DE10245626A1 - Circuitry to reduce ripple for LED arrangement, uses detected light intensity of LEDs to adjust to nominal light intensity for LED traffic lights - Google Patents

Abstract

Brightness, light output or light intensity of LED light source is directly used to change input setting resistance or setting current. Hence setting resistance functions as control resistance or setting current as control current. When control resistance or current very quickly changes value when specific minimum light intensity is reached, back coupling effect is used to reduce ripple without need of large, expensive capacitors. Independent claim for 1) procedure to reduce ripple for LED arrangement 2) circuitry for LED arrangement with at least two parallel LED chains.

Description

The present invention relates relates to a circuit arrangement and a method for reducing ripple with an LED arrangement (“LED Array ").

As LED arrangements (LED: light emitting Diode) apply here in principle all conceivable LED connections such as two or more in parallel interconnected LED chains, in each of which at least one LED component is arranged, with two or more LED components, these in series with each other are connected. But also an LED chain, in which at least one LED component is arranged, with two or more LED components, these are connected in series with one another is included in the term “LED arrangement”.

In order to achieve the best possible cost situation with LED arrangements In traffic light applications, only as many LEDs are required as absolutely necessary necessary used. This means conventionally restrict the LEDs on the for the traffic light application visible LEDs.

At the required response times to be able to comply - d. H. to ensure switching from one operating state to another to be able to -, the LEDs cannot be energized with direct current, because in conventional Great way to do this Capacitor would be necessary. This capacitor would lead to non-compliance with response times. Vibrations occur in the system. This residual ripple (oscillation around an average) is so big that amperage through the LED arrangement z. B. in the peak (peak value) almost twice Value of the average current.

Due to the dependency of the LED lifespan of the power converted in the LED has this residual ripple a very negative impact on the life of such LED arrangement. That the ripple causes an additional one implemented power, which reduces the LED lifespan.

According to the state of the art a high ripple is always present, since this according to the prior art Problem not solved becomes. Conventional A way to comply with the life expectancy requirements high number of LEDs used. However, there is one unfavorable Cost situation.

The conventional way is with a Capacitor or a coil the problem of ripple only very difficult to get a grip on, because they are cumbersome Circuits with active switches necessary, the reliability of the Overall system limited is.

Conventional power supply circuits (power supplies) for Traffic light signal transmitters use MOSFETs to set the required current, FETs or transistors with appropriate wiring. For power supplies transformers are used that match the ones at a traffic light Tension on for Convert LED light sources to compatible voltages. In Germany a voltage of 230 volts alternating current to a voltage of approx. 15 volts DC transformed. It's traditionally here a high ripple.

Traditionally there is always one Setting resistor is provided, which by the power supply circuits emitted current directly affected. This setting resistor is advantageously on the board the LED light source (LED arrangement) outsourced, because then for different LED light sources that also require different currents, only one power supply is necessary. Dependent on of the voltage across the setting resistor flows through it Setting resistance a corresponding setting current for setting the power supply circuit.

It is an object of the present invention Traffic light applications, especially with an LED arrangement, the occurrence to avoid residual ripples. In addition, only low-cost components Find use. Likewise, the number of LEDs required limited to what is necessary his. The LEDs are also to be supplied with alternating current. In addition, compliance with the required response times should be realized become.

The object is achieved by a circuit arrangement with the features of the claim 1 and by a method with the features of the claim 16 solved. Advantageous refinements and developments are specified in claims 2 to 15 and 20 to 24.

According to the present invention, the brightness or the light output power (light output) or the light intensity of an LED light source or LED arrangement can be used directly to change the setting resistance or the setting current mentioned at the beginning. The setting resistor thus functions as a control resistor or the setting current as a control current. If this control resistor or control current changes its value very quickly when a certain minimum light intensity is reached, this feedback effect can be used to reduce the ripple without the need for large, expensive capacitors. At the same time, the minimum light intensity according to the requirements is reliably maintained and the service life in two ways elevated.

First, this is done by reducing the Ripple and secondly because it is no longer like on conventional way is necessary, LEDs with a far above the minimum requirements lying light intensity value to manufacture and deliver in order to have the minimum light intensity at the end of life to be able to comply.

