Ballast for a LED lamp that keeps the current level within a predetermined operating range

Abstract

The present invention discloses a ballast for supplying electrical energy with an efficiency of at least 95% to several LED lamps from an AC source. The ballast is configured to keep the current level that circulates through these lamps within a predetermined range even when there are voltage variations in the AC source. The ballast has a circuit comprising a transformer, an AC to DC rectifier, without any capacitive or inductive device connected in series to said transformer between the AC source and said rectifier, and a current-controlling circuit. The current-controlling circuit can consist of switches that can be selectively connected to primary or secondary coils, two SCRs or a diode bridge using an SCR or a TRIAC, or a circuit that uses an SCR or a TRIAC to cut the current wave, adjusting the current passage time.

Description

[0001] LED LAMP BALLAST THAT MAINTAINS THE CURRENT LEVEL WITHIN A PREDETERMINED OPERATING RANGE

[0002] FIELD OF INVENTION

[0003] The present invention relates to a ballast that includes an electrical circuit that supplies, with high efficiency, a direct current from an alternating current source that may have voltage variations to one or more LED lamps, maintaining the current level within a predetermined operating range to ensure the operation of said lamp if the voltage decreases, and if the voltage increases, to protect it from high current levels that could damage it. This type of device, with its circuit and electrical components, are also known as ballasts or "drivers" or power sources.

[0004] BACKGROUND OF THE INVENTION

[0005] The use of LED (light emitting diode) lamps, also known as solid-state lighting (SSL), has become widespread in all areas of lighting application, at industrial, public service and residential levels, due to their low energy consumption compared to other types of incandescent and fluorescent lamps that provide the same lighting intensity.

[0006] Lighting systems typically include a plurality of LED lamps connected in series in a circuit. Because they are made of diodes, they require a direct current power supply. Therefore, a power source or ballast that supplies direct current is required. One way to construct this power source or ballast is to use a transformer or autotransformer and an alternating current to direct current rectifier, and then connect said LED lamps to alternating current power grids.

[0007] A physical characteristic of LED lamps is the non-linear increase in current level in response to an increase in voltage in the circuit to which said LED lamps are connected. This characteristic of LED lamps is illustrated in Figure 1 and presents a significant problem in the operation of LED lamps, since a small variation in the voltage of the direct current source can cause the current level flowing through the LED lamp to increase disproportionately and damage the LEDs. Since the direct current voltage obtained depends on the alternating current voltage supplied to the circuit, then small variations in the voltage level of the alternating current source can cause large variations in the current level in the LED lamps.

[0008] To prevent excessive current surges through LED lamps due to variations in the AC voltage supplied to the circuit, there are ballast designs that include, in addition to a transformer or autotransformer and a rectifier, devices such as capacitors, inductors and resistors, transistors, TRIACs, and SCRs that limit the current level to acceptable levels. However, the electrical efficiency of these ballasts with their driver devices is good but not very high, on the order of 80% to 90%, and in many cases they increase the complexity of LED lamps and lighting systems.

[0009] Some ballast references are mentioned here, including circuits with an autotransformer and a rectifier, just as examples of the ballasts available for LED lamps.

[0010] US Patent 11,206,722 B2 describes an apparatus for supplying power to an array of LED lamps, which combines an autotransformer with an inductor. The inductor may be connected in series with the transformer, between the AC source and said transformer, or between the transformer and an AC-to-DC rectifier. Inductive elements may be connected or disconnected in series with the transformer to dim or reduce the brightness of the LED lamps.

[0011] Patent Application CN 105491722 A uses an autotransformer with a single coil with an intermediate tap to which a capacitor is connected, which in turn is connected to the power supply circuit of an LED lamp. This circuit produces a current that varies greatly over time because the capacitor charges and discharges very quickly. If this circuit is powered by 60 Hz alternating current, the capacitor will charge and discharge 120 times per second. Depending on the capacitance of the capacitor and the number of LEDs used, the current can vary greatly with each charge and discharge cycle. It is common in this type of circuit to also install a resistor between the capacitor and the LEDs to obtain a smoother current waveform. No mechanism or device is mentioned to limit or control the current passing through the LED lamps due to variations in the voltage source.

[0012] Utility Model CN ​​203378099 U describes a converter or apparatus comprising a step-down autotransformer and a rectifier that supplies direct current to one or more LED lamps. The output voltage of the autotransformer can be varied by means of a switch that can connect one of several output terminals of the autotransformer. This selective variation of the output voltage by operating the selector switch is used to dim the brightness of the LED lamps, and does not mention an automatic controller.

[0013] Patent application US 2018153009 describes a ballast for replacing HID lamps with LED lamps comprising a constant-wattage autotransformer. The autotransformer is connected to an alternating current source via an input terminal and an intermediate connection point (tap) on the coil of said autotransformer.

[0014] The above references do not mention the use of a ballast with a circuit comprising a step-up autotransformer, i.e. a transformer where a primary coil and a secondary coil are connected together such that the output voltage of the secondary coil is higher than the voltage received by the primary coil, and an alternating current to direct current rectifier for feeding one or more LED lamps, where the current supplied to the LED lamps is limited by the core size of the autotransformer and / or by the inductive effect of the autotransformer, without any additional inductive device connected in the alternating current part of said circuit, between the alternating current source and the rectifier.

[0015] There is therefore a need in the lighting market to provide a circuit and method for supplying electrical power to an LED lamp circuit or LED lamp lighting system that operates with high electrical efficiency, measured as the ratio of the output power to the input power of said ballast, greater than 90% and preferably greater than 95%, and that also limits the level of current, and therefore the power, circulating in said circuit. The apparatus proposed herein also has a long life, since it can be constructed with long-life electrical and electronic elements. The present invention satisfies this need and provides a method and apparatus for operating LED lamps without the disadvantages of the prior art. OBJECT OF THE INVENTION

[0016] It is therefore an objective of the present invention to provide a ballast comprising a circuit for supplying electrical power to one or more LED lamps while maintaining the level of current flowing through said LED lamps within a predetermined operating range.

[0017] It is another objective of the invention to provide a ballast comprising a circuit for supplying electrical power to one or more LED lamps while maintaining the current level within a predetermined operating range with high electrical efficiency.

[0018] Another objective of the present invention is to provide a ballast that has a long useful life, of more than 5 years and preferably more than 10 years, thanks to the fact that the circuit described can be built with elements that can have a very long life, which allows reducing maintenance costs, both in terms of labor and spare parts.

[0019] Other objects of the invention will be pointed out later in the description or will be apparent to those skilled in the art.

[0020] BRIEF DESCRIPTION OF THE INVENTION

[0021] The objects of the invention are generally achieved by providing a ballast comprising a circuit for supplying electrical power to one or more LED lamps from an alternating current source, said circuit comprising a transformer and an alternating current to direct current rectifier. The transformer comprises a steel core and at least two coils, a primary coil and a secondary coil. The primary coil has a plurality of terminals configured to be connected to said alternating current source or to said secondary coil or to an alternating current to direct current rectifier, and the secondary coil has a plurality of terminals configured to be connected to said primary coil or to said rectifier.The primary coil and said secondary coil are connected to each other such that the voltage between the terminal of the secondary coil where the rectifier is connected and the terminal of the secondary coil where it is connected to the primary coil is in phase with the voltage between the terminal of the primary coil where it is connected to said secondary coil and the terminal of the primary coil where it is connected to said rectifier. The terminal of the primary coil through which it is connected to the secondary coil is distinct from the terminal of said primary coil through which it is connected to said rectifier.The rectifier comprises at least two alternating current connection points configured to be connected to a terminal of the primary coil of the transformer and to a terminal of the secondary coil, and at least two direct current connection points configured to be connected to the LED lamp and supply direct current to said LED lamp. A first alternating current connection point of the rectifier is connected to a terminal of the secondary coil of the transformer, and a second alternating current connection point of the rectifier is connected to a terminal of the primary coil of the transformer. The transformer is directly connected to the rectifier without any capacitive or inductive devices electrically connected in series with said transformer between the alternating current source and said rectifier.

[0022] DESCRIPTION OF THE FIGURES

[0023] Figure 1 graphically shows an example of the variation in the current level passing through an LED lamp as a function of a variation in the voltage level.

[0024] Figure 2 graphically shows an example of the variation in the power level (P=I*V) consumed in a direct current circuit of LED lamps as a function of the voltage level.

