Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Utilizing three or more electrode solid-state device
Reexamination Certificate
2000-07-28
2002-04-09
Nuton, My-Trang (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Utilizing three or more electrode solid-state device
C327S452000, C327S502000
Reexamination Certificate
active
06369640
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the control of bidirectional switches of medium power, such as, for example, triacs.
2. Discussion of the Related Art
A bidirectional switch includes two main terminals A
1
and A
2
and a gate G. A bidirectional switch capable of switching on when a positive or negative voltage exists between terminals A
1
and A
2
and a current pulse—negative or positive—is made to flow between the control terminal and terminal A
1
that will be called the reference terminal. The bidirectional switch then remains conductive until the current flowing therethrough crosses zero.
In many cases, it is desired to only allow a bidirectional switch to turn on when the voltage across its main terminals is close to zero. This type of control is called a zero crossing control circuit although, in fact, it occurs when the voltage across the bidirectional switch is sufficient to enable its turning on, for example about ten volts.
Several known circuits implement this function.
FIG. 1
illustrates such a zero crossing control circuit described in European patent application No. 0837545 which is incorporated herein by reference. A bidirectional switch TR is connected by a main terminal A
2
to a load L, the series connection of load L with bidirectional switch TR being connected across A.C. voltage terminals I
1
, I
2
, for example, the mains. Terminal I
1
is at a reference potential, for example the ground, and is connected to main terminal A
1
, that is, the reference terminal of the bidirectional switch.
Two complementary transistors are connected between gate G and reference terminal A
1
of bidirectional switch TR. These complementary transistors are an NPN-type bipolar transistor Q
1
and a PNP-type bipolar transistor Q
2
. The emitter of transistor Q
1
and the collector of transistor Q
2
are connected to gate G. The collector of transistor Q
1
and the emitter of transistor Q
2
are connected to terminal A
1
of bidirectional switch TR. The bases of transistors Q
1
and Q
2
are connected to each other and to terminal A
2
via a resistor of high value R
1
. The control order is applied between terminals I
3
and I
4
. Terminal
14
is connected to terminal I
1
and forms a reference terminal. Terminal I
3
is connected to gate G via a resistor R
2
. The control order is a signal having a 0-volt value (the potential of terminals I
1
and I
4
) when the bidirectional switch is not desired to turn on and a negative value, for example −5 volts, when the bidirectional is desired to be turned on.
The circuit operates as follows.
When the voltage on terminal I
2
is high, one of transistors Q
1
or Q
2
is controlled to be turned on. Terminals G and A
1
are then short-circuited by one of the transistors and no control current can flow between terminals G and A
1
. Bidirectional switch TR is thus off.
When the voltage on terminal I
2
is smaller than a given threshold, both transistors Q
1
and Q
2
are off and, if the voltage on control terminal I
3
is negative, a current will flow from terminal A
1
to terminal G and will turn bidirectional switch TR on. Thus, the application of a control order (negative voltage) on terminal I
3
can be considered to be delayed until the voltage on terminal A
2
has fallen to a low value with respect to the voltage on terminal A
1
.
Then, bidirectional switch TR will turn off each time the voltage thereacross falls and becomes close to a zero value. The bidirectional switch will then be turned on again at the beginning of the next (positive or negative) halfwave if the control order is still present.
A disadvantage of this type of circuit is the fact that its positive and negative switching thresholds, that is, the voltage difference across transistors Q
1
and Q
2
beyond which one of them is off, are not precisely known. Indeed, these thresholds, on the order of a few volts, typically approximately 10 volts, depend in particular on the value of resistor R
1
and on the gain of the transistors. Now, on the one hand, it is relatively complex to obtain complementary transistors Q
1
and Q
2
with identical gains. On the other hand, the gains of each of the transistors will vary during their lifetime, especially according to temperature. A dispersion of the value of the maximum positive and negative voltages beyond which the bidirectional switch is inhibited can thus be experimentally observed.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel monolithic structure of a zero crossing control circuit for a bidirectional switch that enables stabilizing the value of the voltage beyond which the bidirectional switch is inhibited.
Another object of the present invention is to provide such a monolithic structure in which the positive and negative inhibition thresholds are identical.
Another object of the present invention is to provide monolithic embodiments of such control circuits.
To achieve these and other objects, the present invention provides a monolithic implementation of a zero crossing control circuit of a bidirectional switch including two transistors of complementary types connected in parallel between the gate of the bidirectional switch and the main reference terminal of the bidirectional switch, the gate of the bidirectional switch being connected to a control source via a first resistor, and each of the control terminals of the transistors being connected to the second main terminal of the bidirectional switch via a second resistor of high value, a zener diode being interposed between the second resistor and each of the control terminals according to a biasing adapted to turning on each of the transistors when the zener threshold is exceeded. According to the present invention, the circuit is formed in the same semiconductor substrate of a first conductivity type as the bidirectional switch.
According to an embodiment of the present invention, the control terminals of the transistors are interconnected and the zener diodes are series connected, anode to anode, between the second resistor and the interconnection node of the control terminals.
According to an embodiment of the present invention, the second resistor is formed in the same first portion of the substrate as the bidirectional switch.
According to an embodiment of the present invention, the zener diodes are formed on the front surface side of the substrate in a layer of the second conductivity type, including, on the front surface side, two regions of the first conductivity type contacted by metallizations, and a region being formed, by deep diffusion from the front surface, under and in contact with the layer.
According to an embodiment of the present invention, a first zener diode is formed in the same portion of the substrate as one of the complementary transistors.
According to an embodiment of the present invention, a second zener diode is formed in a portion of the substrate distinct from a portion where the second transistor is formed.
According to an embodiment of the present invention, a second zener diode is formed in a same portion of the substrate as the second transistor.
According to an embodiment of the present invention, the two complementary transistors are of bipolar type.
According to an embodiment of the present invention, the two complementary transistors are of MOS type.
The foregoing objects, features and advantages of the present invention, will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings.
REFERENCES:
patent: 3743860 (1973-07-01), Rossell
patent: 3883782 (1975-05-01), Beckwith
patent: 3902080 (1975-08-01), St. Clair et al.
patent: 4051394 (1977-09-01), Tieden
patent: 4535251 (1985-08-01), Herman et al.
patent: 4876498 (1989-10-01), Luchaco et al.
patent: 5668496 (1997-09-01), Rebordosa
patent: 5686857 (1997-11-01), Heminger et al.
patent: 5838555 (1998-11-01), Lejeune et al.
patent: 5914628 (1999-06-01), Rault
patent: 25 59 564 (1977-05-01), None
French Search R
Duclos Franck
Ladiray Olivier
Simonnet Jean-Michel
Morris James H.
Nuton My-Trang
STMicroelectronics S.A.
Wolf Greenfield & Sacks P.C.
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