DE102008039526A1 - Current supplying method for LED array in lighting unit i.e. headlight, of motor vehicle, involves controlling adjustable resistors using control electronics based on comparison of measured currents in individual LED branches - Google Patents

Abstract

The method involves supplying current from a power source (2) into an LED array (4), where the power source is connected in series with the LED array. Currents in individual LED branches (6, 8) are measured by a current measuring unit (14), where the LED branches are connected in parallel. The measured currents are compared with one another by a control electronics (16). Adjustable resistors (12) e.g. MOSFET and bipolar transistor, are controlled by the control electronics based on the comparison, such that the currents in the individual LED branches are equal. An independent claim is also included for a circuit arrangement for supplying current to an LED array.

Description

The The present invention relates to a method of power supply an LED array and a circuit arrangement for implementation of the procedure.

such Methods and circuits are known in the art already known in numerous design variants.

For example, is from the EP 1 449 408 B1 a method for powering an LED array and a circuit arrangement for carrying out the method known. The known circuit arrangement for an LED array has at least two parallel-connected LED branches, in each of which at least one LED is connected in series with a controllable resistor. The controllable resistors are part of a control electronics. The LED array is connected to a voltage source here. In order to achieve a predetermined distribution of the currents to the LED branches even with different forward voltages or with a change in the forward voltages, is in the EP 1 449 408 B1 proposed to set the current in the individual LED branches via the controllable resistors designed as transistors so that the voltage dropping across the emitter resistors is about 0.65 V below the common base potential. The currents in the individual LED branches are thus regulated so that the voltages at the emitter resistors are the same. The known circuit arrangement should in particular be suitable so that the predetermined by the dimensioning of the emitter resistors current distribution can be maintained even in case of failure of an LED branch for the remaining LED branches.

Here uses the present invention.

Of the present invention, the object is a method to provide power to an LED array, in which a symmetrical power distribution is ensured on the individual LED branches.

These The object is achieved by a method having the features of the claim 1 solved. The subclaims relate to advantageous Further developments of the invention.

One significant advantage of the method lies in the fact that, in contrast to the known method Ensures a symmetrical distribution of power to the individual LED branches is. This is particularly advantageous in the case when an LED branch, for example, by a defective LED, high impedance fails, because then the current in the other LED branches as far downshifted that these LED branches also off are. A simple and clear error detection is thus synonymous with conventional control devices, usually designed to detect a failure of incandescent bulbs are possible. The essentially equal partial flows in the individual LED branches are alone on through the current source impressed total current determines the can be varied within wide limits. Another adjustment not necessary. Differences in forward voltages the loads, here LEDs, are by the invention Method automatically compensated; The same applies to dynamic changes and nonlinearities. Mixed components with LEDs various forward voltages are also compensated.

A particularly advantageous development of the invention Procedure provides that the variable resistor in the LED branch with the least current flow through the control electronics to one the lowest possible resistance value, in particular approximately 0 Ω, is regulated. In this way, the power loss of the circuit arrangement effectively reduced.

Further Objects of the present invention were to provide a circuit arrangement for Implementation of the method according to the invention and a lighting unit with such a circuit arrangement specify.

These Tasks are performed by a circuit arrangement with the features of claim 3 and a lighting unit with the features of Claim 7 solved. The dependent claims relate advantageous developments.

One significant advantage of the switching device according to the invention is in particular that a power source instead of a voltage source used to power an LED array. Due to the embossed, well-defined currents are the desired ones Luminous properties of the LED array, such as the brightness, ensured.

in principle is that at least a current measurement by number, arrangement and Operation freely selectable within wide suitable limits. For example, it is conceivable that a single current measuring means for measuring each of the currents in the individual LED branches of the LED array is formed. Conveniently, is in each case at least one current measuring means in each case an LED branch in series with the at least one LED and the controllable one Resistor switched.

The Adjustable resistances are on the type, method of operation, material and arrangement freely selectable within wide suitable limits. Advantageously, the controllable resistors as MOSFET or bipolar transistors formed as it is inexpensive and robust standard components.

The Circuit arrangement can for example consist of individual components or modules.

A Particularly advantageous embodiment provides that the power source and the remaining circuit parts as a single integrated Assembly are formed. As a result, the compactness of the circuit arrangement increases and reduces the wiring costs.

Based the attached, rough schematic drawing is the Invention explained in more detail below. It shows the only

FIG. the circuit diagram of an embodiment of the invention Circuitry.

In the Fig. An embodiment of the circuit arrangement according to the invention is shown. The circuit arrangement is here part of a not shown in detail and designed as a motor vehicle headlight unit and has a power source 2 on, which is electrically in series with a LED array 4 is switched. The LED array 4 here represents a light source of the motor vehicle headlamp, for example for generating the low beam, and is in the on state of the low beam through the power source 2 powered.

The LED array 4 here has two electrically parallel LED branches 6 and 8th on. In each of the LED branches 6 and 8th are several LEDs 10 electrically connected in series, namely LED1, LED2 to LEDN in LED branch 6 and LEDN + 1, LEDN + 2 to LED2N in LED branch 8th where N is a natural number. In each of the LED branches 6 and 8th is a controllable resistance 12 namely R1 and R2, with the LEDs 10 electrically connected in series. The controllable resistances 12 are each formed here as a MOSFET. In addition, in each of the LED branches 6 and 8th a current measuring agent 14 with the LEDs 10 and the resistors 12 electrically connected in series. The current measuring means 14 are in signal transmission connection with a control electronics 16 , in turn, in signal transmission connection with the adjustable resistors 12 stands.

