Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/40—Details of LED load circuits
  • H05B45/44—Details of LED load circuits with an active control inside an LED matrix
  • H05B45/48—Details of LED load circuits with an active control inside an LED matrix having LEDs organised in strings and incorporating parallel shunting devices

Definitions

• 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.
• 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 LEDs 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.
• 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.
• 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.
• a driver module for driving LEDs comprises a load path comprising at least one LED string with one or a plurality of LEDs.
• 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.
• a method for driving LEDs comprising the following steps of supplying an alternating voltage such as a mains voltage, and rectifying the alternating
• the rectified voltage is applied to a load path comprising at least one LED string with one or a plurality of LEDs.
• a current for the load path is generated.
• the current for the load path is controlled so that the shape of the current for the load path matches the voltage applied to the load path.
• the shape of the current through the load path, i.e. through the at least one LED string, and through the current source corresponds to the shape of the voltage that is across both the current source and the load path. They have the same shape.
• the current source is programmed to control the current through the LED string to develop totally the shape of the input AC sine-wave.
• the voltage applied to the load path corresponds to the voltage across the load path and the current source.
• the current source comprises a transistor operated in the linear mode.
• the control module is connected to a control pin and a further pin of the transistor to control the current for the load path.
• the control pin corresponds to the gate of the transistor and the further pin corresponds to the source.
• the current source comprises a transistor operated in the linear mode for adapting the current for the load path.
• the current source does not comprise a switching stage for adapting the current through the LEDs.
• the current source comprises a resistor traversed by the current for the load path.
• control module comprises a voltage divider for generating an output voltage that is
• the resistor and the voltage divider are coupled so that the output voltage of the voltage divider has the same time- dependency as the current through the resistor.
• the resistor mentioned here is advantageously connected in series with the transistor.
• the resistor and the voltage divider are coupled in such a way that the output voltage of said voltage divider is connected to the emitter of a transistor of the control module, and that the base of this transistor is connected to the source of the transistor of the current source.
• control module comprises a voltage divider for generating a voltage proportional to the voltage applied to the load path.
• control module is adapted to control the current for the load path on the basis of the generated voltage.
• the driver module comprises input
• the terminals for receiving an alternating voltage such as a mains voltage, and a rectifier for rectifying the received alternating voltage.
• an alternating voltage such as a mains voltage
• a rectifier for rectifying the received alternating voltage.
• alternating voltage is the voltage applied to the load path .
• 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.
• a bypass module is connected in parallel to the further LED string and is adapted to bypass the further LED string.
• 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.
• the bypass module in case the voltage applied to the load path is below a given threshold, 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.
• 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.
• the LEDs of the LED string and of the further LED string are respectively arranged in series. This means that the LEDs of the LED string are connected in series, as well as the LEDs of the LED string.
• a transistor of the driver module in particular an output transistor, can be replaced by a number of parallel transistors.
• the number of parallel transistors in their conductive state may conduct the same current as the replaced transistor. They preferably perform the same switching action as the replaced transistor.
• the number of parallel transistors can be distributed across a LED module and/or a PCB.
• the driver module can comprise a voltage limiter, the voltage limiter preferably comprising a Darlington transistor and/or being connected in series with a voltage supply source.
• the first LED string and/or the second LED string may comprise at least two LED string segments, which can be selectively activated/deactivated by segment switches, preferably according to a binary switching pattern.
• a compensation circuit can reduce the LED current in response to a rising average voltage of the preferably rectified mains voltage.
• the compensation circuit may reduce a mean current, in particular when the mean current increases due to an increasing average voltage of the preferably rectified mains voltage.
• the compensation circuit can reduce the mean current by a specific amount, in particular by the amount the mean current increases due to the increased average mains mean voltage.
• the threshold value can be the breakthrough voltage of a Zener diode.
• the invention proposes to use a current source which is programmed to control the current through the LED string to develop totally the shape of the AC sine-wave .
• transistor operated in the linear mode is used to control the current through the LED string.
• a plurality (at least two) groups of LED strings are used in a switched mode.
• the upper LED string (comprised of two LEDs in the
• the advantage of the invention is that only a single current source is required, which is programmed in the example by a voltage divider.
• a further advantage of the LED driver according to the invention is that it is easily dimmable when using usual dimmers as for example phase cut dimmers.
• a Zener diode is present to limit the current to a maximum value .
• Fig. 1 illustrates a schematic diagram of a driver module 1 for driving LEDs according to the present invention.
