DE102014213853A1 - Circuit arrangement and method for driving LEDs in matrix configuration - Google Patents

Abstract

The invention relates to a circuit arrangement for driving LEDs in a matrix configuration having m columns and n rows, each LED (LED11, LED12, LED21, LED22) of the matrix being activated by activation of a corresponding column driver (S01, S02) the activation of a corresponding row driver (S10, S20) is individually controllable, each with a line of a bias device (12). In this case, the bias device (12) comprises a first bias connection (14) for electrical coupling to the cathodes of m of the LEDs (LED11, LED12) of this line and a second bias connection (16) for electrical coupling to the anodes of m LEDs (LED11, LED 12) of this row, each LED (LED11, LED12, LED21, LED22) of the matrix in each case being coupled via a semiconductor diode (D11, D12, D21, D22) to the associated terminal of a column driver (S01, S02) is, wherein also n semiconductor diodes (D11, D21), which are assigned to the same column, each electrically connected to one another at one of its electrodes. Furthermore, the invention relates to a display device and a household appliance with such a circuit arrangement and to a method for driving LEDs in a matrix configuration.

Description

The invention relates to a circuit arrangement for driving light emitting diodes (Light Emitting Diodes, abbreviated LEDs) in a matrix configuration, wherein each LED of the matrix is individually activatable by activation of a corresponding column driver in connection with the activation of a corresponding row driver, wherein each further per line, a bias device having a first bias connection for electrically coupling to the cathodes of the LEDs of the respective row and having a second bias connection for electrical coupling to the anodes of the LEDs of the respective row.

In the case of LEDs in a matrix arrangement, a blocking voltage is applied to the LEDs in certain states of the control as a matter of principle. 1 represents the simplest example a 2 × 2 matrix (two times two matrix). The thereby flowing blocking current (dashed lines) caused by material migration the failure of LEDs. The avoidance of blocking voltage in a matrix is sought in order to obtain the cost-effective matrix principle without reducing the lifetime.

In this context, the EP 1 916 880 B1 a principle for solving the blocking voltage problem. 2 shows an equivalent circuit diagram with in the EP 1 916 880 B1 proposed solution to a 2 × 2 matrix. If the LED11 is activated, it drops, for example, from a forward voltage of 3.4 volts. So that the LED22 is not operated in the reverse direction, it is biased via the voltage dividers R22A_H / R22A_L and R22C_H / R22C_L with 0.2 volts. Inevitably, the Kirchhoff mesh equation on the LED21 and LED12 must drop 3.6 volts in total. The problem of material migration would be eliminated, but LED21 and LED12 may glow more or less strongly depending on the color due to the voltage applied in the direction of flow.

It is an object of the present invention to provide a circuit arrangement which prevents both a damaging reverse voltage on the LEDs and a glow on non-driven LEDs.

This object is achieved by a circuit arrangement having the features of patent claim 1 and by a method having the features of patent claim 13. Advantageous developments of the present invention are the subject of the dependent claims.

The circuit arrangement according to the invention for driving LEDs in a matrix configuration which has m columns and n rows, wherein each LED of the matrix can be controlled individually by activating a corresponding column driver in conjunction with the activation of a corresponding row driver, has a bias for each row. Device with a first bias connection for electrical coupling to the cathodes of m of the LEDs of this line and a second bias connection for electrical coupling to the anodes of the m LEDs of this line. In other words, the first bias terminal of the biasing means is connected to the cathodes of m of the LEDs of that row and the second biasing terminal of the biasing means is connected to the anodes of the m LEDs of that row.

According to the invention, each LED of the matrix is then coupled in each case via a (non-illuminable) semiconductor diode to the associated terminal of a column drive, wherein also n semiconductor diodes, which are assigned to the same column, are each electrically connected to one another at one of their electrodes, namely via the column driver. The use of the semiconductor diodes has the advantage that they absorb the majority of the applied blocking voltage. Thus, the blocking voltage-sensitive LED are relieved of the applied blocking voltage with the aid of the incapacitated semiconductor diodes. By interconnecting the two bias connections with the cathode and the anode of the respective LED, the voltage drop across each element of a non-actively controlled parallel path can be set specifically.

