Electricity: power supply or regulation systems – Output level responsive – Phase controlled switching using electronic tube or a three...
Reexamination Certificate
1998-04-24
2001-09-25
Sterrett, Jeffrey (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Phase controlled switching using electronic tube or a three...
Reexamination Certificate
active
06294901
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of power dimmers for modulating the operating power of an essentially resistive load, for example, a lamp, powered by an a.c. voltage, for example, the mains voltage.
2. Discussion of the Related Art
FIG. 1
shows a basic diagram of a conventional light dimmer. Such a dimmer is most often based on the use of a triac
1
operating as a bidirectional switch, open in the idle state, connected in series with an incandescent or halogen lamp
2
between two a.c. supply terminals
4
,
5
.
Triac
1
is controlled by a circuit (CONTROL)
3
, the function of which is to supply to gate G of triac
1
closing pulses at a frequency corresponding to double the frequency of supply voltage v. Circuit
3
is generally powered from the a.c. voltage by means of connections
6
,
7
, respectively, to terminal
4
and to the midpoint
8
of the series association of lamp
2
and of triac
1
. Circuit
3
is associated with means (not shown), generally manually controlled, for setting the time of occurrence of the pulses with respect to the beginning of each halfwave of the supply voltage.
The operation of the power dimmer shown in
FIG. 1
is illustrated by
FIG. 2
which shows, in the form of a timing diagram, an example of the current i in lamp
2
and of control voltage v
1
of triac
1
. Signal v
1
corresponds to a pulse train of amplitude V
1
.
In the absence of a triggering current in gate G of triac
1
, the triac is blocked (non-conducting) and no current flows through lamp
2
(neglecting the supply current of circuit
3
which is very low due to the high resistance of lamp
2
and which causes no lighting thereof).
At the beginning of a mains halfwave (shown in dotted lines in FIG.
2
), there is thus no current in the lamp. At a time t
1
, corresponding to the rising edge of a pulse P of signal v
1
, triac
1
turns on and current i in the lamp grows very rapidly to follow the mains sine wave. Triac
1
turns off at the end of the halfwave (time t
2
) and turns back on upon occurrence of the following pulse of signal v
1
.
A problem which arises in such a power dimmer is that the turning-on of the triac causes radioelectric disturbances on the mains, due to the current peaks which occur upon each closing of triac
1
.
To solve this problem, an inductive and capacitive filter is generally used.
FIG. 3
shows an example of conventional power dimmer provided with such a filter.
An inductance L is interposed between lamp
2
and triac
1
, to smooth the current peaks upon closing of triac
1
. Inductance L is associated with a capacitor C connected in parallel on the series connection of inductance L and of triac
1
, that is, connected between terminals
4
and
8
. Capacitor C is used to limit the energy in inductance L. The association of inductance L and of capacitor C forms what is generally called a mains filter.
A disadvantage of using such a mains filter in a power dimmer is that inductance L is a particularly bulky and expensive component. Further, the inductance is not integrable.
Another disadvantage is that the inductance introduces an effect of lamp “flicker” when the dimmer is set at low power. Indeed, at low power, the hold current of the triac is higher than the current through the inductance, which causes oscillations upon switching of the triac.
SUMMARY OF THE INVENTION
The present invention aims at providing a novel power dimmer which overcomes the disadvantages of conventional dimmers.
The present invention aims, more specifically, at providing a novel dimmer which is less bulky than a conventional dimmer.
The present invention also aims at maximizing the integration of such a dimmer.
The present invention aims, in particular, at providing a power dimmer which, while respecting the radiofrequency disturbance standards admissible on the mains, operates correctly at low power.
To achieve these and other objects, the present invention provides a power dimmer for a load powered by an a.c. voltage, of the type including a bidirectional switch associated in series with the load, the switch being normally closed and controllable to be opened upon each halfwave of the a.c. voltage.
According to an embodiment of the present invention, the switch is made bidirectional by means of a rectifying bridge, two output terminals of which provide a rectified a.c. voltage.
According to an embodiment of the present invention, the switch is formed by a first gate turn-off thyristor.
According to an embodiment of the present invention, a resistor of high value is placed between the anode and the gate of the first gate turn-off thyristor.
According to an embodiment of the present invention, the power dimmer includes a second gate turn-off thyristor in parallel with the first thyristor, the gate of the first thyristor being connected to the cathode of the second thyristor via a zener diode, the gate of the second thyristor being connected, via a resistor of high value, to its own anode, and the cathode of the second thyristor being connected, via a storage capacitor, to the most negative output terminal of the rectifying bridge.
According to an embodiment of the present invention, a control signal is applied between the gate of the first thyristor and its cathode, the trip voltage of an opening of the first thyristor being negative or null.
According to an embodiment of the present invention, the control signal is formed by a train of negative or null pulses at a frequency corresponding to double the frequency of the a.c. supply voltage.
According to an embodiment of the present invention, at least the gate of the first thyristor is connected to the most negative output terminal of the rectifying bridge, at least via a transistor, a control terminal of which is connected to the midpoint of a resistive dividing bridge between the two output terminals of the rectifying bridge.
According to an embodiment of the present invention, the voltage dividing bridge is sized so that the threshold turn-on voltage of the transistor is higher than the turn-on voltage of the first thyristor.
According to an embodiment of the present invention, the power dimmer includes a capacitor for damping the switching peaks upon opening of the switch.
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: 3161759 (1964-12-01), Gambill et al.
patent: 3201597 (1965-08-01), Balan
patent: 3440445 (1969-04-01), Kusa
patent: 3952241 (1976-04-01), Takemura et al.
patent: 4061961 (1977-12-01), Baker
patent: 4162440 (1979-07-01), Luteran
patent: 4504778 (1985-03-01), Evans
patent: 4870340 (1989-09-01), Karal
patent: 4876498 (1989-10-01), Luchaco et al.
patent: 4954768 (1990-09-01), Luchaco et al.
patent: 5023516 (1991-06-01), Ito et al.
patent: 5072170 (1991-12-01), Crane et al.
patent: 5107184 (1992-04-01), Hu et al.
patent: 5519263 (1996-05-01), Santana, Jr.
patent: 5657195 (1997-08-01), Rault
patent: 5754036 (1998-05-01), Walker
patent: 5757145 (1998-05-01), Johnson et al.
Galanthay Theodore E.
Morris James H.
SGS-Thomson Microelectronics S.A.
Sterrett Jeffrey
Wolf Greenfield & Sacks P.C.
LandOfFree
Power dimmer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Power dimmer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power dimmer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2493866