FI128615B - Method and device for controlling the output current of a driver device for semiconductor light sources - Google Patents

Abstract

A driver device for light sources (201) comprises a power input (301), an output (302), and between said power input (301) and said output (302) a controllable current source (303, 403) configured to use said electric input power to generate output current. A control circuit (304, 404) is coupled to said controllable current source (303, 403) and configured to control the magnitude of the generated output current. A control input (307) is coupled to said control circuit (304, 404). Said control circuit (304, 404) is programmable to operate in at least a first control mode and a second control mode. In said first control mode said control circuit (304, 404) is configured to define a maximum magnitude of the generated output current in response to analog control information generated within said driver device using an external component (308) coupled to said control input (307). In said second control mode said control circuit (304, 404) is configured to control the magnitude of the generated output current in response to discretevalued control information received through said control input (307).

Description

METHOD AND DEVICE FOR CONTROLLING THE OUTPUT CURRENT OF A DRIVER DEVICE FOR SEMICONDUCTOR LIGHT SOURCES

FIELD OF THE INVENTION The invention is related to the technical field of driver devices for semiconductor light sources. In particular the invention is related to the task of setting the output current of such a driver device to the most suitable value in each situation.

BACKGROUND OF THE INVENTION Various devices and methods are known for setting the output current of driver devices for light sources. Fig. 1 illustrates a known driver device or electronic ballast for a fluorescent lamp 101. This kind of a driver device is known from the patent pub- lication DE 197 57 295 B4. The driver device comprises a power input 102 and an output 103, and between them the series coupling of a first (AC/DC) stage 104, a second (DC/AC) stage 105, and an output (resonance) stage 106. A processor circuit 107 controls the opera- tion of said stages. The driver device comprises a first control input 108 and a second control input 109, which are coupled to respective input connections 110 and 111 of the processor circuit 107. = The first control input 108 is an analog con- N trol input, to which a light sensor 112 can be con- 2 nected. An A/D converter 113 is needed to convert the ON 30 analog output signal of the sensor 112 into digital I form. The second control input 109 is a digital con- * trol input, to which either a digital control bus or a N switch-controlled mains voltage can be connected. De- o pending on which of them is in use, either a serial S 35 bus interface circuit 114 or a voltage-scaling shunt resistor 115 provide a connection to a rectifier 116that in turn constitutes the connection to the input connection 111 of the processor circuit 107. The dashed connections to the rectifier 116 illustrate the mutually alternative nature of these control methods.

Fig. 2 illustrates a known driver device for semiconductor light sources 201. The driver device comprises a power input 202 and an output 203. This particular driver device is of the so-called isolated type, comprising a primary stage 204 and a secondary stage 205 separated by a transformer 206. In this to- pology the controlling processor circuit 207 is locat- ed on the secondary side, so that any exchange of con- trol information between it and the primary stage 204 goes through optoisolator(s) 208. The driver device has two control inputs 209 and 210. The first control input 209 is for attaching an output-current-setting component 211, typically a passive component such as a resistor. The second control input 210 is for making contact to a digital lighting control bus, such as the DALI (Digital Addressable Lighting Interface) bus. A serial bus interface circuit 21? between the second control input 210 and the processing circuit 207 may provide additional flexibility, such as galvanic iso- lation and independence of signal polarity.

If only a constant output current is needed, the second control input 210 and the serial bus inter- face circuit 212 can be omitted. In some other driver 2 devices of the kind shown in fig. 2 the serial bus in- N terface circuit 212 may be tolerant enough so that a 2 30 switch-controlled mains voltage can be connected to N the second control input 210, much like the L and N =E connections to the second control input 109 in the de- * vice of fig. 1. N Despite the relatively large variety of ways o 35 offered for controlling the lights in driver devices S like those in figs. 1 and 2, more flexibility for the luminaire manufacturer might be welcome in some cases.

Safety regulations place strict requirements to insu- lation and power rating of connections and components whenever higher voltages are present, so it would be desirable to have ways of controlling the lights so that only low voltages would be involved.

