• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
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  • 优先权
    • 专利摘要:
    A driver (301, 401, 501, 601, 701) for semiconductor light sources (114) comprises an input (102) for receiving an input voltage and an output (409, 609) for said semiconductor light sources (114). A transformer (104) divides the driver (301, 401, 501, 601, 701) into a primary side and a secondary side. The primary side comprises a primary coil of said transformer (104) and a first internal reference potential line (311). The secondary side comprises a secondary coil of said transformer (104) and a second internal reference potential line (302). A capacitor (303) is coupled between said first (311) and second (302) internal reference potential lines. Said output (409, 609) comprises a grounding pole (402, 602) for making a connection to a functional earth outside said driver (301, 401, 501, 601, 701). The driver (301, 401, 501, 601, 701) comprises an electric connection (308) between said second internal reference potential line (302) and said grounding pole (402, 602).
    公开号:FI20176079A1
    申请号:FI20176079
    申请日:2017-11-30
    公开日:2019-05-31
    发明作者:Harri Naakka
    申请人:Helvar Oy Ab；
    IPC主号:
    专利说明:

    METHOD AND ARRANGEMENT FOR AVOIDING UNWANTED GLOWING
    OF LEDS
    FIELD OF THE INVENTION
    The invention is related to the field of driver devices used to drive semiconductor light sources. In particular the invention is related to avoiding an unwanted glowing effect that could be 10 caused by small amounts of electric current flowing through the LEDs when no current should flow.
    20176079 prh 30 -11- 2017
    BACKGROUND OF THE INVENTION
    Semiconductor light sources, such as LEDs (Light Emitting Diodes), generate light when an electric current flows through a PN junction so that electrons recombine with holes. Without losing generality the designation LED can be used for short to describe all semiconductor light sources.
    Even relatively small amounts of electric current may suffice to produce light in LEDs, which sometimes results in the so-called glow effect. It means that even if the LED driver is in a switched-off (or standby) state and the LEDs it drives should be completely dark, some light is nevertheless generated in the LEDs. The glow effect is generally undesirable, because it may be visually irritating and make users concerned of possible malfunctioning of the lighting. In some cases it has also technically disadvantageous consequences: for example if LED lighting is installed in a space where light-sensitive materials can be handled and the lighting should be turned completely off for such handling, unintentionally glowing LEDs may damage the light-sensitive materials.
    Fig. 1 is a simplified circuit diagram of a known LED driver 101. The two nodes of a power input
    20176079 prh 30 -11- 2017
    102 are to be coupled to the live and neutral lines of AC mains. A schematically shown first stage 103 may comprise rectifying, filtering, and power factor correction circuits. It produces an internal bus voltage for a second stage, which in the driver of fig. 1 is a switched-mode power supply of the flyback type. It comprises a transformer 104, the primary coil of which belongs to a primary current path where a primary current may flow through a switching transistor 105 and a 10 current sensing resistor 106. On the secondary side a diode 107 and a capacitor 108 rectify and smoothen the voltage to be fed to the output 109. A current feedback circuit 110 produces feedback signals, which are transmitted through an optoisolator 111 to the primary 15 side. A control circuit 112 receives the feedback signals through the optoisolator 111 and the current sensing signals from the current sensing resistor 106, and uses them to produce control signals to the first stage 103 and to the switching transistor 105.
    Fig. 2 illustrates schematically a known LED luminaire in which a driver of the kind described above can be used. The luminaire of fig. 2 comprises a body part 201 made of electrically conductive material. The AC mains cable 202 comprises a live wire 203, 25 a neutral wire 204, and a protective earth wire 205.
    The two first-mentioned are coupled to the power input 102 of the driver 101, while the protective earth is connected to the body part 201 of the luminaire. The LEDs 114 are located on a LED module 206, the planar 30 circuit board of which acts both as a support structure and as a heat sink. A control bus connector 207 is provided for connecting the wires of a control bus 208 to the luminaire.
    In fig. 1 the control circuit 112 may receive 35 a standby command through a control input 113. In response to a received standby command it should put the LED driver into standby mode. This means that the LEDs
    114 should not emit light, but the driver 101 should be ready to switch them on as soon as it receives a command to end the standby mode. It has been found that the LEDs 114 have the tendency to glow, at least 5 in certain types of luminaires that have a driver of the kind shown in fig. 1, particularly during standby mode .