Other features, advantages and practicalities The invention is described below using exemplary embodiments. Show it:

1 shows an embodiment of a device according to the invention for a traffic light application with an LED arrangement.

2 shows an LED arrangement (LED array) using an advantageous power distribution circuit for the LED arrangement.

3 shows an LED arrangement (LED array) using a further advantageous power distribution circuit for the LED arrangement.

In the embodiment according to 1 a plurality of LED chains, which are connected in parallel, are connected to a power supply circuit LVS. The power supply circuit LVS with a transformer and a power factor correction circuit is part of a power supply unit connected to a power supply system.

One of the LED chains is designed as a reference chain RK and emits its light onto a photo receiver PE1. The photoreceiver PE1 is connected in series with a resistor Rc, so that a voltage U _RG proportional to the received light intensity drops across it.

The voltage U _RG is fed to a switching transistor MOSFET or T1, which is connected in a series circuit with a resistor RSD and a Zener diode ZD _SD .

The source / drain connections of the Switching transistors T1 are OK with input connections of an optocoupler connected. Since the series circuit of the switching transistor T1, the Series connections of the photoreceiver PE1 and the reference chain connected in parallel with the supply connections of the power supply circuit LVS are connected, at the output of the optocoupler OK one of the light intensity of the LED chain corresponding signal can be removed.

By means of an electronic device EV after 1 there is negative feedback for regulating the light intensity emitted by the LED arrangement to a predetermined target light intensity.

According to 1 the electronic device EV detects the light intensity emitted by the LED light source on a reference chain RK. This has LEDs of identical construction to the other LEDs of the LED arrangement, through which, in particular in normal operation, the same current is driven as through any other chain of the LED light source. The reference chain RK is subject to the same signs of aging as the entire LED arrangement. The light intensity at the reference chain RK serves as the reference light intensity for the entire LED light source. In order to reduce external influences, the reference chain RK is advantageously shielded from the light intensity emitted by the surroundings.

The reference light intensity is using a photo receiver PE1, in particular a photodiode, preferably by means of a PIN Photodiode (I: intrinsic) detected. A PIN photodiode can be compared to a simple photodiode measure even smaller light intensities and signals with higher Detect frequency. The photo receiver Alternatively or cumulatively, PE1 can also be a phototransistor, a phototyristor, a phototriac and / or a photo-Schmitt trigger.

The photocurrent through the photodiode PE1 flows through a resistor R _G (G: gate) to a connection of a power supply circuit LVS of the LED arrangement. The voltage across the resistor R _G is therefore proportional to the light intensity striking the photodiode PE1. This voltage controls an electronic switching element (the switching transistor T1), for example in the form of a MOSFET transistor, which becomes conductive when the control voltage (gate voltage) is sufficiently high. VMOSFETs are suitable when large powers have to be switched. The electronic switching element can also be a bipolar transistor.

The source (S) - drain (Dr) path of the FET is connected in parallel to a photo transmitter (for example to a transmitter diode SD) of an optocoupler OK. The gate-source voltage is built up via the resistor R _G or is applied to it.

All can be used as FET transistors Types, in particular insulating layer or barrier FETs used become. The use of MOSFETs (metal oxides) is particularly advantageous semiconductor FETs).

In particular, they are both self-locking n-channel as well as self-blocking p-channel MOSFET transistors usable. The interconnection must then be adjusted accordingly. Leave n-channel FETs replace themselves with p-channel FETs if the associated circuit is mirrored from the cathode to the anode.

1 shows a self-locking n-channel MOSFET as an electronic switching element.

The photo transmitter of the optocoupler OK can be a transmitter diode SD in the form of an IRED or an LED. The transmission diode SD is connected to an electrical connection via a Zener diode ZD SD, which is polarized opposite to the transmission diode _SD, and to a further electrical connection of the power supply circuit LVS via a resistor R _SD .

According to the embodiment 1 is the electronic switching element that self-locking MOSFET, connected in parallel to the photo transmitter of the optocoupler OK. Depending on the level of the voltage across the resistor R _G , which is proportional to the light intensity striking the photodiode PE1, the MOSFET blocks or conducts. If the reference light intensity is lower than the target light intensity, the MOSFET blocks. If the reference light intensity is above the target light intensity, the MOSFET conducts.

