GB2530766A - Driver module for driving LEDs - Google Patents

Driver module for driving LEDs Download PDF

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Publication number
GB2530766A
GB2530766A GB1417345.4A GB201417345A GB2530766A GB 2530766 A GB2530766 A GB 2530766A GB 201417345 A GB201417345 A GB 201417345A GB 2530766 A GB2530766 A GB 2530766A
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GB
United Kingdom
Prior art keywords
voltage
led string
bypass
load path
d2
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GB1417345.4A
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GB201417345D0 (en
Inventor
Istvan Bakk
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Tridonic Jennersdorf GmbH
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Tridonic Jennersdorf GmbH
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Priority to GB1417345.4A priority Critical patent/GB2530766A/en
Publication of GB201417345D0 publication Critical patent/GB201417345D0/en
Publication of GB2530766A publication Critical patent/GB2530766A/en
Application status is Pending legal-status Critical

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Classifications

    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHTING NOT OTHERWISE PROVIDED FOR
    • H05B33/00Electroluminescent light sources
    • H05B33/02Details
    • H05B33/08Circuit arrangements not adapted to a particular application
    • H05B33/0803Circuit arrangements not adapted to a particular application for light emitting diodes [LEDs] comprising only inorganic semiconductor materials
    • H05B33/0806Structural details of the circuit
    • H05B33/0821Structural details of the circuit in the load stage
    • H05B33/0824Structural details of the circuit in the load stage with an active control inside the LED load configuration
    • H05B33/083Structural details of the circuit in the load stage with an active control inside the LED load configuration organized essentially in string configuration with shunting switches

Abstract

A driver module for driving LEDs comprises: - a load path comprising a series connection of two or more LED strings each comprising at least one LED, wherein each LED string comprises a bypass module W1, W2, W3, W4 which is connected in parallel to the LED string and which is adapted to bypass the LED string, and a control unit CU adapted to activate one or more of the bypass modules in response to changes in the voltage across the load path, which is provided by a rectified alternating voltage such as an AC mains voltage. The control unit may be adapted to selectively activate the bypass modules with a frequency at least ten times higher than the frequency of the AC mains voltage, e.g. above 500Hz.

Description

I

Driver module for driving LEDs The invention is directed on a driver module for driving LEDs directly from an AC supply. Directly' has to be understood that there is no switch mode circuitry in this driver.

It is already known, e.g. from document WO 2013101759 Al, to drive a string of LEDs directly from AC voltage.

According to this document the string of LEDS is divided * ** in several sub-groups. Raising amplitude of the sine wave of the mains AC voltage implies that more and more stages *.**..

* of LED5 are switched to be operative. At the same time, *". : each time an additional group of the series connection of * ** LEDs is switched on, a current source with increasing power is switched on. Thus, not only an increasing number of LEDS will be switched on, but also stepwise the current through the LED string will increase in order to roughly match the shape of the sine-wave of the AC voltage.

Document Us 2003/164809 Al discloses, a circuit for a plurality of LEDs. The circuit comprises a serial path comprising the LEDs and a constant current sink. In addition to this constant current sink, further switchable constant current devices are connected with the serial path. Depending on the input voltage, some of the further switchable constant current devices may be switched.

Thereby, it is disadvantageous that the circuit comprises several current sources and that current sources have to be switched on and off.

The present invention proposes an improved solution for driving LEDS.

The invention now has a new approach to make the current flowing through the LED string match the shape of the AC sine-wave of the mains voltage.

According to a first aspect of the invention, a driver module for driving LEDs is proposed. The driver module comprises a load path comprising a series connection of two or more LED strings each comprising at least one LED.

Each LED string comprises a bypass module which is * ** connected in parallel to the LED string and which is adapted to bypass the LED string. The control unit is * adapted to activate one or more of the bypass modules in ". : case the voltage across the load path is between a first * *.

and a second voltage level. The control unit is adapted to selectively change the activated bypass module, preferably that all bypass modules are activated at least once with the period where the voltage across the load path is between a first and a second voltage level.

All bypass modules are de-activated in case the voltage across the load path is as above the first voltage level.

All bypass modules are activated in case the voltage across the load path is as below the second voltage level.

At least two of the bypass modules are activated at the same time when the voltage across the load path is between the first and a third voltage level.

The alternating bypassing of either the LED string in case the voltage across the load path is below a first voltage level follows a switching pattern where the first LED strings are turned on and off alternatingly following a pattern or by random selection.

The driver module may comprise a current source connected in series with the load path for generating a current for the load path. The driver module comprises a control module for controlling the current for the load path so that the shape of the current for the load path matches the voltage applied to the load path.

* ** According to a further aspect of the invention, a method :.: 15 for driving LEDs is proposed. The method comprising the * ***.* * following steps of supplying an alternating voltage such as a mains voltage, and rectifying the alternating voltage. The rectified voltage is applied to a load path comprising at least one LED string with one or a plurality of LEDs. According to the:nput voltage which forms the voltage over the load path one or more of the bypass modules are selectively activated, preferably alternatingly activated.