[0025] Figure 3 shows a schematic diagram of a preferred embodiment of a ballast circuit of the present invention, in which a step-up autotransformer and a rectifier are used.

[0026] Figure 4 shows a schematic diagram of an embodiment of a ballast circuit of the present invention, in which a transformer is used having a primary coil which has an intermediate tap and a secondary coil separated from the primary coil connected to each other and a rectifier.

[0027] Figure 5 shows a schematic diagram of an embodiment of the ballast circuit and method of the present invention in which an autotransformer and a transformer connected in parallel with the alternating current front and a rectifier are used.

[0028] Figure 6 shows the behavior of voltage and current in each half cycle of conduction in the LED lamp, as well as the effect of the inductance value of the ballast circuit according to the invention, so that the variation of the current with respect to time in said circuit has a slope that does not allow the current to increase too quickly and thus does not exceed the predetermined current level.

[0029] Figure 7 shows a schematic diagram of an embodiment of the ballast circuit of the present invention, where the autotransformer has several independent secondary coils and switches operated by a controller that selectively connect or disconnect one or more of said secondary coils to regulate the average current supplied to the LED lamp.

[0030] Figure 8 shows the schematic diagram of an embodiment of the ballast circuit of the present invention, where the transformer has two intermediate taps in the primary coil and switches operated by a controller that selectively connect or disconnect the connections of said taps to regulate the average current supplied to the LED lamp.

[0031] Figure 9 shows the schematic diagram of an embodiment of the ballast circuit of the present invention, where the autotransformer has several independent secondary coils and switches operated by a controller that selectively connect or disconnect said secondary coils to regulate the average current supplied to the LED lamp.

[0032] Figure 10 shows the schematic diagram of an embodiment of the ballast circuit of the present invention, where the autotransformer has a primary coil and a secondary coil, both of which have multiple connection terminals that allow both the power supply and the rectifier to be connected at different connection points and there are multiple switches operated by a controller, which selectively connect or disconnect said connection points to regulate the average current supplied to the LED lamp.

[0033] Figure 11 shows the schematic diagram of an embodiment of the ballast circuit of the present invention, which has an autotransformer having a primary coil and a secondary coil connected together and a rectifier operated by a controller to regulate the average current supplied to the LED lamp.

[0034] Figure 12 shows indicative graphs of the current of the ballast circuit of the invention where the average current supplied to an LED lamp is controlled by means of electronic devices that selectively suppress one or more half-cycles of conduction.

[0035] Figure 13 shows an indicative graph of the current of the ballast circuit of the invention where the average current supplied to an LED lamp is controlled by means of electronic devices that selectively control the firing of some SCRs (Silicon Controlled Rectifier, also called Thyristors).

[0036] Figure 14 shows the schematic diagram of an embodiment of the ballast circuit of the present invention, which additionally comprises varistors to protect the circuit from voltage spikes in the power supply.

[0037] DETAILED DESCRIPTION OF THE INVENTION

[0038] Some embodiments of the invention are described herein and it is understood that the various embodiments shown in this application have been included only to illustrate the spirit and scope of the invention and should in no way be construed as limiting, since the invention will be defined only by the scope of the appended claims.

[0039] To facilitate reading the detailed description of the invention, equivalent or similar elements of each described embodiment are referred to with the same numerals.

[0040] Referring to Figure 1 , the variation in the current level flowing through an LED lamp is shown as a function of the voltage applied to the lamp's power supply circuit. It is known that, in an LED lamp, when the voltage is lower than the trigger voltage V1 , the current through the LED is zero. The trigger voltage to turn on an LED is the voltage level that initiates the passage of current through it. Once the trigger voltage Vi is reached, the current increases very rapidly as the voltage level increases. Upon reaching the operating voltage or nominal voltage V2, the current reaches the nominal operating current value IN. If the voltage continues to increase, the current continues to increase very significantly, which increases the temperature of the LED and this increase in temperature can cause the LED to burn out and thus suffer irreparable damage.

[0041] This operating curve is affected by variations in LED temperature, as well as by small variations in the manufacturing of the LEDs that make up a lamp.

[0042] The ballast must have a very high efficiency to offer advantages in the operating cost of an LED lamp, that is to say, to have few losses, such as: (1) Heating losses due to the resistance of the connection cables and the components of the alternating current circuit and the direct current circuit to which the LED lamp is connected. As these losses are directly proportional to the square of the current (l 2*R), it is advisable that the current level be low, which is obtained if a "step-up" autotransformer is used since, if the voltage is increased, for a given power level, the current level will be lower. In other words, according to the invention, the output voltage level of the autotransformer is greater than the input voltage level to said autotransformer, and the current in the cables, coils and diodes is small, thus having lower losses.

[0043] (2) Losses due to the conversion of electric flux to magnetic flux in the transformer core. If a transformer is used to power an LED light, all the power supplied to the LEDs must be converted by it, first from current to magnetic flux and then from magnetic flux to current, requiring a large and expensive core. For example, to power a 100-watt LED light, a 100- to 120-volt-ampere transformer is typically required.

[0044] By using an autotransformer, the circuit is much more efficient, as only a small proportion of the power supplied to the LED lamp needs to be converted from current to magnetic flux and from magnetic flux to current.

[0045] For example, to power a 100 Watt LED lamp with a step-up autotransformer, if the primary winding is 120 Volts and the secondary is 20 Volts, to have an output voltage of 140 Volts, an autotransformer with an output capacity of 100 to 120 Volt-Amperes is required, but the autotransformer core would only be 15 to 25 Volt-Amperes, so it is much smaller and therefore much cheaper.

[0046] The ballast of the present invention has lower losses compared to ballasts currently in use, so the efficiency of the ballast claimed here, measured as the ratio of the electrical power supplied to the LEDs to the electrical power supplied to the ballast, is greater than 95%. In other words, the losses measured with respect to the input power are less than 5%.

[0047] Other types of ballasts or power supplies for LED lamps are of the type known as “switching-mode supplies,” and they typically have efficiencies of 80 to 91%, so having a ballast with an efficiency greater than 95% is very attractive for LED lamp manufacturers and end users.

[0048] It is important to mention that switching power supplies have a different operating principle and require large electrolytic capacitors for their construction. This has the disadvantage that the capacitors become damaged over time, resulting in a short lifespan for these power supplies, generally 3 to 5 years.

[0049] Since the ballast of the invention does not require electrolytic capacitors for its construction, it can have a very long life, which can reach more than 5 years, but possibly reach 10 years of life without causing problems in the field, thus obtaining additional savings in maintenance costs, both in labor and spare parts.

[0050] Figure 2 shows a graphic example of the variation in power in the LED lamp as a function of a variation in the RMS alternating current voltage level.

[0051] For example, if a transformer-based ballast is supplied with a nominal voltage of 120 Volts RMS, the resulting nominal power Pn is approximately 100 Watts. The graph shows that if the voltage level is varied 5% above the nominal voltage Vn, which corresponds to a nominal power level Pn, the power level would be approximately 50% higher than the nominal power level, and if the voltage drops 5% below the nominal voltage Vn, the power level would drop by approximately 40% with respect to the nominal power.

[0052] Therefore, using a transformer-based ballast connected to an alternating current source that can have variations over time of 5% with respect to the nominal voltage, results in the LED lamp having variations in power of up to 40% down or 50% up from the nominal power.

[0053] However, if the AC voltage received by the circuit is constant over time, the power will be constant over time.

[0054] It has been found experimentally that, in accordance with the invention, for a power level (Watts) of an LED lamp connected to a circuit comprising an autotransformer and an alternating current to direct current rectifier, when a variation in the voltage of the alternating current source arises, there is a moderate variation in the voltage supplied to the LED lamp, and, consequently, the LED lamp does not burn out, although the power in it does increase.

[0055] Figure 3 shows a ballast 10, according to the present invention, comprising a transformer 16 having a coil 29, which coil is composed of two coils connected in series, the primary coil 30 and the secondary coil 36, where the primary coil 30 is formed by the turns between the terminal 52 connected to the alternating current source and the connection tap 54 also connected to the alternating current source, thus defining an effective number of turns Np (turns of the primary winding). The secondary coil 36 is formed by the turns between the terminal 54 connected to the alternating current source and the terminal 60 connected to the rectifier 26, defining a number of turns Ns (turns of the secondary winding). The coils of a transformer are also often referred to as windings.

[0056] According to the invention, the alternating current voltage source 32 is fed into terminals 52 and 54, and the rectifier 26 is connected to terminals 52 and 60. The output voltage to the rectifier 26 between terminals 52 and 60 is greater than the voltage between terminals 52 and 54 of the primary coil 30.