SUMMARY An objective of the invention is to present a driver device for light sources, and a method for con- trolling the output current of a driver device for light sources, in which a simple and effective control of the output current can be achieved with only a small number of components. Another objective of the invention is that it conforms easily to electric safe- ty regulations. A further objective of the invention is to enable flexible control of the output current of a variety of driver device types. Yet another objec- tive of the invention is that it enables combining the controlling of output current with other ways of con- trolling the operation of the driver device.

These and other advantageous objectives of the invention are achieved by making the driver device comprise a common control input through which either analog or discrete-valued control signals can be cou- pled in according to need.

According to a first aspect there is provided © a driver device for light sources. The driver device D comprises a power input for receiving electric input 5 power, an output for outputting output current of con- W 30 trolled magnitude to said light sources, and between © said power input and said output a controllable cur- E rent source configured to use said electric input pow- N er to generate said output current. The driver device & comprises a control circuit coupled to said controlla- = 35 ble current source and configured to control the mag- N nitude of the generated output current, and a control input coupled to said control circuit. Said controlcircuit is programmable to operate in at least a first control mode and a second control mode. In said first control mode said control circuit is configured to de- fine a maximum magnitude of the generated output cur- rent in response to analog control information gener- ated within said driver device using an external com- ponent coupled to said control input. In said second control mode said control circuit is configured to control the magnitude of the generated output current in response to discrete-valued control information re- ceived through said control input.

According to an embodiment the control cir- cuit comprises a processor, and in said first control mode said control circuit is configured to define said maximum magnitude of the generated output current in response to an analog potential at an input connection of said processor. The control circuit may comprise an analog potential generation circuit, coupled to said input connection of the processor, for generating an analog potential as said analog control information. Said control input may provide a connection to said analog potential generation circuit for making said external component affect the generation of said ana- log potential in said analog potential generation cir- cuit. This involves the advantage that a simple cir- cuit solution can be used, and the principle can be applied to a wide variety of driver device implementa- = tions.

N According to an embodiment said analog poten- 2 30 tial generation circuit comprises a voltage divider S coupled to said input connection, and said control in- Ek put is a two-pole connection, each pole of which is * connected to different point of said voltage divider. N This involves the advantage that a robust and reliable o 35 circuit solution can be built using relatively low- S priced components.

According to an embodiment the control cir- cuit comprises a processor, and an input connection of said processor is coupled to said control input In said second control mode said control circuit may be 5 configured to interpret a first potential at said in- put connection as a first discrete value of said dis- crete-valued control information and a second, differ- ent potential at said input connection as a second discrete value of said discrete-valued control infor- mation.

This involves the advantage that a discrete- values control signal can be brought to the processor with little or no additional insulation or other secu- rity measures.

According to an embodiment in said second control mode said control circuit is configured to measure durations of periods during which the poten- tial of said input connection remains at one of said first or second potentials.

This involves the ad- vantage that despite the relatively small number of discrete values of the controlling signal a relatively versatile controlling protocol can be employed.

According to an embodiment in said second control mode the control circuit is configured to change the magnitude of said generated output current as a response to periods during which the potential of said input connection is at the second potential, and maintain the magnitude of said generated output cur- = rent unchanged as a response to periods during which N the potential of said input connection is at the first 2 30 potential.

This involves the advantage that users can ON be offered a control mode that many of them are famil- =E iar with already. * According to an embodiment in said second N control mode the control circuit is configured to o 35 switch the generation of said output current on or off S as a response to periods shorter than a predetermined time limit during which the potential of said inputconnection is at the second potential, and change the magnitude of said output current as a response to pe- riods longer than said predetermined time limit during which the potential of said input connection is at the second potential.

This involves the advantage that us- ers can be offered a control mode that many of them are familiar with already.

According to an embodiment in said second control mode the control circuit is configured to change the magnitude of said output current as a re- sponse to periods longer than said predetermined time limit during which the potential of said input connec- tion is at the second potential, the extent of such change being proportional to the length of the period for which the potential of said input connection re- mains at the second potential.

This involves the ad- vantage that users can be offered a control mode that many of them are familiar with already.

According to an embodiment the driver device comprises a primary stage coupled to said power input and a secondary stage coupled to said output, and a transformer between said primary and secondary stages for transferring electric energy from said primary stage to said secondary stage, so that said control circuit and said control input are on the same side of said transformer as the secondary stage.

