Electric lamp and discharge devices: systems – Current and/or voltage regulation
Reexamination Certificate
2003-01-09
2004-12-14
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
C315S307000, C315S2090SC, C315S219000, C315S224000, C315SDIG004
Reexamination Certificate
active
06831426
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns an electronic device, or dimmer, for regulating the power supply. Specifically, said dimmer makes possible, in a simple, reliable, effective, and acoustically noiseless way, to supply loads, in particular lighting power devices, such as filament lamps, for motion picture, television, and theatre applications.
The present invention further concerns a system for controlling and regulating the power supply applied to a plurality of loads, comprising such dimmers.
BACKGROUND OF THE INVENTION
A dimmer is an electronic device capable to control alternate voltage applied to a load, generally a filament lamp, through delivering a selected portion of the mains sinusoid by means of an electronic power switch. In particular, when the power supply is decoupled from the load at the beginning of each half-cycle of the mains sinusoid, the dimmer applies to the load a waveform named forward phase control or FPC, having very steep power up fronts and sinusoidal power down. Conversely, when the power supply is coupled to the load at the beginning of each half-cycle of the mains sinusoid, the dimmer applies to the load a waveform named reverse phase control or RPC, having sinusoidal power up and very steep power down fronts.
After the development of the first power solid state electronic devices, which assure a controlling capability better than valves, dimmers have been developed employing devices know as triacs, or bidirectional thyristors, operating as electronic switches; such triacs comprise two controlled rectifiers, or SCR, connected in antiparallel configuration. A triac may be turned on in any moment, and it turns off only when the current becomes smaller than a minimum conduction value.
Due to such characteristics, said dimmers operate according to the FPC control. Since very steep leading edges are harmful for the lamp filaments, besides producing both electrical and acoustic noise, in order to slow the leading edges down, said dimmers are provided with large inductors, which assure high efficiency and great circuit simplicity.
However, such dimmers have the drawback to be very expensive and still very noisy.
In recent years, dimmers have been developed employing as electronic switches, power solid state devices known as insulated gate bipolar transistors, or IGBTs. With respect to triacs, IGBTs offer the advantage to be able to be controlled for turning on and off, and to be able to operate also in linear region and to be progressively turned off.
In particular, U.S. Pat. No. 5,004,969 discloses a phase control power switching circuit having a couple of IGBTs, connected in reverse series configuration between a load and alternate current source, for controlling the current flow through the load. The two IGBTs are alternatively driven through commutating means such a way that each IGBT alternatively operates between conduction and interdiction at the desired phase angle of the current flow. In particular, such a circuit, which is usable as a dimmer, is based on the interaction of a constant frequency source, a flip-flop, and a delay circuit.
However, the dimmer disclosed in U.S. Pat. No. 5,004,969, which is described as operating according to the RPC control, has some drawbacks.
First of all, it is not capable to regulate the descent slope of the power down fronts of the RPC waveform applied to the load (similarly, it would not be capable to regulate the rise slope of the power up fronts of FPC waveform). This produces quicker power down times for lower values of current delivered to the load, and, hence, it makes complex to select the desired phase angle in order to control the power up times of the load lamps.
Moreover, efficiency is smaller, the dimmer suffers from a high circuit complexity and is acoustically rather noisy.
U.S. Pat. No. 5,239,255 discloses a phase controlled power modulation system which again employs a couple of IGBTs, connected in reverse series configuration between a load and an alternate current source, for modulating the power supply applied to the load. The two IGBTs are driven by a transition shaper that controls the rate of change of the voltage applied to the load. The dimmer further comprises a phase controller, for controlling the transition shaper, a device for protecting the IGBTs, and an asymmetric waveform selector. The dimmer may operate according to the FPC control, according to the RPC control, or, by means of the asymmetric waveform selector, according to an asymmetric hybrid control, wherein the power delivered to the load during the first half-cycle of the supply alternate current is different from the power delivered during the second half-cycle.
However, also the dimmer disclosed in U.S. Pat. No. 5,239,255 has some drawbacks.
First of all, in case overload conditions occur, due for example to a situation of cold lamp, the filament of which has a resistance about ten times lower than the one of the filament at operative temperature, transition shaper voltage control does not detect conditions of excessive current delivered to the load. Therefore, monitoring of possible overload conditions is carried out by the protecting device which indirectly operates on the shaper through the asymmetric waveform selector, making the dimmer circuit extremely complex. Moreover, despite of such circuit complexity, the dimmer is not much versatile, since the slope of both power up and power down fronts may be selected among very few values predetermined by the circuit components.
Consequently, the dimmer is also expensive and not completely effective.
Furthermore, it is still acoustically noisy under overload conditions.
Other dimmers, which are presently available on the market, comprise an IGBT and a rectifier bridge, or two IGBTs with reverse conducting diode. Such dimmers have RPC operating characteristics, wherein the descent time of the power down front is limited by IGBT dissipation. Time of about 500 microseconds may be obtained under reasonable dissipation. Also, such dimmers may similarly operate according to FPC operating mode.
Even offering some advantages, such as sinusoidal leading edges having reduced noise and trailing edges having variable slope obtained without using expensive large inductors, these last dimmers still have the drawbacks of having a low efficiency and a considerable circuit complexity, and of being excessively noisy for applications to show environments.
Acoustic and electrical noise of presently available dimmers forces to place all dimmers far away from the supplied lamps which are used in show environments, preferably within a dedicated room which is far and acoustically insulated from the show room where the lighting devices supplied by the same dimmers are mounted. This causes the presence of a lot of cables in the room to be lighted in all the cases where a multiplicity of lamps is needed, as it happens in television or motion picture studios, or in theatre stages, producing high cost of the electric installation. Moreover, currents with high harmonic content pass through the cables, causing cross talks and interference among the various circuits.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electronic device, or dimmer, for regulating the power supply applied to a load, which is both acoustically and electrically noiseless during supplying operations of power loads, in particular lighting power devices.
It is still object of the present invention to provide such an electronic device which make possible, in a reliable and effective way, to regulate the rise slope of the power up fronts and the descent slope of the power down fronts of the power waveforms applied to the load.
It is another object of the present invention to provide such a device which has a high efficiency and a great circuit simplicity, consequently being simple to be realised and having cost at least comparable to the cost of conventional dimmers.
It is specific subject matter of this invention an electronic device, or dimmer, for regulating the power su
Brevetti Paolo
De Sisti Fabio
Torni Andrea
Arent Fox PLLC.
De Sisti Lighting S.p.A.
Tran Chuc
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