• Fig. 2 illustrates a schematic diagram of a driver module 1 for driving LEDs according to another embodiment of the present invention.
• Fig. 3 shows a circuit detail according to an embodiment of a driver module according to the present invention.
• Fig. 4 shows a further circuit detail according to an embodiment of a driver module according to the present invention.
• Fig. 5 shows yet a further circuit detail according to an embodiment of a driver module according to the present invention .
• Fig. 6 shows still a further circuit detail according to an embodiment of a driver module according to the present invention.
• the driver module 1 for driving LEDs D10, Dll, D12, D13 shown in Fig. 1 is supplied with an input voltage Vin 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 first input with the higher electric potential is connected to a first terminal of a resistor Rl .
• a diode Fl e.g. a transient-voltage-suppression (TVS) diode, is provided between the second terminal of the resistor Rl and the second input terminal 3.
• This optional diode Fl is used for protecting the driver module 1 e.g. from voltage spikes .
• the input voltage Vin is applied to a rectifier for converting the alternating voltage (AC) to a rectified voltage (DC).
• AC alternating voltage
• DC rectified voltage
• the output of the bridge rectifier Dl is a full-wave rectified voltage V provided between a positive terminal + and a negative terminal - of the rectifier Dl .
• the negative terminal - corresponds to ground, while the positive terminal + at node A represents voltage VA.
• the preferably rectified input voltage VA is applied to a resistor R2 and a capacitor CI that are connected in series between node A and ground.
• An advantage of the LED driver according to the present invention is that it is easily dimmable when using usual 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.
• the elements Rl, R2 and CI are 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 CI represent damping elements avoiding ringing effects - in view of capacities provided on the dimmer - caused when operated with usual dimmers.
• a load path 4 comprising two LED sets or LED strings 5, 6 is connected to node A, i.e. to the voltage VA.
• a first load path 4 comprising two LED sets or LED strings 5, 6 is connected to node A, i.e. to the voltage VA.
• Each LED set 5, 6 comprises at least one LED, preferably a plurality of LEDs connected in series and/or in parallel.
• the two LEDs 10, 11 of the first LED set 5 schematically represent a plurality of LEDs coupled in series.
• the two LEDs 12, 13 schematically represent a series of coupled LEDs for the second LED set 6.
• the anode of the LEDs is connected towards node A.
• the driver module 1 now comprises a current source 7 for controlling the current flowing through the LEDs 10, 11, 12, 13 and through the LED sets 5, 6.
• the current source 7 is advantageously operated so that the current through the LEDs follows the shape of the sine-wave of the rectified voltage VA.
• the current source 7 is set up for driving a non-constant current through the load path 4 and thus through the LED sets 5, 6.
• the current source 7 comprises a switch in the form of a transistor Ml for controlling the current through the
• Said transistor Ml is connected in series with the
• Said transistor Ml is implemented as a power transistor.
• the transistor Ml is
• FET field-effect transistor
• MOSFET metal-oxide-semiconductor field effect transistor
• the drain of the transistor Ml is connected to the cathode of the last serial connected LED D13 of the second LED set 6.
• the source of the transistor Ml is coupled to a
• 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 7 and the transistor Ml are controlled by a control module 8.
• the control module 8 comprises a switch and particularly a transistor Ql that is preferably a bipolar junction transistor of the NPN-type. Said transistor Ql is coupled to the transistor Ml, in that e.g. its collector C is connected to the gate G of
• transistor Ml while its base B is connected to the source S of transistor Ml.
• the collector of transistor Ql is further coupled to node A via a series arrangement of two resistors R3, R4.
• the collector C and the emitter E of transistor Ql are linked to each other via a resistor R5.
• a resistor R6, a tunable Zener diode Ul and a capacitor C2 are respectively connected in parallel between ground and the emitter E of transistor Ql .
• the current source 7 is controlled or programmed by the control module 8, and preferably by a voltage divider.
• Such a voltage divider can be formed on the one hand by the serial arrangement of resistors R3, R4 and on the other hand by the serial arrangement of resistors R5, R6,
• the output of the voltage divider - i.e. the voltage across the resistors R5, R6 - is applied to the gate of the power transistor Ml of the current source 7 and to the collector of the transistor Ql.
• the control module 8 i.e. the programming circuitry for the current source 7 , is made such that the voltage across the resistor R7 equals the voltage across the resistor R6.
• the current through the resistor R7 will then have the same time-dependency as the current through the resistor R6.
• a further voltage divider is thus defined by the resistors R3, R4, R5 on the one hand and by the resistor R6 on the other hand.