    Prior art solutions exist in which glowing is prevented with an actively controlled switch at or 10 close to the output 109. The use of an actively controlled switch makes the circuit more complicated, because the control signal must be produced and conveyed to the right place in the circuit at the right time.
    20176079 prh 30 -11- 2017
    SUMMARY
    It is an objective of the invention to present a driver for semiconductor light sources that is capable of preventing semiconductor light sources coupled to said driver from glowing. It is also an objec20 five of the invention to present a driver in which preventing the glowing does not require active switching. A further objective of the invention is to present a driver in which glowing can be prevented despite galvanic isolation between primary and secondary 25 sides of the driver and despite the so-called Y capacitor between the primary and secondary sides. A yet further objective of the invention is to present a luminaire in which the glowing of the semiconductor light sources can be prevented.
    These and further advantageous objectives are achieved by providing a grounding pole in the output of the driver for connecting to functional earth outside the driver, and by making an electric connection of sufficiently high DC impedance between said ground35 ing pole and an internal reference potential line of the secondary side of the driver.
    20176079 prh 30 -11- 2017
    The characteristic features of a driver according to the invention are recited in the characterizing part of the appended independent claim directed to a driver. The invention concerns also a luminaire, 5 the characterizing features of which are recited in the independent claim directed to a luminaire. Advantageous embodiments of the invention are presented in the depending claims.
    BRIEF DESCRIPTION OF THE DRAWINGS
    The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, illustrate embodiments of the invention and together with 15 the description help to explain the principles of the invention. In the drawings:
    Figure 1 is a circuit diagram of a prior art LED driver,
    Figure 2 is a schematic illustration of a 20 known luminaire,
    Figure 3 illustrates what may cause glowing,
    Figure 4 illustrates a principle according to an embodiment,
    Figure 5 illustrates a principle according to an embodiment,
    Figure 6 illustrates parts of a driver according to an embodiment, and
    Figure 7 illustrates a luminaire according to an embodiment.
    DETAILED DESCRIPTION
    Fig. 3 illustrates a finding of what may cause glowing, as well as a suggested cure.
    Fig. 3 is a simplified schematic of a driver
    301 for semiconductor light sources 114. It comprises
    20176079 prh 30 -11- 2017 an input 102 for receiving an input voltage and an output 109 for outputting an output current for the semiconductor light sources 114. Block 103 illustrates schematically a first stage of the driver 301. It may 5 comprise for example rectifying, filtering, and power factor correction circuits. It is configured to produce an internal bus voltage for a second stage, which in the driver of fig. 3 is a switched-mode power supply (SMPS) of the flyback type. For the following con10 siderations the topology selected for the second stage
    SMPS is not important, and it could quite as well be e.g. a buck converter, a boost converter, or some other DC to DC converter.
    Within the second stage the driver 301 com15 prises a transformer 104 that divides the driver into a primary side and a secondary side. The primary side comprises a primary coil of the transformer 104, and a (first) internal reference potential line 301. The secondary side comprises a secondary coil of the 20 transformer 104, and a (second) internal reference potential line 302. The internal reference potential lines can also be called internal zero voltage lines or internal grounds.
    A capacitor 303 is coupled between the first and second internal reference potential lines. This is the so-called Y capacitor, and its function is to reduce electromagnetic interference. The transformer 104 makes the primary and secondary sides of the driver galvanically isolated from each other, and the capaci30 tor 303 is the only connection that crosses the isolation border. The use of a Y capacitor that bridges the primary and secondary sides of a galvanically isolated switched-mode power supply is a known practice and it is widely used in all kind of power supplies coupled 35 to receive AC mains, including LED drivers.
    The rectifying diode 107 and the smoothing capacitor 108 on the secondary side are coupled as and
    20176079 prh 30 -11- 2017 configured to work similarly as in known LED drivers. A current sensing resistor 304 is shown in the middle of the second internal reference potential line between the lower pole of the output 109 and the second5 ary coil of the transformer 104. No actual current sensing circuitry is shown in fig. 3, but this is just a graphical simplification.
    Fig. 3 shows also a capacitor 305 that represents the stray capacitance between the coils of the 10 transformer 104. Stray capacitance of this kind is an inherent feature of all transformers. Its magnitude depends on the configuration of the transformer. In devices like LED drivers it is customary to use relatively small-sized transformers and aim at a strong 15 electromagnetic coupling between the primary and secondary coils, which typically tends to lead also to a relatively large stray capacitance.