[0057] When the terminal of the secondary coil, through which it is connected to said primary coil, is directly connected to a terminal of the primary coil, so that the two coils are connected in series, it is known as an autotransformer. In accordance with the invention, this connection is made without any inductive or capacitive element between said primary and secondary coils.

[0058] An LED lamp 12 comprising a plurality of individual LEDs 14 is connected to a rectifier 26, which provides direct current to said lamp 12.

[0059] A capacitor 50 is connected in parallel with the LED 12. This capacitor is optional and can be connected to smooth the current supplied to the LED. When this optional capacitor is used, a resistor can also be connected to limit the charging and discharging of the capacitor, which is not shown in the figure.

[0060] In another embodiment of the invention shown in Figure 4, a circuit of a ballast 10 for an LED lamp is illustrated, similar to that shown in Figure 3, with the difference that the primary coil 30 has two intermediate taps 56A and 56B. In this circuit, the rectifier 26 is not connected to the input terminal 52, but is connected to the intermediate tap 56B. In this way, the voltage supplied to the rectifier 26 is decreased. The other components and connections of the circuit of the ballast 10 are similar and have the same function as described with reference to Figure 3.

[0061] The rectifier 26 may also be connected to the input terminal 52 of the primary coil 30 instead of being connected to the intermediate tap 56B.

[0062] In another embodiment of the invention, the second alternating current connection point of the rectifier is connected to a terminal of the primary coil where it is connected to said alternating current source or to a terminal of the primary coil located between the terminal of the primary coil to which the secondary coil is connected and the terminal of the primary coil through which the alternating current source is connected.

[0063] The primary coil 30 is connected to an alternating current source 32 and the secondary coil 36 is connected to said primary coil 30 at tap 56A.

[0064] Both coils 30 and 36 have their polarity indicated by a dot 53 at the bottom right of each. The voltage between the terminal of the secondary coil where the rectifier is connected and the terminal of the secondary coil where it is connected to the primary coil is in phase with the voltage between the terminal of the primary coil where it is connected to said secondary coil and the terminal of the primary coil where it is connected to the rectifier.

[0065] The alternating current source 32 has two connection lines, one called "Neutral" and the other called "Phase," as is commonly understood by electrical engineers. The "Neutral" line must be connected to the input terminal 52 of the primary coil 30, which is indicated by a dot 53 on the coils. The "Phase" line must be connected to the output terminal 54 of the primary coil 30. If these connections were made in reverse, the ballast would still function, but the rectifier's output voltage level would be higher with respect to ground, which would require wires with greater electrical insulation, which could increase the ballast's manufacturing cost.

[0066] The intermediate tap 56A is connected to the input terminal 58 of the secondary coil 36, such that the voltage of the tap 56A is added to the voltage of the secondary coil 36. This resulting voltage will be greater than the voltage at terminal 56A, and may be greater or less than the voltage supplied by the alternating current source 32, depending on the number of turns in the windings between the intermediate taps and the number of turns in the secondary coil.

[0067] Because the voltages are in phase, the voltage across the secondary coil 36 can be calculated as follows:

[0068] Intermediate Tap Voltage 56 A = Input Voltage * ( Ni / Np ) where Ni is the number of turns between terminal 52 and the intermediate tap 56 A of the primary coil 30, and Np is the total number of turns in the primary coil 30.

[0069] Similarly, the voltage at the intermediate tap 56 B will be:

[0070] Intermediate Tap Voltage 56 B = Input Voltage * ( N2 / Np ) where N2 is the number of turns between terminal 52 and intermediate tap 56 B of primary coil 30, and Np is the total number of turns in primary coil 30.

[0071] The voltage of the secondary coil 36, which is the voltage between the input terminal 58 and the output terminal 60, is calculated as follows:

[0072] Secondary Voltage = Input Voltage * (Ns / Np) where Ns is the number of turns in the secondary coil 36 and Np is the total number of turns in the primary coil 30.

[0073] The voltage supplied to rectifier 26 is calculated as follows:

[0074] Voltage Supplied to the Rectifier = Intermediate Tap Voltage 56 A + Secondary Voltage - Intermediate Tap Voltage 56 B

[0075] This voltage is fed to the rectifier 26 which in turn feeds the LED lamp 12.

[0076] If the rectifier were connected to terminal 52 instead of Intermediate Tap 56 B, then the voltage supplied to rectifier 26 would be calculated as:

[0077] Voltage Supplied to Rectifier = Intermediate Tap Voltage 56 A + Secondary Voltage The circuit shown in Figure 4 is not exactly an autotransformer, because the input terminal 58 of the secondary coil 36 is not connected to the output terminal 54 of the primary coil 30, and therefore not all the current flowing through the secondary coil 36 is magnetically coupled with the current in the primary coil 30, but only a part of it, thus having a circuit a little different from that of a step-up autotransformer.

[0078] The circuit with the connection between the primary and secondary coils and the rectifier shown in Figure 4 is referred to in this description as the “Step-up Connection.” It could also be made by connecting the rectifier 26 to the input terminal 52 instead of being connected to tap 56 B. It is so named because the voltage at terminal 60 of the secondary winding 36 is greater than the voltage at its connection point to the primary winding on tap 56 A.

[0079] A ballast with this connection is similar to that of sodium vapor or metal additive ballasts of the Constant Wattage Autotransformer type, with the difference that the Constant Wattage Autotransformer uses a core that has a magnetic shunt and also has a capacitor in series, and the ballast of the present invention uses a conventional transformer or autotransformer and there is no capacitor connected in series.

[0080] The voltage delivered to the rectifier may be less than, equal to, or greater than the voltage supplied from the alternating current source 32, depending on the number of turns in the primary coil 30, the number of turns between terminals 52 and 56B, the number of turns between terminal 52 and 56A, and the number of turns in the secondary coil 36, and whether the connection of the rectifier 26 is made at terminal 52 or tap 56B.

[0081] The voltages mentioned above are calculated when there is no load on the transformer or autotransformer. When a load is applied to the circuit, the voltages decrease as explained below.

[0082] An alternating current to direct current rectifier 26, which may be of the diode bridge type or other type of rectifiers, is connected to terminal 52 or 56B of the primary coil 30 and terminal 60 of the secondary coil 36. One or more LED lamps 12 14 are connected to the rectifier 26 to supply a direct current to said lamp 12 with a high efficiency, greater than 90% and preferably greater than 95%.

[0083] Two circuits configured in accordance with the invention for the manufacture of the ballast 10 are shown in Figures 3 and 4. One is a step-up autotransformer and the other is a step-up winding connection in a transformer.

[0084] In another embodiment of the invention, shown in the diagram of Figure 5, the ballast circuit 10 comprises an autotransformer 16A and a transformer 16B. The autotransformer 16A has a primary coil 30A having a terminal 54A, which is connected to a secondary coil 36A at input terminal 58A. Similarly, the transformer 16B also has a secondary coil 36B, which has an input terminal 58B and an output terminal 60B.

[0085] The output terminal 60A of the secondary coil 36A is connected to the input terminal 58B of the secondary coil 36B of the second transformer 16B. In this way, the voltage supplied to the LED lamp is the sum of the voltage at the output terminal 54A plus the voltages of the secondary coil 36A and the secondary coil 36B, since all these voltages are in phase.

[0086] There are various ways to obtain a certain output voltage from the second transformer 16B which will be the sum of two or three voltages which can be the voltage of an intermediate tap 56A or of the output terminal 54A of the primary coil 30A, plus the voltage of the secondary coil 36A of the first autotransformer 16A plus the voltage of the secondary coil 36B of the second transformer 16B.

[0087] The secondary coil 36B of the second autotransformer 16B may also be connected directly to an intermediate tap 56A of the first autotransformer 16A or to the output terminal 54A of the first autotransformer 16A.

[0088] The above-mentioned connections between the primary coil and the secondary coil of the autotransformer 16 in Figures 3 and 4, or of the transformers 16A and 16B in Figure 5, of the ballast 10 have the following advantages:

[0089] The voltage supplied to the rectifier 26 and to the LED lamp 12 14 depends on the type of connection and is always the result of the sum of the input voltage to the secondary coil 36 or 36A plus the voltage of the secondary coil 36 or 36A.