The alternating bypassing of either the LED string in case the voltage across the load path is below a first voltage level follows a switching pattern where the first LED strings are turned on and off alternatingly following a pattern or by random selection.

Advantageously, the driver module comprises input terminals for receiving an alternating voltage such as a mains voltage, and a rectifier for rectifying the received alternating voltage. Advantageously, the rectified alternating voltage is the voltage applied to the load path.

Advantageously, the load path comprises a further LED string with one or a plurality of LEDs, the further LED string being connected in series with the LED string.

Advantageously, a bypass module is connected in parallel to the further LED string and is adapted to bypass the further LED string.

Advantageously, the bypass module is adapted to bypass the further LED string in case the voltage across the further LED string is not sufficient to switch it on. * .*

Advantageously, in case the voltage applied to the load * **.** * path is below a given threshold, the bypass module is *:*. adapted to bypass the further LED string such that the current for the load path flows through the LED string but not through the further LED string. ** . * S * * S.

Advantageously, in case the voltage applied to the load path is above said given threshold, the bypass module does not bypass the further LED string such that the current for the load path flows through the LED string and through the further LED string.

Advantageously, the LEDs of the LED string and of the further LED string are respectively arranged in series.

This means that the LED5 of the LED string are connected in series, as well as the LEDs of the LED string.

Advantageously, the voltage applied to the load path corresponds to the voltage across the load path and the current source.

Advantageously, the current source comprises a transistor operated in the linear mode for adapting the current for the load path.

This means that advantageously the current source does not comprise a switching stage for adapting the current through the LEDs.

Advantageously, the control module comprises a voltage * ** divider for generating a voltage proportional to the voltage applied to the load path. Advantageously, the * * control module is adapted to control the current for the load path on the basis of the generated voltage.

To summarize, the invention proposes to use a current **. 20 source which is programmed to control the current through the LED string to develop totally the shape of the AC sine-wave -In an embodiment, a transistor operated in the linear mode is used to control the current through the LED string.

In a preferred embodiment, a plurality (at least two) groups of LED strings are used in a switched mode.

Thus, when the AC voltage is above a certain threshold, the upper LED string (comprised of two LEDs in the example) is switched operative (the shunting transistor is switched off), such that the current flows through all LEns of the string. Below the mentioned voltage, one of the groups of LEDs is bypassed and the current will only flow through the remaining LEDs.

The advantage of the invent ton is that only a single current source is required.

Further features, advantages and objects of the present invention will become evident from the following detailed description of preferred embodiments of the invention, when taken in conjunction with the figure of the enclosed drawing.

FIG. 1 illustrates a schematic diagram of a driver module * * 1 for driving LEns and a switching scheme according to the :.: 15 present invention.

*.**** * * FIG. 2 -S illustrate a schematic diagram of a driver * ** module 1 for driving L.EDs and a switching scheme according to the present invention. 0t * * * * * **

*:* FIG. 6 illustrates another schematic diagram of a driver module 1 for driving LEDs according to the present invention.

The driver module 1 for driving LEDs Dl, 132, 133, 134 shown in Fig. 1 is supplied with an input voltage yin in the form of an alternating voltage such as a mains voltage.

The alternating voltage is applied between a first input terminal 2 and a second input terminal 3 acting as reference terminal or neutral.

The input voltage yin is applied to a rectifier for converting the alternating voltage (AC) to a rectified voltage (DC). The embodiment of Fig. 1 preferably comprises a bridge rectifier Dl comprising tour diodes in bridge configuration. The output of the bridge rectifier Dli, D12, D13, Dl4 is a full-wave rectified voltage V provided between a positive terminal + and a negative terminal -of the rectifier. The negative terminal -corresponds to ground, while the positive terminal + at node A represents voltage VA.

An advantage of the LED driver according to the present * invention is that it is easily dimmable when using usual 15 dimmers as for example phase cut dimmers, wherein the *****.

* voltage generated by such a phase cut dimmer may be *:*. applied to the input terminal 2, 3 of the driver module.

A load path 4 comprising two LED sets or LED strings Dl, ** S D2, D3, D4, DE, D, D7, D8 is connected to node A, i.e. to + the voltage VA. A first LED string Dl, D2 is thereby connected in series with a second LED string D3, D4 within the load path 4. Each LED string Dl, D2, D3, D4, D5, D, D7, D8 comprises at least one LED, preferably a plurality of LEDs connected in series and/or optionally in parallel.

In the particular embodiment of Fig. 1, the two LEns Dl, D2 of the first LED string schematically represent a plurality of LEDs coupled in series. Also, the two LEDs D3, D4 schematically represent a series of coupled LEDs for the second LED string. The anode of the LEDs is connected towards node A. For the particular LED sets of Fig. 1, this means that the anode of the first LED Dl of the first LED string is coupled to node A and voltage VA.

