EP2818027A1 - Method for operating a circuit arrangement for a light-emitting diode field fed with constant current, comprising fault detection - Google Patents

Abstract

The present invention relates to a method for operating a circuit arrangement having a power source (I), - having a light-emitting diode field (1, 2, 3) in series to the power source (I), wherein the light-emitting diode field (1, 2, 3) comprises at least two series circuits (1, 2, 3) which comprise at least one light-emitting diode (D1, D2, D3) and a controllable switching element (S1, S2, S3), comprising a control and/or regulation means (C) for the light-emitting diode field (1, 2, 3) and - comprising a voltage sensor (V1), wherein the controllable switching elements and the power source (I) are actuated by the control and/or regulation means (C) in such a way that the control and/or regulation means (C) actuate the closing of the controllable switching element (S1, S2, S3) of at least one series circuit (1, 2, 3) of the light-emitting diode field (1, 2, 3) by a control pulse at the control input of the controllable switching element (S1, S2, S3) during a cycle period (Tcycle) for a pulse duration (T1, T2, T3) determined by the control and/or regulation means (C) and - that the control and/or regulation means (C) actuate the power source (I) shortly before or at the latest simultaneously with the end of a pulse duration (T1, T2, T3) such that the current is reduced, specifically by the amount of current through the series switching (1, 2, 3), the controllable switching element (S1, S2, S3) of which is actuated to open at the end of the pulse duration (T1, T2, T3) by the control and/or regulation means (C). During successive cycle periods (Tcycle), one of each of the controllable switching elements of the series circuits (1, 2, 3) is switched on alone by the control and/or regulation means (C) for a period of time referred to as a diagnosis time (Tdiag).

Description

 METHOD FOR OPERATING A CIRCUIT ARRANGEMENT FOR ONE

 ONSTANTSTROMGESPEISTES LIGHT DIODE FIELD, WITH ERROR DETECTION

description

The invention relates to a method for operating a circuit arrangement

 with a power source,

 with a light-emitting diode array in series with the current source, the light-emitting diode array comprising at least two series circuits comprising at least one light-emitting diode and a controllable switching element,

 with a control and / or regulating means and

 with a voltage sensor,

wherein the controllable switching elements and the current source are controlled by the control and / or regulating means and in such a way

 - That the control and / or regulating means controls the controllable switching element of at least one series connection of the LED array during a clock period for a determined by the control and / or regulating means pulse duration by a control pulse at the control input of the controllable switching element to close and

 - That the control and / or regulating means shortly before or at the same time with the end of a pulse duration, the current source so that the current is reduced, by the amount of current through the series circuit whose controllable switching element at the end of the pulse duration from the control - And / or control means is driven to open.

Such a method is disclosed in the German patent application with the official file number DE 10 2010 060 857.2. The application further discloses a circuit arrangement and a control and / or regulating means with which the method can be carried out. The pulse durations during which the controllable switching elements of the series circuits are driven to close are selected in the disclosed method such that the LEDs of the parallel-connected series circuits have the same average brightness. Controllable switching elements in series with light-emitting diodes with a low forward voltage will result in succession its switched on for a shorter time as controllable switching elements in series with light emitting diodes with a high forward voltage.

In the said German patent application is not disclosed how to proceed when it comes to a failure of one of the light-emitting diodes. A failure of a light-emitting diode could, for example, be caused by a short circuit of the light-emitting diode or an interruption of the current path via the light-emitting diode.

For these two possible failure scenarios, a solution is offered with the present invention, with which first the failure is detected and how to proceed after the detection of the failure to deal with the failure.

The invention was based on the problem to improve a method of the type mentioned so that a failure detection is possible.

This problem is solved according to the invention in that, during successive clock periods, at least one of the controllable switching elements of the series circuits is switched on by the control and / or regulating means for a period of time known as the diagnosis time alone. During this diagnostic time, therefore, a current can flow only through the light-emitting diode arranged in series with the closed controllable switching element. According to the electrical properties of the light emitting diode and the controllable switching element then sets a voltage across the energized series circuit. This voltage can be detected and be a basis for failure detection.