[0090] In the case of connection with an intermediate tap 56A, the voltage at the intermediate tap 56A will always be a fixed proportion of the input voltage to the primary coil 30, which depends on the number of turns between terminals 52 and 56A and the number of turns in the primary coil 30. If more than one transformer is used, the output voltage will be the sum of the output voltages of said transformers.

[0091] For a ballast 10 having a single autotransformer 16, the voltage supplied to the rectifier 26 is the sum of two voltages, either that of the intermediate tap 56 A or that of the alternating current source at terminal 54, plus the voltage of the secondary coil 36.

[0092] If the rectifier 26 is connected to an intermediate tap 56 B as shown in Figure 4, the voltage applied to said rectifier 26 will be the sum of the voltage between the two intermediate taps 56 A and 56 B plus the voltage of the secondary coil 36.

[0093] The core 34 of the autotransformer 16 converts the voltage of the primary coil 30 into magnetic flux, and then converts said magnetic flux into the output voltage and current of the secondary coil 36. The core 34 of the autotransformer 16 is manufactured in a predetermined size and the dimensions of said core 34 can be designed to limit the current that is supplied to the lamp 12 of LED 14.

[0094] Since the current supplied to the LED lamp 12 14 depends on the size of the core 34 of the autotransformer 16, the output current of said autotransformer 16 cannot grow indefinitely, but reaches maximum values ​​every half cycle. The magnitude of the maximum output current depends on the volt-ampere capacity of the core 34 of the autotransformer 16, which is proportional to its cross-sectional area, therefore, the magnitude of the current supplied to the rectifier 26 and consequently to the LED lamp 12 14 is limited and does not increase exponentially when the voltage of the alternating current source 32 increases unexpectedly. In this way, the autotransformer 16 acts as a limiter of the maximum current supplied to the LED lamp 12 14.

[0095] The current supplied by the autotransformer 16 to the rectifier 26 increases as the voltage of the alternating current source 32 increases, but this increase has a relatively small slope that allows control of the same without putting the physical integrity of the LEDs 14 at risk.

[0096] The circuits constructed in accordance with the invention allow the power supplied to the LED lamp 12 to be controlled in an operating range that is safe for the LED lamp 12.

[0097] Furthermore, according to the invention, the transformer or autotransformer provides an inductive effect large enough to prevent the current from increasing too quickly, thus protecting the LED lamp.

[0098] The voltage flowing through an LED lamp, connected to a ballast according to the invention, can be calculated using the following equation:

[0099] VLED = VTR - I*RTR - VRE - Le * dl / dt where:

[0100] VLED = Voltage received by the LED lamp

[0101] VTR = Voltage received by the transformer

[0102] GO T R = Voltage that is decreased by the effect of the resistance of the transformer coil(s)

[0103] VRE = Voltage decreased across the rectifier diodes

[0104] Le * dl / dt = Voltage decreased by the added inductive effect of the circuit components, mainly the transformer or autotransformer.

[0105] Therefore, by designing or selecting the components of the ballast circuit such that the magnitude of the aggregate inductive effect of all its components (Le) is large enough, the current flowing through the LED lamp is prevented from increasing excessively quickly (dl / dt) in each half cycle, thus protecting the lamp, without the need to include any additional inductive or capacitive components connected in signal with said LED lamp. In some embodiments of the invention, this inductive effect is designed or selected to have a magnitude between 1 and 30 millihenries, preferably between 5 and 15 millihenries, and more preferably between 8 and 12 millihenries for a lamp with an input power of between 50 and 400 Watts.

[0106] That is, for a lamp with an input power of 200 Watts, the inductive effect is designed or selected such that its magnitude is between 1 and 30 millihenries per 200 Watts of lamp input power, preferably between 2 and 16 millihenries per 200 Watts of lamp input power, and more preferably between 4 and 12 millihenries per 200 Watts of lamp input power.

[0107] If the voltage supplied by the alternating current source 32 is constant, then the power supplied to the LEDs will be constant and no control mechanisms or devices will be required to maintain the power supplied to the LEDs 14 within a desired operating range, but if the voltage supplied by the alternating current source 32 is not constant, as is the case in most real operating situations, then it will be necessary to include in the ballast 10 mechanisms and / or control devices that ensure that the power developed in the operation of the lamp 12 of LED 14 is maintained within a desired operating range.

[0108] Some power control mechanisms use a current sensor, for which a shunt resistor 44 connected in series with the LED lamp 12 could be used, as shown in Figure 3, or Hall Effect current sensors, magnetic current sensors or thermal current sensors can be used.

[0109] In the circuit shown in Figures 3 through 5, elements can be added to ensure that the current supplied to the LED lamp will be non-intermittent, or more continuous. To achieve this, a capacitor 50, shown in Figures 3 through 4, can be used, or the inductor 62 shown in Figure 5 can be used.

[0110] AUTOTRANSFORMER SIZE AND VOLTAGE SELECTION

[0111] The autotransformer is usually constructed of silicon steel, and can be constructed using "El" laminations, but can also be constructed using "Ul" laminations for a more compact size. The windings or coils can be made of copper or aluminum wire.

[0112] There is a commonly used technique for manufacturing transformers that consists of making the core with silicon steel tape, then covering it with an insulating material, and finally making the windings or coils with copper or aluminum wire, thus creating a toroidal transformer. Generally, toroidal transformers tend to be slightly more efficient, and also more expensive, than transformers with "El" or "Ul" laminations.

[0113] The present invention may use autotransformers with “El” laminations or “Ul” laminations or be of toroidal construction.

[0114] In order for the present invention to be commercially viable, it is necessary for the ballast's efficiency to be high, i.e., greater than 80%, preferably greater than 90%, and more preferably greater than 95%. The higher the efficiency, the better, as this means that there are fewer losses in the lighting system comprising the lamp 12, and also that the lamp 12 will have a higher efficacy in Lumens per Watt.

[0115] To achieve high efficiency, it is necessary to have a set of LEDs that have a high voltage and low current. For example, if the alternating current source 32 supplies the autotransformer 16 with a voltage level of 120 volts RMS, then the maximum voltage or peak voltage across the primary coil 30 will be 120 volts multiplied by the square root of 2, that is,

[0116] Peak Voltage = Input Voltage X 1 .4142

[0117] Peak Voltage = 120 X 1 .4142 = 169.7 Volts

[0118] If the voltage of secondary coil 36 is for example, 30 Volts RMS, the peak voltage on this secondary coil would be:

[0119] Secondary Peak Voltage = 30 X 1.4142 = 42.4 Volts

[0120] If these two coils are connected in series, as is the case in Figure 3, the Peak Voltage supplied to the rectifier 26 would be:

[0121] Peak Output Voltage = 169.70 + 42.4 = 212.1 Volts

[0122] The LED trigger voltage will be between these two values, that is, between 170 and 212 volts, preferably close to the average of these two values. For this example, the LED trigger voltage should be around 190 volts, that is, preferably between 180 and 200 volts.

[0123] A ballast 10 according to the present invention exhibits the highest efficiency values ​​when the secondary coil 36 has between 10% and 45% of the turns that the primary coil 30 has.

[0124] It has been noticed that the efficiency is very high, greater than 95%, if the secondary coil 36 is connected in series with the primary coil 30 as shown in Figure 3.

[0125] In some embodiments of the invention, if a circuit such as that shown in Figure 4 is used, high efficiencies are obtained when the secondary coil 36 is connected to an intermediate tap 56A having a voltage between 60% and 90% of the total voltage of the primary coil 30.

[0126] It has been observed that the output voltage of the secondary coil 36, that is, the voltage that is fed to the rectifier 26 and to the LEDs, stops being sinusoidal at the moment in which the LEDs begin to conduct the electric current, and this phenomenon is due to the fact that while the voltage provided by the primary coil remains almost sinusoidal all the time, the voltage of the secondary coil is significantly reduced due to the voltage drop produced by a high current in the primary and secondary coils, which multiplied by the resistance of said coils, produces a drop in the output voltage, also due to the inductive effect of the transformer or autotransformer.

[0127] Figure 6 shows the behavior of an LED lamp when powered by a ballast in accordance with the present invention, without any element to smooth the current supplied to the LED lamp.

[0128] The horizontal axis shows the time, that is, each half cycle of the alternating current.

[0129] There are two vertical axes, on the left side the voltage axis, and on the right side the current axis.

[0130] The voltage curve V1 is the sinusoidal voltage obtained from the secondary coil with respect to the input terminal, before connecting the LED lamp.