Since the conductive transistor (MOSFET) bridges the transmitter diode SD of the optocoupler OK and thus draws current from the transmitter diode SD of the optocoupler OK, the “resistance” of the photo receiver PE _{O K of} the optocoupler increases or its output current I _A decreases Photo receiver PE _{O K} is advantageously provided as a phototransistor, but it can alternatively or cumulatively also be a photodiode, a phototyristor, a phototriac and / or a Photo-Schmitt trigger.

The decrease in the output current I _A controls the power supply circuit LVS of the LED arrangement in such a way that the electrical power P supplied to the LED arrangement is reduced by lowering the supply voltage and / or the supply current. A reduction in the output electrical power P can also be carried out by correcting the power factor.

The light intensity emitted by the LED arrangement is consequently reduced.

The output current I _{A of} the optocoupler thus changes from a very large value (or from a very small value of the resistance of the phototransistor PE _OK ) if the light intensity striking the (PIN) photodiode PE1 is below the required value, too much small values if the required light intensity impinging on the (PIN) photodiode PE1 is slightly exceeded. The resistance of the phototransistor PEo _K changes conversely to very large values.

Due to the negative feedback provided by the electronic device EV for regulating the light intensity emitted by the LED arrangement to a predetermined desired light intensity, the electronic device EV functions in the “opposite direction” when the light intensity falls below the desired light intensity. That is, a decrease in the light intensity below the desired light intensity reduces the control voltage Resistor R _{G in} such a way that the MOSFET blocks and the transmitter diode SD of the optocoupler is energized by the electronic switching element MOSFET, which increases the output current I _{A of} the photoreceiver PE _{O K of} the optocoupler OK. The increased output current provides information for the power supply circuit LVS to increase the electrical power P supplied to the LED arrangement

The light intensity emitted by the LED arrangement is consequently increased.

The output signal of the optocoupler OK in the form of its output current I _A takes over the control of the power supply circuit LVS (power-supply) of the LED arrangement, which in particular sets the current through the LED arrangement to a high amperage at a high output current I _A , and at a low output current I _A in particular reduces the current through the LED arrangement to a minimum value, which is also predetermined. The power output to the LED arrangement can also be changed by changing the AC voltage applied to the LED arrangement or by changing the power factor.

Because in this system for power regulation the system can use no capacitors or coils react and modulate within the frequency of the residual ripple.

In 1 In particular, there are robust components such as resistors R, diodes D, light-emitting diode LEDs, a MOSFET transistor, a zener diode ZD _SD and an optocoupler OK as well as photo receivers PE1 and PE _OK and a transmitter diode SD. The output current I _{A of} the optocoupler is further processed in the power supply. The power supply includes a power factor correction device, a transformer for conversion into the required AC voltage level and a current / voltage or. Power supply circuit LVS for delivering electrical power P to the LED arrangement. The power supply unit supplies the LED arrangement with alternating voltage or alternating current and is connected to the electrical power network.

According to a further embodiment a negative feedback of the light intensity emitted by the LED arrangement Power output to the LED arrangement also by an electronic Device EV enables in which the electronic switch or the electronic switching element in the form of a MOSFET to the photosender (e.g. transmitter diode SD) of the Optocoupler OK is connected in series and is self-conductive. The MOSFET can have an n-channel or a p-channel. In order to the transmitter diode SD also emits when the control voltage between Gate and source on the MOSFET is too low.

According to the invention, those mentioned Circuit arrangements executed working procedures claimed.

According to further preferred embodiments of the present invention, the LED chains are corresponding 2 and 3 interconnected that a current distribution intended for the LED arrangement is maintained even when the forward voltage changes in the individual chains, for example in the event of a short circuit of an LED component.

When linking the power distribution circuit according to the 2 with the circuit after 1 the anodes of the LEDs lie on one connection of the power supply circuit LVS of the circuit arrangement and the emitters of bipolar transistors via resistors Rx2 on another Connection of the power supply circuit LVS of the circuit arrangement.

When linking the power distribution circuit according to the 3 with the circuit after 1 are also the cathodes of the LEDs on one connection of the power supply circuit LVS of the circuit arrangement and the emitters of bipolar transistors via resistors Rx2 on another connection of the power supply circuit LVS of the circuit arrangement.