For applicability of the invention, neither the number of columns m nor the number of lines n may be equal to one, since otherwise no parallel active path is not possible. Of course, columns and rows are interchangeable and represent in particular only the type of electrical connection and not necessarily a specific geometric arrangement of the LEDs to each other.

In a preferred embodiment, the electrically interconnected electrodes of the semiconductor diodes are the anodes of the semiconductor diodes. This results in the advantage that the LED chips usually mounted on the cathode side with a conductive adhesive LED chips can be arranged on the same reference potential.

Alternatively or additionally, the electrical coupling of the bias device to the cathodes of the m LEDs can be provided in at least one line in each case via at least one resistor, in particular via m resistors.

According to a further aspect of the invention, the bias device has a voltage divider. Particularly advantageous here can be a multipart ohmic voltage divider can be used with at least two taps, which is designed for electrical coupling to the anodes or cathodes of the LED of the respective row.

The voltage divider may include at least one resistor. In a particularly preferred embodiment, however, the voltage divider has a diode, in particular a Zener diode. This results in the advantage that a certain potential difference can be realized independently of the current through the voltage divider. In particular, in the case of a transverse current drain from the ohmic voltage divider, it is therefore possible to minimize the effect on the voltage divider without having to interpret it unnecessarily low-impedance and therefore loss-rich.

In a further advantageous embodiment, the anode bias voltages generated by the respective bias devices per row are different for each of the m lines. As a result, variations of the LED current and / or the LED forward voltage can be taken into account, for example as a result of using LEDs of different colors.

Preferably, the circuit arrangement is designed to apply non-activated LEDs in operation with a maximum voltage of 0.5 volts in the flow direction, preferably at most 0.2 volts in the flow direction to increase the distance from a glow limit at which the first light emission of the LED occurs. As a result, unintentional lighting of a non-driven LED can be reliably avoided.

According to a further aspect of the invention, unenergized LEDs are subjected to a voltage of at least 0.0 volts in the direction of flow, preferably at least 0.1 volts in the direction of flow, in order to prevent damage to the LEDs by an inverse current.

In a further advantageous embodiment, the bias device is designed to provide different anode bias voltages for m LEDs of a line with different currents and / or forward voltages. This makes it possible in particular to use different LEDs within a row.

Preferably, the circuit arrangement according to the invention can be used in a display device, resulting in a display device according to the invention.

Furthermore, such a display device may be used in a household appliance, resulting in a household appliance according to the invention.

The inventive method for driving LEDs in a matrix configuration comprising m columns and n rows comprises the steps of coupling a first terminal of a biasing device to the cathodes of m LEDs in the matrix configuration, wherein the biasing means and the m LEDs are each associated with the same row, and coupling a second terminal of the bias means associated with that row to the anodes of the m LEDs in that row. Furthermore, in the method, provision is made in each case of a semiconductor diode for coupling each LED of the matrix to the associated terminal of a column driver, wherein n semiconductor diodes, which are assigned to the same column, are electrically connected to one another at each of their electrodes. In other words, each LED of the matrix is connected to a semiconductor diode such that the current provided by the associated terminal of the column driver for the respective driven LED flows over the semiconductor diode.

In the following the invention is explained in more detail with reference to the figures.

Showing:

1 the general operating principle of a 2 × 2 LED matrix with corresponding column and row drive according to the prior art;

2 an equivalent circuit diagram of a 2 × 2 matrix with a potential control according to the prior art;

3 an equivalent circuit diagram of a 2 × 2 matrix with a potential control according to the invention, and

4 An embodiment of a circuit arrangement according to the invention a 2 × 2 matrix with line-dependent bias.

An exemplary LED matrix in a 2x2 configuration is hereafter accordingly 1 explained. Starting from a common reference potential GND, a first current source I10 and a second current source I20 are each coupled via a switch S10 or S20 to a row drive of the LED matrix. In this case, the switch S10 of the first row drive is connected to the cathode of a LED11 and the cathode of a LED12. Further, the switch S20 of the second row driver is connected to the cathode of an LED21 and the cathode of an LED22. Furthermore, the anodes of the LED11 and the LED21 via a switch S01 a first Column drive coupled to a supply potential VCC. Furthermore, the anodes of the LED12 and the LED22 are coupled to the supply potential VCC via a switch S02 of a second column drive. Thus, for example, in the case of a closed switch S01 the column drive and, in the case of a closed switch S10 of the row drive, a current flow through the LED11. This results, for example, via the LED11, a voltage drop in the flow direction of 3.4 volts. The switches S02 and S20 are open. This results in a parallel path as in 1 shown in dashed lines to the LED11 consisting of the LED21, LED22 and LED22, the LED21 and LED12 are operated in the flow direction and the LED22 in the reverse direction. As a result, a voltage drop in the flux direction of approximately zero volts results at the LED21 and the LED12, while the LED22 results in a reverse voltage drop of 3.4 volts at the LED22.