The load path 4 comprises a series connection of two or more LED strings each comprising at least one LED Dl, D2, D3, D4, D5, D6, D7, D8. Each LED string Dl, D2 comprises a bypass module Wi which is connected in parallel to one of the LED strings Dl, D2 and which is adapted to selectively bypass the LED string Dl, D2. A control unit CU is adapted to activate one or more of the bypass modules Wi, W2, W3, W4 in case the voltage across the load path 4 is between a first and a second voltage level, whereby the control unit CU is adapted to selectively change the activated bypass module, preferably that all bypass modules Wi, W2, W3, W4 are activated at least once with the period where the voltage across the load path 4 is between a first and a second voltage level. a * * . " 15

S

* .0*s * * For example the first voltage level may be equal to the forward voltage of the full LED string. The second voltage level may be equal to the forward voltage of one LED string.

C-', S * * 20 * ,* f. All bypass modules Wi, W2, W3, W4 may be de-activated in case the voltage across the load path 4 is as above the first voltage level. All bypass modules Wl, W2, W3, W4 are activated in case the voltage across the load path 4 is as below the second voltage level.

At least two of the bypass modules Wi, W2, W3, W4 may be activated at the same time when the voltage across the load path 4 is between the first and a third voltage level.

As an example the load path comprises a series connection of a number of N LED strings each comprising at least one LED Dl, D2, D3, D4, D5, D6, D7, D8.

Preferably for this example all LED strings comprise the same number of LED. Again a bypass module Wl, W2, W3, W4 is connected in parallel to each of the N LED strings Dl, D2 and which are adapted to bypass the LED string Dl, D2.

The control unit CU may detect a value M which is the next higher multiple of the forward voltage of one LED string Dl, D2 in relation to the actual voltage across the load path 4. A number of CM-i) bypass modules Ni, W2, W3, W4 may be deactivated at the same time when the voltage across the load path 4 is below the product of M multiplied by the forward voltage (Vf group) of one LED string Dl, D2.

A number of CM-i) bypass modules Wi, W2, W3, W4 may be * .s :.: 15 deactivated at the same time when the voltage across the load path 4 is above the product of M-l multiplied by the forward voltage of one LED string Dl, D2.

This means, if (M-l) x Vf group c yin < M x Vf group than CM-lI groups are bypassed.

All bypass modules Wl, W2, W3, W4 may be deactivated at the same time when the voltage across the load path 4 is above the forward voltage of all LED strings Dl, D2, D3, D4, D5, D6, D7, D8.

As an example in a minimal configuration the load path 4 comprises at least a first LED string Dl, D2 with one or a plurality of LEDs and at least a second LED string D3, D4 with one or a plurality of LEDs. The second LED string D3, D4 is being connected in series with the first LED string Dl, D2. A first bypass module Wl is connected in parallel to the first LED string Dl, D2 and is adapted to bypass the first LED string Dl, D2. A second bypass module W2 is connected in parallel to the second LED string D3, D4 is adapted to bypass the second LED string D3, D4.

The first bypass module Wi and the second bypass module W2 are controlled by a control unit CU. The control unit CU is adapted to deactivate the bypass the first bypass :..:. 15 module Wi and the second bypass module W2 in case the voltage across the load path 4 is above a certain first voltage level. * * . * *.

The control unit CU is adapted to alternatingly bypass either the first LED strinc Dl, D2 or the second LED ° string D3, D4 in case the voltage across the load path 4 * is below a certain first voltage level. The alternating bypassing of either the first LED string Dl, D2 or the second LED string D3, D4 in such case (where the voltage across the load path 4 is below a certain voltage level) may follow a switching pattern where the first LED string Dl, D2 and the second LED string D3, D4 are turned on and of f alternatingly following a pattern or by random selection.

As an extension of this example the load path 4 may comprise at least a third LED string DS, D6 with one or a plurality of LEDs.

The third LED string D5, D6 is being connected in series with the first LED string Dl, D2 and the second LED string D3, D4. A third bypass module W3 is connected in parallel to the third LED string D5, D6 and is adapted to bypass the third LED string D5, D6. The control unit CU may be adapted to alternatingly bypass two LED strings selected out of the first LED string Dl, D2, the second LED string D3, D4 and the third LED string 05, 06 in case the voltage across the load path 4 is below a certain first voltage level.

The control unit CU may be adapted to alternatingly bypass either the first LED string Dl, D2, the second LED string D3, D4 or the third LED string D5, 06 in case the voltage across the load path 4 is below a certain second voltage level.

* The control unit CU may adapted to selectively activate *** the bypass modules with a frequency at least ten times higher than the frequency of the AC mains voltage, preferably above 500 Hz. * *.

* The control unit CU may be adapted to selectively activate each bypass module at least once during the time period where the voltage over the load path 4 is between the product of 94-1) multiplied by the forward voltage of one LED string Dl, D2 and the product of M multiplied by the forward voltage of one LED string Dl, D2.

An example for the invention shall be further explained by the figures 2 to 5. The load path 4 is formed by four LED strings with four bypass modules in parallel. The first LED string Dl, 02, the second LED string D3, 04, the third LED string D5, D6 and the forth LED string D7, D8 are arranged in a series connection. A first bypass module VU is connected in parallel to the firs LED string Dl, D2 and is adapted to bypass the third LED string Dl, D2. A second bypass module W2 is connected in parallel to the firs LED string D3, D4 and is adapted to bypass the third LED string D3, D4. A third bypass module W3 is connected in parallel to the third LED string D5, D6 and is adapted to bypass the third LED string D5, DE. A forth bypass module W4 is connected in parallel to the third LED string D7, DR and is adapted to bypass the third LED string D7, DR.

