EP3935920A1

EP3935920A1 - Control and/or regulating means, circuit assembly, and method for reducing the current maximum in a light-emitting diode field

Info

Publication number: EP3935920A1
Application number: EP20706214.2A
Authority: EP
Inventors: Bernd-Ulrich HAGEMEIER; Sarah Knoop; Carsten Wilks
Original assignee: Hella GmbH and Co KGaA
Current assignee: Hella GmbH and Co KGaA
Priority date: 2019-03-08
Filing date: 2020-02-18
Publication date: 2022-01-12
Also published as: US11723132B2; US20220174797A1; DE102019105954A1; CN113557794A; WO2020182428A1

Abstract

The invention relates to a control and/or regulating means for controlling and/or regulating a light-emitting diode field with n LEDs, where n>2, comprising outputs at which control and/or regulating signals can be tapped in order to control and/or regulate controllable switching elements, wherein switch-on times and/or switch-off times (I) of pulses can be defined by the control and/or regulating means using the control signals and/or regulating signals, one and/or more controllable switching elements (4) can be actuated during the ascertained pulse for an opening or closing process, a number of k groups can be defined, and each LED is assigned to one of the k groups such that each of the k groups _j· contains light-emitting diodes, where 1 ≤ j ≤ k; and (II) a reference time α_j = α₁...α_k can be determined for each group and the switch-on and the switch-off time (I) of the pulse for each LED of each group can be ascertained on the basis of the reference time α_j = α₁...α_k, where 1 ≤ p_j ≤ m_j.

Description

Control and / or regulating means, circuit arrangement and method for reducing the current maximum in a light-emitting diode field

description

The invention relates to a control and / or regulating means for controlling and / or regulating a light-emitting diode array with n LEDs, where n> 2, with outputs at which control and / or regulating signals for controlling and / or regulating controllable switching elements can be tapped

wherein with the control and / or regulating means switch-on times and / or switch-off times of pulses through the control signals and / or re

gel signals are definable and one and / or more controllable switching elements can be controlled during the determined pulses for closing or opening.

A circuit arrangement and a method for operating the circuit arrangement.

In the case of light-emitting diode fields, the brightness of each individual pixel is controlled via a pulse-width-modulated (current) signal with a pulse with a pulse width PW = 0 ... 100%.

In today's systems, all the LEDs of a LED array usually be at time t = 0 _a simultaneously turned on and then turned off successively at the end of its respective pulse at time.

This leads to a strong pulse current load in the supply of such a light-emitting diode array, in particular for switch-t = _a 0th

This in turn increases the requirements for the supply of these systems and can lead to problems with EMC.

Such a light-emitting diode field is located, for example, in newly developed LED headlights with tens of thousands of light-emitting diodes within a light-emitting diode field. Here it is desirable to reduce the maximum current in the system. and to equalize the current curve overall in order to achieve better EMC conditions and to enable a more favorable design of the LED supply.

This is where the present invention begins.

The invention is based on the object of proposing a control and / or regulating means, a circuit arrangement and a method with which the maximum current consumed by a light-emitting diode array can be reduced.

This object is achieved in a first variant according to the invention in that a control and / or regulating means for controlling and / or regulating a light-emitting diode field with n LEDs, where n> 2, with outputs at which control and / or Re - Gel signals for controlling and / or regulating controllable switching elements can be tapped, with the control and / or regulating means switching on times and / or switching off times of pulses by the control signals and / or

Control signals can be defined and one and / or more controllable switching elements can be activated during the determined pulses for closing or opening, whereby a number of k groups can be defined, each LED is assigned to one of the k groups, so that each of the k groups contains m _j light-emitting diodes , where 1 £ j £ k and

is, for each group a reference time a _j =

a ₁ ... a _{k can be} determined and the switch-on and switch-off time of the pulse for each LED one

each group can be determined as a function of the reference point in time a _j = a ₁ ... a _k , where 1 £ p _j £ m _j .