    Another component that is schematically shown in fig. 3 is the heatsink 306 on which the LEDs 114 20 are mounted. At the time of writing this text it is typical that some of the heat generated in LEDs during operation is dissipated in a heatsink that can be e.g. a metallic plate that simultaneously constitutes a structural part of the LED module. In order to take 25 best advantage of the heat-dissipating properties of a heatsink it is advisable to make the thermal conductance between the LEDs and the heatsink as good as possible. Some electric insulation is required, though, at least between the electrically conductive parts of 30 the LEDs and the heatsink, because otherwise the heatsink would short the LEDs electrically.
    If the insulation between the LEDs and the heatsink is not very thick, significant capacitive coupling may occur between the electrically conductive 35 parts of the LEDs and the heatsink. The same is true for the conductive tracks that link the LEDs together in the LED module: they may experience significant ca
    20176079 prh 30 -11- 2017 pacitive coupling with the heatsink. This capacitive coupling is schematically shown in fig. 3 as capacitors with dashed lines, with capacitor 307 as an example .
    As an important additional detail, the heatsink 306 may be grounded, or coupled to the functional earth of the luminaire. Now here is a possible cause of glowing. When the driver 301 is in standby mode, no power is needed on the secondary side and 10 consequently the switch 105 of the second stage SMPS does not receive any switching pulses but remains open. However, since a mains AC voltage is nevertheless present at the input 102, some common-mode stray currents may propagate into the driver and run through 15 the available current paths of the primary side. Some of such stray currents may become coupled to the secondary side through the Y capacitor 303 and/or the stray capacitance 305 of the transformer 104. Further, some of these currents may reach the output 109 and 20 flow to the LEDs 114, where the stray capacitive couplings 307 to the heatsink 306 and further to functional ground complement the current path so that some current eventually flows through the PN junction of at least some of the LEDs 114. This makes the LEDs 114 25 glow.
    A cure for this problem is shown schematically in fig. 3. An electric connection 308 may be established between the second internal reference potential line 302 and functional earth outside the driver 301.
    Any stray currents that may occur on the secondary side will bleed into functional earth through the electric connection 308, which prevents any such current from flowing to the LEDs 114. Consequently the LEDs 114 will not glow.
    The DC impedance of the electric connection
    308 should be sufficiently high in order not to make too large leakage current escape to the functional
    20176079 prh 30 -11- 2017 earth during normal operation. Currents that cause glowing in the LEDs may be in the order of microamperes and it is only currents of this magnitude that need to flow through the electric connection 308, so even a relatively high DC impedance of the electric connection 308 may do. Basically the aim is just to offer the stray currents an easier path to flow through the electric connection 308 than through the combination of all stray capacitances 307 in the LED module .
    Fig. 4 illustrates schematically a driver 401 in which the principle shown above in fig. 3 is implemented in practice. The driver 401 comprises a threepole output 409, which comprises a grounding pole 402 for making a connection to a functional earth outside the driver 401. The electric connection between the second internal reference potential line 302 and the grounding pole 402 comprises a resistor 404. The resistance of the resistor 404 should be selected on the basis of the criteria given above: large enough to keep excessive leakage currents from escaping to functional earth during normal operation, but simultaneously small enough to offer stray currents a significantly easier path to the functional earth than through any stray capacitances in a LED module. A resistor of at least 1000 ohms, preferably in the order of about ten kilo-ohms, has been found to work well in a driver the output power of which is in the order of some tens of watts.
    In some cases the stray currents that cause glowing have a significant AC component. In such cases the electric connection between the second internal reference potential line and the grounding pole in the output may have comprise a capacitor, or the connection may even be predominantly capacitive. Fig. 5 illustrates an embodiment in which the electric connec9 tion comprises a capacitor 505 coupled in parallel with a resistor 504.
