Circuit and method for controlling a grounded LED module

Abstract

Circuit (120, 220, 320) for driving a grounded LED module (160, 260, 360) with a plurality of series-connected LEDs (162, 262, 362), comprising: an LED driver (130, 230, 330) with a rectifier (132, 232, 332) for rectifying an AC voltage into a DC voltage, a smoothing capacitor (134, 234, 334) for smoothing the DC voltage, and an electronic switch (136, 236, 336) for switching the smoothed DC voltage based on a control signal; and a circuit output (150) with a first output (252, 352) and a second output (254, 354) for connecting the LED module, wherein a connection is provided between the LED driver and the circuit output. a glow current diode (140, 240, 340) is arranged to suppress a glow current that arises when the electronic switch is off, wherein the glow current diode (140, 240,340) is directly connected on the one hand to the smoothing capacitor and on the other hand to the circuit output.

Description

The invention relates to a circuit for controlling a grounded LED module with a plurality of series-connected LEDs, comprising an LED driver with a rectifier for rectifying an AC voltage into a DC voltage, a smoothing capacitor for smoothing the DC voltage and an electronic switch for switching the smoothed DC voltage based on a control signal, and a circuit output with a first and a second connection for connecting the LED module. Controlling an LED module with a circuit containing an electronic switch offers the advantage of remote control, for example, via a bus system. Unlike conventional mechanical switches, which mechanically disconnect the phase supply to a lamp when switched off, thus completely reducing the current flow, electronic switches often cannot achieve such a complete disconnection. In practice, parasitic capacitances in electronic switches can result in a small residual current, known as a glow current, even when switched off. With highly efficient light sources such as LEDs, this poses a problem: especially in darkness, even glow currents of just a few microamps can cause the LEDs to glow visibly. This is generally undesirable. Parasitic capacitances are practically unavoidable. They can occur, for example, when LEDs are placed close to a grounded metal core on the circuit board. The parasitic capacitance can reach values ​​of approximately 100 pF for each LED. In particular, the glowing current can occur when the parasitic capacitances are charged during the positive half-wave (phase positive relative to ground) and discharged again during the negative half-wave. Various circuits have been proposed in the prior art to suppress glow currents. However, these circuits are either very complex or cannot completely suppress the glow current. It is therefore an object of the present invention to provide a circuit for controlling a grounded LED module in which at least one of the above-mentioned disadvantages from the prior art does not occur. According to the invention, this is achieved by placing a glow current diode between the LED driver and the circuit output to suppress a glow current when the electronic switch is off. The invention also includes embodiments in which the generation of a glow current is not completely prevented, but is at least significantly reduced. According to the invention, the glow current diode is therefore arranged particularly after the smoothing capacitor, i.e., between the smoothing capacitor and the LED module. The glow current diode is preferably arranged in the current flow direction, i.e., in the direction of the direct current through the LEDs caused by the smoothed DC voltage. In the switched-on state, it therefore does not block the current flow through the LEDs. In embodiments of the invention, the circuit comprises several capacitors. The smoothing capacitor is the capacitor in the circuit that is connected to a terminal of the rectifier, e.g., the negative terminal of the rectifier. In embodiments of the invention, the smoothing capacitor, as defined by the present invention, is the capacitor that is connected to a terminal of the rectifier and has sufficient capacitance to smooth out any residual ripple of the rectifier. In embodiments of the invention, the smoothing capacitor can, for example, have a capacitance of at least 1 µF or at least 10 µF. The rectifier may be a bridge rectifier. The smoothing capacitor can, for example, be connected to the negative or positive terminal of the bridge rectifier. In embodiments of the invention, the glow current diode has no further functions in the circuit other than suppressing the glow current. Preferably, the glow current diode is designed to be able to block at least one peak voltage of the supply AC voltage, e.g. the mains voltage. The glow current diode allows current to flow in only one direction, thus effectively decoupling the smoothing capacitor from the downstream LED module. This effectively suppresses the glow current. The positioning of the glow current diode according to the invention eliminates the need for a downstream circuit to suppress the glow current. In particular, for example, additional electronic switches that are solely intended to suppress a glow current can be dispensed with. According to the invention, the glow current diode is arranged directly between the LED driver and the first output, and the electronic switch is configured to switch the second output. Thus, one output can be decoupled via the electronic switch and the other output via the glow current diode. This results in a particularly simple yet efficient suppression of the glow current. The glow current ceases after a very short time (typically less than 1 second) and is therefore hardly distinguishable from a normal switch-off. In a further embodiment of the invention, it is provided that the glow current diode is arranged between the LED driver and the first output and that a coil is arranged between the LED driver and the second output, wherein the coil in particular has an inductance of more than 1mH. In certain embodiments of the invention, a constant current flows through the LED module and the coil when the LED driver is permanently switched on. When switched off, the coil prevents any residual ripple voltage at the circuit output from causing a glow current through the LED module. Among other functions, the coil can thus also contribute to decoupling the LED module from the LED driver. In a further embodiment of the invention, it is provided that the first output is configured to be connected to a positive terminal of the LED module and the second output is configured to be connected to a negative terminal of the LED module. In other embodiments of the invention, the first output is configured to be connected to a negative terminal of the LED module and the second output is configured to be connected to a positive terminal of the LED module. In a further embodiment of the invention, it is provided that the glow current diode is arranged between the smoothing capacitor and the circuit output, wherein in particular the glow current diode is directly connected on the one hand to the smoothing capacitor and on the other hand to the circuit output. Directly connected in this context means that no other components are interposed. This results in suppression of the glow current with a particularly low component count. In a further embodiment of the invention, it is provided that only passive components, in particular only the glow current diode or only the glow current diode and one or more coils, are arranged between the LED driver and the LED module. Since the glow current diode already effectively suppresses the glow current, active components (e.g., electrical switches, especially transistors) can be dispensed with. In a further embodiment of the invention, the circuit, apart from the glow-in-the-dark