The power source 2 and the remaining circuit parts 4 to 16 are designed here as a single integrated module.

in the The process according to the invention will be described below explained in more detail with reference to FIGS.

The dipped headlight of the motor vehicle headlight is turned on in a manner known to those skilled in the art, whereupon the power source 2 the LED array 4 supplied with a predetermined power and the LEDs 10 of the LED array 4 to shine. The two adjustable resistors 12 are here initially controlled to a resistance of about 0 Ω in order to keep the power loss as low as possible. The formulation about 0 Ω in this context means that virtually unavoidable component tolerances and internal component resistance practically lead to a resistance of approximately 0 Ω.

By means of the current measuring means 14 now becomes the respective current flow in the two LED branches 6 and 8th measured and as an output signal of the respective current measuring means 14 for further processing to the control electronics 16 forwarded. In the control electronics 16 the measured currents are compared with each other and the controllable resistances 12 are regulated depending on the settlement made. Here are the controllable resistances 12 from the control electronics 16 so regulated that the currents in the individual LED branches 6 and 8th of the LED array 4 are essentially the same size.

This thus happens independently of that by the power source 2 in the LED array 4 fed total current that is variable within wide limits and depending on the particular application. In detail, the control electronics checks 16 by the aforementioned comparison, in which of the LED branches 6 . 8th the lowest current flows. Is this, for example, the LED branch 6 , so would the resistance of the variable resistor 12 in the LED branch 6 through the control electronics 16 in the manner known to those skilled so far lowered, so the current in the LED branch 6 so far up-regulated, until that the current flow in the LED branch 6 same as in the LED branch 8th is.

Due to the fact that here are both controllable resistors 12 This has not been lowered to about 0 Ω, this is not possible. Therefore, in such a case as here, where the current of an LED branch, here LED branch 6 , not further regulated, so can be increased, the current in the other LED branches, here LED branch 8th , downcast, so humiliated. This happens because the control electronics 16 the controllable resistance 12 in the LED branch 8th such that its resistance is increased accordingly.

Due to the method according to the invention is a symmetrical distribution of the total current to the individual LED branches 6 . 8th of the LED array 4 ensured.

The The invention is not limited to the present embodiment limited. For example, the inventive Method and the circuit arrangement for its implementation also with other lighting units and also on other technical Fields can be used advantageously. Also the number of LED branches as well as the LED's in the individual branches is in wide appropriate Borders selectable. For example, it is an advantage of Invention that the number of LEDs per LED branch from each other can differentiate. Also, it is conceivable that in a single LED branch or also in different LED branches different designs of LEDs with, for example, divergent forward voltages be used.

2

power source

4

LED array

6

LED branch

8th

LED branch

10

LED

12

adjustable resistance

14

Current measuring means

16

control electronics

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 1449408 B1 [0003, 0003]

Claims (7)

Method for powering an LED array ( 4 ) with at least two parallel-connected LED branches ( 6 . 8th ), in each of which at least one LED ( 10 ) with a variable resistor ( 12 ) is connected in series, and with a control electronics ( 16 ) for controlling the resistances ( 12 ) and one with the LED array ( 4 ) in series power source ( 2 ), the method comprising the following steps: - power supply to the LED array ( 4 ) by the power source ( 2 ), - Measurement of the currents in the individual LED branches ( 6 . 8th ) by at least one current measuring means ( 14 ), - Comparison of the measured currents with each other in the control electronics ( 16 ) and - regulation of the resistances ( 12 ) depending on the comparison carried out, the controllable resistances ( 12 ) from the control electronics ( 16 ) are regulated such that the currents in the individual LED branches ( 6 . 8th ) are substantially the same size. Method according to Claim 1, characterized in that the controllable resistance ( 12 ) in the LED branch ( 6 . 8th ) with the lowest current flow through the control electronics ( 16 ) is controlled to the lowest possible resistance, in particular about 0 Ω. Circuit arrangement for a LED array ( 4 ) for carrying out one of the methods according to claim 1 or 2, with at least two parallel-connected LED branches ( 6 . 8th ), in each of which at least one LED ( 10 ) with a variable resistor ( 12 ) is connected in series and with a control electronics ( 16 ) for controlling the resistances ( 12 ), characterized in that the LED array ( 4 ) for power supply in series with a power source ( 2 ) and the controllable resistances ( 12 ) by the control electronics ( 16 ) in dependence on the output signals of at least one current measuring means ( 14 ) for measuring the currents in the individual LED branches ( 6 . 8th ) are controllable. Circuit arrangement according to claim 3, characterized in that in each case at least one current measuring means ( 14 ) in each case an LED branch ( 6 . 8th ) in series with the at least one LED ( 10 ) and the variable resistor ( 12 ) is switched. Circuit arrangement according to Claim 3 or 4, characterized in that the controllable resistances ( 12 ) are formed as MOSFET or bipolar transistors. Circuit arrangement according to one of Claims 3 to 5, characterized in that the current source ( 2 ) and the remaining circuit parts ( 4 - 16 ) are formed as a single integrated assembly. Lighting unit, in particular for a motor vehicle, characterized in that the lighting unit is a circuit arrangement according to one of claims 3 to 6.