• the output of this voltage divider - i.e. the voltage across the resistors R6 - is applied to the emitter of the transistor Ql, and sets what the drain current of the power transistor Ml will be.
• the base-emitter voltage of the transistor Ql of the control unit 8 corresponds, i.e. is approximately equal, to the voltage across the diode D2 of the current source 7.
• the voltage across the resistor R7 corresponds, i.e. is approximately equal, to the voltage across the diode D2 of the current source 7.
• the tunable Zener diode Ul can e.g. be a standard
• the anode of the tunable Zener diode is connected to ground, while its cathode and a reference terminal of the tunable Zener diode Ul are connected to the emitter E of transistor Ql.
• the tunable Zener diode Ul sets a voltage reference.
• the diode Ul is present to limit the current to a maximum allowable value .
• a bypass module 9 is connected in parallel to the first set of LEDs 5 so that the LED set 5 can be bypassed depending on the voltage VA applied to the anode of the LED set 5 and to the bypass module 9.
• the bypass module 9 comprises two transistors Q2, Q3 arranged according to a Darlington circuit 23.
• transistors Q2, Q3 are e.g. in the form of bipolar
• junction transistors and preferably of the PNP-type.
• 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 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 .
• the rectified voltage VA is applied to the emitter E23 of the Darlington 23.
• the collector C23 of the Darlington is connected to the cathode of the LED set 5, i.e. at the joining node between both LED sets 5, 6.
• the emitter E23 and collector C23 of the Darlington 23 are connected in parallel to the LED set 5, such that the bypass module 9 can indeed bypass the LED set 5 if the Darlington 23 is switched on.
• a further transistor Q4 e.g. a bipolar junction
• transistor preferably of the PNP-type is coupled to the Darlington 23, in that their respective emitters are connected and in that the base B23 of the Darlington is connected to the collector of the transistor Q4.
• resistor R8 is also connected between base B23 and
• a parallel RC circuit composed of capacitor C4 and resistor R9 is connected between emitter and base of the transistor Q4.
• the base of the transistor Q4 is further coupled to ground via a serial arrangement of a Zener diode Z3 and of a resistor RIO .
• the bypass module 9 is adapted to bypass the LED set 5 when the rectified AC voltage VA is below a given threshold. On the contrary, the bypass module 9 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 through the Zener voltage of the Zener diode Z3 which may be for instance 270 Volt.
• the reason for switching operative the LED set 5 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 set 5. On the other hand, if the applied voltage VA is too low, i.e. below said threshold, the voltage across both LED sets 5, 6 will not be sufficient to switch on both LED sets 5, 6.
• FIG. 2 illustrates a schematic diagram of a driver module 1 for driving LEDs according to another embodiment of the the invention.
• the circuit of Fig. 2 is similar to the circuit of Fig. 1. The difference is that the current source 7 with the transistor Ml and the control module 8 is replaced by resistors R61 and R71.
• the resistors R61 and R71 act as ballasting resistors and limit the current through the LED.
• the resistor R61 is only switched in series to the LED set 6 when the Darlington circuit 23 is switched on and the LED set 5 is bypassed.
• the invention is not limited to two LED sets 5, 6.
• the driver module can comprise a third LED set (not shown) comprised in the load path 4 in series with the two LED sets 5, 6.
• a second bypass module (not shown) can be provided in parallel to the third LED set.
• the bypass module 9 connected to the LED set 5, and the second bypass module connected to the third LED set are then configured in such a way that the LED set 5 and the third LED set are switched operative at different threshold of the rectified AC voltage. For a low value of the AC voltage only the LED set 6 will be switched on, the two other LED sets being bypassed. For a higher value, both LED sets 5, 6 will be on, while only the third LED set will be bypassed. For an even higher value of the AC voltage, all three LED sets will be switched on, such that the current will flow through the all three LED sets and the overall light output can be increased.
• a switch may however be used in a bypass module coupled to a subgroup of the LEDs. Additionally, in order to allow for a better heat
• transistors used in the circuits previously described can be "split" into at least two transistors. This means that one transistor is replaced by at least two resistors and the current previously fed to the one transistor is now fed to the replacement transistors, the replacement transistors together performing the switching function of the replaced transistor. This results in the heat dissipation not being concentrated on one transistor, but being spread to the replacement transistors.
• LED drivers In typical (e.g. switched mode) LED drivers, power losses are distributed throughout the circuit, for instance within a transformer, a switch, an output diode, snubbers etc. The losses are caused, since the components used in the driver are not ideal, which in theory would lead to the losses being zero.