The control unit CU may be adapted to detect the input voltage which forms the voltage over the load path 4.

Depending on the detected voltage over the load path 4 the control unit CU can determine the number of LED strings which have to be bypassed and thus de-activated and can ****. determine the number of LED strings which have to be activated and thus shall not be bypassed. According to the invention the control unit CU may keep the number of activated LED strings constant for a certain voltage over the load path but may alter the selection which LED strings out of the load path 4 are activated at the same * time. The remaining LED strings may be bypassed and thus de-activated at the same time.

Figure 2 shows an example with a voltage over the load path 4 which is above the forward voltage of a single LED string but below the double of the forward voltage of a single LED string. This means that at such voltage level an activation and operaticn of a single LED string is efficient. Therefore the control unit activates as a first step the bypass modules Wi, W2 and W3 and whereby on the forth LED string D7, DR is activated. After a certain time, e.g. lms, the control unit CU activates the bypass module W4 in combination with the activation of the bypass modules W2 and W3 and de-activates the bypass module Wl.

This means that only LED string Dl, D2 is activated now.

As a next step the control unit CU activates the bypass module Wl in combination with the activation of the bypass modules W3 and W4 and dc-activates the bypass module W2.The LED string D3, D4 is now activated. As a next step the control unit CU activates the bypass module W2 in combination with the activation of the bypass modules WI.

and W4 and dc-activates the bypass module W3.The LED string D5, D6 is now activated. In a next step the cycle starts again and the control unit activates the bypass modules Wi, W2 and. W3. The forth LED string D7, D8 is activated.

This alternating activation of LED strings will continue as long as the voltage over the load path 4 is in the range between the forward voltage of a single LED string and the double of the forward voltage of a single LED string. The switching period for activation of one LED string may be for instance ims which is equal to a 7 switching frequency of 1kHz. Compared to the 50Hz or 60 Hz *t.

o frequency of the AC mains voltage such frequency is high and not visible for a human eye.

For the example of figure 2 the number M would equal two.

At every time there is only one LED string active as (M-l) equals one.

Figure 3 shows an example with a voltage over the load path 4 which is above the double of the forward voltage of a single LED string but below the triple of the forward voltage of a single LED string. This means that at such voltage level an activation and operation of two LED strings in series is efficient. Therefore the control unit activates as a first step the bypass modules Wi and W2 and whereby on the third LED string D5, D6 and the forth LED string D7, D8 are activated. After a certain time, e.g. ims, the control unit CU activates the bypass module W3 in combination with the activation of the bypass modules W2 and de-activates the bypass module Wl. This means that first LED string Dl, D2 and forth LED string D7, D8 are activated now. As a next step the control unit CU activates the bypass module W4 in combination with the activation of the bypass modules W3 and de-activates the bypass module W2 and Wl.The first LED string Di, D2 and second LED string D3, D4 are now activated. As a next step the control unit CU activates the bypass module W2 in combination with the activation of the bypass modules Wi and de-activates the bypass module W3 and W4.The LED second LED string D3, D4 and the third LED string D5, D6 *4**s* :. : are now activated. In a next step the cycle starts again and the control unit activates the bypass modules W2 and 143. The forth LED string D7, D8 and the first LED string Dl, D2 are activated. * . * * .* *s*

* This alternating activation of LED strings will continue as long as the voltage over the load path 4 is in the range between the double of forward voltage of a single LED string and the triple of the forward voltage of a single LED string. Again the switching period for activation of one LED string may be for instance lms which is equal to a switching frequency of 1kHz.

For the example of figure 3 the number M would equal three. At every time there are two LED strings active as 94-1) equals two.

Figure 4 shows an example with a voltage over the load path 4 which is above the triple of the forward voltage of a single LED string but below the quadruple of the forward voltage of a single LED string. This means that at such voltage level an activation and operation of three LED strings in series is efficient. Therefore the control unit CU activates as a first step the bypass modules Wi and the second LED string D3, D4, the third LED string 05, D6 and the forth LED string D7, D8 are activated. After a certain time, e.g. ims, the control unit Cu activates the bypass module W2 and de-activates the bypass modules VU, W3 and W4. This means that first LED string Dl, D2, third LED string D5, D6 and forth LED string D7, 08 are activated now. As a next step the control unit CU activates the bypass module W3 and de-activates the bypass module W2, W4 and Wl.The first LED string Dl, D2, second LED string D3, D4 and the forth LED string D7, D8 are now activated. As a next step the control unit CU activates the bypass module W4 and de-activates the bypass module Wi, W3 and W2.The first LED string Dl, D2, second LED string 03, 04 and the third LED string 05, 06 are now activated. In a next step * * * the cycle starts again and the control unit activates the bypass modules Wl. The forth LED string D7, D8, third LED string D5, D6 and the second LED string D3, D4 are activated.