    The second internal reference potential line is typically one section of a current path that goes 5 from the cathode-end output pole to the lowerpotential end of the secondary coil in the transformer 104. The electric connection between the second internal reference potential line and the grounding pole may be more or less direct, and go through various in10 termediate components. For effectively preventing the LEDs from glowing, the impedance of the electric connection should be low enough so that the stray currents on the secondary side favor this route to the
    functional earthandnottheonethrough theLEDs and15 their heatsink. Figs. 4and5alsoillustrate somealterna-fives regardinghowtheelectricconnectionexplainedabove is locatedinrelationto acurrent sensing re-sistor on the secondaryside,ifthe drivercomprises
    20176079 prh 30 -11- 2017 one. In figs. 4 and 5 the secondary side of the driver can be said to comprise a first current path between one of the poles in the output 409 and a current sensing resistor 304, and a second current path between the current sensing resistor 304 and one end of the 25 secondary coil in the transformer 104. (The pole mentioned here is, to be exact, one of the poles for coupling the semiconductor light sources, not the grounding pole 402.) In fig. 4 the electric connection that is to be used to prevent glowing connects the second 30 current path to the grounding pole 402, whereas in fig. 5 the electric connection connects the first current path to the grounding pole 402. Making the connection to the grounding pole 402 at a point as close as possible to the output 409 may help to ensure that 35 most of the currents that could otherwise cause glowing are really shorted to the functional earth.
    20176079 prh 30 -11- 2017
    Fig. 6 is a somewhat more detailed example of some parts of a driver for semiconductor light sources. The input and the first stage of the driver are not shown in fig. 6, but they are assumed to exist 5 on the left side of the parts shown in fig. 6. The second stage is again a switched-mode power supply of the flyback type, and the electric connection between the second internal reference potential line and the grounding pole 602 is basically of the kind shown 10 above in fig. 5.
    The current feedback circuit 610 comprises the current sensing resistor 304 as well as an error amplifier 611 configured to compare the potential on the right-hand side of the current sensing resistor 15 304 to a reference potential. A secondary side control circuit 612 is configured to produce the reference potential. The control circuit 612 is an internal control circuit of the driver and it can control various operations of the driver. The control circuit 612 can 20 be for example a microcontroller or a microprocessor or other kind of programmable circuit. The functions that are described in this text as pertinent to a control circuit can also be distributed among two or more microprocessors, microcontrollers, or other kinds of 25 circuits.
    If the error amplifier 611 finds the potential on the right-hand side of the current sensing resistor 304 to be higher than the reference potential, its output goes low. This lights up the photodiode in 30 the optoisolator 611, which gives a feedback signal to the primary side control circuit 613.
    Circuit 614 is a voltage regulator configured to produce a stable supply voltage for the optoisolator 611, the error amplifier 611, and the control cir35 cuit 612 .
    The driver of fig. 6 comprises a control input 615 for receiving control signals. Whether or not the control input 615 is bidirectional for also transmitting information to other devices is of no importance to the present invention. The control input 615 may be for example a DALI interface (Digital Ad5 dressable Lighting Interface) and it may comprise various receiving, transmitting, amplifying, filtering, and/or other interfacing circuitry. The control input 615 may also be a wireless interface.
    The internal control circuit 612 is coupled
    10to thecontrol input615and configured tousere- ceivedcontrol signalstocontroloperationsofthe driver .In particular,thecontrolcircuit 612iscon- figuredto switch, inresponse toa receivedcontrol signalindicating standbystate,the driverinto a15standbystate in whichno output current is tobeout- put through the output609. The control circuitmay use various ways to putthedriverinto standby state.
    20176079 prh 30 -11- 2017
    For example it can give a zero reference potential to the error amplifier 611, which causes the error ampli20 fier 611 output a low level signal for as long as it has some operating power left. Continuous burning of the photodiode in the optoisolator 611 then gives a feedback signal to the primary side controller 613 that the last-mentioned interprets as a command to en25 ter standby mode. The control circuit 612 can also use some other signaling method to convey a standby command to the primary side. Components and circuit configurations for conveying such standby commands are known on the technical field and they are not de30 scribed here in more detail.
    Fig. 7 illustrates schematically a luminaire according to an embodiment. The luminaire comprises a driver 701, which may be for example a driver of the kind described above with reference to any of figs. 4, 35 5, or 6. One or more semiconductor light sources 114 are coupled to the output 609 of the driver 701. The semiconductor light sources are place in a LED module
    20176079 prh 30 -11- 2017
    206, in which a heatsink is connected to the one or more semiconductor light sources through a thermally conductive connection. Although possibly not intended, there may also be a capacitive electric coupling be5 tween at least some of the semiconductor light sources 114 and the heatsink.