• LED drivers have well- defined theoretical losses caused by current passing through transistors, e.g. a linear control transistor. For example, a 25 Watts LED driver operating at 80% efficiency will need to dissipate 5 Watts, in particular in an output transistor .
• PCBs may be made of composite material, being for example composed of woven glass fabric surfaces and a paper core combined with epoxy resin (CEM-1) . This material does not conduct heat well and may hinder a heat transfer away from a heat source, such as a transistor. This is also the case for other materials used for PCBs that do not allow for a good heat dissipation themselves.
• one transistor only e.g. an output transistor
• these lower power transistors are connected in parallel, each dissipating fewer power or heat than the replaced transistor when conducting the current. These low power transistors can then be physically distributed across a surface of the PCB or LED module, which results in the heat loss being spread across the PCB to increase the available heat dissipation area.
• Fig. 3 shows an exemplary detail arrangement of parallel transistors according to this aspect of the invention.
• transistors Q4'-Q23' are also switched to be conductive.
• a current flows e.g. from connection point 3A to connection point 3C/3D through transistors Q4'-Q23', or portions thereof.
• the transistors can also be differently dimensioned.
• a resistor R16'-R35' is connected.
• Capacity C9' which links the base of transistor Q3' with connection point 7C is optional and can be replaced by other
• connection points 3C and 3D may be linked to the ground potential.
• connection point 3A which connects to the base of transistor Q3', may be connected at the connection point of the replaced gate of transistor Ml, while connection point 3C may be connected at the lower potential connection point of resistor R7 resistor R16' may replace resistor R7.
• the emitter of transistor Q4' may then be connected to a diode D2 connected in series with resistor R16', but also to capacitor C3, analog to the source S of transistor Ml.
• Connection point 3B may be connected to the cathode of LED D13; connection point 3D may be connected to the lower potential side of resistor RIO.
• a (series) voltage limiter 40 can be used to increase transient immunity. Especially when a large number of parallel output transistors are used (e.g. 20 as in the example of Fig. 3), these
• transistors advantageously are of low cost. This limits the ratings and performance available by the transistors and in particular, it limits the voltage capability, for example to 300V. Although the voltage limit is typically sufficient to handle high voltage drops during normal operation, but it can make the circuit vulnerable to transients. For example, a combination of transistors of a specific voltage and a LED string of a specific voltage can limit the overall voltage capability to a specific value.
• VDR variable voltage dependent resistor
• a transistor preferably a Darlington transistor DA40, illustrated with transistors Q24' and Q25' is provided, which is on, i.e. switched to its conductive state, in normal operation and which is preferably connected in series with a rectified mains supply.
• a resistor R39' is connected between nodes 41 am 42 .
• at least one Zener diode Z2' , Z3' is connected.
• transistor can be a 300V transistor connected as an emitter follower. In normal operation the transistor is fully conductive, and drops very little voltage. However the follower emitter output is limited to 400V by the Zener diodes Z2' , Z3' clamping the base terminal of the transistor, so that additional input voltage is dropped across the transistor. This allows the system to survive transients up to 700V. Additional voltages are clamped by the voltage dependent resistor, which may be played as an alternative to the diode Fl of the example of Fig. 1 or 2, for example extending overall transient capability to beyond 1 kilo Volts. An optional jumper Jl is also shown, which allows bridging transistor Q25' and allows to model circuits, in which transistor Q25' is not used.
• connection point 4A may be connected to the positive terminal + of bridge rectifier Dl, while connection point 4C may be connected to the negative terminal - of the bridge rectifier Dl .
• Connection point 4B may be connected to the higher
• connection point 4D may be connected to the lower potential side of capacity CI.
• the series connection of resistor R2 and capacity CI may be connected before the detail of Fig. 4.
• a binary switching pattern can be used to obtain different physical LED string length by switching LED string segments, which are advantageously of different length.
• These LED string segments can be suitable to replace LED string 5 and/or LED string 6 of Fig. 1 or 2 connected in load path 4, especially betwine the high potential connetion point of load path 4 and the drain D of transistor Ml/collector of transistor Q3 f .
• LED string segments 51, 52, 53 can be used. In the example of Fig.
• LED string segment 51 comprises one LED
• LED string segment 52 comprises two LEDs
• LED string segment 53 comprises four LEDs.
• the LED string segments 51, 52, 53 can be selectively switched on and off by segment switches 54, 55 and 56.
• segment switch 54 is switched on, i.e. to its conductive state
• LED string segment 51 is off, as it is bridged.
