SYSTEM AND METHOD OF AUTOMATIC DIMMER LOADING IN DIMMER-CONVERTER ARRANGEMENTS

The present invention provides systems and methods for automatic dimmer loading in a cut-phase dimmer-converter arrangement, the method including providing minimum dimmer hold-on current by continuously loading of the dimmer with the current grater than minimum hold-on dimmer current without current measurement means or with using of measurement means by measuring a first current across the dimmer to form a current output signal and compensating for a drop in the dimmer output current by adding a load current across said dimmer to ensure that a total current comprising a sum of the first current and the load current always exceeds a threshold current for continuous operation of the dimmer.

In all the figures similar reference numerals identify similar parts.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that these are specific embodiments and that the present invention may be practiced also in different ways that embody the characterizing features of the invention as described and claimed herein.

The concept of the present invention is particularly suitable for dimmer—electronic converter—load systems used in the lighting industry although it is not limited thereto. For the sake of simplicity, the concept will be explained for lighting systems, but this should not be deemed as limited thereto.

The operational principles of the present invention are explained in reference toFIG. 2, showing the functional structure of Automatic Dimmer Loader (ADL)20connected after an input rectifier23of an electronic converter213.

An input AC voltage is passed through a conventional TRIAC dimmer22and rectified by a rectifier23, which is connected to ADL20. The ADL comprises an energy receiver unit26(ERU), connected to a rectifier23through a decoupling diode D124and a ballast25, which defines the current flows to Energy Receiver Unit26. Ballast25is controlled by a Ballast Control System28, which has two inputs, namely an input from current sensor212and feedback211from electronic converter213, which disables or enables the operation of the ADL depending on the operational status of electronic converter213.

If the converter status is “on,” then the operation of the ADL is disabled and vice versa. In addition, Ballast Control System28enables or disables the operation of ADL20based on the actual value of the electronic converter input current. If the latter drops to a value close to the latching current of the dimmer's TRIAC, then Bak last Control System28enables the operation of ADL20in order to prevent dropping under the latching current of the dimmer's TRIAC. Otherwise it disables the operation of ADL20. Energy receiving unit control means27are connected in parallel to Energy Receiver Unit26and is used in order to achieve the zero initial conditions suitable for proper operation of ADL20and protect from over-voltage conditions of Energy Receiver Unit26. The energy received by Energy Receiver Unit28can be dissipated or converted. This energy also may be transferred to the Dimmer Loader Load210or utilized for powering of electronic converter's control circuits through decoupling diode D229or utilized in any other form.

The Ballast Control System28receives power from Energy Receiver Unit26. This input can be used for Energy Receiver Unit26overvoltage protection. The Ballast Control System28should interrupt the ballast current during Energy Receiver Unit26overvoltage conditions.

Ballast Control System28can be implemented as an analog, digital or mixed signal control system. Energy Receiver Unit26can be implemented as a capacitor, but not is limited thereto.

In the case where the start-up at small dimmer angles must be maintained, two basic restrictions are preferably fulfilled:During the hold-on period, the voltage difference between instantaneous mains voltage and voltage on the Energy Receiver Unit26VERUshould be greater than the forward voltage drop of the voltage of the dimmer's TRIAC14, (Vmains−VERU)>VF, otherwise the conditions for TRIAC14conduction and system start are insufficient.Inverter214start-up time depends on the input voltage in the following manner: the higher the input voltage, the shorter the duration of the inverter's start-up. At small operating angles of the dimmer, the inverter's start-up time may be significantly longer due to the low input voltage. In order to shorten the inverter's start-up time and consequently shorten the latching period of ADL20, the inverter's start-up time can be reduced by appropriate design of the power supply circuits of the inverter.

FIG. 3is a detailed functional block diagram, which illustrates the method of dimmer latching, i.e., the implementation of energy receiver unit26and energy receiving unit control means27described with reference toFIG. 2. The circuitry inFIG. 3includes an input rectifier33; a decoupling diode34; a ballast35; a storage capacitor36with resistor37connected in parallel in order to provide zero initial conditions, wherein storage capacitor36can receive maximum energy; and a decoupling diode39adapted to decouple the load from storage capacitor36. Ballast Control System38controls the behavior of ballast35in order to provide sufficient current for latching the dimmer for time period T, required to start the operation of the electronic converter. Moreover, after startup of the converter, ballast control system38disconnects storage capacitor36by interrupting the ballast current and energy stored in capacitor36dissipates on resistor37in order to enable receiving energy at any moment if ballast control system38connects ballast35to storage capacitor36.

The current flowing through ballast35provides, together with dimmer's load (electronic converter), current sufficient for normal operation of the dimmer.

In a case where the ballast35is an electronic converter, control system38can add minimum current to the current drawn by the dimmer's load, in order to achieve normal operation of the dimmer.