The grouping of the individual LEDs of a light-emitting diode field into groups and the assignment of different reference times to determine the switch-on and switch-off times lead to a distribution of the pulses over a clock period. This measure reduces the maximum current in the system and flattens the current curve. Required brightness distributions often have small gradients with regard to the brightness between neighboring LEDs, that is to say that neighboring LEDs must have a similar brightness and thus have a similar pulse. This is the case in particular when a light-emitting diode field is used in a headlight and the target light distributions to be expected there.

In order to maximize the advantages of the proposed invention, it is therefore sensible for each LED to be assigned to one of the k groups such that adjacent LEDs are assigned to different groups.

The LEDs in a group should be distributed in such a way that no LED blocks of neighboring light-emitting diodes are formed within a group.

In the following it is shown by way of example how a meaningful assignment of the light-emitting diodes to the k groups can take place. It is assumed that this is a matrix LED system in which the LEDs are arranged in columns and rows. Other geometries can easily be classified in a similar way.

For k = 2, the individual LEDs of a light-emitting diode field should be assigned to groups 1 and 2 as follows:

1212121212121212 ...

2121212121212121 ...

1212121212121212 ...

For k = 3, the individual LEDs of a light-emitting diode field could be assigned to groups 1, 2 and 3 as follows:

123 123 123 123 123 ...

231231231231231 ...

312312312312312 ... For k = 5, a meaningful assignment of the individual LEDs of a light-emitting diode field is, for example, the following:

1425314253 ...

2531425314 ...

3142531425 ...

4253142531 ...

It can be advantageous that the reference point in time a _j = a ₁ ... a _{k can} be chosen at random. This saves computational effort within the control and / or regulating means.

However, the objective can be to separate the switch-on times or the switch-off times from one another as far as possible, since a reduction in the maximum current can be achieved by not switching all LEDs on simultaneously or in quick succession.

The reference time a _j = a ₁ ... a _k can advantageously be determined as follows:

k = 1: a ₁ is freely selectable,

k = 2: a ₁ = 0, a ₂ = T,

with i = 1 ... k— 2,

where T is a clock period.

From the determined reference times a _j = a ₁ ... a _k , it is possible to determine the switch-on time and the switch-off time of the pulse for each LED in a group. It can be provided that the switch-on time of the pulse for each

LED of a group depending on a can be calculated according to the formula:

and the switch-off time of the pulse for each LED in a group in

dependence on a can be calculated according to the formula:

in which

- a _j = a ₁ ... a _k ,

- = pulse width of the p. Light emitting diode in the j. Group in% of T.

The switch-on time and the switch-off time of the pulses for each light-emitting diode in a group can be calculated for all desired forms of implementation using the formulas given.

For the above-mentioned case that all light-emitting diodes are to be switched on at the beginning of a clock period, this means a reference time a _j = 0. If this value for a is inserted in the formulas, the result is and

. So all impulses are at the beginning

switched on after the pulse period and switched off again after the pulse duration of each LED.

The same principle applies in the event that all light-emitting diodes are to be switched off simultaneously at the end of the clock period and the individual switch-on time must be calculated for each pulse. In this case the reference point in time a _j = T is to be inserted in the formulas. An individual switch-on time of the pulse for each light-emitting diode and a common switch-off time at the end of the clock period are easily recognizable. For each reference time a _j that lies within a clock period, the formulas show how long before the reference time each pulse is switched on and how long after the reference time each pulse is switched off.

The given formulas result in pulses that are as evenly distributed as possible over a clock period.

Since the number of k groups to be formed is limited by the technical possibilities, k should be chosen according to the principle “as large as necessary, as small as possible”.

This object is achieved in a second variant according to the invention in that with the control and / or regulating means

- A mean value M _{PW of} the pulse widths PW _{i can be} calculated according to the formula

- Depending on the mean value M _PW, a number of k groups can be determined according to the formula

- each LED is assigned to one of the k groups.

According to the invention, the control and / or regulating means can be set up in such a way that results of simulations are stored in order to determine the optimal number of k.