diode, contains no other components for suppressing a glow current when the electronic switch is off. In other words, although further components may be arranged between the LED driver and the circuit output in embodiments of the invention, these play no role, or no significant role, in suppressing a glow current. By eliminating the need for additional components to suppress the glow current, a particularly simple and cost-effective suppression of the glow current is achieved. In a further embodiment of the invention, the electronic switch is provided to be a transistor, in particular a MOSFET, which is controlled by a BUS system and / or by a pulse width modulation control. This allows for low-loss electronic dimming of the LED module and prevents a glow current when the module is switched off. In embodiments of the invention, the LED driver and the LED module are arranged separately, e.g., on different circuit boards. According to the invention, the glow current suppressor can be arranged on the LED driver. This can be particularly advantageous for retrofitting existing LED modules with an LED driver that suppresses glow current. In other embodiments of the invention, the glow current diode is arranged on the LED module. This allows for particularly effective suppression of the glow current. Further technical features and advantages of the present invention will become clear with reference to the description of preferred embodiments and the accompanying figures. The figures show the following: Fig. 1 shows a schematic circuit diagram of an arrangement with a circuit according to the invention for controlling a grounded LED module; Fig. 2A shows a simplified circuit diagram of another arrangement with a circuit according to the invention for controlling a grounded LED module; Fig. 2B shows a simplified circuit diagram of another arrangement with a circuit according to the invention for controlling a grounded LED module; Fig. 3 shows a circuit diagram of another arrangement with a circuit according to the invention for controlling a grounded LED module. In the schematic circuit diagram of an arrangement 100 shown in Fig. 1, a circuit 120 according to the invention is supplied with an alternating voltage from an alternating voltage source 110 via a supply input 121. The circuit 120 comprises an LED driver 130, a glow current diode 140, and a circuit output 150. An LED module 160 is connected to the circuit output 150. The LED module 160 comprises a plurality of LEDs 162 connected in series and a ground connection 164. In the LED driver 130, the AC voltage is first rectified in a rectifier 132. The rectified AC voltage may still exhibit residual ripple. Subsequently, a smoothing capacitor 134 smooths the rectified AC voltage to a smooth DC voltage. The electronic switch 136 is then configured to switch the smoothed DC voltage depending on a control signal, which can be provided, for example, via a control signal input 138. Between the LED driver 130 and the LED module 160 controlled by the circuit 120, the glow current diode 140, which decouples the LED module 160 from the LED driver 130, is arranged between the smoothing capacitor 134 and the circuit output 150 in such a way that a glow current via the ground 164 through the LEDs 162 of the LED module 160 can be suppressed. Figures 2A and 2B show simplified circuit diagrams of arrangements 200 comprising circuits 220 according to the invention. An AC voltage source 210 supplies the LED driver 230 with AC voltage via two supply terminals 221a and 221b. The rectifier 232 rectifies the AC voltage into a DC voltage, and a constant current module 233 generates a constant DC current. Any remaining ripple is smoothed by the smoothing capacitor 234. A switch 236 is controlled via a control signal input 238 and switches the power supply to the LED module 260 on or off. A neon indicator diode 240 is arranged between the LED driver 230 and a first output 252 of the circuit 220. In the embodiment shown in Fig. 2A, this diode can, for example, be arranged in the supply line to the positive output 252, while the switch 236 switches the supply line to the negative output 254. In other embodiments of the invention, however, it can also be provided that the neon indicator diode 240 is arranged in the supply line to the negative output 254, while the switch 236 switches the supply line to the positive output 252. In the embodiment shown in Fig. 2A, only the glow current diode 240 and the electronic switch 236 are arranged between the smoothing capacitor 234 and the LED module 260. Thus, effective glow current suppression is ensured with very few components. In other embodiments of the invention, the electronic switch 236 can also be configured to take over the function of the constant current source 233. In the embodiment shown in Fig. 2B, additional components are provided beyond those of the embodiment shown in Fig. 2A: The electronic switch 236 is not directly controlled via an external control signal input 238, but rather via an intermediate pulse-width modulation (PWM) controller 237. This controller receives a control signal via the control signal input 238, which specifies a desired dimming level of the LED module 260. The PWM controller 237 then calculates switch control signals from this signal, which it uses to switch the electronic switch 236 accordingly. Furthermore, a coil 242 is provided in the supply line from the LED driver 230 to the second terminal 254. Among other functions, this coil can also contribute to suppressing a glow current. In the embodiment shown in Fig. 2B, only the glow-in-the-dark diode 240, the electronic switch 236, and the coil 242 are arranged between the smoothing capacitor 234 and the LED module 260. Thus, effective glow-in-the-dark suppression is ensured with very few components. Typically, an LED driver 130 according to the invention further comprises at least one constant current source (not shown in Fig. 1) which converts the DC voltage into a predetermined constant current. Fig. 3 shows a detailed circuit diagram of an arrangement consisting of a circuit 320 with an LED driver 330 (comprising a rectifier 332, a smoothing capacitor 334, an electronic switch 336, and a pulse-width modulation controller 337) and a grounded LED module 360. A glow current diode 340 and several inductors 342a, 342b, 342c are located between the LED driver 330 and the first and second outputs 352, 354. Two inductors 342a, 342b are arranged in series between the LED driver 330 and the second output 354, and one inductor 342c is arranged between the LED driver 330 and the first output 352. The circuit 320 also includes a capacitor C468. This is not connected to an output of the rectifier 332 and is not a smoothing capacitor as defined in the invention. Another diode 341 is arranged between the positive and negative leads to the first and second outputs 352, 354. The rectifier 332 is powered via a first and a second AC voltage connection 321a, 321b. When powered via the public power grid, these are typically phase and neutral conductors. The electronic switch 336 comprises a MOSFET Q430 and resistors R471, R443, and R444. The gate of the MOSFET Q430 is controlled by the pulse-width modulation (PWM) controller 337, which includes a control chip U400 and resistors R430, R431, R400, R451, and R452. The PWM controller 337 also includes capacitors C400, C401, C402, and C450. The PWM controller 337 is controlled via a control signal input 338. The LED module 360 ​​includes, in addition to the LEDs 362 connected in series, a large number of parasitic capacitances 363. These are shown as dotted lines in Fig. 3, since they are not intentionally included components, but rather unavoidable capacitances that arise, for example, from a small distance between the LEDs and the grounded metal core of the circuit board.