In order to synchronize transformation of the energy stored in storage capacitor36, conversion means should be provided. In a case where the ballast is a resistive one, it is difficult to provide only minimum latching current of the dimmer in the case of wide input voltage changes because resistive ballast should be chosen in order to provide latching current at minimal input voltage and minimal conduction angle, when the dimmer conducts the current during the short time of the mains period.

HereVin—min—actual instantaneous voltage at minimum main operating voltage and conduction angle of the dimmer;V—the maximum voltage on capacitor Cchg;Imin—latching current of the dimmer plus certain safety margin.

The storage capacitor value, C, can be calculated according to the following energy balance equation

HereT—maximum time needed to start of the electronic converter;V—the maximum voltage on capacitor Cchg.VRMS—the RMS value of the mains voltageIRMS—the RMS value of the ballast resistor current in the worst case (when dimmer almost always conducts) and can be calculated by the following equation (in this case it is equal to charge current of the capacitor):

HereVRMS—RMS mains voltageRballast—resistance of the ballast resistor

In this case minimum current drawn by storage capacitor36at minimum input voltage but at maximum voltage point dimmer is loaded by enlarged current and this current charges the load capacitor.

In a case where the ballast is able to provide its output constant current under any input conditions, for example by using of conversion means it is able to provide lower RMS current relating to the resistive ballast option. For this option output constant current should provide minimum dimmer current at maximum input voltage,

HereVinput max—maximum instantaneous input voltage value;Imin—a current which is greater than max latching current of the dimmer's TRIAC by a certain safety margin;Vmin—the minimal voltage on capacitor Cchg;C of the storage capacitor36can be calculated according to the following energy balance equation

HereT—maximum time needed to start of the electronic converter;I—ballast output constant current which provides at the input of the ballast current greater than max latching current of the dimmer's TRIAC by a certain safety margin in any dimmer conditions.V—the maximum voltage on capacitor Cchg;

In described above solution sufficient dimmer current is provided under any input conditions. The current drawn from the dimmer to special storage capacitance changes with the input voltage, but its RMS value is lower relative to the resistive ballast option. The charging current of the storage capacitor is constant for any input voltage point. For this solution a lower energy is received by storage capacitance in order to provide stable dimmer operation and as result a lower value of the storage capacitor is required.

In the case where the ballast is able to provide its input constant current (minimum dimmer current) under any input conditions, for example by using conversion means, the capacitance C of the storage capacitor36can be calculated according to the following energy balance equation (valid for constant current):

HereT—maximum time needed to start the electronic converter (in the worst case it can be equal to or less than conduction time of the dimmer during the main half-period);I—a current which is greater than max latching current of the dimmer's TRIAC by a certain safety margin;V—the maximum voltage on capacitor Cchg.VRMS—the RMS value of the main voltage.

In the above described solution the minimum dimmer current is provided under any input conditions. In this solution, the current drawn from the dimmer to a special storage capacitance does not change with the input voltage. The current drawn to a storage capacitor at a maximum input voltage has the same value as for any other input voltage point. The energy received by the storage capacitance in order to provide stable dimmer operation is smaller than in other solutions and as result a significantly lower value of the storage capacitor is required.

The Ballast Control System38has an additional input311for feedback from the Inverter in order to disable the operation of the dimmer loader30after the start of the Inverter. In general, the operation of the dimmer loader during operation of the Inverter is not necessary since the consumption current of the Inverter is sufficient to hold on the dimmer. However, dimmer loader30may be activated to operate during every half-cycle of the mains period if, for example, the Inverter's load is very low and the consumption current approaches the hold-on current of the TRIAC.

The capacitor36is charged by dimmer loader30via diode34and Ballast35. Capacitor36is discharged by the discharge resistor37, when the power supply is turned off, or through diode39and main load capacitor310during operation of electronic converter.

FIG. 4illustrates the wave forms40that explain the operation of the Automatic Dimmer Loader. Vin41is an AC voltage that TRIAC Dimmer32produces inFIG. 3. Vrect42is the rectified voltage after input Rectifier33. Icharge43is the charging current of storage capacitor36. Icharge43is a high-frequency pulsed current. Ballast Control System38chooses appropriate values of the current and width of current pulse in order to maintain the energy balance defined above. Iin44is the current smoothed by an input EMI filter (which is not shown).

The main advantages of the ADL and method of the present invention are:flexible control system, which maintains a stable operation of the system even at very small angles of the dimmer;no distortions of the input signal; and

useful for a wide range of loads, e.g. lamps, drivers and other applications where there is a need to hold on the dimmer.

FIG. 5shows the functional structure of an independent ADL58for the dimmer loading, constructed in accordance with the principles of the present invention.

ADL58is connected to the output of the TRIAC dimmer52which, in turn, is fed from AC Source51. ADL58comprises an input current sensing means510; a full wave rectifier53, which rectifiers input AC voltage and whose output is connected to the input terminals of a ballast54; ballast54which controls the dimmer52output current by using of sensing means510, connected to the output terminals of rectifier53; the energy receiving unit56and its control means57connected to the output terminals of ballast54. Energy receiving unit control means57provide initial conditions for dimmer loader58operation. Ballast control system55controls ballast54current and has mains voltage input511and current feedback510. Ballast control system55has control output512, which is connected to control input of energy receiving unit control means57in order to synchronize ballast control system55and energy receiving unit control means57.

