EP3794907A1

EP3794907A1 - Circuit configuration canceling out reverse voltage drop in a light emitting diode (led)

Info

Publication number: EP3794907A1
Application number: EP19720587.5A
Authority: EP
Inventors: Onder Sunetci; Musa OZDEMIR; Mucahit Bacaksiz; Hakan Ozkahraman
Original assignee: Arcelik AS
Current assignee: Arcelik AS
Priority date: 2018-05-18
Filing date: 2019-04-29
Publication date: 2021-03-24
Also published as: WO2019219366A1

Abstract

The present invention relates to a LED driver circuit (1) comprising at least one first switching member (4) and at least one second switching member (5) electrically connected in series to at least one first and at least one second LED (2, 3) each of which is independently drivable. Tertiary switching members (7) are arranged between the ground connection and a common node (6) connecting the outlet ends of said first and second LEDs (2, 3).

Description

CIRCUIT CONFIGURATION CANCELING OUT REVERSE VOLTAGE DROP IN A LIGHT EMITTING DIODE (LED)

The present invention relates to a reverse voltage protection circuit configuration protecting a light emitting diode (LED) against reverse voltage drops and thereby preventing it from malfunctioning.
Semi-conductive structures such as LEDs are susceptible to damage due to application of reverse voltage and LEDs break down when power is applied thereon under certain circumstances. Therefore, reverse voltage protection which require special circuit designs is needed for LEDs.
In a matrix format, LEDs are usually arranged in rows and columns and each LED can be addressed by specifying its row and column position. Due to the fact that micro-controllers have pins with maximum output current, transistors can be used as switching members to control a power supply for driving a plurality of LEDs simultaneously. Since LEDs may be subjected to reverse voltage when driven multiply, a circuit configuration is needed to prevent semi-conductive LED components from breaking down.
The present invention enables realizing a circuit configuration enabling, in connection with a switching member in the form of a transistor, a LED group to be protected against reverse voltage, and thereby canceling out a reverse voltage value which a LED in said LED group might be subjected to.
State of the art patent document no. US2011017972 discloses a light emitting structure comprising a substrate having a first face, a second face, and a p-n junction formed between a p-type layer and an n-type layer, wherein the p-type layer and the n-type layer are used as a reverse voltage protection diode. A buffer layer is provided on the substrate, and a light emitting diode (LED) is fabricated on the buffer layer. The LED is then electrically coupled to the reverse voltage protection diode so as to form an anti-parallel diode pair configuration.
Reverse voltage protection can be provided for a LED by means of an anti-parallel diode, inhibiting application of reverse operating voltage to the LED. However, since such type of alternative solutions require using an additional diode for each LED, they increase productions costs due to the employed additional diodes or transistors and are therefore not preferred. Additional costs pose a significant problem considering the number of additional members required, particularly when a large LED matrix is used.
The present invention enables realizing an electric circuit characterized by the features defined in claim 1, comprising a plurality of LEDs driven between on/off positions by a plurality of switching members controlled by a micro-controller, in which a switching member in off position is prevented from applying reverse voltage to a LED.
The aim of the present invention is to realize an electric circuit comprising a plurality of LEDs driven between on/off positions by a plurality of switching members, in which a switching member in off position is prevented from applying reverse voltage to a LED.
The LED driver circuit of the invention comprises a plurality of switching members each one of which energizes a plurality of LEDs. Said switching members are preferably bipolar junction transistors (BJT) triggered by a control signal controlled by a micro-controller.
In addition, reverse voltage is canceled out by means of a switching member used between the ground connection and a common node connecting the outlet of a plurality of LEDs. The switching member used in the outlet end of the LEDs, is controlled similar to the switching members energizing the LEDs. In fact, the switching member disposed on the outlet end of the LED which is not energized and which is intended not to be applied reverse voltage thereon, is controlled by the same signal with the switching member whose function is to energize the related LED. Thus, reverse voltage problem is solved without highly increasing the costs in LED driver circuits with large matrix configurations, by using a single switching member for each LED group.
Accompanying drawings are given solely for the purpose of exemplifying the electrical circuit of the invention with LED reverse voltage protection function, whose advantages over the prior art are outlined above and explained in detail hereinafter.
The drawings are not meant to delimit the scope of protection as identified in the claims nor should they be referred to alone in an effort to interpret the scope identified in said claims without recourse to the technical disclosure in the description of the present invention.
Figure 1 is a simplified circuit diagram of a LED driver circuit in which the current flowing through a turned-on LED completes its path through a turned off LED.
Figure 2 is a simplified circuit diagram in which null reverse voltage is provided on the turned off LED of the LED driver circuit, in an embodiment of the invention.
The elements in the figures are numbered individually and the correspondence of these numbers are given hereinafter.