This involves the advantage that the driver device can be made to = conform to for example SELV regulations.

N According to an embodiment said control input 2 30 is a first control input, and the driver device com- S prises a second control input.

The control circuit may Ek be coupled to said second control input and configured * to receive digital control commands through said sec- N ond control input.

This involves the advantage that o 35 even more versatile control of the driver device is S possible.

According to an embodiment the control cir- cuit is configured to receive programming commands through said second control input, and to respond to predefined programming commands by assuming a selected one of said first and second control modes.

This in- volves the advantage that a driver device can be flex- ibly configured for various applications.

According to an embodiment the driver device is a driver device for semiconductor light sources.

This involves the advantage that the technology in question can be applied to the most popular and prom- ising lighting technology known at the time of writing this text.

According to a second aspect there is provid- ed a method for controlling an output current of a driver device for light sources.

The method comprises responding to the presence of an external component at a control input of the driver device by defining a maximum of said output current as a value determined by an electric characteristic of said external compo- nent, and responding to discrete-valued control infor- mation received through said control input by control- ling the magnitude of the generated output current in accordance with the lengths of periods of said re- ceived discrete-valued control information.

According to an embodiment the method com- prises switching the generation of said output current = on or off as a response to periods shorter than a pre- N determined time limit during which a conductivity of a 2 30 first magnitude is observed at said control input, and S changing the magnitude of said output current as a re- Ek sponse to periods longer than said predetermined time * limit during which a conductivity of said first magni- N tude is observed at said control input.

This involves o 35 the advantage that users can be offered a control mode S that many of them are familiar with already.

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, illus- trate embodiments of the invention and together with the description help to explain the principles of the invention. In the drawings: Figure 1 illustrates a known electronic bal- last for fluorescent lamps, Figure 2 illustrates a known driver device for semiconductor light sources, Figure 3 illustrates a driver device for light sources, Figure 4 illustrates a driver device for light sources, Figure 5 illustrates an exemplary interface circuit at a control input, Figure 6 illustrates the operation of a driv- er device in a first control mode, Figure 7 illustrates the operation of a driv- er device in another form of a first control mode, and Figure 8 illustrates the operation of a driv- er device in a second control mode.

DETAILED DESCRIPTION © Fig. 3 illustrates schematically a driver de- < vice for light sources 201. In this example the light O sources 201 are semiconductor light sources, such as N 30 leds, but the invention is in no way limited to driver 7 devices for semiconductor light sources. The same E principle can be applied in all driver devices for any N kind of light sources in which the magnitude of the LO output current needs to be controlled. > 35 The driver device comprises a power input 301 for receiving electric input power. In this case thepower input 301 is shown as a simple two-pole input, one pole of which is to be coupled to the live line and the other to the neutral line of a mains voltage.

Other kinds of power inputs are possible; as the most straightforward example, a power input like that in fig. 3 may comprise a third pole that is to be coupled to protective earth.

The power input 301 could also be configured to receive DC power.

The driver device comprises an output 302 for outputting output current of controlled magnitude to the light sources 201. A two-pole output 302 is suita- ble in many cases; for example for leds one pole of the output 302 is the anode side output and the other poles is the cathode side output.

Other kinds of out- puts may be used for other kinds of light sources.

Between the power input 301 and the output 302 the driver device comprises a controllable current source 303 that is configured to use the electric in- put power received through the power input 301 to gen- erate the output current of controlled magnitude at the output 302. The exact implementation of the con- trollable current source 303 is not important to the present description.

As an example, the controllable current source 303 can be a single-stage, two-stage, or multi-stage power converter.

In addition to the output 302 shown in fig. 3 it may have other outputs for other sets of light sources, for example so that x the controllable current source 303 comprises a common N first stage that supplies electric energy to two or 2 30 more second stages that are coupled in parallel.

The S capability of controlling the magnitude of the output Ek current may apply to only one or a few of such paral- * lel second stages or to all of them.

N The driver device comprises a control circuit o 35 304 that is coupled to the controllable current source S 303 and configured to control the magnitude of the output current that it generates.

Numerous possibili-

ties exist for implementing such control.

As an exam- ple, the controllable current source 303 may comprise a switched-mode power supply, such as a buck converter for example, as its output stage.