It can then be provided that the method for setting up the control and / or regulating means has at least the following steps:

- Required brightness distributions that are to be achieved with the light-emitting diode field are simulated in a simulation,

- The pulses of the individual LEDs in a group for the required brightness distribution are determined using the simulation,

- For different numbers of groups, a current distribution in the LED field is simulated based on the impulses, - an optimal number of k groups is determined based on the power distribution,

- The information determined on the basis of the simulation is transferred to the control and / or regulating means.

The invention also relates to a circuit arrangement for controlling and / or regulating a light-emitting diode field. The circuit arrangement according to the invention has a control and / or regulating means according to claims 1 to 7, a power source for each LED and a light-emitting diode field, the light-emitting diode field comprising at least two series circuits each comprising at least one light-emitting diode and a controllable switching element , wherein a control connection of each controllable switching element is connected to an output of the control and / or regulating means.

It can be provided that each current source of the circuit arrangement according to the invention can be regulated by the control and / or regulating means, the current being i = i _max when the controllable switching element is closed and i = 0 when the controllable switching element is open.

The method for operating a circuit arrangement according to the invention has at least the following steps:

- a number of k groups are determined by the control and / or regulating means or transferred to the control and / or regulating means or determined randomly,

- each LED is assigned to a group,

- a reference point in time a _j = a ₁ ... a _{k is} specified for each group,

- the switch-on and switch-off time of the pulse for each

LEDs of each group are determined as a function of the reference point in time a _j = a ₁ ... a _k - The control and / or regulating means (1) controls the controllable switching elements for the determined switch-on time and the determined switch-off time of the pulse for each light-emitting diode of each group

to close or open.

The method for operating a second variant of the circuit arrangement also has at least the following steps:

- A mean value M _{PW of} all pulse widths PW _i is calculated according to the formula

calculated.

- depending on the mean value M _PW , a number of k groups is determined according to the formula,

- each LED is assigned to one of the k groups.

The advantage of the present invention is that with an increasing number of groups, the maximum of the current within a light-emitting diode field is significantly reduced and becomes more continuous.

Since the number of groups cannot usefully be increased infinitely, the present invention also provides a possibility of achieving a sensible effort / benefit balance.

The invention is explained in more detail below with reference to the accompanying drawings. It shows:

Fig. 1 block diagram of a circuit arrangement according to the invention for

Controlling and / or regulating a light emitting diode field

2a, 2b are flow diagrams to illustrate the determination of the reference times and the switch-on and switch-off times

3 shows an example of a pulse distribution according to the invention for k = 5

Fig. 4 simulated current distribution with a different number of

Groups for a real brightness distribution 1 shows a block diagram of a circuit arrangement 5 according to the invention for controlling and / or regulating a light-emitting diode array 2.

The circuit arrangement 5 according to the invention can be implemented, for example, by an integrated circuit, in particular a commodity chip or an ASIC. Other designs of the circuit arrangement 5 are entirely conceivable.

The light-emitting diode field 2 is assumed here as a matrix LED system, as it is used in newly developed headlights of motor vehicles.

The individual light-emitting diodes LED ₁₁ , LED ₁₂ , ... are arranged in rows and columns to one another. However, the invention is not limited to light-emitting diode arrays with light-emitting diodes arranged in rows and columns.

It is easily imaginable here that the light-emitting diode field 2 has a different arrangement of the light-emitting diodes LED ₁₁ , LED ₁₂ ,...

In today's headlights, LED systems with 15,000-25,000 light-emitting diodes LED ₁₁ , LED ₁₂ , ... are used.

The individual LEDs can be operated via a controllable switching element 4 which is activated for opening or closing. The brightness of the individual light-emitting diodes LED ₁₁ , LED ₁₂ ,... Is set over the duration of the closed controllable switching element 4.

The required brightness of the individual light-emitting diodes LED ₁₁ , LED ₁₂ , ... can be determined on the basis of image data that can be transferred from a control device 8 to the control and / or regulating means 1.

It is also conceivable that the required brightness values are transferred directly to the control and / or regulating means 1. The controllable switching elements 4 are switched on and off at such a high frequency that it cannot be seen by the human eye.