    In order to prevent the semiconductor light sources 114 from glowing there is a conductive coupling between a grounding pole 602 of the output 609 10 of the driver 701 and the heatsink. In fig. 7 the conductive coupling is made so that a conductor 702 goes from the grounding pole 602 to an electrically conductive body 703 of the luminaire, to which electrically conductive body also the heatsink is coupled for exam15 pie through metallic screws 704 that attach the LED module 206 to the electrically conductive body 703. The conductor 7 02 could also go from the grounding pole 602 more directly to the heatsink, for example so that the connector that now appears at the other end 20 of the conductor 702 would be placed under one of the screws 704.
    The driver 701 may comprise a casing that encloses at least a majority of the electric components of the driver and that is made of an electrically in25 sulating material. While such an electrically insulating cover involves some definitive advantages, it also acts as an electric insulator that does not offer as easy routes for grounding any stray currents than a metallic casing for example.
    An AC mains cable 202 is coupled to the luminaire so that a live wire 203 and a neutral wire 204 are coupled to an input 102 of the driver 701, and a protective earth wire 205 is coupled to the conductive body 703 of the luminaire. A control connector 207 is 35 provided for connecting the wires of a control bus to the luminaire.
    It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not 5 limited to the examples described above, instead they may vary within the scope of the claims. For example, it is not necessary to have the grounding pole as an integral pole of the same connector that also has the output poles to which the anode and cathode ends of 10 the LED module should be connected; it is possible that the driver has a separate connector for the grounding pole. In yet another embodiment the grounding pole is an electrically conductive track that leads to a screwhole, through which the driver is to 15 be attached to an electrically conductive body of a luminaire .
    权利要求:
    Claims (8)
    [1] 1. A driver for semiconductor light sources, comprising :
    5 - an input for receiving an input voltage,
    - an output for outputting an output current for said semiconductor light sources,
    - a transformer that divides the driver into a primary side and a secondary side, of which the primary side
    10 comprises a primary coil of said transformer and a first internal reference potential line, and of which the secondary side comprises a secondary coil of said transformer and a second internal reference potential line, and
    15 - a capacitor coupled between said first and second internal reference potential lines, characterized in that
    - said output comprises a grounding pole for making a connection to a functional earth outside said driver,
    [2] 2 0 and
    - the driver comprises an electric connection between said second internal reference potential line and said grounding pole.
    2. A driver according to claim 1, wherein
    25 said electric connection comprises a resistor, the resistance of which is at least 1000 ohms.
    [3] 3. A driver according to claim 1 or 2, wherein said electric connection comprises a capacitor.
    [4] 4. A driver according to claim 3, wherein
    30 said capacitor is coupled in parallel with a resistor in said electric connection.
    [5] 5. A driver according to any of the preceding claims, wherein:
    - the secondary side comprises a first current path
    35 between one of the poles in said output for coupling the semiconductor light sources and a current sensing resistor,
    20176079 prh 30 -11- 2017
    - the secondary side comprises a second current path between said current sensing resistor and one end of said secondary coil, and
    - said electric connection connects said first current 5 path to said grounding pole.
    [6] 6. A driver according to any of the preceding claims, comprising a casing that encloses at least a majority of the electric components of said driver and that is made of an electrically insulating material.
    10
    [7] 7. A driver according to any of the preceding claims, comprising:
    - a control input for receiving control signals, and
    - an internal control circuit coupled to said control input and configured to control operations of the
    15 driver;
    wherein said control circuit is configured to switch, in response to a received control signal indicating standby state, the driver into a standby state in which no output current is to be output through said 20 output.
    [8] 8. A luminaire, comprising:
    - a driver according to any of the preceding claims,
    - one or more semiconductor light sources coupled to said output,
    25 - a heatsink connected to said one or more semiconductor light sources through a thermally conductive connection, and
    - a conductive coupling between said grounding pole and said heatsink.
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    同族专利:
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    引用文献:
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    FI20176079A|FI128187B|2017-11-30|2017-11-30|A driver for semiconductor light sources, and a luminaire|FI20176079A| FI128187B|2017-11-30|2017-11-30|A driver for semiconductor light sources, and a luminaire|
    DE102018130072.7A| DE102018130072A1|2017-11-30|2018-11-28|METHOD AND ARRANGEMENT FOR AVOIDING UNWANTED GLIMMING OF LEDS|
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