Driver circuit for an LED lighting tube, LED lighting tube and method for providing a controlled DC output power

Abstract

The invention provides a driver circuit, an LED lighting tube and a method for providing a controlled DC output power. An open loop control is used for controlling the DC output power in the case that a voltage of an AC input power is in a first voltage range. A closed loop control is used for controlling the DC output power in the case that the voltage of the AC input power is in a second voltage range.

Claims

1. A driver circuit for an LED lighting tube, the driver circuit comprising: a set of external connecting pins for receiving an AC input power; a set of internal connecting pins for connecting the driver circuit to electric poles of at least one LED light engine; a transformer circuit, wherein the set of external connecting pins is arranged on a primary side of the transformer circuit and wherein the set of internal connecting pins is arranged on a secondary side of the transformer circuit; and a controller circuit for controlling transmission of electrical energy from the primary side to the secondary side of the transformer circuit for providing a controlled DC output power at the set of internal connecting pins; wherein the controller circuit is configured and arranged to control said transmission in an open loop control when the at least one LED light engine comprises a plurality of light engines; and wherein the controller circuit is further configured and arranged to control said transmission in a closed loop control when the at least one LED light engine comprises only one light engine.

2. The driver circuit according to claim 1, wherein the open loop control operates at lower voltage values than the closed loop control.

3. The driver circuit according to claim 1, wherein the closed loop control is based on a parameter of the DC output power.

4. The driver circuit according to claim 3, wherein the closed loop control is based on a current value of the DC output power.

5. The driver circuit according to claim 1, further comprising a rectifier circuit connected to the set of external connecting pins for rectifying the AC input power, wherein a recognition of a number of the LED light engines connected to the driving circuit is derived from a voltage of a rectified input power.

6. The driver circuit according to claim 5, further comprising a sampling resistor arranged to carry the rectified input power, wherein the recognition of the number of the LED light engines connected to the driving circuit is based on a voltage drop between the sampling resistor and ground.

7. The driver circuit according to claim 1, further comprising a switching circuit driven by the controller circuit and configured to switch a current through a winding of the primary side of the transformer circuit, wherein the open loop control is based on a voltage drop between the switching circuit and ground.

8. An LED lighting tube comprising: an LED light engine with at least one light-emitting diode; and the driver circuit according to claim 1; wherein the set of internal connecting pins is connected to electric poles of the LED light engine.

9. A method for providing a controlled DC output current, the method comprising: receiving an AC input power at a primary side of a transformer circuit; controlling transmission of electrical energy from the primary side of the transformer circuit to a secondary side of the transformer circuit with a controller circuit; providing the controlled DC output current on the secondary side of the transformer circuit based on the transmitted electrical energy; and delivering the controlled DC output current to at least one light engine; wherein said transmission is controlled in an open loop control when the at least light engine comprises a plurality of light engines; and wherein said transmission is controlled in a closed loop control when the at least light engine comprises only one light engine.

10. The method according to claim 9, wherein the closed loop control is based on a parameter of a DC output power.

11. The method of claim 9, wherein the closed loop control includes a regulating circuit connected between the secondary side of the transformer circuit and the controller circuit.

12. The driver circuit according to claim 1, wherein the closed loop control further comprises a regulating circuit connected between the secondary side of the transformer circuit and the controller circuit.

Description

(1) FIGS. 1 and 2 show schematic illustrations of driver circuits according to embodiments of the present invention. FIGS. 1 and 2 further serve to illustrate a method for providing a controlled DC output current, in particular to an LED light engine of a retrofit LED lighting tube according to another embodiment of the present invention.

(2) FIG. 3 schematically shows an LED lighting tube according to another embodiment of the present invention.

(3) FIGS. 4 and 5 schematically show, as has been described above, a singled-slot luminaire and a tandem luminaire, respectively.

(4) Elements that are identical, similar or have an identical or similar effect are provided with the same reference numerals in the figures. The figures and the size relationships of the elements illustrated in the figures among one another should not be regarded as to scale. Rather, individual elements may be illustrated with an exaggerated size to enable better illustration and/or better understanding.

(5) With reference to FIG. 1, a first embodiment of a driver circuit 10 is described on the basis of schematic illustrations. It should be understood that the functions, concepts and steps described with respect to the driver circuit 10 can be seen as part of, or as forming, a method for providing a controlled DC output power according to one embodiment of one of the aspects of the present invention.