In addition to the light-emitting diode field 2, the circuit arrangement 5 according to the invention comprises at least one current source 6. The current source 6 is a controllable current source 6.

It is conceivable that the circuit arrangement 5 according to the invention for each

Light-emitting diode LED ₁₁ , LED ₁₂ , ... in the light-emitting diode field 2 has a current source 6 and a controllable switching element 4. Such a design is possible, for example, with the novel LED headlights mentioned at the beginning.

In addition, in a circuit arrangement 5 according to the invention, at least one control and / or regulating means 1 according to the invention is provided. The control and / or regulating means 1, preferably a plurality of outputs 3. The control and / or regulating means 1 is connected to the controllable current source 6 and the controllable switching elements 4 of the light-emitting diode array 1 via these outputs 3.

The control and / or regulating means can also have at least one input 9. Image data for determining the required brightness, for example, can be transferred via this input.

The control and / or regulating means 1 according to the invention is set up in such a way that the process steps required to achieve a desired brightness distribution of the light-emitting diodes LED ₁₁ , LED ₁₂ ,... Of the light-emitting diode field 2 can be run through autonomously.

In the control and / or regulating means 1 according to the invention, this is achieved by first defining a number of k groups and assigning each LED to one of the k groups. The number of necessary groups can be determined on the one hand by a calculation within the control and / or regulating means 1 during operation.

It is also conceivable to define a number of groups in advance and to transfer them to the control and / or regulating means 1.

Within the control and / or regulating means 1 it is also provided that a unit 7 for determining the reference times a _j = a ₁ ... a _{k is} present.

The reference times a _j = a ₁ ... a _k can be determined in different ways. If the computational effort is to be minimized, the values can, for example, be selected randomly with the aid of a random generator.

The unit 7 is preferably set up in such a way that it calculates the reference time a _j = a ₁ ... a _k from the determined value of the number of groups.

In the circuit arrangement according to the invention, the unit 7 is set up in such a way that it determines the reference time a _j = a ₁ ... a _k , taking into account the number of groups, as follows:

k = 1: a ₁ is freely selectable,

k = 2: a ₁ = 0, a ₂ = T,

with i = 1 ... k— 2,

where T is a clock period.

Depending on the reference times then available

a _j = a ₁ ... a _k can the control and / or regulating means 1 according to the invention

Switch-on and switch-off time of the pulse for each LED in a group

determine. For this purpose, a formula is used in unit 7 to calculate the switch-on time and the switch-off time of the pulse for each LED in a group

deposited. In the present case, the following formulas for the unit are provided:

Switch-on time

Switch-off time

Based on the determined switch-on and switch-off times, the

Controlled ble switching elements 4 for closing or opening.

While the controllable switching element is closed, the controllable current source supplies the required current i in order to make the selected light-emitting diode light up and to achieve the required brightness distribution.

2a, 2b show flowcharts for better illustration of the determination of the reference times and the switch-on and switch-off times. Fig. 2a shows an outer loop and Fig. 2b shows an inner loop.

As a preparatory measure, the number of k groups is determined according to one of the variants described in FIG. 1 and each light-emitting diode is assigned to a group, so that each group contains m _j light-emitting diodes. This information is fed into the system in a suitable manner.

The flowchart begins in an outer loop in which the individual groups are worked through one after the other. The value of j therefore runs from j = 1 to j = k.

At first j: = 1 is set, i.e. the first of the k groups is considered. In a first step, the reference time ai for the first group is now established according to one of the methods presented. As already shown, this can happen, for example, randomly, in accordance with a stored table or using the formulas presented.

After defining the reference time for the group just under consideration, the inner loop of the application starts.

In the inner loop, the switch-on time and the switch-off time are determined recursively for each assigned light-emitting diode p _{j of} the group considered in this run.

The value of p _j runs through all values until the number of light-emitting diodes in the respective group m _{j is} reached.

First, j = 1, so that the light-emitting diodes pi of the first groups are passed through.