The power distribution circuit and the LED chains are in series. All LED chains with control arrangements lie parallel to the electronic device EV for negative feedback the luminous intensity emitted by the LED arrangement for the output of the Power supply circuit LVS to the LED arrangement.

According to how the advantageous current distribution circuit works in an LED arrangement 2 and 3 : The LED chains x are each connected in series with a combination of a transistor Tx with a resistor Rx2 in the emitter branch in order to maintain an intended current distribution on the individual LED chains x. X denotes a running index from 1 to the maximum number of LED chains.

The resistance Rx2 influences the Current distribution in the individual LED chains. Here is the resistance value Rx2 is inversely proportional to the associated collector current.

A corresponding control circuit acts on the basic connections Bx of the transistors Tx with a predetermined current. One control circuit each a bipolar transistor and an emitter resistor form a current source, which determines the current in the respective branch. This power source forms one regulation arrangement each.

In addition, all base connections are Bx of the transistors Tx set to the same potential.

The application by the control circuit takes place in that the base connections Bx of the transistors Tx device with a predetermined current, as a series connection made up of a diode Dx and an electrical resistor Rx1 is.

The diodes Dx and the resistors Rx1 enable providing one for the function of the electrical control arrangement necessary power supply the respective transistor base. As the difference between the supply voltage, the Forward voltage of an LED chain and the common base voltage the transistors are connected to the control circuit of a transistor its corresponding collector base voltage. A change in the forward voltage of an LED chain (e.g. by short-circuiting a LED) is changed by changing the corresponding collector Intercepted basic voltage, so that the collector current does not change or changes very little. This is inversely proportional to the associated emitter resistance Rx2.

In addition, the diodes Dx prevent a current flow of one LED branch in one others.

An advantageous LED arrangement comprises at least two LED chains (chain x) connected in parallel to one another, in each of which at least one LED ( 2 ) arranged, with each LED chain (x) having a control arrangement (x) for regulating a current distribution between the individual LED chains is connected in series.

Since this embodiment is either on npn- or pnp transistors, the following two variants are possible: It is particularly advantageous if the respective control arrangement contains a bipolar transistor (Tx), the collector terminal (Cx) is connected to the cathode side of the associated LED chain and its emitter connection (Ex) each over an electrical resistance (Rx2) directly or indirectly with a connection of the Power supply circuit (LVS) connected to the circuit arrangement is, with the basic connections (Bx) of the transistors (Tx) for symmetrizing the current distribution are electrically conductively connected to one another, and being a drive circuit the basic connections (Bx) of the transistors (Tx) with a predetermined current.

A circuit arrangement is also advantageous for one LED arrangement, being the respective control device contains a bipolar transistor (Tx), the Collector connection (Cx) with the anode side of the associated LED Chain is connected and its emitter connection (Ex) each via a electrical resistance (Rx2) directly or indirectly with a Connection of the Power supply circuit (LVS) connected to the circuit arrangement is, with the basic connections (Bx) of the transistors (Tx) for symmetrizing the current distribution are electrically conductively connected to one another, and wherein a control device the basic connections (Bx) of the transistors (Tx) with a predetermined current.

The diodes Dx and the resistors Rx1 enable providing one for the function of the electrical control arrangement necessary power supply the respective transistor base. As the difference between the supply voltage, the Forward voltage of an LED chain and the common base voltage the corresponding collector base is connected to the control circuit Tension. A change in the forward voltage of an LED chain (e.g. due to short circuit an LED) is changed by changing the corresponding collector Base voltage intercepted so that the collector current and so that the corresponding chain current does not change or changes very little. This is inversely proportional to the associated emitter resistance Rx2.