• segment switch 55 is switched on
• LED string segment 52 is off.
• segment switch 56 is switched on, LED string segment 53 is off.
• the three exemplary LED string segments 51, 52, 53 can hence be activated or deactivated in a binary fashion, in particular to obtain 7 different LED overall string lengths (with the addition of an eighth variant with the length 0, when all segment switches 54-56 are conductive) .
• a different number would lead to more or less possible LED string length combinations.
• the three LED string segments 51, 52, 53 exemplary shown in Fig. 5 have relative lengths of 1, 2 and 4, so they can be switched in binary sequence to obtain the different overall lengths.
• the activation or deactivation of the LED string segments can follow the mains voltage waveform rise and fall, so that the LED string voltage of the activated LED string segments 51, 52, 53 closely matches the mains voltage at any instant.
• This function could be implemented by e.g. a controller which controls the by-passing of the LED strings by controlling the segment switches 54, 55, 56.
• the switches 54, 55, 56 of course can be realized as transistors (bipolar, FET, MosFET, ).
• Such a controller which controls the by-passing of the LED strings by controlling the segment switches 54, 55, 56.
• the switches 54, 55, 56 of course can be realized as transistors (bipolar, FET, MosFET, ).
• Such a controller which controls the by-passing of the LED strings by controlling the segment switches 54, 55, 56.
• microcontroller ASIC, IC, Certainly may monitor the supply voltage (e.g. rectified mains), or may control a
• the segment switches 54, 55, 56 for bypassing of the LED string segments 51, 52, 53 may also be
• a compensation circuit 60 (c.f. Fig. 6) can be used in the above described circuits to improve line voltage regulation.
• the LED current supplied by linear control transistor ( s ) can be modulated by the varying voltage across each mains half-cycle, so that each half-cycle of current mimics the sinusoidal waveform of the mains voltage.
• TDD thermal heat dissipation
• RMS root-means-square
• the compensation circuit 60 can be added as shown in Fig. 6.
• the compensation circuit adjusts the mean current downwards, in response to rises in the average voltage of the rectified mains. Because it is preferably controlled by the average mains voltage, it does not affect the current waveform shape.
• the method uses a current source which is programmed by the mains voltage, to produce a sinusoidal current. This gives a very high power factor.
• the compensation circuit 60 can reduce the LED current with rising average mains voltage, in order to maintain constant brightness. This is
• the primary controller modulates the current according to the mains sine wave.
• this naturally increases the mean current as the mean voltage increases, so the compensation circuit reduces it by an equal amount.
• the compensation circuit 60 can be connected with a connection point 6A to the high potential side of resistor R2, while a connection point 6C may be connected to the low potential side of capacity CI.
• connection point 6B can be connected to the high potential side of resistor R3, while a connection point 6D may be connected to the low potential side of resistor R6.
• the compensation circuit 60 can be connected with the connection point 6A to the high potential side of resistor R2, while the connection point 6C may be connected to the low potential side of capacity CI.
• a connection point 6B can be connected to the high potential end of the load path 4/LED string 5, while the connection point 6D may be connected to the low potential side of resistor R61.
• connection point 6A The closest connection of connection point 6A to
• connection point 6C is a voltage divider formed by a series connection of resistor R7' and resistor R12' .
• a capacity CI' and a resistor R15' are connected in parallel to the resistor R12' of the voltage divider R7' , R12' via diode D9' , the anode of which is connected to a midpoint of the voltage divider R7', R12' .
• a series connection of a Zener diode Zl' ' , a resistor Rll', a resistor R14', and diodes D2' and D3' is connected.
• a collector of a first transistor Q2' of Darlington transistor DA60 is connected.
• the base of the first transistor Q2' is connected to the lower potential side of resistor Rll', but also to a capacity C8', which connects the base of the first transistor Q2' to connection point 6C/6D.
• the emitter of the first transistor Q2' is
• Zener diode Zl' ' When at Zener diode Zl' ' the break-through voltage is reached due to the increasing mean voltage, a transistor, in particular the Darlington transistor DAGO comprising the first and second transistor Q2' and Ql' , becomes conductive. Therefore, the path of resistor R8, transistor Ql' and resistor RIO' becomes conductive and the means current is reduces till the means voltage falls below the break-through voltage of Zener diode Zl''.

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• 2013
  • 2013-11-21 EP EP13193856.5A patent/EP2876977B1/de active Active
• 2014
  • 2014-11-21 WO PCT/EP2014/075283 patent/WO2015075182A2/en active Application Filing
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