[0131] The voltage curve V2 is the output voltage of the secondary coil 36, with respect to the input terminal, once the LED lamp is connected, and fed to the rectifier 26. The voltage follows a sinusoidal wave until the LED Triggering Voltage is reached, marked on the left side as Vdis. Once it reaches the LED Triggering Voltage level, the voltage undergoes a significant decrease, due to the voltage drop that appears when the current begins to be conducted by the LEDs. This voltage drop corresponds to the product of the current by the resistance of the primary and secondary coils and by the voltage drop due to the inductive effect.

[0132] Output Voltage = Induced Voltage - Current X Coil Resistance

[0133] - Voltage Drop due to Inductive Effect

[0134] The current curve, labeled "I LED," remains at zero until the LED lamp's trigger voltage is reached. Once this value is reached at time T 1 , it begins to slowly increase due to inductive effects in the transformer or autotransformer, and presents a nearly constant slope until it begins to stabilize and finally drops to zero at time T2. The current remains at zero until the next half cycle.

[0135] If the magnitude of the inductance of the circuit to which the LEDs are connected increases, the ILED current curve, shown as a dotted line, begins to circulate at T3. This helps protect the LED lamp from an excessive increase in current and therefore the power supplied to the LED lamp.

[0136] The cross-sectional area of ​​the autotransformer core and the number of turns of the windings determine the maximum current supplied to the LED lamp, as well as the slope of the current with respect to time in each half cycle.

[0137] In prior art designs, the use of isolation transformers to power LED loads has been shown, but these designs require that all of the power supplied to the LED lamp be converted in the transformer first to magnetic flux and then to voltage and current in the secondary coil.

[0138] For those prior art designs, a transformer with a 100- to 120-volt-ampere core is required to power a 100-watt LED lamp.

[0139] In the designs proposed in this invention, only a portion of the power supplied to the LEDs needs to be converted to magnetic flux and then to voltage and current in the secondary coil. The remainder of the power comes directly from the AC source feeding the primary coil.

[0140] This feature has the advantage that the autotransformer core used does not need to be as large, which translates into a requirement for an autotransformer with a much smaller cross-section, since the autotransformer will be acting as a step-up autotransformer.

[0141] For example, for a connection like the one shown in Figure 3, with an autotransformer that is powered at 120 volts and with an output voltage of 140 volts, that is, the voltage between terminals 54 and 60 is 20 volts, and a LED lamp of 100 nominal Watts, it will be sufficient to connect an autotransformer with a core with a much smaller cross section, with a capacity of 15 to 25 Volt-Amperes, which makes this autotransformer much smaller, cheaper and more efficient.

[0142] This is the main advantage of the proposed designs, the significant savings of more than 60% in the cost of the autotransformer required to operate the LED lamp of a given wattage.

[0143] However, the proposed designs have the disadvantage of not having galvanic isolation, which implies that the construction of the LED lamp must have better insulation in the LED plates and in the wiring used, increasing the manufacturing cost of the lamp a little, although the savings in transformer costs and the reduction in losses amply justify this increase in the cost of the LED plates and the insulation of the cables.

[0144] CURRENT OR POWER CONTROL MECHANISMS

[0145] If the alternating current source has a substantially constant and uniform voltage level over time, it is possible to use the circuits shown in Figures 3 to 5 without putting the physical integrity of the LED lamp at risk, since the average current that will pass through them will always be the same.

[0146] However, in most cases the supplied voltage will not be perfectly uniform and it will then be necessary to incorporate control mechanisms to maintain the current and / or power of the LED lamp within a desired range.

[0147] Current or power control mechanisms can be divided into two types:

[0148] First type: Those that vary the output voltage level of the autotransformer, which is the voltage supplied to the rectifier that feeds the LED lamp, by varying the connection point between the primary coil and the secondary coil and / or by modifying the number of turns of the secondary coil and / or by modifying the connection point of the rectifier bridge to the primary and secondary coils and / or by modifying the connection point of the alternating current source to the primary coil.

[0149] In these circuits, the current supplied by the autotransformer to the LED lamp depends on 5 factors:

[0150] (1 ) the supply voltage,

[0151] (2) the connection point between the primary coil and the secondary coil, this point being able to be the output terminal of the primary coil as already mentioned,

[0152] (3) the ratio of turns between the primary coil and the secondary coil, (4) the connection point between the rectifier bridge and the primary and secondary coils, and

[0153] (5) the connection point of the power supply to the primary coil.

[0154] This type of control mechanism is based on manipulating, by means of switches or selectors, the proportion between the output voltage delivered to the diode bridge 26 and the LED lamp and the input voltage fed to the circuit.

[0155] Second type: Those that limit the current supplied to the LED lamp by cutting the wave, using solid state elements such as transistors, SCRs, TRIACs, IGBTs or other types of transistors.

[0156] This category also includes control mechanisms that regulate the proportion of conduction cycles or half-cycles to regulate the average current supplied to the LED lamp.

[0157] The two types of power or current control mechanisms can be mixed.

[0158] An example of the first type is shown in Figure 7. With reference to Figure 7, numeral 10 generally designates a ballast comprising an electrical power supply circuit for supplying a lighting system comprising one or a plurality of lamps 12 and LEDs 14 connected in series to said circuit. It is understood that an LED lamp may consist of one or more light-emitting diodes (LEDs) within the same container.

[0159] The electric power supply circuit 10 comprises a transformer 16, a plurality of switches 18, 20 and 22 which are operated by a controller 24 and an alternating current to direct current rectifier which may be a diode bridge 26. The switches 18, 20 and 22 may be of any type suitable for the particular application of the invention, for example: electromechanical relays or electronic switches.

[0160] The AC-to-DC rectifier 26 can be a diode bridge, consisting of four conventional diodes, or it can be made up of low-loss diodes, such as Schottky diodes. To prevent the diode bridge from overheating, it can be mounted on a heat sink made of copper or aluminum, cooled by natural convection, or it could also have a small fan.

[0161] In one embodiment of the invention, the transformer 16 comprises a primary coil 30 connected to an alternating current source 32, a ferromagnetic core 34 and a plurality of secondary coils 36, 38, 40 and 42. The secondary coils 36, 38, 40 and 42 have different numbers of turns and can be selectively connected by operating the respective switches 18, 20 and 22 as explained below.

[0162] The secondary coils 36, 38, 40 and 42 have preselected numbers of turns so that when connected and disconnected by their respective switch 18, 20 or 22 each one feeds a predetermined voltage level to the rectifier 26. In one of the embodiments of the invention, the transformer 16 has 4 secondary coils.

[0163] When the controller 24 operates the switches 18, 20 or 22 the number of effective turns in the secondary coil is modified and, consequently, the ratio between the output voltage and the input voltage is modified.

[0164] For example, if transformer 16 is built to be supplied with 120 volts of alternating current, it could have 10 turns per volt, and thus have 1200 turns in the primary coil 30. The secondary coil 36 could thus have 160 turns to deliver 16 volts, the secondary coil 38 would have 80 turns to deliver 8 volts, the secondary coil 40 would have 40 turns to deliver 4 volts and finally the secondary coil 42, which would always be connected, would have 200 turns to deliver 20 volts.

[0165] Selecting the number of turns in the secondary coils is very important, as it determines the relative size of the steps or steps in the ratio between the output voltage and the input voltage. To adequately control the average current or power supplied to the LED lamp, these steps or steps must be small, allowing the ratio between the output voltage and the input voltage to be varied in small increments, preferably between 1 and 4% of the input voltage.

[0166] The smaller the steps, the more precise the control of the current or average lamp power. Preferably, the smallest step is sized between 1 and 4% of the input voltage, and the other steps are multiples of this smallest step.

[0167] To measure the current, a resistor 44 is connected in the circuit connecting the LED lamp 12 to the rectifier 26, so that a signal indicative of the level of current 46 flowing through the LED lamp 12 is taken.

[0168] Switch 18 has two connection positions and can connect terminal 18 A to terminal 18 B in a first position or to terminal 18 C in a second position. Similarly, switch 20 can connect terminal 20 A to terminal 20 B in a first position or to terminal 20 C in a second position. Likewise, switch 22 can connect terminal 22 A to terminal 22 B in a first position or to terminal 22 C in a second position.