The buck converter may comprise a power switch and its driver circuit, and the driver circuit may have an internal] control input, the potential of which (with reference to an internal reference potential of the driver device) de- fines the effective magnitude of the output current.

The control circuit 304 may couple a potential of se- lected magnitude to the internal control input of the driver circuit in the buck converter.

As another example, assuming again that the controllable current source 303 comprises a switched- mode power supply as its output stage, the control circuit 304 may exercise PWM (pulse width modulation) control of the switched-mode power supply.

A control line may go from the control circuit 304 to an inter- nal enabling input in a driver circuit of the switched-mode power supply.

The control circuit 304 may repeatedly switch the potential of the control line between high and low values, thus repeatedly ena- bling and disabling the switched-mode power supply, at a duty cycle that is proportional to the desired mag- nitude of the output current.

As yet another example, the output stage of the controllable current source 303 may comprise a = current measurement and feedback loop, in which the N momentary voltage across a current-sensing resistor is 2 30 compared to a reference voltage.

The control circuit S 304 may provide the controllable current source 303 =E with said reference voltage, or with an electric po- * tential level that affects the generation of the ref- N erence voltage. o 35 The control circuit 304 may practice two or S more ways of controlling the magnitude of the generat- ed output current in the same circuit.

As an example,

the control circuit 304 may provide a reference volt- age to a current measurement and feedback loop in or- der to set the maximum allowable output current, and additionally provide the driver circuit of a buck con- verter with a continuous sequence of enabling control pulses of the PWM type.

All these and other possible ways of making the control circuit 304 control the magnitude of the generated output current are schematically represented in fig. 3 with the control signal arrow 305. Measure- ments in the controllable current source 303 may re- sult in measurement signals being coupled to the con- trol circuit 304; these are schematically represented in fig. 3 with the measurement signal arrow 306. The driver device comprises a control input 307 that is coupled to the control circuit 304. The control input 307 may take the physical form of a con- nector that is accessible from outside the driver de- vice.

In the example of fig. 3 the control input 307 has two poles, but it may have only one pole or more than two poles.

A control input with two poles in- volves the advantage that it is easy to match with many kinds of external components that can be used for the purpose of affecting the output current, as will be described in more detail later.

The control circuit 304 is programmable to operate in at least a first control mode and a second x control mode.

These control modes are preferably mutu- N ally exclusive so that a control circuit that operates 2 30 in the first control mode cannot simultaneously oper- N ate in the second control mode, and vice versa.

In =E this text a circuit being programmable means in gen- * eral that its operation can be affected by storing a N software instruction in a memory, or changing a previ- o 35 ously stored software instruction in a memory, or us- S ing software tools to effect the setting or selectionof a parameter value or operating mode for use by thecontrol circuit. In some sources the act of setting or selecting a parameter value or operating mode for use by the control circuit is called configuring, but in this text such configuring is covered by the term pro- gramming.

Of said first and second control modes, in the first control mode the control circuit 304 is con- figured to define a maximum magnitude of the generated output current in response to analog control infor- mation that is generated within the driver device us- ing an external component coupled to the control input

307. As an example of such an external component a re- sistor 308 is shown in fig. 3. In order to keep manu- facturing costs low it is advantageous if a relatively cheap passive component, such as a resistor 308, can be used as the external component.

Multiple ways exist for generating the analog control information within the driver device using an external component, for example the resistor 308, cou- pled to the control input 307. A common feature of them is that some electric characteristic (like re- sistance, for example) of the external component is taken as a part of some piece of circuitry that is otherwise internal to the driver device. During opera- tion of the driver device said piece of circuitry then assumes some state, in which the analog control infor- mation appears as a value of a quantity at a particu- 2 lar point, from which there is a direct or indirect N coupling to a circuit and/or process that defines a 2 30 maximum value of the output current of the driver de- N vice. Ek The range of acceptable values of the respec- * tive electric characteristic of the external component N depends on the way in which the analog control infor- o 35 mation is generated in the driver device. If a resis- S tor is used as the external component, it is possible to devise the generation of the analog control infor-

mation so that a very wide range of resistance values are acceptable.

As limiting cases, infinite and zero resistances can be considered.