(6) The driver circuit 10 comprises a first external connecting pin 11 and a second external connecting pin 12 for connecting the driver circuit 10 to a luminaire, in particular to a CCG luminaire which, in turn, may be connected to the AC mains powerline. The CCG luminaire may be a single-slot luminaire having a single slot for a lighting tube, or may be a tandem luminaire having two or more slots for lighting tubes.

(7) The driver circuit 10 further comprises a rectifying circuit 14 configured to rectify an AC input power received between the first and the second external connecting pins 11, 12 to provide a rectified DC power at an internal node 18 of the driver circuit 10.

(8) The driver circuit 10 also comprises a transformer circuit 33 with a primary winding 32 at a primary side of the transformer and a secondary winding 34 at a secondary side of the transformer circuit 33, wherein the first and the second side are galvanically isolated. The primary winding 32 and the secondary winding 34 are arranged with opposite polarity, or winding direction, as marked in FIG. 2 by the black dots.

(9) At the secondary side of the transformer circuit 33, a first internal connecting pin 51 and a second internal connecting pin 52 of the driver circuit 10 are arranged. The first and the second internal connecting pins 51, 52 are directly or indirectly connected to, or configured for directly or indirectly connecting to, a light engine of an LED lighting tube. The first and the second internal connecting pins 51, 52 are used for providing a controlled DC output power to said light engine, as will be described in the following.

(10) A controller circuit 25 of the driver circuit 10 is configured and arranged to drive a switching circuit 38 to switch a current stemming from the rectified current at the node 18 through the primary winding 32 on or off. As a result, a current through the secondary winding 34 at the secondary side may be switched on and off.

(11) The switching may be performed as part of a pulse-width modulator function. In other words, the current through the primary winding 32 may be switched on and off according to a duty cycle so as to create, by transmission of corresponding electric energy via the transformer circuit 33, a desired output current at the secondary side, in particular at the first and second internal connecting pins 51, 52.

(12) The controller circuit 25 is configured for controlling transmission of electrical energy from the primary side to the secondary side of the transformer circuit 33 by driving the switching element 38 accordingly. More specifically, the controller circuit 25 is configured and arranged to control said transmission in an open loop control based on a parameter of the AC input power if the voltage of the AC input power is in a first voltage range; and to control said transmission in a closed loop control if the voltage of the AC input power is in a second voltage range.

(13) It has already been described above that in this way, the driver circuit 10 is advantageously configured to indirectly react to the type of luminaire (i.e. single-slot or tandem) in which a LED lighting tube with said driver circuit 10 is installed, and automatically the optimal way of controlling the DC output power is selected and applied.

(14) For this goal, the first voltage range may be defined as from 0V to 198V, 198V being excluded, and the second voltage range may be defined as from 198V to 264V, 198V being included.

(15) The controller circuit 25 is configured to receive, at a first pin PIN1, a first signal based on the rectified input power and to receive, at a second pin PIN2, a second signal based on a voltage drop at a first sensing resistor 40 connected between ground and a ground-side of the switching element 38.

(16) The controller circuit 25 is further configured to receive, at a third pin PIN3, a third signal from the secondary side of the transformer circuit 33 as a feedback signal in the closed loop control. At a fourth pin PIN4, the controller circuit 25 outputs driving signals for driving the switching circuit 38 based on the first, the second and/or the third signal.

(17) Between the first internal node 18 and the first pin PIN1 of the controller circuit 25, two branches are connected in parallel: the first branch comprises a first resistor 20, preferably only the first resistor 20. The other branch comprises a first capacitor 22 and a second resistor 24 connected in series. The node between the first capacitor 22 and the second resistor 24 is grounded, i.e. directly connected to ground. The first capacitor 22 is also referred to as an input capacitor C.sub.IN.

(18) The dotted end of the secondary winding 34 is connected, over a diode 46, to the first internal connecting pin 51. The non-dotted end of the secondary winding 34 is connected to ground. Between the first internal connecting pin 51 and the non-dotted end of the secondary winding 34, a capacitor 48 is connected in parallel to the series connection of the secondary winding 34 and the second diode 46. The second diode 46 is arranged such that it transmits a current from the dotted end of the secondary winding 34 towards the first internal connecting pin 51.

(19) Between the non-dotted end of the secondary winding 34 and the second internal connecting pin 52, a second sensing resistor 50 is connected. Since the non-dotted end of the secondary winding 34 is connected to ground, the second sensing resistor may also be said to be connected between ground and the second internal connecting pin 52.