[0169] By selectively connecting the terminals of each switch, the secondary coils 36, 38 and 40 are connected or disconnected to the circuit that supplies the rectifier 26, thus varying the effective number of turns of the coils that are operating and consequently, the voltage and current received by the rectifier 26 can be varied to increase the level of direct current circulating through the LED lamp 12 when the voltage received by the primary coil 30 of the autotransformer is less than a predetermined voltage level, or the level of direct current received by the rectifier 26 can be decreased when the voltage received by the primary coil 30 of the autotransformer is greater than a predetermined voltage level, thus protecting the LED lamp 12 from damage caused by a high current level. In this example, coil 42 is always connected to the circuit, and its number of turns will always be present in the secondary coil.

[0170] The level of direct current passing through the LED lamps 14 is measured by a current measuring device 45 that generates a signal 46 indicative of the level of current that is passed to a controller 24 such that said controller 24 generates control signals 48 A, 48 B and 48 C that act on the switches 18, 20 and 22 respectively.

[0171] Another way to control the ratio of output voltage to input voltage is by manipulating the connection point between the primary coil and the secondary coil. This is shown in Figure 8, which illustrates another embodiment of the present invention.

[0172] In Figure 8, the primary coil 30 has two intermediate taps 56 A and 56 B, for example, at 50% and 75% of the number of turns of the primary coil.

[0173] If the primary coil has 1200 turns and is supplied at 120 volts, then the intermediate tap 56A will be at 600 turns from the input terminal 52 and will deliver 60 volts, and the intermediate tap 56B will be at 900 turns from the input terminal 52 and will deliver 90 volts with respect to the input terminal 52.

[0174] The third possible connection point is the output terminal 54 of the primary coil, thus achieving that the autotransformer 16 acts as a step-up autotransformer.

[0175] Three switching devices 62A, 62B and 62C are used, which allow the connection point of the primary coil 30 with the secondary coil 36 to be selected. These switching devices can be electromechanical relays or contactors, or solid state devices such as SCRs or TRIACs.

[0176] When the controller 24 acts on the switches 62A, 62B and 62C, the ratio between the output voltage and the input voltage is changed.

[0177] The controller 24 measures the current being delivered to the LEDs 14 by the current sensor 45, and generates control signals 48A, 48B or 48C which act on the switching devices 62A, 62B and 62C respectively to select the connection point between the primary coil 30 and the secondary coil 36, and thus maintain the current within a predetermined range. Obviously, there can only be at most one control signal present at any one time, otherwise a short circuit would occur in the primary coil.

[0178] In this design, the controller 24 could even turn off the lamp by not generating any control signal, and the LEDs would be off.

[0179] Another embodiment of this type of control for the present invention is shown in Figure 9.

[0180] In this embodiment, the autotransformer 16 has an output terminal 54 and three secondary coils 40, 38 and 36, and there are three switches 62A, 62B and 62C which are connected to the input and / or output terminals of the said three secondary coils 40, 38 and 36. By operating only one of the three switches, the number of effective turns in the secondary coil is modified.

[0181] If, for example, switch 62 A is activated, coils 40, 38 and 36 are used. If switch 62 B is activated, only coils 38 and 36 are used, leaving coil 40 inoperative. Finally, if switch 62 C is operated, only coil 36 operates. In this way, by operating one of the three switches, the number of effective turns in the secondary coil is modified and, consequently, the proportion between the output voltage and the input voltage.

[0182] The controller 24 measures the current supplied to the rectifier 26 and to the LEDs 14, and generates control signals 48A, 48B or 48C to modify the number of effective turns in the secondary coil and consequently the ratio of output voltage to input voltage in order to maintain the current or power within a predetermined operating range. If none of the 3 switches 62A, 62B and 62C are operated, the lamp will remain off since no current can flow to the LED lamp.

[0183] Another embodiment of this type of control for the present invention is shown in Figure 10.

[0184] In this embodiment, the transformer 16 has a primary coil 30 and a secondary coil 36 connected in series. The primary coil 30 has multiple connection terminals 54, 56 A, 56 B and 52 for connecting the alternating current source 32 through switches to the primary coil, and also has multiple terminals 56 C and 56 D for connecting the bridge rectifier 26 to the primary coil 30, through switches.

[0185] The secondary coil 36 also has multiple connection terminals 60 and 61 for connecting the rectifier 26 to the output terminal of the secondary coil 36.

[0186] The controller 24 measures the current in the circuit and generates the control signals 48A, 48B, 48C, 48D, 48E, 48F, 48G and 48H to modify the effective number of turns and therefore the ratio between the output voltage and the input voltage to thus control the current and power in the LED lamp 12.

[0187] Switches 62A and 62B, controlled by control signals 48A and 48B respectively, modify the connection point of the alternating current voltage source 32 to the output terminal of the primary coil 30, either at terminal 54 or 56 A respectively.

[0188] Switches 62C and 62D, controlled by control signals 48C and 48D respectively, modify the connection point of the alternating current voltage source 32 to the input terminal of the primary coil 30, either at terminal 56B or 52 respectively.

[0189] By operating these 4 switches, the number of effective turns of the transformer 16 that receive the power from the alternating current source 32 is modified, thus modifying the voltage in both the primary coil 30 and the secondary coil 36 of the transformer.

[0190] Switches 62E and 62F, controlled by control signals 48E and 48F respectively, modify the connection point of the primary coil 30 with the rectifier 26, to connect to terminal 56C or 56D respectively.

[0191] Switches 62G and 62H, controlled by control signals 48G and 48H respectively, modify the connection of the output terminal of the secondary coil 36 with the rectifier bridge 26, by connecting with terminal 60 or 61 respectively.

[0192] By selectively operating switches 62A to 62H, the number of effective turns in the primary 30 and secondary 36 coils is modified, and therefore the ratio of output voltage to input voltage, thereby modifying the voltage supplied to the LED lamp 12, which can be controlled in a number of values ​​to control the current and power of the LED lamp 12 in a predefined range.

[0193] The number of connection combinations that can be made according to the invention depends on the number of connections for each connection point. In the embodiment shown in Figure 10, there are 2 for the input terminal of the primary coil 30, 2 for the output terminal of the primary coil 30, 2 for the connection between the primary coil 30 and the rectifier 26 and 2 for the connection between the secondary coil 36 and the rectifier 26, thus giving 2 X 2 X 2 X 2 = 16 possible combinations, allowing the current to be controlled in 16 different “steps”.

[0194] Relays with one input terminal and two output terminals can also be used, as shown in Figure 7, one normally open and one normally closed, thus requiring only 4 relays and 4 control signals.

[0195] The figures show two connection points for each terminal, but there can be 3 or 4 at any of the connection points, so that if for example 4 connection points with 4 switches are used at the input of the primary coil 30, and 4 connection points with 4 switches at the output of the primary coil 30, then there would be 4 X 4 X 2 X 2 = 64 steps using 4 + 4 + 2 + 2 = 12 switches.

[0196] An arrangement of this type also allows the lamp 12 to be turned off, for example, by not operating any of the switches 48A and 48B, since in this way the lamp would remain off.

[0197] Switches can be electromechanical or solid state for long life with minimal maintenance.

[0198] In any of the embodiments shown in Figures 7 to 10, the switches may be electromechanical relays or contactors, or solid state switches such as SCRs, TRIACs, MOSFETs or IGBTs, and may be of the type that start conducting current at any time, known as “random-crossing” in English, or of the type that start conducting current when the voltage passes through zero, known as zero-crossing.

[0199] WAVE CUT CONTROL

[0200] In another embodiment of the invention, the current controller circuit is based on controlling the current supplied to the LED lamp by means of wave chopping.

[0201] An embodiment of the present invention is shown in Figure 1 1 , but it should be understood that wave cutting can be performed in various ways.

[0202] The transformer 16 is connected to the alternating current power supply 32 via terminals 52 and 54, and terminal 54 is connected to the secondary coil 36 at the input terminal 58, and the output terminal 60 is connected to a rectifier comprising two conventional diodes 26A and 26B, and two SCRs 26C and 26D.

[0203] A controller 24 measures the current supplied to the LEDs 14 by means of a current sensor 45 that generates a control signal 46, and regulates the time that the two SCRs 26C and 26D are fired, by generating a control signal 48D, allowing them to operate 100% of the time making the LEDs operate at full power, or only a portion of each half cycle of the alternating current. In this way, the current and therefore the power supplied to the LEDs 14 is controlled, in a number of possible power values, for example, from 10% to 100% of the maximum power that the LEDs 14 can receive.

[0204] The controller 24 may even turn off the lamp 12 by not generating any control signal 48D for the SCRs 26C and 26D.