For this purpose, p ₁ : = 1 is initially set, that is to say the first light-emitting diode of the first group is considered.

On the basis of the reference value for the first group, a switch-on time and a switch-off time are determined below for this light-emitting diode.

Once this has happened, the next step is to check whether the value of p _j corresponds to the value of m _j , ie the inner loop has been processed for all light-emitting diodes in the group under consideration.

If the query is answered with "no", the value of p _j is increased by 1 and the inner loop is run through again.

If the query is answered with "yes", the inner loop ends and you return to the outer loop. Here it is checked whether the value of j corresponds to the value of k and thus all groups have been processed.

If the query is answered with "no", the value of j is increased by 1, ie the next group is considered. The recursion starts again.

If the query is answered with "yes", all necessary calculations have been carried out. The process ends.

3 shows an exemplary representation of a pulse distribution determined according to the invention for k = 5.

The time, in this case a clock period T, is plotted on the x-axis.

The current of the controllable current source 6 is plotted on the y-axis.

When switched on, the current i = i _{max flows} ; when switched off, i = 0.

Using the calculation method presented for a _j = a ₁ ... A ₅ , the reference times result from the calculation model explained under FIG. 1

Based on these reference times, the switch-on time and switch-off time of the pulse for each light-emitting diode of each group

determined by using the formulas given under FIG. 1 for the calculation.

The present example shows an impulse for each of the 5 groups. This would mean that there would only be one light emitting diode in each group. In practice, a large number of light emitting diodes are assigned to a group. The assumption that a light-emitting diode is assigned to each of the k groups is used exclusively for better clarity in FIG. 3. By determining the reference times according to the invention and calculating the switch-on time and the switch-off time, a uniform distribution of the pulses over a clock period is achieved.

In reality, a large number of light-emitting diodes LED ₁₁ , LED ₁₂ , ... of a light-emitting diode field 2 are assigned to each group. Each of these light-emitting diodes has a pulse for setting the desired brightness.

This means that the current required within a clock period is not constant i = i _max or i = 0, but rather has to be set as the current requirement of the switched-on light emitting diodes specifies.

The aim of the present invention is to reduce the maximum current within the circuit arrangement and to harmonize the current curve.

4 shows a simulated current distribution with a different number of groups for a real brightness distribution. In the present case, the number of k groups is not determined, but a comparison of different numbers is carried out in order to clarify the influence of the number of groups k on the current distribution.

The switch-on times and the switch-off times are calculated using the formulas described under FIG. 1.

The simulation involves a real arrangement with several thousand light-emitting diodes, which are assigned to the different groups according to the criteria shown in FIG. 1.

Here shows

L1 the current curve for k = 1, if all the LEDs are switched on at a ₁ = 0, L2 the current curve for k = 2, where a ₁ = 0, a ₂ = T is assumed, L3 is the current curve for k = 3, assuming

L4 is the current curve for k = 5, assuming

men will.

The current i _{max was} assumed dimensionless with i _max = 1.

As a result, it can be seen here that the maximum current is significantly reduced with an increasing number of groups and the current curve becomes flatter and more continuous. The reduction in the current maximum becomes smaller with an increasing number of k, which underlines the importance of the determination of the required number of groups shown. For the implementation, a cost / benefit analysis must be carried out with the aid of the present invention.

List of reference symbols

1 control and / or regulating means

2 LED field

3 outputs

4 controllable switching elements

5 circuit arrangement

6 power source

7 Unit for determining the reference times

8 control unit

9 entrance

LED ₁₁ , LED ₁₂ , ... light-emitting diodes

Switch-on or switch-off time

a _j = a ₁ ... a _k reference times

Claims

1. Control and / or regulating means (1) for controlling and / or regulating a

Light-emitting diode array (2) with n LEDs, where n> 2, with outputs (3) at which control and / or regulating signals for controlling and / or regulating controllable switching elements (4) can be tapped,

with the control and / or regulating means (1)

- Switch-on times and / or switch-off times ^from

Pulses through which control signals and / or regulation signals can be defined,

- One and / or more controllable switching elements (4) can be controlled during the determined pulses for closing or opening, characterized in that

- a number of k groups can be specified,

- Each LED is assigned to one of the k groups, so that each of the k groups contains m _j light-emitting diodes, where

is

- a reference point in time a _j = a ₁ ... a _{k can be} determined for each group,

- the switch-on and switch-off time of the pulse for

each LED of each group can be determined depending on the reference point in time a _j = a ₁ ... a _k , where 1 £ p _j £ m _j .

