
shows the shape of current I in the load as a function of time. Due to the presence of resistor R
1
, the GTO thyristor naturally turns on at the beginning of each positive halfwave of voltage Vac (times t1). Circuit
6
is meant to turn off the GTO thyristor when supply voltage Vac reaches a predetermined level. In the illustrated example, circuit
6
includes a reference diode or avalanche diode Z, the cathode of which is connected to the midpoint of a resistor bridge R
2
, R
3
. The values of resistors R
2
, R
3
are chosen so that diode Z starts an avalanche when voltage Vac reaches the level at which the supply of load
1
is desired to be interrupted. Between the cathode gate of the GTO thyristor and terminal
3
is connected a switch
7
, for example a thyristor, which turns on when diode Z becomes conductive, after which switch
5
turns off (time t2) and the current through the load abruptly drops to zero, as illustrated in
FIG. 2
in dotted lines. Then, the current remains at zero until the beginning of the next positive halfwave where this sequence is repeated.
As mentioned previously, the abrupt variation of the current on the supply line at times t2 can cause electromagnetic disturbances.
To solve this problem, a low-pass filter
8
is conventional provided between each of terminals
2
,
3
, and circuit
4
. Filter
8
includes, for example, inductors L
1
and L
2
and a capacitor C. A first end of each of inductors L
1
, L
2
is connected to one of the respective terminals
2
,
3
. The second ends of inductors L
1
and L
2
are interconnected by capacitor C and are respectively connected to the terminals of the series circuit including the GTO thyristor and load
1
. For a
1
-A switched current, the values of inductors L
1
, L
2
typically are on the order of 150 &mgr;H, and the capacitance of capacitor C typically is 470 nF. A disadvantage of this type of conventional solution is that such a filter
8
is bulky, non-integrable and expensive.
SUMMARY OF THE INVENTION
The present invention aims at providing a novel switching circuit which can be used without any filter.
The present invention also aims at providing such a switching circuit which is essentially realizable in the form of a monolithic component.
To achieve these and other objects, the present invention provides a switching circuit of the type including a gate turn-off thyristor biased to be normally on, further including, between the gate and a supply line, a capacitor and a controllable switch connected in parallel.
According to an embodiment of the present invention, the controllable switch is a bipolar transistor.
According to an embodiment of the present invention, the anode and cathode gates of the thyristor are interconnected via a resistor.
According to an embodiment of the present invention, a control terminal of the switch is connected to the anode of a reference diode, the cathode of which is connected to the midpoint of a resistor bridge.
The present invention also provides a bidirectional switching circuit formed of the antiparallel association of two switching circuits according to any of the preceding embodiments.
The present invention also provides a switching circuit made in monolithic form in a semiconductor substrate of a first conductivity type including first and second areas defined by first and second insulating walls, the first area including the thyristor made in lateral form, its cathode gate being connected to the first wall, and including the resistor bridge; the second area including the switch and the diode, the switch being a vertically-formed bipolar transistor; and the rear surface of the first area being coated with an insulating layer which lets free at least a portion of the rear surface of the first wall, a metallization covering the entire rear surface and ensuring with the first insulating wall a connection between the thyristor cathode gate and the transistor collector.
According to an embodiment of the present invention, the switching circuit made in monolithic form includes on the N-type upper surface side of the substrate:
in the first area:
a first heavily-doped P-type anode region covered with a first metallization;
a second heavily-doped N-type cathode region covered with a second metallization;
a third heavily-doped N-type region, coated with a third metallization and in contact with the substrate, corresponding to the anode gate;
a fourth heavily-doped P-type cathode gate region, in contact with the first insulating wall;
a fifth heavily-doped P-type region, in short-circuit, through the third metallization, with the third region, and in contact with a sixth lightly-doped P-type region, the sixth region further being in contact with the fourth region and forming a resistor between the anode and cathode gates;
lightly-doped P-type regions, the ends of which form one piece with heavily-doped P-type regions coated with respective metallizations, one of the metallizations short-circuiting a P-type region, corresponding to one of the resistors of the resistor bridge, and a heavily-doped N-type region; and
in the second region:
a lightly-doped P-type well, forming the base of the transistor, in which are formed heavily-doped N-type regions, covered with respective metallizations, corresponding to the emitter of the transistor and to the cathode of the diode; and
on the rear surface side of the substrate, a heavily-doped N-type region forming the collector of the transistor.
According to an embodiment of the present invention, the second area includes on the upper surface side a heavily-doped N-type channel stop ring at the periphery of the well, the ring being covered with a metallization.
The present invention also provides a switching circuit made in monolithic form in a semiconductor substrate of a first conductivity type including first and second areas defined by insulating walls; the first area including the thyristor made in lateral form and the resistor bridge; the second area including the switch and the diode, the switch being a laterally-formed bipolar transistor; the connection between the thyristor cathode gate and the transistor collector being made on the front surface side.
According to an embodiment of the present invention, the switching circuit made in monolithic form includes on the N-type upper surface side of the substrate:
in the first area:
a first heavily-doped P-type anode region covered with a first metallization;
a second heavily-doped N-type cathode region covered with a second metallization;
a third heavily-doped N-type region, coated with a third metallization and in contact with the substrate, corresponding to the anode gate;
a fourth heavily-doped P-type cathode gate region, separated from the first insulatin
Guitton Fabrice
Ladiray Olivier
Magnon Didier
Simonnet Jean-Michel
Galanthay Theodore E.
Morris James H.
STMicroelectronics S.A.
Tran Toan
Wolf Greenfield & Sacks P.C.
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