With a number of n series connections, according to the invention, each controllable switching element can be switched on for the diagnosis time in n consecutive clock periods. This ensures that the failure of one light-emitting diode is detected at the latest after n clock periods. But it is also possible to choose a different rhythm in the control of the controllable switching elements to close. In particular, it is also possible to select random controllable switching elements to be closed during the diagnosis time. The diagnostic time during which a controllable switching element is driven to close may be part of the pulse duration during which the same switching element is driven to close in all clock periods. The total duty cycle of the controllable switching element during the clock period then changes as little as the average brightness of the LEDs in series with the controllable switching element. The pulse durations during which the remaining controllable switching elements are closed during the same clock period remain unaffected by the diagnosis time. Because of the diagnostic time, if necessary, the beginning or the end of the pulse durations for the activation of the other controllable switching elements must be shifted from clock period to clock period.

If the pulse durations during which the controllable switching elements are switched on within one clock period can be shifted to one another such that several or all controllable switching elements are switched on during a diagnostic time within the clock period alone, it is possible to use several or all light emitting diodes of the light emitting diode array with respect to to investigate one of the described failures. Eventually, a pulse duration must be shared, so that one of the controllable switching elements is turned on for two periods during a clock period, these periods together forming the pulse duration.

The diagnostic time can be at the beginning of the pulse duration and after the expiry of the diagnostic time, other controllable switching elements can be controlled to close.

According to the invention, the diagnosis time may be at the beginning of a clock period.

The diagnostic time can be 50 ps. But longer or shorter diagnosis times are possible. The diagnostic time may be the same or different in duration from clock period to clock period.

The circuit arrangement can have a voltage sensor with which the voltage across the light-emitting diode field is detected during the diagnosis time. The voltage across the LED field varies depending on the characteristics the light emitting diode and the closed controllable switching element, which is why it can be concluded from the measured voltage on the functionality of the light emitting diode.

The voltage detected during the diagnosis time over the light-emitting diode array can be compared by the control and / or regulating means with a predetermined value. Upon exceeding the predetermined value plus a predetermined tolerance by the detected voltage, the controllable switching element, which was closed during the detection during the diagnosis time, permanently, i. also be switched off for the following clock periods. Probably due to an interruption of the current path through the series connection failed

LED is then permanently switched off.

If the predetermined value minus a tolerance due to the detected voltage is undershot, the controllable switching element, which was closed during the detection during the diagnosis time, can be permanently switched off. At a small or compared to small voltage across the light emitting diode array or the only switched series connection can be connected to a short circuit of the

LEDs are closed, which is why the permanent shutdown makes sense.

After a permanent shutdown by means of the control and / or regulating means, the pulse durations during which the remaining controllable switching elements are closed can be extended and / or the current of the switched-off series circuit can be distributed to the remaining series circuits. Thus, although the average brightness of the still functioning light-emitting diodes is increased, the average brightness of the entire circuit can u. U. despite the permanently disconnected light emitting diode or LEDs are maintained. It should be noted, however, that the thermal and electrical load capacity of the LEDs or controllable switching elements that are not switched off permanently, is not exceeded.

Reference to the accompanying drawings, the invention is explained in more detail below. Showing: 1 shows a block diagram of the circuit arrangement with which the method according to the invention can be carried out,

 2 shows a course of currents in the circuit arrangement according to the invention during a first clock period,

 Fig. 3 shows a course of currents in the circuit arrangement according to the invention during a second clock period and

 4 shows a course of currents in the circuit arrangement according to the invention during a third clock period.

The circuit arrangement illustrated in FIG. 1 comprises a light-emitting diode array composed of three series circuits D1, R1, S1, D2, R2, S2, D3, R3, S3. Each series circuit 1, 2, 3 comprises a light-emitting diode D1, D2, D3, a resistor R1, R2, R3 and a switch S1, S2, S3. Corresponding to the indices of the designations of the components, the following will be spoken of the first series circuit 1, the second series circuit 2 and the third series circuit 3.