In order to prevent the blocking voltage applied to the LED22, a bias device according to the prior art has been used 12 supplemented, which exemplifies in 2 is shown. This includes the bias device 12 a first voltage divider consisting of the series connection of a resistor R22A_H and a resistor R22A_L, wherein the resistor R22A_H is coupled to the supply potential VCC and the resistor R22A_L is coupled to the reference potential GND. Furthermore, the bias device comprises a voltage divider consisting of the series connection of a resistor R22C_H and a resistor R22C_L, wherein the resistor R22C_H is coupled to the supply potential VCC and the resistor R22C_L is coupled to the reference potential GND. In this case, the connection point of the two resistors R22A_H and R22A_L is at a first bias connection 14 the bias device 12 led out and the connection point of the resistor R22C_H and the resistor R22C_L on a second bias connection 16 , For a clearer illustration, the series circuit comprising the switch S01 of the column drive, the LED11, the switch S10 of the row drive and the current source I10 between the two potentials VCC and GND is shown in a line. Parallel to the LED11, the series circuit of LED21, LED22 and LED12 is arranged, wherein the LED21 and LED12 are arranged in the flow direction and the LED22 in the reverse direction. The connection point of the cathode of LED21 and the cathode of LED22 is in this case with the second bias connection 16 Further, the connection point of the anode of the LED 22 to the anode of the LED 12 is connected to the first bias terminal 14 , As in the previous example, a voltage of 3.4 volts also falls here via the LED11; according to Kirchhoff's mesh rule, indicated by M1, a voltage of 3.4 volts must also be dropped across the LED21, LED22 and LED12. In the example shown, the potential is set so that there is a low forward voltage of 0.2 volts across the LED22, or in other words a blocking voltage of minus 0.2 volts. The remaining voltage is divided between the two LED21 and LED12, with 1.8 volts across each of the two LED21 and LED12 dropping in the direction of flow.

In the development according to the invention 3 In Fig. 1, an additional semiconductor diode D22 having the same orientation as LED22 is inserted between the LED22 and the LED12, in other words, both the LED22 and the semiconductor diode D22 are reverse-biased. Here, the training on the in 1 and 2 build up circuits shown. The bias device 12 has in this embodiment, two voltage sources U22A and U22C, which are both related to the common reference potential GND and each with the first bias connection 14 or the second bias connection 16 are coupled. Further, the connection point of the cathode of the LED21 to the cathode of the LED22 is via a coupling resistor R22C to the second bias terminal 16 and the connection point of the anode of the LED22 to the cathode of the semiconductor diode D22 via a coupling resistor R22A to the first bias connection 14 , The arrangement of the remaining elements is identical to the representation in FIG 2 , The inventive insertion of the semiconductor diode D22 results in the present example, a potential distribution as described below. Above the LED21 and the LED12 results in each case a voltage drop of 0.1 volt in the flow direction, further also results over the LED22 a voltage drop of 0.1 volts in the flow direction or in other words minus 0.1 volts in the reverse direction. The semiconductor diode D22 absorbs the majority of the blocking voltage in the amount of approximately 3.3 volts in the reverse direction. The circuit described here uses ordinary silicon diodes, such as the Standard type 1N4148 , in series with the LEDs, which take over the blocking voltage. Silicon diodes can permanently withstand a reverse current and are therefore suitable for this purpose. To ensure that no LED is exposed to a negative voltage, they are subjected to a low positive voltage via a suitably dimensioned circuit. Only a silicon diode in series without additional circuitry would slow down, but not completely prevent, the process of material migration in the LED due to its lower reverse saturation current. Since the semiconductor diode D22 receives the reverse voltage in series with LED22, potential control is possible such that the Kirchoff's mesh equation for M1 is satisfied without an LED glowing unintentionally. The Coupling resistors R22A and R22C can also be considered as internal resistance of the sources U22A and U22C, respectively, added to this.