LED driver circuit
First LED
Second LED
First switching member
Second switching member
Common node
Tertiary switching member

ON. On position
OFF. Off position
Vcc. Supply voltage
The electrical circuit of the invention, in the form of a LED driver circuit (1) comprises a plurality of LEDs (2, 3) driven between on/off positions by a plurality switching members (4, 5) controlled by a micro-controller, and prevents application of reverse voltage to a LED (2, 3) by said switching member (4, 5) in off position.
The electrical circuit of the invention comprises a power tap converting AC voltage to DC voltage and feeding a micro-controller (not shown in the figures) and other electrical circuit components. The LED driver circuit (1) is connected to a digital outlet of the micro-controller. A LED matrix can be arranged in rows and columns, and a given number of LEDs can thus be addressed by specifying a row and column position. For the sake of simplicity, in the drawings given for the sole purpose of exemplifying the embodiments of the invention, the LEDs are driven between on/off positions in a one-dimensional manner. A person skilled in the art would know that a LED can be driven according to relevant rows and columns.
The LED driver circuit (1) of the invention comprises at least one first switching member (4) and at least one second switching member (5) feeding at least one first LED (2) and at least one second LED (3) each of which is independently drivable. Said switching members (4, 5) are preferably bipolar junction transistors (BJT) triggered by a control signal provided by the micro-controller.
The LED driver circuit (1) of the invention comprises tertiary switching members (7) provided between the ground connection and a common node (6) connecting the outlet ends of said at least two first or at least two second LEDs (2, 3). The tertiary switching members (7) are used to prevent application of inverse voltage on a first or a second LED (2, 3) when it is turned off.
In an embodiment of the invention, PNP BJTs are opted as the transistors, and their emitters are connected to a DC terminal and their bases are driven by a digital outlet. When a given number of LEDs (2, 3) are energized by the first switching member (4), the current passing through a turned on LED completes its path via a LED which is electrically directly, i.e. serially connected to the second switching member (5), and it this case, a reverse voltage drop may damage a LED (2, 3) connected to said second switching member (5) which is turned off at that moment. A current which passes through a turned on LED and completes its path at a turned off LED, is shown by dashed lines in Figure 1.
In order to prevent the LEDs (2, 3) from being damaged, the tertiary switching member (7) connected to the common node (6) on the LED group (2, 3) which is not energized, is turned off, enabling the ends of the inactive LEDs (2, 3) to float. In this manner, an inverse voltage of null level is formed at a LED (2, 3) serially connected to a switching member (4, 5). A LED (2, 3) connected to a switching member (4, 5) which is not online at that moment, is protected against inverse voltage by means of the circuit configuration of the invention.
In this embodiment, when the first switching member (4) is turned on, emitter-collector current flows through the transistor and feeds the LEDs (2, 3) electrically connected to said first switching member (4).
In brief, the present invention enables realizing a LED driver circuit (1) comprising at least one first switching member (4), at least one second switching member (5) and tertiary switching members (7) electrically connected in series to at least one first and at least one second LED (2, 3) each of which is independently drivable.
In another embodiment of the invention, the switching members (4, 5, 7) are preferably bipolar junction transistors (BJT) triggered by a control signal.
In another embodiment of the invention, the emitters of the bipolar injunction transistors (BJTs) are connected to a DC terminal and their bases are driven by a control signal.
In another embodiment of the invention, a tertiary switching member (7) is controlled by the control signal of the switching member (4, 5) used in energizing the LED (2, 3) to which the tertiary switching member (7) is connected. In this embodiment, the LED (2, 3) intended to be turned on is energized by the DC terminal by means of the first or the second switching member (4, 5) and the circuit is completed by the tertiary switching member (7) controlled by the same control signal. The floating position of the LED (2, 3) intended to be turned off, is maintained by jointly controlling and turning off the switching members (4, 5, 7) disposed on both of its ends.
A LED driver circuit (1) is realized by means of the present invention, providing LED reverse voltage protection, minimizing additional costs and not compromising functional efficiency compared to the alternative solutions.

Claims

A LED driver circuit (1) comprising at least one first switching member (4) and at least one second switching member (5) electrically connected in series to at least one first and at least one second LED (2, 3) each of which is independently drivable, and energizing said LEDs (2, 3), characterized by tertiary switching members (7) arranged between the ground connection and a common node (6) connecting the outlet ends of said at least two first or at least two second LEDs (2, 3).
A LED driver circuit (1) according to claim 1, characterized by the switching members (4, 5, 7) which are bipolar junction transistors (BJT) triggered by a control signal.
A LED driver circuit (1) according to claim 2, characterized by said bipolar junction transistors (BJTs) whose bases are driven by a control signal.
A LED driver circuit (1) according to claim 2 or 3, characterized by the tertiary switching members (7) controlled such that when one of the first and the second LED (2, 3) is in on position, reverse voltage does not flow through the other LED (2, 3) which is in off position.
A LED driver circuit (1) according to claim 4, characterized by the tertiary switching member (7) controlled by the control signal of the first or the second switching member (4, 5) controlling the first or the second LED (2, 3) to which the tertiary switching member (7) is connected.
A LED driver circuit (1) according to claim 5, characterized by the tertiary switching member (7) being connected to the second LED which is in off position when the first switching member (4) and the tertiary switching member (7) connected to the first LED (2), are in on position.