Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Utilizing three or more electrode solid-state device
Reexamination Certificate
2000-12-20
2003-04-01
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Utilizing three or more electrode solid-state device
C327S453000, C327S447000
Reexamination Certificate
active
06542022
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the pulse control (repetitive or single-shot) of one or several MOS-type switches or the like. The present invention more specifically relates to a voltage pulse generator to control such switches. In the present description, a “MOS switch or the like” designates any switch to be controlled by a voltage level such as, for example, MOS transistors or IGBTs. The present invention more specifically relates to the control of such switches used in the field of power regulation to control the operation of industrial or household equipment. In such a field, power semiconductor components switched to effect a so-called conduction angle control (or phase control) in which a power switch is only turned on for a portion of the duration of each halfwave or of one halfwave out of two of the supply voltage are often used. Such systems are currently used in the field of domestic lighting to form light dimmers, and in many other applications to provide power controllers.
2. Discussion of the Related Art
Power regulation by conduction angle control has the well-known disadvantage of generating, on the mains, harmonics due to the fact that the switch (for example, a triac) is turned on when a relatively high voltage is present thereacross. The harmonics cause electromagnetic disturbances and are a major problem. Various standards have been developed to require the manufacturer to avoid generating such disturbances. A simple way of avoiding the reinjection of harmonics on the mains consists of filtering them out. However, adding a passive filter to a controller is a serious handicap in terms of bulk, weight, and cost. To avoid this filter, it has also been envisaged to basically tackle the problem, by controlling the current variation speed (di/dt) upon switchings. Unfortunately, neither thyristors, nor triacs—which are ideal components for fabricating a variator due to their robustness, to their immunity against overcharges, to their switching ease and to their low on-state dissipated power—allow control of di/dt.
FIG. 1
shows an example of a power switch with a controlled di/dt of the type to which the present invention more specifically applies. Such a circuit, preferably monolithic, includes two power components A and K and two control terminals G
1
and G
2
. Switch
1
includes the parallel assembly of a MOS or IGBT-type component
2
and of a thyristor-type component
3
, and means for inhibiting the thyristor-type component during a turn-on phase of the switch that is ensured by the IGBT-type component
2
. IGBT power transistor
2
and power thyristor
3
are connected in parallel between terminals A and K. The anode of thyristor
3
and the collector of IGBT
2
are connected to anode A. The cathode of thyristor
3
and the IGBT emitter are connected to cathode K. In the embodiment of
FIG. 1
, a diode D is connected in antiparallel to thyristor
3
between terminals A and K. IGBT
2
is connected to a first control terminal G
1
by its gate. The control of thyristor
3
is ensured by a high-voltage MOS transistor
4
(or by a second IGBT) connected between the anode of thyristor
3
and its gate. The source of high-voltage transistor
4
is connected to cathode K via a low-voltage MOS transistor M, the gate of which is connected to a second control terminal G
2
. The gate of transistor
4
is, preferably, connected to terminal G
1
. Alternatively, an impedance may be provided between the gates of transistors
2
and
4
, or individualized signals may be provided for each of transistors
2
,
4
, and M.
Switch
1
of
FIG. 1
is a one-way component. Thus, two switches of this type must be used in series-opposition to obtain a fullwave power controller. For example, the terminal A of a first switch
1
such as shown in
FIG. 1
is connected to a first terminal of a load to be supplied, the other terminal of which is connected to a first mains voltage application terminal. The other mains voltage application terminal is then connected to the terminal A of a second switch
1
, the terminal K of which is connected to terminal K of the first switch.
The operation of the circuit of
FIG. 1
will be explained in relation with
FIGS. 2A
to
2
C that respectively show, in the form of timing diagrams, voltage V
g2
on gate G
2
, voltage V
g1
on gate G
1
, and current I
AK
between anode A and cathode K of switch
1
of
FIG. 1. A
positive halfvave of voltage V
AK
between terminals A and K is considered. At a time tl, included in the first half of a halfwave of the mains voltage according to the desired conduction angle, gate G
2
of transistor M is controlled to turn on transistor M, so that the gate and the cathode of thyristor
3
are short-circuited and that this thyristor cannot be turned on. At a time t
2
, subsequent to time t
1
and also chosen according to the desired conduction angle, a voltage ramp having its slope controlled to obtain the desired di/dt is applied to gate G
1
of IGBT
2
. This ramp results for example from the application of a square or pulse signal through a fixed or variable impedance (of low power since it is a control signal), for example, a resistor or an RC filter. As soon as the voltage on terminal G
1
exceeds a threshold value V
th
, current I
AK
starts progressively increasing to reach a value depending on the mains voltage and on the impedance of the load at this time. Then, at a time t
3
, the signal on gate G
2
is cut off to turn off transistor M. Since transistor
4
has been turned on by the ramp applied on gate G
1
and on its own gate, the current flowing through transistor
4
triggers thyristor
3
. Thyristor
3
turns on and its conduction is predominant over that of IGBT
2
since, generally, a thyristor exhibits a lower voltage drop than a MOS or IGBT power transistor. Then, at a time t
4
, the signal on gate G
1
is cut off, so that IGBT
2
and transistor
4
definitively turn off. Thus, towards the end of the halfwave, at a time t
5
, current I
AK
falls under a hold value Ih and the thyristor turns off. Gate voltage G
1
has been interrupted to prevent IGBT
2
turning on again.
Each of the IGBT
2
and the transistor
4
can be replaced by an IGBT or MOS or bipolar power transistor. Other monolithic power switch circuits with a controlled di/dt of the type to which the present invention applies are described in U.S. patent application Ser. No. 09/467,357 assigned to the present assignee, that is incorporated by reference.
As appears from the description of the operation of the power switch of
FIG. 1
, said switch must be controlled by two voltage pulses upon each halfwave of the A.C. voltage. Additionally, the pulse for controlling transistor M must have a control. The provision of such pulses results in several constraints. A first constraint is that said pulses are voltage pulses while it is more frequent, in the field of power variation, to control components (for example, triacs) with current pulses. A second constraint is that it is here necessary to control two switches (IGBT
2
and transistor M) while in conventional triac-based power variation circuits, a single gate is controlled. A third constraint as compared to circuits using triacs is that the control voltage must have a given polarity.
Of course, the solution that comes to mind to implement the control of such a power switch is to use a digital circuit (for example, based on a microprocessor) to generate, in a perfectly controlled way, the desired voltage pulses. However, such a solution has the disadvantage of being particularly expensive and of requiring an auxiliary power supply for a digital component.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a voltage pulse generator that respects the previously-indicated constraints and that overcomes the disadvantages of a digital solution.
Another object of the present invention is to provide a pulse generation circuit, most components of which are integrable.
Another object of the present invention is to pro
Destouches Mickael
Gonthier Laurent
Jalade Jean
Cunningham Terry D.
Engelson Gary S.
Morris James H.
STMicroelectronics S.A.
Wolf Greenfield & Sacks P.C.
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