For the example of figure 4 the number P4 would equal four.

At every time there are three LED strings active as (M-l) equals three.

Figure 5 shows an example with a voltage over the load path 4 which is above the quadruple of the forward voltage of a single LED string. This means that at such voltage level an activation and operation of all four LED strings in series is efficient. Therefore the control unit CU de-activates all of the bypass modules and the first LED string Dl, D2, the second LED string D3, D4, the third LED string D5, D6 and the forth LED string D7, D8 are activated.

For the example of figure 5 the number M would equal five.

At every time there are all four LED strings active as (H- 1) equals four.

For the example of the figures 2 to 5 the first voltage level is equal to the forward voltage of the full LED string. The second voltage level is equal to the forward voltage of one LED string.

* *. 15 * * * All bypass modules Wi, W2, W3, W4 are de-activated in case the voltage across the load path 4 is as above the first ** . * voltage level (example of figure 5). All bypass modules Wl, W2, W3, W4 may be activated in case the voltage across * 20 the load path 4 is as below the second voltage level S (example not shown). * *.

At least one bypass module is activated in case the voltage across the load pata 4 is as above the second voltage level. Three of the four bypass modules are activated in case the voltage across the load path 4 is as above the second voltage level but below the double of the second voltage level. The double of the second voltage level equals the third voltage level in this example. At least two of the bypass modules Wl, W2, W3, W4 would be activated at the same time when the voltage across the load path 4 is between the first and a third voltage level.

The examples shown in the figures 2 to 5 describe a typical sequence of operation of a driving module 1 according to the invention for a rising edge of the AC mains voltage which might be applied at the input terminals of the driving module 1. Those examples show the sequence during the first 900 of one cycle of the AC mains voltage. When the AC mains voltage decreases again the same sequence will be initiated in reverse direction.

The number of LEDs per LED string would be selected according the nominal peak voltage of the AC mains voltage. For instance in case of a 230V AC mains voltage the nominal peak voltage would be 32W. This means in case : ** 15 of the four LED strings of this example that the overall a.. * forward voltage of the load path and thus of the overall S..... * .

series connection of LED would be selected to be around a. S * * 280V in order to enable stable and efficient operation of all four LED strings. As the example of figures 2 to 5 is * 20 using four LED strings the forward voltage of a single LED ° string would be a quarter of 280 V meaning it equals 70V. * S.

* If the forward voltage of a single LED is around 3.5 V (three point five Volts) it would need 20 LEDs per LED string.

The number of LED strings may vary but the number of parallel bypass modules has to be selected according to the number of LED strings. The same applies for the number of control outputs of the control unit CU in order to control the bypass modules.

The control unit CU may be adapted to detect the waveform and shape of the input voltage, whereby the control unit CU may control the bypass modules according to the detected input voltage, e.g. may detect a dimming information or an emergency lighting situation, and preferably may perform a dimming operation. For instance the control unit CU may detect a phase cut signal.

The control unit CU may detect an emergency lighting situation. For instance there might be supply system where the mains supply is switched over from a AC mains to a DC voltage or a rectified AC voltage. The control unit CU may detect such change of the input voltage and may change control of the bypass units accordingly. For instance in case of a switch over to a DC supply the control unit may activate a certain number of bypass modules with a given or random switching pattern. Preferably there is only a : ** 15 limited number of LED Strings active at one time. The number of LED strings which shall be active at one time * *..** * . during emergency may be programmed or defined by a user. *. I * . * * *.

-The driver module 1 may also comprise a wired or wireless interface for dimming control, e.g. a DALI interface, an i-iov interface, a Bluetooth interface, a Zigbee interface Iii * or an infrared interface.

Dimming of the driver module 1 may be performed by limitation of the number of LED strings which are active at the same time or by introduction of pauses where all LED strings are bypassed (by activating all bypass modules for a short time). Such pauses may be repeated at high frequency which is not visible for the human eye.

According to another example of the invention the load path may comprise a series connection of a number of several LED strings each comprising at least one LED Dl, D2, D3, D4, D5, D6, D7, D8. Preferably for this example at least of the LED strings comprises less LED than the other LED strings. The control unit CU may activate this LED string in order to compensate variations in the input voltage. The activation of this LED string with less LED combined with other LED strings can enable that the voltage of the activated part of the load path (of all activated LED strings) may better fit to the actual input voltage. The activation of this LED string with less LED may be independent from the switching (activation) scheme of the other LED strings as described for this invention.

In addition to this example there might be another LED string with more LED than the LED string with less LED but with less LEDs than the other LED strings. For instance there might be formed a driver module 1 with three LED strings of four LED, one LED string with two LED and one * LED string with only one LED. Of course there might be again two LED strings with only one LED which might also be activated alternatingly (in case one LED string with one LED should be activated). es.

The driver module 1 may comprise a current source Ii for controlling the current flowing through the LEDs Dl, D2, D3, D4, D5, D, D7, D8 and thus through the LED strings.

The current source Il is advantageously operated so that the current through the LEDs follows the shape of the sine-wave of the rectified voltage VA which is the voltage over the load path 4. The current source Il is set up for driving a non-constant current through the load path 4 and thus through the LED strings.