4 shows a 2 × 2 LED matrix, in which the principle of the invention for each LED was applied in the matrix. Starting from the in 1 In addition, LED11 is now coupled to switch S01 via semiconductor diode D11, furthermore, LED12 is coupled to switch S02 via semiconductor diode D12, LED21 is connected via semiconductor diode D21 coupled to the switch S01 and the LED22 is coupled via the semiconductor diode D22 to the switch S02. A series resistor R10 or R20 replaces the current source I10 or I20 1 where R10 and S10 have changed positions as well as S20 and R20. The series resistors R10 and R20 can thus be assigned directly to the LED matrix, in the simplest case, therefore, the column or row drivers, which are represented here only as switches, be realized in the simplest case by NPN or PNP transistors.

In the general case, a voltage divider can be arranged as an implementation of a voltage source with internal resistance at each anode and cathode of each LED of the 2 × 2 matrix. The dimensioning depends on the desired bias voltage and on the LEDs. In the present embodiment between the cathode of the LED11 and the cathode of the LED12 existing electrical connection then three voltage dividers are necessary per line, that is a total of six voltage divider. This achieves maximum flexibility, and by adapting resistors, the circuit can be adapted to different forward voltages and LED currents. Without additional effort, it is possible to use different LEDs per line. If you also want to control different LEDs within a row, this is possible by inserting a further series resistor with additional circuitry. The circuit works by the line-dependent anode bias in all states, this also allows dimming by pulse width modulation (PWM).

In an advantageous development, a single and / or common voltage divider per row is used to connect the anodes of the LED, which are assigned to this row via coupling resistors. In particular, the voltage divider, which is designed to connect the cathodes of the LED of the respective row, can also be combined with the voltage divider coupled on the anode side, whereby the voltage divider in FIG 4 shown voltage divider which comprises three resistors R10x, R10y and R10z. In this case, R10y is coupled on one side directly to the common potential of the anodes of the LED11 and the LED12, on the other side via a coupling resistor R11 to the anode of the LED11 and furthermore via a coupling resistor R12 to the anode of the LED12. The common connection point of the anodes of the LED11 and the LED12 with the resistor R10y is coupled to the reference potential GND via the resistor R10z. The common connection point of the resistors R10y, R11 and R12 is also coupled to the supply potential VCC via the resistor R10z.

The corresponding circuit arrangement of the second line results equivalently, the first digit of the indices is here to change from one to two, such. From R10z to R20z or from LED12 to LED22.

Thus, the bias device includes 12 in the example shown, the three resistors R10x, R10y and R10z, where the junction of R10x and R10y is the first bias terminal 14 and wherein the connection point of R10y and R10z is the second bias connection 16 represents.

This arrangement allows the adjustment of the anode bias voltage regardless of the forward voltage or the current from the LED and is also independent of the switching state of the line switches S10 and S20. The embodiment according to 4 is merely illustrative of the invention and is not limitative of it. In particular, the assignment of rows and columns is interchangeable, as well as the arrangement of current sources or series resistors and switches. Furthermore, the order of arrangement of the respective LED with its associated semiconductor diode can vary without departing from the spirit of the invention. For example, the LED11 and LED12 of a row can also be connected to one another on the anode side instead of the cathode side, or even have no direct connection to one another at all. The exchange of the reference potential GND with the positive supply potential VCC is also possible, in which case the orientations of the LEDs and the semiconductor diodes must be adapted accordingly.

The circuit arrangement according to the invention can be operated in a single mode with only one actively activated switch of the column control and the row control, whereby a maximum of one LED lights up at a certain time. But it can also be provided to operate the circuit arrangement in a column mode, where in each case a switch of the Column drive is actively controlled and any number of switches of the line control are actively controlled. Using an external, controllable power source as in the 1 to 3 It is also possible to activate several switches of the column control, without having to divide the current dimensioned for one LED into several LEDs and, as a result, reduce the brightness of the individual LED.

It has thus been shown by means of a circuit arrangement and an associated method how the avoidance of the blocking voltage on LEDs in a matrix circuit can be achieved.