In addition, the diodes Dx prevent a current flow of one LED branch in one others.

falls in an LED chain an LED by short circuit, so reduced the forward voltage of the LED chain, but this is due to the associated control arrangement is compensated by the collector base voltage on the associated transistor elevated. Because of changes in the forward voltage of an LED chain via the electrical resistors Rxl only the base current of the transistors Tx flows (approx. factor 100..250 smaller than the collector current) the Rx1 be dimensioned so that a very small change the current by Rx1 (in the range <1 mA) already a big change of the voltage drop across the Rx1, causing the different Forward voltages in the individual LED chains can be compensated. The Sum of forward voltage of the LED chain and the collector base voltage of the associated one Transistor corresponds to the difference between the supply voltage and the base potential of the transistors, since all base connections continue have the same potential. The respective collector currents of the LED Chains stay just as close constant.

falls an LED in an LED chain due to burnout ("open contact" or contact interruption) out, so flows no more electricity due to the defective chain. The voltage between the collector and Basis of the associated Transistor Tx breaks down. At the base of the transistor defective chain must still be as potential as at the base inputs of the remaining transistors. This is due to the common electrical Connection of the transistor bases achieved, through which the corresponding compensation currents can flow. The take over intact LED chains first the equalizing currents. These additional substreams then flow over the respective Dx and Rx1 and over the common electrical connection of the transistor bases in the Base of the now operated as a diode of the failed Chain and through its emitter resistance Rx2. By interconnection all basic inputs the remaining intact are kept at the same potential The chain continues to chain according to the dimensioning of the emitter resistors Rx2 given distribution. Here are the emitter resistance values Rx2 is inversely proportional to the emitter current, which is the sum results from base and collector current.

With the advantageous power distribution circuits can in case of change of forward voltages in LED chains the chain currents and thus the light intensities emitted by the LED chains are stabilized.

The description of the invention Hand of the embodiments is self-evident not as a limitation the invention to understand this.

Claims (24)