Claims

Circuit (120, 220, 320) for driving a grounded LED module (160, 260, 360) with a plurality of series-connected LEDs (162, 262, 362), comprising: an LED driver (130, 230, 330) with a rectifier (132, 232, 332) for rectifying an AC voltage into a DC voltage, a smoothing capacitor (134, 234, 334) for smoothing the DC voltage, and an electronic switch (136, 236, 336) for switching the smoothed DC voltage based on a control signal; and a circuit output (150) with a first output (252, 352) and a second output (254, 354) for connecting the LED module, wherein a connection is provided between the LED driver and the circuit output. a glow current diode (140, 240, 340) is arranged to suppress a glow current that arises when the electronic switch is off, wherein the glow current diode (140, 240,340) is directly connected on the one hand to the smoothing capacitor and on the other hand to the circuit output. Circuit (120, 220, 320) according to claim 1, wherein the glow current diode (140, 240, 340) is arranged between the LED driver (130, 230, 330) and the first output (252, 352) and the electronic switch (136, 236, 336) is configured to switch the second output (254, 354). Circuit (120, 220, 320) according to claim 2, wherein the glow current diode (140, 240, 340) is arranged between the LED driver (130, 230, 330) and the first output (252, 352) and an inductor (242, 342a, 342b, 342c) is arranged between the LED driver and the second output (254, 354), wherein the inductor in particular has an inductance of more than 1mH. Circuit (120, 220, 320) according to claim 2 or 3, wherein the first output (252, 352) is configured to be connected to a positive terminal of the LED module and the second output is configured to be connected to a negative terminal of the LED module (160, 260, 360). Circuit (120, 220, 320) according to one of the preceding claims, wherein only passive components, in particular only the glow current diode (140, 240, 340) or only the glow current diode and one or more coils (242; 342a, 342b, 342c), are arranged between the LED driver (130, 230, 330) and the LED module (160, 260, 360). Circuit (120, 220, 320) according to one of the preceding claims, wherein the electronic switch (136, 236, 336) is a transistor, in particular a MOSFET, which is controlled by a BUS system and / or by a pulse width modulation control (237, 337). Circuit (120, 220, 320) according to one of the preceding claims, wherein the circuit, apart from the glow current diode (140, 240, 340), does not include any further components for suppressing a glow current when the electronic switch is off. Circuit (120, 220, 320) according to one of the preceding claims, wherein the LED driver (130, 230, 330) and the LED module (160, 260, 360) are arranged separately from each other and the glow current diode (140, 240, 340) is arranged on the LED driver.

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