With the optional control of the LED current by the current source Ii the variation of the input voltage may be compensated. For the example of the figures 2 to S where only four LED strings are existing the forward voltage of one LED string is relatively high and thus the voltage range for one of the switching schemes of figures 2 to S are wide. This means that the operation voltage of a LED string will have a difference of 70V within such range.

The current source Il may comprise a switch in the form of a transistor Ml for controlling the current through the LEDs. Said transistor Mi. is connected in series with the LED sets 5, 6, and particularly with the second LED set 6.

Said transistor Ml is implemented as a power transistor.

The transistor Ml may be a field-effect transistor (FET), and preferably an N-channel metal-oxide-semiconductor S.....

* S field effect transistor (MOSFET). * * . . S **

To control the current through the LEDs, the transistor Ml *". : is advantageously operated in the linear mode i.e. in the * ** ohmic mode. In this linear mode, the transistor Ml is turned on and the gate-source voltage of the transistor Ml is above the threshold voltage Vth. The characteristic of drain current versus drain-to-source voltage is nearly linear for e.g. small values of the drain-source voltage.

The current source Ii and the transistor Ml may be controlled by the control unit CU.

According to the present invention, a bypass module Wi is connected in parallel to the first string of LEDs Dl, D2 so that the LED string Dl, D2 can be bypassed depending on the voltage VA applied to the load path 4.

The bypass module Wi may comprise a MOSFET, a bipolar transistor or two transistors Q2, Q3 arranged according to a Darlington circuit 23. The transistors Q2, Q3 are e.g. in the f on of bipolar junction transistors, and preferably of the PNP-type. Alternatively, the transistors Q2, Q3 can also be of the NPN-type, or they can be of opposite type, one NPN and one PNP, and arranged according to a Sziklai configuration.

Both transistors Q2, Q3 may have a common collector in that their respective collectors are connected together.

The transistors are further on coupled such that the emitter current of the transistor Q3 becomes the base current of the transistor Q2. The transistor Q2 is * ** connected as an emitter follower and the transistor Q3 as * . * *** * * a common emitter amplifier.

*.*.** * * According to the present invention, the bypass module Wl is adapted to bypass the LED string Dl, D2 when the rectified AC voltage VA is below a given threshold. On the *. .: contrary, the bypass module Wi is switched off if said rectified AC voltage VA is above said given threshold.

Above this threshold, the shunting transistor 23 (Darlington circuit 23) is switched off so that current will flow through the LED set 5. The switching of the bypass module may be controlled the control unit CU.

The reason for switching operative the LED string Di, D2 above said given threshold is the efficiency of the driver module. Above said threshold the voltage VA applied to the load path 4 is indeed sufficient for lighting said LED string Dl, D2. On the other hand, if the applied voltage VA is too low, i.e. below said threshold, the voltage across both LED strings Dl, D2, D3, D4 will not be sufficient to switch on both LED strings Dl, D2, D3, D4.

The control unit CU may be formed by a microcontroller or other kind of an integrated circuit for instance an application specific integrated circuit or a FPGA. The energy supply for the control unit may be coupled to the current source Il and may be powered out of the current source Ii.

FIG. 6 illustrates a schematic diagram of a driver module 1 for driving LEDs according to another embodiment of the invention. The circuit of Fig. 5 is similar to the circuit of Fig. 1. The difference is that the current source Il with the transistor Ml is shown as a controllable current source Il. The current source Ii may be controlled by control unit CU.

There may be placed a capacitor Cl, C2, C3, C4, CS arranged in parallel to each of LED strings. The capacitors Cl, C2, C3, C4, Cs act as energy storage elements and may filter out high frequency parts of the LED current and may smooth the LED current.

The invention is not limited to four LED strings Dl, D2, P3, D4, PS, P. D7, D8. E.g. the driver module can comprise a fifth LED string (not shown) comprised in the load path 4 in series with the four LED strings Dl, D2, D3, D4, PS, P, P7, PS. Also, a fifth bypass module (not shown) can be provided in parallel to the fifth LED string.

For a low value of the AC voltage only one LED string will be switched on for a certain time of a switching period within the defined voltage range, the other LED strings being bypassed. For a higher value, two LED strings will be on, while at least another LED string will be bypassed.

For an even higher value of the AC voltage, all LED strings will be switched on, such that the current will flow through the all LED strings and the overall light output can be increased.

Advantageously, there is no switched current source in the LED driver of the invention. A switch may however be used in a bypass module coupled to a subgroup of the LEDs.

The first input with the higher electric potential may be connected to a first terminal of a resistor lU. A diode El, e.g. a transient-voltae-suppression (TVS) diode, is provided between the second terminal of the resistor Ri and the second input terminal 3. This optional diode Fl is used for protecting the driver module 1 e.g. from voltage * * spikes. ** . * . . * **

The preferably rectified input voltage VA is applied to a *". : resistor R2 and a capacitor CX that are connected in * series between node A and ground. *

The optional elements Ri, R2 and CX may present in order to enable a dimming operation using a phase cut dimmer as they form a passive bleeding circuit. Furthermore, the mentioned elements Rl, R2 and Cl represent damping elements avoiding ringing effects -in view of capacities provided on the dimmer -caused when operated with usual dimmers.