2. Control and / or regulating means (1) according to claim 1,

characterized in that each LED is assigned to one of the k groups in such a way that adjacent LEDs are assigned to different groups.

3. control and / or regulating means (1) according to claim 1 to 2, characterized in that the reference times a _j = a ₁ ... a _{k can} be selected at random.

4. Control and / or regulating means (1) according to claim 1 to 2,

characterized in that the reference times a _j = a ₁ ... a _k can be determined as follows:

k = 1: a ₁ is freely selectable,

k = 2: a ₁ = 0, a ₂ = T,

with i = 1 ... k— 2,

where T is a clock period.

5. Control and / or regulating means (1) according to one of claims 1 to 4, characterized in that the switch-on time of the pulse

for each LED of a group depending on a can be calculated according to the formula:

in which

- a _j = a ₁ ... a _k ,

- = pulse width of the p. Light emitting diode in the j. Group in% of T.

6. Control and / or regulating means (1) according to one of claims 1 to 4, characterized in that the switch-off time of the pulse

This can be calculated for each LED of a group depending on a according to the formula:

in which

- a _j = a ₁ ... a _k ,

- = pulse width of the p. Light emitting diode in the j. Group in% of T.

7. Control and / or regulating means (1), in particular according to claim 1 or 2, for controlling and / or regulating a light emitting diode array (2) with n LEDs, with outputs (3) at which control and / or regulating signals for controlling and / or control of controllable switching elements (4) can be tapped, with the control and / or regulating means (1)

- Switch-on times and / or switch-off times ^from

- A mean value M _{PW of} all pulse widths PW _{i can be} calculated according to the formula

- each LED is assigned to one of the k groups.

8. A method for programming a control and / or regulating means (1) with the features of claims 1 to 7,

wherein the method comprises at least the following steps:

- Required brightness distributions that are to be achieved with the light-emitting diode field (2) are reproduced in a simulation,

- For different numbers of groups, a current distribution in the LED field (2) is simulated on the basis of the pulses,

- an optimal number of k groups is determined on the basis of the current distributions,

- The information determined on the basis of the simulation is sent to the

Transferring control and / or regulating means (1).

9. A circuit arrangement (5) for controlling and / or regulating a light-emitting diode field (2)

- a control and / or regulating means (1) according to claims 1 to 7,

- a power source (6) for each LED,

- a light emitting diode field (2),

wherein the light-emitting diode field (2) comprises at least two series circuits each comprising at least one light-emitting diode and one controllable switching element (4), a control connection of each controllable switching element (4) having an output (3) of the control and / or Control means (1) is connected.

10. Circuit arrangement (5) according to claim 9,

characterized in that

each current source (6) of the circuit arrangement (5) can be regulated by the control and / or regulating means (1), the current being i = i _max when the controllable switching element is closed and i = 0 when the controllable switching element is open.

11. A method for operating a circuit arrangement (5) with the features of claim 9,

wherein the method comprises at least the following steps:

- a number of k groups are determined by the control and / or regulating means (1) or transferred to the control and / or regulating means (1) or determined at random,

- each LED is assigned to a group,

- the switch-on and switch-off time of the pulse for

each light emitting diode of each group are determined depending on the reference time a _j = a ₁ ... a _k - The control and / or regulating means (1) controls the controllable switching elements (4) for the determined switch-on time and the determined switch-off time of the pulse for each

Light-emitting diode of each group for closing or opening.

12. A method for operating a circuit arrangement (5) with the features of claims 9,

wherein the method comprises at least the following steps:

calculated.

- each LED is assigned to one of the k groups.