(20) An electric node between the second sensing resistor 50 and the second internal connecting pin 52 is connected to a pin of a regulating circuit 54. The regulating circuit 54 is connected to the third pin PIN3 of the controller circuit 25. The dashed line between the regulating circuit 54 and the third pin PIN3 indicates that additional circuits may be provided in between.

(21) In particular, a galvanic isolator such as an opto-isolator is provided between the third pin PIN3 and the regulating circuit 54 to keep the primary and the secondary side of the transformer circuit 33 galvanically isolated from each other.

(22) When the voltage of the input power received at the external pins 11, 12 is high, i.e. within the second voltage range, then the regulating circuit 54 is configured to transmit a signal based on a voltage drop over the second sensing resistor 50, to the third pin PIN3. In other words, the controller circuit 25 is then set to a closed loop control with the signal received at the third pin PIN3 as a feedback signal. As has been explained above, the voltage of the input power being high, i.e. in the second voltage range, indicates that the lighting tube with the driver circuit 10 is installed singly in a single-slot luminaire.

(23) If the voltage of the input power received at the external pins 11, 12 is low, i.e. within the first voltage range, then the controller circuit 25 is configured and arranged to perform an open loop control of the DC output current based on the signals at the first pin PIN1 and/or at the second pin PIN2.

(24) The first and the second voltage range may be set in particular by choosing the resistance values of the first sensing resistor 40 on the primary side of the transformer circuit 33, and of the second sensing resistor 50 on the secondary side of the transformer circuit 33.

(25) FIG. 2 shows a schematic circuit diagram of a driver circuit 10 according to another embodiment of the present invention. The driver circuit 10 may be configured exactly as shown in FIG. 2, that is, with all the elements as they are depicted in FIG. 2. The driver circuit 10 of FIG. 2 is a variation of the driver circuit 10 of FIG. 1, wherein some further details have been added. The description of elements that have already been described with respect to FIG. 1 is occasionally omitted.

(26) The driver circuit 10 of FIG. 2 comprises, as a rectifying circuit, a bridge rectifier 14 formed as a diode bridge comprising at least four diodes. The bridge rectifier 14 comprises two branches with two diodes arranged in the same direction and in series each, the two branches connected between a grounded node 16 on the one end and an internal node 18 on the other hand. The first external connecting pin 11 is directly connected to a node between the two diodes on one branch of the bridge rectifier 14 and the second external connecting pin 12 is directly connected to a node between the two diodes on the second branch of the bridge rectifier 14.

(27) The driver circuit 10 further comprises a transition-mode PFC controller circuit 25, or a current-mode PFC controller circuit operating in transition mode (TM). In particular, the transition-mode PFC controller may be the L6562 integrated circuit by ST Microelectronics or its predecessor, the pin-to-pin compatible L6561 integrated circuit. It should be understood that instead of the L6562 any other integrated circuit with the same or comparative functions may also be used in the driver circuit 10. For example, a pin-to-pin compatible successor integrated circuit of the L6562 integrated circuit may be used. In the following, the driver circuit 10 will be explained in more detail with reference to with the L6562 integrated circuit as the transition-mode PFC controller circuit 25.

(28) The L6562 integrated circuit is configured with the following pins: INV inverting input of an error amplifier COMP output of the error amplifier MULT main input to a multiplier CS input of a PWM comparator ZCD a boost inductor's demagnetization sensing input for transition-mode operation GMD ground GD gate driver output VCC supply voltage of both a signal part of the integrated circuit and the gate driver.

(29) For a detailed explanation of the pins as well as the entire function of the L6562 integrated circuit, reference is made to the data sheet of the L6562 integrated circuit cited above.

(30) With respect to FIG. 1, the following identifications are made: the first pin PIN1 may be identified with the MULT pin of the L6562; the second pin PIN2 may be identified with the CS pin of the L6562; the third pin PIN3 may be identified with the INV pin of the L6562; and the fourth pin PIN4 may be identified with the GD pin of the L6562.

(31) Between the first internal node 18 and MULT pin of the L6562, the first resistor 20, the first capacitor 22 and the second resistor 24 are connected as described with respect to FIG. 1.