[0205] The wave cutting can be done with two SCRs and two diodes as shown in Figure 1 1 or it can be done using a conventional diode bridge where there are diodes 26A and 26B and SCRs 26C and 26D, and using a single SCR or a single TRIAC connected in signal between the diode bridge and the LED lamp, or using a single TRIAC or two SCRs in back to back connection between the transformer and the rectifier.

[0206] A manual controller can also be used to trigger the 26C and 26D SCRs and adjust the power with a potentiometer.

[0207] In another embodiment of the invention, the average current or power level supplied to the LEDs 14 can be manipulated with the circuit of Figure 11 by controlling the ratio of current conduction cycles or half-cycles. It is known that the human eye cannot distinguish changes in illumination that occur faster than 30 times per second. Taking advantage of this characteristic of the human eye, it is possible to control the current level and power of the lamp 12 by controlling the ratio of conduction cycles or half-cycles.

[0208] For example, for a luminaire operating at 60 Hz, there are 60 cycles or 120 half-cycles of current conduction every second.

[0209] If the lamp is to be operated at 100% power, then the 120 half-cycles of conduction are activated, as shown in Figure 12, above.

[0210] If the lamp is to be operated at 80% power, then the SCRs are turned on in 4 out of 5 cycles or half cycles.

[0211] If the lamp is to be operated at 75% power, then the SCRs are turned on in 3 out of every 4 cycles or half cycles, as shown in Figure 12, in the second line from the top.

[0212] If the lamp is to be operated at 66% power, then the SCRs are turned on in 2 out of every 3 cycles or half cycles, as shown in Figure 12, in the third line from the top.

[0213] If the lamp is to be operated at 60% power, then the SCRs are turned on in 3 out of every 5 cycles or half cycles.

[0214] If it is desired to operate the lamp at 50% power, then the SCRs are turned on in 1 out of every 2 cycles or half cycles, as shown in Figure 12, on the bottom line, and in this way, the lamp power can be controlled by controlling the proportion of cycles or half cycles of conduction with respect to the total cycles or half cycles in a given period of time.

[0215] If the circuit of Figure 1 1 is used with a wave-cut current control mechanism, the average current and thus the amount of power consumed by the lamp 12, as well as the amount of light emitted by the lamp 12, can be regulated.

[0216] Using this current control mechanism, the current waveform is modified, as shown in the upper part of Figure 13, where the waveform of the current flowing through the LEDs 12 is observed if the wave chopping is not done, that is, if the SCRs are allowed to operate 100% of the available time, from time T1 to time T2.

[0217] If the SCRs only allow the current to pass from time T3 to time T2, then the average current will decrease significantly, thus having an average current that can be controlled in a plurality of values, from 5 or 10% to 90 or 100% of the average current consumed by the lamp 12, varying the moment in which the SCRs are triggered. This variation can be regulated manually by means of a circuit that includes a potentiometer and an optostat, or it can be regulated using an electronic controller that generates the trigger signal digitally.

[0218] To perform wave-cut switching on or to switch on a certain proportion of cycles or half-cycles, various semiconductors can be used, for example, SCRs, TRIACS or Power Transistors such as IGBTs or MOSFETs.

[0219] In some embodiments of the invention, it is possible to combine these two techniques to regulate the average current delivered to the LEDs 14; for example, to obtain an average current of 87%, full power can be delivered for 3 cycles, and on the fourth cycle, a current corresponding to 50% of the nominal current can be supplied to the LEDs 12. By combining these two techniques, it is possible to regulate the average power delivered to the LEDs 12 over a plurality of values.

[0220] The present invention provides an apparatus and a method for operating one or more LED lamps 12 comprising a transformer or autotransformer with advantages in operating costs and equipment costs in addition to the fact that the operation of said LED lamps 12 is carried out with a high efficiency, greater than 90% and preferably greater than 95%, greater than that obtained if a conventional transformer or a switching power supply is used.

[0221] In some embodiments of the invention, the rectifier has a heat sink, and optionally a fan, to prevent the temperature of the rectifier from exceeding a predetermined value.

[0222] In some embodiments of the invention, the rectifier 26 is selected from the group comprising a conventional diode bridge, a low loss diode bridge, and a diode bridge formed by Schottky diodes.

[0223] The present invention allows a ballast to be manufactured using electrical and electronic components that can have a very long life, and thanks to this, offer a minimum useful life of 5 years, being able to reach up to 10 or 15 years without failing in the field, thanks to the fact that the ballast can use transformers or autotransformers of robust construction, and the control electronics could be manufactured using long-life electronic components, avoiding the use of components that could fail in less than 5 years, such as electrolytic capacitors.

[0224] To smooth the current wave supplied to the LEDs 14, elements such as a capacitor 50 connected in parallel with the LEDs 14 and / or an inductor 62 connected in signal with the LEDs 14 can be added between the rectifier 26 and the lamp 12, as mentioned above.

[0225] In electrical networks there may be voltage spikes of very short duration and very high magnitude, which can damage electronic circuits and LEDs 14. These voltage spikes can have an amplitude of up to 6000 Volts and a duration that can range from 10 to 500 microseconds, and are caused by atmospheric discharges, operation of switches when there are inductive loads, starting or stopping of motors, starting or stopping of welding equipment, etc.

[0226] Figure 14 shows a circuit according to the invention optionally comprising two surge protection elements.

[0227] The protection elements can be metal oxide varistors, known in English as “MOV” or “Metal Oxide Varistors”, but other types of protection elements could also be used, such as gas tube surge arresters, spark gaps, SCRs, avalanche diodes, or transient absorption zener diodes.

[0228] In Figure 14, a varistor 68 is shown connected in parallel with the alternating current source 32, and a varistor 72 is connected in parallel with the LED lamp 12. In a ballast there may be one or more protection elements connected, and they may be the same or different, i.e. a spark gap tube may be connected in parallel with the alternating current source 32 and a metal oxide varistor with its fuse in parallel with the LED lamp 12.

[0229] The 68 varistor can be of the type that at the end of its useful life goes into open circuit, or it can be of the type that at the end of its useful life goes into short circuit, for which a 70 fuse would have to be installed in conjunction with the 68 varistor to prevent the lamp from no longer being able to operate when the 68 varistor burns.

[0230] The fuse 70 can be a conventional fuse or it can also be a self-resetting fuse, so that when a voltage spike occurs, the varistor 68 absorbs the voltage spike, and if the current exceeds a certain value, the fuse opens momentarily due to the increase in temperature produced by the current that passed through it, and after a few minutes, when it cools down, it closes again and then the varistor 68 can continue protecting the circuit that powers the LED lamp 12.

[0231] Similarly, a fuse 74 can be connected in series with the varistor 72 if necessary, and this fuse 74 can be a conventional fuse or a self-resetting fuse.

[0232] These protection elements can be connected as shown in Figure 14 in parallel with the alternating current source 32, which is how the varistor 68 is shown connected, but they can also be connected in parallel with the terminals 52 and 56A of the primary coil 30, or in parallel with the terminals 58 and 60 of the secondary coil 36.

[0233] The protection elements can also be connected in parallel with the input of the rectifier 26, at terminals 52 and 60, or in parallel with the output of the rectifier 26, which is the power supply to the LED lamp 12, which is as shown in the varistor 72.

[0234] In each of these positions, either the varistor alone can be connected, or the varistor and a conventional fuse or a self-resetting fuse can be connected in series.

[0235] In each of these positions, another type of protection element can also be connected, or a protection element with its respective fuse to protect the ballast 10 and the LED lamp 12 from transient voltage spikes.

[0236] All of these protective elements are installed with the intention of extending the life of the ballast, thus reducing the maintenance costs of the LED12 lamp.

[0237] It is understood that only some of the preferred embodiments of the invention have been described herein and that many changes may be made to the described embodiments as best adapt the invention to a particular use, without departing from the spirit and scope thereof, which is defined in the appended claims.

[0238] Having described the invention, it is considered to present novelty, inventive activity and industrial application, so the invention defined in the following claims is claimed as property.