The invention enables a driver module 1 for driving LEns with less flicker and higher usage of the LED and thus higher efficiency of the overall LED unit compared to known solutions.

The LED string& may be arranged on the same board, e.g. the same PCB, as the control unit CU and the bypass modules. In an alternative embodiment the LED strings can be arranged on one or more PCBs separated from the board with the control unit CU and the bypass modules which enables a modular approach for building up the driver module 1. * *e * * * *** * * * ** . * * * * ** ** * * * * * ** * *

Claims (17)

  1. Claims 1. Driver module (1) for driving LEDs, wherein the driver module (1) comprises: -a load path (4) comprising a series connection of two or more LED strings each comprising at least one LED (Dl, D2, D3, D4, D5, D6, D7, D8), wherein each LED string (Dl, D2) comprises a bypass module (Wi, W2, W3, W4) which is connected in parallel to the LED string (Dl, D2) and which is adapted to bypass the LED string (Dl, D2), * *. wherein the control unit (CU) is adapted to activate one :: or more of the bypass modues (wl, W2, W3, w4) in case the * voltage across the load path (4) is between a first and a second voltage level, whereby the control unit (CU) is adapted to selectively change the activated bypass module, preferably that all bypass modules (Wi, W2, W3, W4) are activated at least once with the period where the voltage across the load path (4) is between a first and a second voltage level. * 25
    [first voltage level = forward voltage of the full LED string] [second voltage level = forward voltage of one LED string]
  2. 2. Driver module according to claim 1, whereby all bypass modules (Wi. W2, W3, W4) are de-activated in case the voltage across the load path (4) is as above the first voltage level.
  3. 3. Driver module according to claim 1 or 2, whereby all bypass modules (Wi, W2, W3, W4) are activated in case the voltage across the load path (4) is as below the second voltage level.
  4. 4. Driver module according to one of the claims 1 to 3, whereby at least two of the bypass modules (Va, W2, W3, W4) are activated at the same time when the voltage across the load path (4) is between the first and a third voltage level. * ..
  5. 5. Driver module according to one of the claims 1 to 4, * S Wherein the load path (4) comprises a series connection of a number of N LED strings each comprising at least one LED (Dl, D2, D3, D4, D5, D6, D7, D8), wherein a bypass module (Wi, W2, W3, W4) is connected in parallel to each of the N LED strings (Di, D2) and which are adapted to bypass the LED string (Dl, D2), whereby the control unit (CU) detects a value N which is the next higher multiple of the forward voltage of one LED string (Dl, D2) in relation to the actual voltage across the load path (4), whereby a number of CM-i) bypass modules (Wi, W2, W3, W4) is deactivated at the same time when the voltage across the load path (4) is below the product of M multiplied by the forward voltage of one LED string (Dl, D2).
    (N-i) x Vf group c yin c N x Vt group -> CM-i] groups bypassed I
  6. 6. Driver module according to claim 5, whereby a number of (M-l) bypass modules (Wl, W2, W3, W4) is deactivated at the same time when the voltage across the load path (4) is above the product of (M-l) multiplied by the forward voltage of one LED string (Dl, D2).
  7. 7. Driver module according to claim 6, whereby all bypass modules (PU, W2, W3, W4) are deactivated at the same time when the voltage across the load path (4) is above the forward voltage of all LED strings (Dl, D2, D3, D4, D5, DG, D7, D8).
  8. 8. Driver module (1) for driving LEDs, * *. wherein the driver module (1) comprises: -a load path (4) comprising at least a first LED string * (Dl, D2) with one or a plurality of LEDs, wherein the load path (4) comprises at least a second LED string (D3, D4) with one or a plurality of LEDs, the second LED string (D3, D4) being connected in series with the first LED string (Dl, D2), and a first bypass module (Wi) which is connected in parallel to the first LED string (Dl, D2) and which is adapted to bypass the first LED string (Dl, D2), and a second bypass module (W2) which is connected in parallel to the second LED string (D3, D4) is adapted to bypass the second LED string (D3, D4), whereby the first bypass module (Wl) and the second bypass module (W2) are controlled by a control unit (CU), wherein the control unit (CU) is adapted to deactivate the bypass the first bypass module (Wi) and the second bypass module (W2) in case the voltage across the load path (4) is above a certain first voltage level, and wherein the control unit (CU) is adapted to alternatingly bypass either the first LED string (Dl, D2) or the second LED string (D3, D4) in case the voltage across the load path (4) is below a certain first voltage level.
  9. 9. Driver module according to claim 1 or 8, whereby the alternating bypassing of either the first LED string (Dl, D2) or the second LED string (D3, D4) in case the voltage across the load path (4) is below a certain voltage level follows a switching pattern where the first LED string (Dl, D2) and the second LED string (D3,, D4) are turned on and off alternatingly following a pattern or by random selection.* *.
  10. 10. Driver module according to claim 9, wherein the load path (4) comprises at least a third LED S.....