The series circuits 1, 2, 3 are connected in parallel. The light-emitting diodes D1, D2, D3 are arranged within the series circuits so that their anodes abut against a common node. The controllable switching elements S1, S2, S3 also have a common node. The resistors R1, R2, R3 are arranged between the diodes D1, D2, D3 and the controllable switching elements S1, S2, S3.

In addition to the light-emitting diode array, the circuit arrangement comprises a current source I, which is connected upstream of the anode-side node. The current source I is a controllable current source.

Downstream of the switch element-side node is a parallel circuit, are arranged in the measuring resistors. In a first branch of the parallel circuit, a controllable switching element S4 is arranged. The controllable switching element is advantageously a transistor whose emitter collector path forms a first measuring resistor and thus the measuring resistor of the first branch of the parallel circuit. In a second branch, a measuring resistor R4 is arranged. In a third branch is a series connection of a measuring resistor R5 and a arranged nem controllable switching element S5. The parallel circuit is connected via ground to the current source I.

In the circuit arrangement, a voltage sensor V1 and a current sensor V2 is provided. The voltage sensor V1 detects the voltage between the anode-side node and the ground potential. The current sensor V2 detects the current through the light-emitting diode array via the detour of measuring the voltage which drops across the parallel connection of the measuring resistors.

In addition, an inventive control and / or regulating means C is provided in the circuit arrangement. The control and / or regulating means C has several inputs and several outputs. About these inputs and outputs is the control and / or regulating means C with the controllable current source I, the controllable switching elements S1, S2, S3 of the LED array, the controllable switching elements S4, S5, the parallel connection of the measuring resistors, the voltage sensor V1 and the current sensor V2 connected.

In detail, the connections between the components or components and the inputs or outputs of the control and / or regulating means are produced as follows:

A first input of the control and / or regulating means C is connected to the current sensor V2. Via the first input E1, the control and / or regulating means C can be supplied with the current intensity detected by the current sensor V2 or with an equivalent voltage thereto.

A second input E2 of the control and / or regulating means is connected to the voltage sensor V1. Via this input E2, a signal can be supplied to the control and / or regulating means which indicates the voltage between the a node-side node and the ground potential.

First outputs A11, A12, A13 of the control and / or regulating means are connected to control terminals of the controllable switching elements S1, S2, S3 of the series circuits 1, 2, 3 of the LED array connected. Control pulses can be applied to the switching elements via these first outputs A11, A12, A13 in order to close them.

A second output A2 is connected to the controllable current source I. Via this second output A2, a signal can be given by the control and / or regulating means to the controllable current source I in order to set the current supplied by the current source I.

The control and / or regulating means, which may be a microcontroller or an ASIC, is set up such that the light-emitting diodes D1, D2, D3 have a desired brightness. For this purpose, due to tolerances of the characteristics of the light emitting diodes, in particular different forward voltages of the light emitting diodes and different currents in the series circuits 1, 2, 3 are necessary. The current source is adjusted by the control and / or regulating means C so as to provide a current sufficiently large enough to supply power to the series circuit whose LED has the highest forward voltage. This is, for example, the light emitting diode D3 in the third series circuit 3. The first series circuit 1, however, should have the light emitting diode D1 with the lowest forward voltage and the second series circuit 2 has a light emitting diode D2 with a mean forward voltage.