(32) The GD pin of the L6562 is connected to a gate pin of a field effect transistor 38 as one example of a switching circuit, in particular a metal-oxide-semiconductor field-effect transistor, or MOSFET. Between the internal node 18 and the drain of the field-effect transistor 38, the first primary winding 32 of the transformer circuit 33 of the driver circuit 10 is connected. The MOSFET 38 is preferably an N-channel MOSFET. Between a source of the field-effect transistor 38 and ground, the first sensing resistor 40 is connected.

(33) A node between the source of the field-effect transistor 38 and the first sensing resistor 40 is connected to the CS pin of the L6562 integrated circuit, as described with respect to the second pin PIN2. Directly connected between the INV pin of the L6562 integrated circuit and the COMP pin of the L6562 integrated circuit, a third resistor 42 and a second capacitor 44 are connected in parallel.

(34) Further connected between the ground and the VCC pin of the L6562 integrated circuit, a third capacitor 30 is connected. In parallel with the third capacitor 30, a second primary winding 36 and a first diode 28 are connected in series. The first diode 28 is arranged such that it transmits a current from the side of the second primary winding 36 towards the VCC pin of the L6562 integrated circuit.

(35) A node electrically connected between the first diode 28 and the second primary winding 36 is, over a fourth resistor 26, connected to the ZCD pin of the L6562 integrated circuit. Over a common transformer core, the first primary winding 32 and the second primary winding 36 are magnetically coupled with the secondary winding 34. The winding direction, of the first primary winding 32 and the second primary winding 36 are opposite. The winding direction, or polarity, of the first primary winding 32 and the secondary winding 34 are opposite. Accordingly, the winding direction, or polarity, of the second primary winding 36 and the secondary winding 34 are equal, as indicated by the location of the black dots in the symbols for the windings 32, 34, 36.

(36) The secondary side of the transformer circuit 33 is configured in the same way as described above with respect to FIG. 1.

(37) The electric node between the second sensing resistor 50 and the second internal connecting pin 52 is connected to a pin of a three-terminal adjustable shunt regulator 54 as one example of a regulating circuit.

(38) Preferably, the TL431 integrated circuit by Texas Instruments is used as the three-terminal adjustable shunt regulator 54. Regarding properties of the TL431 integrated circuit, it is referred to the datasheet of the TL431 integrated circuit cited above. It should be understood that instead of the TL431 integrated circuit, a wide range of other three-terminal adjustable shunt regulators may be used. In the following, the driver circuit 10 will be described further with reference to the TL431 integrated circuit as a preferred choice.

(39) In said preferred choice, the electric node between the second sensing resistor 50 and the second internal connecting pin 52 is connected to a cathode pin 56 of the TL431 integrated circuit. An anode pin 58 of the TL431 integrated circuit is connected to ground. A reference pin 60 of the TL431 integrated circuit 54 is connected to the INV pin of the L6562 integrated circuit 25 indirectly by means of a connecting circuit, indicated by the dashed line in FIG. 2. The connecting circuit comprises a galvanically insulating circuit such as an octo-isolator. In this way, the primary and the secondary side of the transformer circuit 33 are kept galvanically isolated.

(40) Regarding the functioning of the driver circuit 10 of FIG. 2, it is referred to the detailed description of the driver circuit 10 of FIG. 1.

(41) FIG. 3 schematically shows an LED lighting tube 100 according to another embodiment of the present invention. FIG. 3 illustrates that the LED lighting tube 100 comprises a driver circuit 10 according to the present invention as well as an LED light engine 70 to which the driver circuit 10 is connected, via the internal connecting pins 51, 52, for providing the DC output power to supply at least one light-emitting diode (LED) of the LED light engine 70.

(42) The invention is not restricted by the description based on the embodiments. Rather, the invention comprises any new feature and also any combination of features, including in particular any combination of features in the patent claims, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.

Reference Numerals

(43) 1 single lighting tube CCG luminaire 2 CCG 3 LED lighting tube 4 tandem circuitry CCG luminaire 10 driver circuit 11 first external connecting pin 12 second external connecting pin 14 rectifying circuit 16 ground node 18 internal node 20 first resistor 22 first capacitor 24 second resistor 25 controller circuit 26 third resistor 28 first diode 30 third capacitor 32 first primary winding 33 transformer circuit 34 secondary winding 36 second primary winding 38 switching circuit 40 first sensing resistor 42 fourth resistor 44 second capacitor 46 second diode 48 fourth capacitor 50 second sensing resistor 51 first internal connecting pin 52 second internal connecting pin 54 regulating circuit 56 cathode pin 58 anode pin 60 reference pin 70 light engine 100 LED lighting tube