LIST OF REFERENCE NUMBERS

10, 20

 LED matrix

12

 Bias means

14

 first bias connection

16

 second bias connection

D11, D12, D21, D22

 Semiconductor diode

I10, I20

 power source

LED11, LED12, LED21, LED22

 LED

R10, R20

 dropping resistor

R10x, R10y, R10z, R20x, R20y, R20z

 Voltage divider resistor

R11, R12, R21, R22, R22A, R22C

 coupling resistor

R22A_H, R22A_L, R22C_H, R22C_L

 Voltage divider resistor

S01, S02, S03, S04

 switch

U22A, U22C

 Bias voltage source

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1916880 B1 [0003, 0003]

Cited non-patent literature

• Standard Type 1N4148 [0028]

Claims (13)

Circuit arrangement for driving LEDs in a matrix configuration having m columns and n rows, each LED (LED11, LED12, LED21, LED22) of the matrix being activated by activation of a corresponding column driver (S01, S02) in conjunction with activation of a corresponding column driver Row driver (S10, S20) is individually controllable, each with one line of a bias device ( 12 ) with - a first bias connection ( 14 ) for electrical coupling to the cathodes of m of the LEDs (LED11, LED12) of this row, and - a second bias connection ( 16 ) for electrical coupling to the anodes of the m LEDs (LED11, LED12) of this row, characterized in that each LED (LED11, LED12, LED21, LED22) of the matrix in each case via a semiconductor diode (D11, D12, D21, D22) with a is coupled to respective terminals of an associated column driver (S01, S02), wherein n semiconductor diodes (D11, D21) associated with the same column are each electrically connected together at one of their electrodes. Circuit arrangement according to Claim 1, characterized in that the electrodes which are connected to one another electrically are the anodes of the semiconductor diodes (D11, D21). Circuit arrangement according to one of the preceding claims, characterized in that per line, the electrical coupling of the first bias terminal ( 14 ) is provided with the anodes of the m LEDs (LED11, LED12) via at least one resistor, in particular over m resistors (R11, R12). Circuit arrangement according to one of the preceding claims, characterized in that per line, the electrical coupling of the second bias terminal ( 16 ) is provided with the anodes of the m LEDs (LED11, LED12) via at least one resistor, in particular via m resistors. Circuit arrangement according to one of the preceding claims, characterized in that in at least one line the bias device ( 12 ) comprises a voltage divider, which preferably comprises at least one resistor (R10x, R10y, R10z). Circuit arrangement according to claim 5, characterized in that the voltage divider comprises a diode, in particular a Zener diode. Circuit arrangement according to one of the preceding claims, characterized in that by the bias device ( 12 ) each anode line voltages generated per line are different for each of the n lines. Circuit arrangement according to one of the preceding claims, characterized in that the circuit arrangement is designed to operate in operation non-activated LEDs ( 3 : LED21, LED22, LED12) with a maximum voltage of 0.5 V in the direction of flow, preferably a maximum of 0.2V in the flow direction to increase the distance from a glow limit at which the first light emission of the LED occurs. Circuit arrangement according to one of the preceding claims, characterized in that non-driven LEDs ( 3 : LED21, LED22, LED12) with a voltage of at least 0.0 V in the flow direction, preferably a minimum of 0.1V in the flow direction are applied to prevent damage to the LEDs by an inverse current. Circuit arrangement according to one of the preceding claims, characterized in that the bias device is designed to provide different anode bias voltages for m LEDs (LED11, LED12) of a line with different currents and / or forward voltages. Display device with a circuit arrangement according to one of the preceding claims. Domestic appliance with a display device according to claim 11. Method for driving LEDs in a matrix configuration having m columns and n rows, comprising the steps of: - coupling a first terminal ( 14 ) a bias device ( 12 ) with the cathodes of m LEDs (LED11, LED12) in the matrix configuration, wherein the bias device and the m LEDs are each assigned to the same row, and - coupling a second terminal ( 16 ) of the bias device ( 12 ), which is associated with this row, with the anodes of the m LEDs (LED11, LED12) in this row, characterized by the further step: - providing in each case a semiconductor diode (D11, D12, D21, D22) for coupling each LED (LED11, LED12, LED21, LED22) of the matrix with the associated terminal of a column driver (S01, S02), wherein n semiconductor diodes, which are assigned to the same column, are electrically connected to each other at one of their electrodes.

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