The current supplied by the controllable current source I divides at the anode-side node into the respective currents which flow through the series circuits 1, 2, 3. The current distribution depends on the components of the series circuits 1, 2, 3. Among these components are also the LEDs D1, D2, D3 with their different forward voltages. The currents are distributed in such a way that the series connection with the light-emitting diode with the lowest forward voltage, ie the first series connection, carries the largest current, while the series connection with the light-emitting diode D3 with the largest forward voltage, namely the third series circuit 3, leads the lowest current. Thus, the third light-emitting diode D3 with the highest forward voltage provides the desired Hel _¬ ligkeit, the current of the controllable current source I must be adjusted so that the necessary for providing the desired brightness flow through the third serial circuit 3 and therefore by the third light-emitting diode D3 flows ,

However, this leads to currents in the other two series circuits 1, 2 which are larger than the currents required to supply the desired brightness through the light emitting diodes D1 and D2. The light-emitting diodes D1 and D2 or the series circuits 1 and 2 are therefore switched on and off. This results in a current through the first and the second series circuit 1, 2, which corresponds on average to the current which is necessary for producing the desired brightness.

Switching on and off takes place at such a high frequency that it is invisible to the human eye.

In the example of Figures 2, 3 and 4 three temporally successive clock cycles Tcycle are shown. Within the clock periods, the controllable switching element S3 is turned on in the third series circuit 3 for a pulse duration T3. Analogously, the controllable switches S1, S2 of the first and the second series circuit 1, 2 are switched on for pulse durations T1, T2, the pulse duration T2 being smaller than the pulse duration T3 and the pulse duration T1 being smaller than the pulse duration T2. The pulse durations T1, T2, T3 are chosen so that on average of the clock periods T, a current flows through the series circuit 1, 2, 3, which supplies on average the desired brightness of the light-emitting diodes. The controllable current source I is controlled so that at the end of the respective pulse durations T1, T2, T3, the current Iges supply of the controllable current source I is reduced by the current consumption of the switched off at the end of the pulse duration T1, T2, T3 series connection. Thus, the controllable current source I supplies exactly the current Iges, which is necessary for the supply of the switched series circuits.

At the beginning of the clock cycles Tcycle a period is provided, which is referred to as diagnosis time Tdiag. During this time, only one of the controllable driven to close, so that during this time only a series circuit is flowed through by a current. In accordance with the electrical properties of the current-carrying series circuit 1, 2, 3, a voltage across the light-emitting diode field arises during the diagnosis time Tdiag, which voltage is detected via the voltage sensor V1. If the detected voltage is within a specified tolerance range, it can be assumed that the LED works as desired. If, however, a deviation of the detected voltage is detected, that is, the voltage is not within the tolerance range, the controllable switching element, which was turned on during the diagnostic time Tdiag, during which the deviation was detected, permanently switched off.

During the clock periods Tcycle all pulse durations T1, T2, T3 are always the same length, so that the same average brightness is always provided by the light emitting diodes D1, D2, D3. The diagnostic times Tdiag are thus part of the pulse durations. So that during the diagnostic times despite the same pulse durations T1, T2, T3 always only one controllable switching element is turned on, the times of the beginning and the times of the end of the pulse durations T1, T2, T3 are shifted in the illustrated example with respect to the diagnosis time Tdiag when the switching elements are not turned on during the diagnostic time Tdiag.

LIST OF REFERENCE NUMBERS

I controllable power source

V1 voltage sensor

 V2 current sensor

 D1 LED of the first series connection

 R1 resistor of the first series connection

 51 controllable switch of the first series connection

D2 LED of the second series connection

 R2 resistor of the second series circuit

 52 controllable switch of the second series circuit

D3 LED of the third series connection

 R3 resistor of the third series connection

 53 controllable switch of the third series connection

C control and / or regulating means

 54 controllable switch in the first branch of the parallel connection of measuring resistors

 R4 resistor in the second branch of the parallel connection of measuring resistors

55 controllable switch in the third branch of the parallel connection of measuring resistors

 R5 Resistor in the third branch of the parallel connection of measuring resistors