Ballast control system55ensures that consumption current from the dimmer52is greater than hold-on current of dimmer's TRIAC. This can be achieved by monitoring the consumption current and its derivative this enables to achieve required consumption current at any conditions.

FIG. 6shows the functional structure of an improved ADL60with energy utilization means constructed in accordance with the principles of the present invention. This structure is shown as an internal part of an electronic converter. Terminals of the AC source61are connected to the input terminals of a TRIAC dimmer62. Output terminals of TRIAC dimmer62are connected to the input terminals of electronic converter's input rectifier64through a current sensor63. Output terminals of the rectifier64are connected to an input bulk capacitor65of an inverter66. Input terminals of a full wave rectifier67are connected in parallel to input terminals of rectifier64. The negative terminals of both rectifiers64and66are connected together. A positive terminal of rectifier67is connected to a first terminal of inductor68, to the voltage feedback input of ballast control system611, and an input terminal of ballast610. The second terminal of inductor68is connected to the anode of diode69, drain of a MOSFET transistor614, and cathode of diode617. Anodes of Zener diode613and diode617are connected together. The source of a MOSFET614is connected to the negative terminal of rectifier67. The output terminal of the ballast is connected to the first terminal of capacitor612, cathode of Zener diode613, and the voltage feedback input of ballast control system611. The second terminal of capacitor612is connected to the negative terminal of rectifier67. The ballast control signal from the output terminal of the ballast control system611is connected to the control terminal of ballast610. Boost converter control signal from the output terminal of the ballast control system611is connected to the gate terminal of the MOSFET transistor614. The output terminal of the internal power supply616is connected to the power terminal of the ballast control system611. Input terminal of power supply616may be sourced from positive terminal of rectifier64or67. The output terminal of current sensor63is connected to the input terminal of the ballast control system611. The ballast control system611also takes the feedback input615from inverter66.

The control system611operates in the following way: ballast610is configured so that it is normally closed, in order to conduct the current, at the time when the input voltage is initially applied. Capacitor612starts to consume current and the voltage on it rises. After a certain voltage rise ballast control system611starts its normal operation, i.e., it maintains the current flowing through TRIAC dimmer62at a level higher than the hold-on current of the latter. If the current consumption of the electronic converter approaches the value close to the dimmer's hold-on current, the control system611starts to maintain dimmer62current by means of ballast610current, at a level higher than the dimmer's latching current. The boost effect enables consumption of the required current from the dimmer at any given time. Zener diode613, together with diode617, prevent the rise of capacitors612voltage above a certain voltage level during the ADL operation.

The considerations for choosing the value of the capacitance of capacitor612are different from the ones described above in connection to energy equations (1), (2) and (3). In the present case, the capacitor612provides the initial conditions for dimmer latching during the delay when the boost converter is starting. In the case where ballast control system611is supplied from capacitor612when the boost converter starts, the ballast control system611reduces the charge current of capacitor612down to the level sufficient for power supplying of control system611from capacitor612and boost converter ensures current consumption from the dimmer at level greater that hold-on current of the dimmer62. In this case, capacitor612loads the dimmer through ballast610for a period of time defined by the boost converters start-up time, which is typically in the range of 1-2 ms in the worst case. Therefore, the capacity of capacitor612is significantly lower, by about five to ten times, than in the former case where the capacitor36ofFIG. 3operates throughout the whole operating period of the dimmer in the worst case, i.e., without dimmer load. Furthermore, in the structure ofFIG. 6, better energy utilization is achieved whereby all the energy consumed by the boost converter is transferred to the input bulk capacitor65of the electronic converter for further power conversion. The structure ofFIG. 6provides significant advantages for low power applications and improves the overall efficiency of the power conversion system.

The references cited herein teach many principles that are applicable to the present invention. Therefore the full contents of these publications are incorporated by reference herein where appropriate for teachings of additional or alternative details, features and/or technical background.

It is to be understood that the invention is not limited in its application to the details set forth in the description contained herein or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention as hereinbefore described without departing from its scope, defined in and by the appended claims.

FIG. 7shows the operational waveforms70of the adaptive loader described relative toFIG. 6. At time to DIAC15of the dimmer breaks down and TRIAC14is open, with reference to the components of prior artFIG. 1. Current starts to flow. Its value is defined by ADL and is greater than TRIAC14latching current. The electronic converter has not started yet. At time t1 the electronic converter starts its operation and the current flowing through dimmer's TRIAC14is defined by the load of the electronic converter. At time t2 the current flowing through the dimmer's TRIAC14and ADL maintains the current at the level greater than dimmer's TRIAC14latching current up to time t3 when dimmer’ TRIAC14is turned off. In the next half period of the main voltage the process is repeated.