Circuit arrangement for reducing ripple in an LED arrangement, characterized in that a power supply circuit (LVS) delivers current / voltage or electrical power (P) to the LED arrangement, the LED arrangement emitting a corresponding light intensity, which is produced by a corresponding Information from an electronic device (EV) relating to the output of the electrical power (P) is fed to the power supply circuit (LVS) so that a predetermined setpoint light intensity is adjusted. Circuit arrangement according to claim 1, characterized in that the electronic device (EV) one for detecting the photodetector (PE1) emitted by the LED arrangement having. Circuit arrangement according to Claim 2, characterized in that a current generated at the photoreceiver (PE1) flows via a resistor (R _G ) to an electrical connection of the power supply circuit (LVS) of the LED arrangement, a voltage across the resistor (R _G ) is proportional to the strength of the light striking the photoreceiver (PE1). Circuit arrangement according to claim 2 or 3, characterized characterized in that the photoreceiver (PE1) is a photodiode, a PIN photodiode, a phototransistor, a phototyristor, a Phototriac and / or a Photo Schmitt trigger. Circuit arrangement according to Claim 3 or 4 insofar as this is referred back to Claim 3, characterized in that the voltage across the resistor (R _G ) switches an electronic switching element (FET) in such a way that a transmitting diode (SD ) of an optocoupler (OK) is de-energized or energized, so that an output current (I _A ) of a photo receiver (PE _{O K} ) of the optocoupler (OK) becomes small or large. Circuit arrangement according to claim 5, characterized in that the current / voltage or power output of the power supply circuit (LVS) to the LED arrangement is proportional to the amount of the output current (I _A ) serving as information. Circuit arrangement according to claim 5 or 6, characterized in that the photo receiver (PE1), the electronic switching element (FET), the transmitter diode (SD) and the photo receiver (PE _{O K} ) of the optocoupler (OK) have steep UI characteristics in the range of the desired light intensity so that yourself the output current (I _A ) changes significantly when the emitted light intensity deviates from the nominal light intensity. Circuit arrangement according to one of claims 5 to 7, characterized in that the optocoupler (OK) as a transmitting diode (SD) an IRED or LED or as a photo receiver (PE _{O K} ) a phototransistor, a photodiode, a phototyristor, a phototriac and / or has a Photo Schmitt trigger. Circuit arrangement according to one of claims 5 to 8, characterized in that the transmitting diode (SD) of the optocoupler (OK) via a Zener diode (ZD _SD ) with opposite polarity to the transmitting diode ( _SD ) with an electrical connection and via a resistor (R _SD ) a further electrical connection of the power supply circuit (LVS) can be connected. Circuit arrangement according to one of claims 5 to 9, characterized in that parallel to the transmitter diode (SD) of the Optocoupler (OK) the electronic switching element (FET) is arranged that when exceeded or falling below the target light intensity in the conductive or blocking State passes bridged or not bridged the transmission diode (SD) of the optocoupler (OK) and so that the transmitter diode (SD) of the optocoupler (OK) is de-energized or energized on. Circuit arrangement according to one of claims 5 to 10, characterized in that the electronic switching element a FET transistor, in particular a MOSFET transistor, or a Bipolar transistor is. Circuit arrangement according to claim 11, characterized in that the MOSFET or FET is self-locking. Circuit arrangement according to claim 11 or 12, characterized characterized in that the MOSFET or FET has an n-channel. Circuit arrangement according to one of claims 2 to 13, characterized in that the photoreceiver (PE1) emits one Reference luminous intensity detected, this emitted reference light intensity by a reference chain (RK) is generated, through which the same current flows as through any other chain of the LED array, and that this reference light intensity for through the entire LED arrangement emitted light intensity is the reference variable. Circuit arrangement according to claim 14, characterized in that the reference chain (RK) from that emitted by the environment Shielded light intensity is. Method for reducing ripple in a LED arrangement, with output by a power supply circuit (LVS) of current / voltage or electrical power (P) to the LED arrangement, due to the LED arrangement emitting a corresponding Light intensity, by information from an electronic device (EV) on the output of electrical power (P) from the power supply circuit (LVS) is negative-coupled, so that a predetermined target light intensity is adjusted becomes. The method according to claim 16, with - detecting an exceeding or falling below the target light intensity by means of the light intensity emitted by the LED arrangement by means of a photoreceiver (PE1), - then switching an electronic switching element (FETs) and switching a transmitter diode (SD) Optocoupler (OK), - Change in the output current (I _A ) of a photo receiver (PE _{O K} ) of the optocoupler (OK), - Lowering or increasing the current / voltage or power output of the power supply circuit (LVS) to the LED arrangement. A method according to claim 17, with currentless switching the transmission diode (SD) of the optocoupler (OK) by bridging the transmission diode (SD) of the optocoupler (OK) by the electronic switching element (FET). Method according to one of Claims 17 to 18, with - application of a control voltage for the electronic switching element to a resistor (R _G ) by - flowing a current generated in the photoreceiver (PE1) via this resistor (R _G ) to an electrical one Connection of the power supply circuit (LVS) of the LED arrangement, the voltage across the resistor (R _G ) being proportional to the strength of the light striking the photoreceiver (PE1). Circuit arrangement according to one of claims 1 to 15, wherein the LED arrangement with at least two parallel connected LED chains (chain x), in each of which at least one LED ( 2 ) is arranged, characterized in that for each LED chain (chain x) in each case a control arrangement (RAx) for controlling a proposed current distribution on the individual LED chains is connected in series. Circuit arrangement according to Claim 20, characterized in that the respective control arrangement (RAx) contains a bipolar transistor (Tx), the collector connection (Cx) of which is connected to the cathode side of the associated LED chain and the emitter connection (Ex) of each an electrical resistor (Rx2) is connected directly or indirectly to a connection of the power supply circuit (LVS) of the circuit arrangement, the base connections (Bx) of the transistors (Tx) being electrically conductively connected to one another for balancing the current distribution, and a control circuit for the base connections ( Bx) of the transistors (Tx) with a predetermined current. Circuit arrangement according to claim 20, characterized in that the respective control arrangement (RAx) is a bipolar transistor (Tx) contains whose collector connection (Cx) each with the anode side of the associated LED Chain is connected and its emitter connection (Ex) each via a electrical resistance (Rx2) directly or indirectly with a Connection of the Power supply circuit (LVS) connected to the circuit arrangement is, with the basic connections (Bx) of the transistors (Tx) to symmetrize the current distribution with one another are electrically conductively connected, and wherein a drive circuit the basic connections (Bx) a predetermined current is applied to the transistors (Tx). Circuit arrangement according to claim 21 or 22, characterized characterized in that the control device, one between each the cathode side or the anode side of each LED chain (x) and the respective base connection (Bx) of the associated transistor (Tx) arranged series connection of a diode (Dx) and one electrical resistance (Rx1). Circuit arrangement according to one of claims 1 to 15 and 20 to 23, characterized in that between the supply network (power network) and the current / voltage or power supply circuit (LVS) a power factor correction device and / or a transformer are / is switched.