Tcycle clock period

 T1 pulse duration

 T2 pulse duration

 T3 pulse duration

 II current through series connection 1

 12 Current through series connection 2

 13 Current through series connection 3

 Iges total current through the LED field

 Tdiag diagnostic time

Claims

claims 1. Method for operating a circuit arrangement  with a current source (I),  - With a light-emitting diode array (1, 2, 3) in series with the current source (I), wherein the light emitting diode array (1, 2, 3) at least two series circuits (1, 2, 3), the at least one light emitting diode (D1, D2 , D3) and a controllable switching element (S1, S2, S3), - With a control and / or regulating means (C) for the light-emitting diode array (1, 2, 3) and  with a voltage sensor (V1),  wherein the controllable switching elements and the current source (I) are controlled by the control and / or regulating means (C) in such a way, - that the control and / or regulating means (C) is the taxable  Switching element (S1, S2, S3) at least one series circuit (1, 2, 3) of the light-emitting diode array (1, 2, 3) during a clock period (Tcycle) for one of the control and / or regulating means (C) determined pulse duration (T1 , T2, T3) by a control pulse at the control input of the controllable switching element (S1, S2, S3) for closing drives and  - That the control and / or regulating means (C) just before or at the same time with the end of a pulse duration (T1, T2, T3), the current source (I) controls so that the current is reduced, by the amount of current by the series circuit (1, 2, 3) whose controllable switching element (S1, S2, S3) is driven to open at the end of the pulse duration (T1, T2, T3) by the control and / or regulating means (C),  characterized by in that during successive clock cycles (Tcycle) by the control and / or regulating means (C) one of the controllable switching elements of the Series circuits (1, 2, 3) for a designated as diagnostic time (Tdiag) time period is driven solely to close. 2. The method according to claim 1, characterized in that in a number of n series circuits in n consecutive clock periods (Tcycle) each controllable switching element (S1, S2, S3) for the diagnosis time (Tdiag) is driven to close. 3. The method according to claim 1 or 2, characterized in that the diagnosis time during which a controllable switching element (S1, S2, S3) is driven to close, part of the pulse duration (T1, T2, T3), while the same switching element (S1, S2, S3) in all clock periods (Tcycle) is driven to close. 4. The method according to any one of claims 1 to 3, characterized in that the diagnosis time (Tdiag) at the beginning of the pulse duration (T1, T2, T3) and after the expiry of the diagnostic time (Tdiag) and other controllable switching elements (S1, S2, S3 ) can be triggered to close. 5. The method according to any one of claims 1 to 4, characterized in that the diagnosis time (Tdiag) at the beginning of a clock period (Tcycle) is located. 6. The method according to any one of claims 1 to 5, characterized in that the diagnosis time (Tdiag) is 50 \ is. 7. The method according to any one of claims 1 to 6, characterized in that the circuit arrangement comprises a voltage sensor (V1), with which during the diagnostic time (Tdiag), the voltage across the light-emitting diode array (1, 2, 3) is detected. 8. The method according to claim 7, characterized in that during the Diagnosis time detected voltage across the LED array of the control and / or regulating means (C) compared with a predetermined value becomes. 9. The method according to claim 8, characterized in that when exceeding the predetermined value plus a predetermined tolerance by the detected voltage, the controllable switching element (S1, S2, S3), which was closed during the detection during the diagnostic time (Tdiag), permanently ie also for the following clock periods (Tcycle) is switched off. 10. The method according to claim 8 or 9, characterized in that at a  Falling below the predetermined value minus a tolerance by the detected voltage, the controllable switching element (S1, S2, S3), which was closed during the detection during the diagnostic time (Tdiag), permanently switched off. 11. The method according to claim 9 or 10, characterized in that after a permanent shutdown by means of the control and / or regulating means (C), the pulse durations (T1, T2, T3), during which the remaining controllable switching elements (S1, S2, S3 ) are extended. 12. Control and / or regulating means (C) for a light-emitting diode array (1, 2, 3)  with at least two first outputs (A11, A12, A13), at which control signals for controlling controllable switching elements (S1, S2, S3) of the light-emitting diode array (1, 2, 3) can be tapped off and  with a measuring signal input (E2) to which a sensor signal of a voltage sensor (V1) can be applied  characterized,  in that the control and / or regulating means (C) is suitable and arranged for carrying out a method according to one of Claims 1 to 11.