    * string (D5, D6) with one or a plurality of LEDs, the third LED string (D5, D6) being connected in series with the first LED string (Dl, D2) and the second LED string (D3, D4) and a third bypass module (W3) which is connected in parallel to *the third LED string (D5, DG) is adapted to bypass the third LED string (D5, D6), and wherein the control unit (Cu) is adapted to alternatingly bypass two LED strings selected out of the first LED string (Dl, D2), the second LED string (D3, D4) and the third LED string (D5, D6) in case the voltage across the load path (4) is below a certain first voltage level.
  11. 11. Driver module according to claim 10, wherein the control unit (Cu) is adapted to alternatingly bypass either the first LED string (Dl, D2), the second LED string (D3, D4) or the third LED string (D5, D6) in case the voltage across the load path (4) is below a certain second voltage level.
  12. 12. Driver module (1) according to one of the preceding claims, wherein the driver module l) comprises: -input terminals (2, 3) for receiving an alternating voltage (yin) such as a AC mains voltage with a frequency of 50 or 60 Hz, -a rectifier (Dll, D12, D13, D14) for rectifying the received alternating voltage, wherein the rectified alternating voltage is the voltage (VA) applied to the load path (4), whereby the control unit (CU) is adapted to selectively activate the bypass modules with a frequency at least ten * ** times higher than the frequency of the AC mains voltage, preferably above 500 Hz.
    0*t*** * . *:°.
  13. 13. Driver module (1) according to claim 12 in combination with one of the claims 5 to 8, whereby the control unit (CU) is adapted to selectively *:*. activate each bypass module at least once during the time period where the voltage over the load path (4) is between the product of (M-l) multiplied by the forward voltage of one LED string (Dl, D2) and the product of N multiplied by the forward voltage of one LED string (Dl, D2).
  14. 14. Driver module (].) according to one of the preceding claims, Comprising a capacitor (Cl, C2, C3, C4, Cs) arranged in parallel to each of LED strings.
  15. 15. Driver module (1) according to one of the preceding claims, whereby the control unit (CU) is adapted to detect the waveform and shape of the input voltage, whereby the control unit (CU) may control the bypass modules according to the detected input voltage, e.g. may detect a dimming information or a emergency lighting situation, and preferably may perform a dimming operation.
  16. 16. Driver module (1) according to one of the preceding claims, wherein the driver module (1) comprises: -a current source (Ii) connected in series with the load path (4) for generating a current for the load path (4), and -the control unit (CU) for controlling the current for the load path (4) so that the shape of the current for the load path (4) matches the voltage (VA) applied to the load * path (4) * . ** * * . . * **
  17. 17. Driver module according to preceding claim 18, wherein the current source (Il) comprises a transistor *:*. (Ml) operated in the linear mode, and the control unit (8) is connected to a control pin (G) and a further pin (5) of the transistor (Ml) to control the current for the load path (4).19. Driver module according to any of the preceding claims, wherein the current source (Il) comprises a transistor (Ml) operated in the linear mode for adapting the current for the load path.20. Driver module according to any of the preceding claims, wherein the current source (Ii) comprises a resistor (RI) traversed by the current for the load path (4), and the control module (8) comprises a voltage divider (R3-R4-R5, R6) for generating an output voltage (VR6) that is proportional to the voltage (VA) applied to the load path (4), wherein the resistor (RI) and the voltage divider (R3-R4-RS, RE) are coupled so that the output voltage (VRE) has the same time-dependency as the current through the resistor (R7).21. Method for driving LEDs, the method comprising the following steps: * ** -supplying an alternating voltage (yin) such as a mains * * * " * voltage, ****** * -rectifying the alternating voltage, -applying the rectified voltage to a load path (4) comprising a series connection of two or more LED strings each comprising at least one LED (Dl, D2, D3, D4, D5, D6, D7, D8) wherein each LED string (Dl, D2) comprises a bypass module (Wi, W2, W3, W4) which is connected in parallel to the LED string (Dl, D2) and which is adapted to bypass the LED string (Dl, D2) selectively activating one or more of the bypass modules (Wi, W2, W3, W4) in case the voltage across the load path (4) is between a first and a second voltage level, preferably that all bypass modules (Wi, W2, W3, W4) are activated at least once with the period where the voltage across the load path (4) is between a first anda second voltage level.
GB1417345.4A 2014-09-30 2014-09-30 Driver module for driving LEDs Pending GB2530766A (en)

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GB1417345.4A GB2530766A (en) 2014-09-30 2014-09-30 Driver module for driving LEDs
DE102015202814.3A DE102015202814A1 (en) 2014-09-30 2015-02-17 Switched AC direct driver for LEDs
ATGM9004/2015U AT16192U1 (en) 2014-09-30 2015-09-28 Switched AC direct driver for LEDs
PCT/AT2015/050240 WO2016049671A1 (en) 2014-09-30 2015-09-28 Switched direct ac driver for leds

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WO2016049671A1 (en) 2016-04-07
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DE102015202814A1 (en) 2016-03-31

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