Claims

CLAIMS 1. A ballast comprising a circuit for supplying electric power to one or more LED lamps from an alternating current source, said circuit comprising: a transformer comprising a steel core and at least two coils, a primary coil and a secondary coil, said primary coil having a plurality of terminals, configured to be connected to said alternating current source or to said secondary coil or to an alternating current to direct current rectifier, and said secondary coil having a plurality of terminals configured to be connected to said primary coil or to said rectifier,wherein said primary coil and said secondary coil are connected to each other such that the voltage between the terminal of the secondary coil where the rectifier is connected and the terminal of the secondary coil where it is connected to the primary coil is in phase with the voltage between the terminal of the primary coil where it is connected to said secondary coil and the terminal of the primary coil where it is connected to said rectifier, and where the terminal of the primary coil through which it is connected to the secondary coil is distinct from the terminal of said primary coil through which it is connected to said rectifier,an alternating current to direct current rectifier comprising at least two alternating current connection points configured to be connected to a terminal of the primary coil of said transformer and to a terminal of the secondary coil to receive alternating current and at least two direct current connection points configured to be connected to the LED lamp and supply direct current to said LED lamp, wherein a first alternating current connection point of the rectifier is connected to a terminal of the secondary coil of the transformer, and a second alternating current connection point of the rectifier is connected to a terminal of the primary coil of the transformer, and wherein said transformer is directly connected to the rectifier without any capacitive or inductive device electrically connected in series with said transformer between the alternating current source and said rectifier.

2. The ballast according to claim 1, wherein the terminal of the secondary coil through which it is connected to said primary coil is directly connected to one terminal of the primary coil, so that the two coils are connected in series, forming an autotransformer, without any inductive or capacitive elements between them.

3. The ballast according to claim 1, wherein the secondary coil is connected to a terminal of the primary coil located between the terminals of said primary coil through which it is connected to the alternating current source.

4. The ballast according to any of claims 2 to 3. 3, where the second alternating current connection point of the rectifier is connected to a terminal of the primary coil where it is connected to said alternating current source or to a terminal of the primary coil located between the terminal of the primary coil to which the secondary coil is connected and the terminal of the primary coil through which the alternating current source is connected.

5. The ballast according to any of claims 1 to 3. 4, where the maximum current fed to the LED lamp and its growth rate per unit of time are regulated by means of the magnitude of the inductance of said transformer or autotransformer or by the size of the core of said transformer or autotransformer or by a combination of both factors.

6. The ballast according to claim 5, wherein the inductive effect of said transformer or autotransformer is designed or selected such that its magnitude is between 1 and 30 millihenries, preferably between 2 and 16 millihenries, and more preferably between 4 and 12 millihenries for every 200 Watts of input power.

7. The ballast according to any one of claims 1 to 6, wherein the electrical efficiency, measured as the ratio of the output power to the input power of said ballast, is equal to or greater than 90%.

8. The ballast according to any one of claims 1 to 6, wherein the electrical efficiency, measured as the ratio of the output power to the input power of said ballast, is equal to or greater than 95%.

9. The ballast according to any of claims 1 to 8, wherein the transformer is selected from the group comprising a transformer manufactured with “El” laminations, a transformer manufactured with “III” laminations, a transformer of toroidal construction, and a high-efficiency transformer.

10. The ballast according to any one of claims 1 to 4, wherein said secondary coil is connected to said primary coil at a plurality of terminals through switches that allow each terminal of said secondary coil to be selectively connected and disconnected to said primary coil.

11. The ballast according to any one of claims 1 to 4, wherein the transformer has a plurality of secondary coils, and these secondary coils are connected to a plurality of switches that allow selectively varying the ratio between the output voltage and the input voltage of the transformer.

12. The ballast according to any one of claims 1 to 4, wherein the transformer has a plurality of output terminals in the secondary coil, and these terminals are connected to a plurality of switches, and in turn said plurality of switches are connected to the rectifier, such that the selective operation of said plurality of switches allows to selectively vary the ratio between the output voltage and the input voltage of the transformer.

13. The ballast according to any one of claims 1 to 4, wherein the transformer has a plurality of terminals in the primary coil of the transformer, and these terminals are connected to a plurality of switches, and in turn said plurality of switches are connected to the rectifier, such that the selective operation of said plurality of switches allows to selectively vary the ratio between the output voltage and the input voltage of the transformer.

14. The ballast according to any of claims 1 to 4, wherein the transformer has a plurality of connection terminals in the primary coil of the transformer, and these terminals are connected to a plurality of switches, and in turn said plurality of switches are connected to the alternating current source, such that the selective operation of this plurality of switches allows to selectively vary the ratio between the output voltage and the input voltage of the transformer.

15. The ballast according to any of claims 10 to 14, further comprising a current sensor that produces a first signal indicative of the level of direct current flowing through said LED lamp and a controller that receives said first signal and produces a second signal. control that is used to actuate at least one of said switches.

16. The ballast according to claim 10, further comprising a current sensor that produces a first signal indicative of the level of direct current flowing through said LED lamp and a controller that receives said first signal and produces a second control signal that is used to actuate at least one of said switches selectively to change the connection terminal of the primary coil that is connected to the secondary coil.

17. The ballast according to any of claims 10 to 16, wherein said switches are electromechanical relays.

18. The ballast according to any of claims 10 to 16, wherein said switches are electronic or solid-state switches, either of the type that start conduction at any time, known in English as “random crossing” or of the type that start conduction when the voltage crosses zero, known in English as “zero crossing”.

19. The ballast according to any of claims 1 to 4, further comprising a current sensor that produces a first signal indicative of the level of direct current flowing through said LED lamp, a solid state switch connected in signal with said LED lamp and a controller that receives said first signal and produces a second control signal that is used to actuate said solid state switch.

20. The ballast according to claim 19, wherein said second control signal allows adjusting the proportion of the time of each cycle or of each half cycle that the direct current circulates through said LED lamp.

21. The ballast according to claim 19, wherein said second control signal allows adjusting the direct current flow in a percentage of cycles or half cycles.

22. The ballast according to any of claims 15, 16, 19, 20 or 21, wherein said current sensor is selected from the group comprising a shunt resistor connected in signal with the LED lamp, a Hall Effect sensor, a magnetic sensor or a thermal sensor.

23. The ballast according to any of claims 1 to 4, wherein said circuit further comprises a second transformer having a second primary coil configured to be connected to the current source. alternates in parallel with said transformer and a second secondary coil configured to be connected in series to said rectifier.

24. The ballast according to any of claims 11 or 15, wherein the number of turns of the secondary coils is selected in such a way as to allow varying the ratio between the output voltage of said ballast and the input voltage to said ballast in steps or steps less than 10% of said input voltage.

25. The ballast according to any of claims 10, 12, 13, 14, 15 or 16, wherein the number of turns between the connection terminals of the primary coil or the secondary coil is selected in such a way as to allow varying the ratio between the output voltage of said ballast and the input voltage to said ballast in steps or steps less than 10% of said input voltage.

26. The ballast according to any one of claims 1 to 25, wherein the circuit further includes a capacitor connected in parallel with the LED lamp, to smooth the current waveform passing through it.

27. The ballast according to any one of claims 1 to 25, wherein the circuit further includes an inductor connected in series between the rectifier and the LED lamp, to smooth the current waveform passing through it.

28. The ballast according to any of claims 1 to 25, wherein the transformer capacity measured in Volt-Amperes is between 5% and 40% of the value of the power measured in Watts of said LED lamp.

29. The ballast according to any one of claims 19 to 21, wherein said solid state switch comprises two SCRs or two TRIACs within the rectifier, or a single SCR or a single TRIAC connected in series between the rectifier and the LED lamp, or a TRIAC or two SCRs in back-to-back connection connected in series between the transformer and the rectifier.

30. The ballast according to any of claims 19 to 20, wherein said circuit comprises a wave-cut current control mechanism by means of SCRs, TRIACs or Power Transistors such as IGBTs or MOSFETs.

31. The ballast according to any one of claims 1 to 4, wherein said rectifier is selected from the group comprising a conventional diode bridge, a low-loss diode bridge and a diode bridge formed by Schottky diodes.

32. The ballast according to any one of claims 1 to 4, wherein said rectifier has a heat sink, and optionally a fan.

33. The ballast according to any of claims 1 to 4, further comprising one or two surge protection elements, connected in parallel with the alternating current source, in parallel with terminals of the primary coil, in parallel with terminals of the secondary coil, in parallel with the input of the rectifier, or in parallel with the LED lamp.

34. The ballast according to claim 33, further comprising a conventional fuse or an automatic resetting fuse connected in series with each of said transient voltage spike protection elements connected to the ballast.

35. The ballast according to any of claims 33 or 34, wherein the elements for protection against transient voltage spikes are selected from the group comprising metal oxide vahstors, gas tube surge arresters, spark gaps, SCRs, avalanche diodes, and transient absorption zener diodes.

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