An infinite resistance coupled to the control input 307 means leaving the poles of the control input 307 open, while zero re- sistance means using a piece of a good conductor such as copper wire to short-circuit the two poles of thecontrol input 307. In the second control mode the control cir- cuit 304 is configured to control the magnitude of the generated output current in response to discrete- valued control information received through the con- trol input 307. The fact that such control information is discrete-valued means that it consists of strings or sequences of at least two distinct values, as a difference to continuous-valued information that may assume any value within an essentially continuous range.

A typical case of a discrete-valued control in- formation is the use of exactly two distinct values, which may be referred to as the “high” and “low” val- ues, or the "17 and “0” values, or the “yes” and “no” values, or the “true” and “false” values, or the “on”

and “off” values.

The fact that such control information is re- ceived through the control input 307 means that the source of the information, i.e. the device that de- fines which of the distinct values is valid at any = particular moment of time, must be located elsewhere N than within the driver device.

Electric connections 2 30 (which may involve galvanic, capacitive, inductive, ON and/or other connections through which information can Ek be transferred in electric form) connect such an ex- * ternal device to the control input 307. As an example, N fig. 3 illustrates an external switch 309, the two o 35 poles of which are galvanically connected to the re- S spective two poles of the control input 307. Theswitch 309 may be open or closed, corresponding to two distinct values. Fig. 4 illustrates another driver device for light sources 201. The power input 301, the output 302, and the control input 307 can be similar to the correspondingly numbered parts in fig. 3. Also in fig. 4 a resistor 308 and a switch 309 are shown as exam- ples of an external component and an external source of discrete-valued control information respectively that can be coupled to the control input 307. The driver device of fig. 4 comprises a pri- mary stage 401 that is coupled to the power input 301, and a secondary stage 403 that is coupled to the out- put 302. A transformer 402 between the primary 401 and secondary 403 stages is used to transfer electric en- ergy from the primary stage 401 to the secondary stage

403. The transformer 402 provides galvanic isolation between the primary 401 and secondary 403 stages. The primary stage 401 may comprise for example rectifying, filtering, and/or power factor correcting functions. The secondary stage 403 comprises the controllable current source that is configured to use electric in- put power (received through the power input 301, the primary stage 401, and the transformer 402) to gener- ate the output current of controlled magnitude to the light sources 201. In the topology of fig. 4 the control circuit x 404 and the control input 307 are on the secondary N side, i.e. on the same side of the transformer 402 as 2 30 the secondary stage 403. Thus the exchange of control S information and measurement results between the con- Ek trol circuit 404 and the secondary stage 403 can take * place through galvanic connections. In order to main- N tain the galvanic isolation between the primary and o 35 secondary sides of the driver device, optoisolators S 405 are provided on the path of control informationand measurement results, if any, between the control circuit 404 and the primary stage 401.

Already in the embodiment of fig. 3 it may be noted that the control input 307 may be built so that it only involves relatively low voltages, in the order of some volts at the most, as well as extremely small currents. This means that any electric connections to and from the control input 307 can be made with rela- tively simple hardware, for example with cables that only need thin insulation layers, and/or with a switch 309 that does not need to be rated for high voltages or currents, and/or with structures that only need relatively short safety distances to other parts. This is a significant advantage in comparison to such prior art driver devices in which switch-controlled inputs could be provided from the mains voltage.

If the driver device is an isolated one, like in fig. 4, the connections to the secondary side - in- cluding the control input 307 - can be made to comply with the SELV (Safety Extra Low Voltage) regulations. This emphasizes further the advantages mentioned above, because it is then sure that only low and safe voltages are involved even with reference to the ground potential. Another feature seen in fig. 4 is the appear- ance of a second control input 406. The control cir- cuit 404 is coupled - through an interface circuit 407 2 - to the second control input 406 and configured to N receive digital control commands through the second 2 30 control input 406. The second control input 406 may be S for example a control bus connection through which the =E driver device may be connected to a digital lighting > control bus, such as a DALI bus. The second control N input 406 may be also a wireless input, so that the o 35 second control input 406 and the interface circuit 407 S together constitute a wireless communications inter- face. The wireless communications standard used bysuch a wireless communications interface may be for example an NFC (Near Field Communications) standard, a Bluetooth standard, a ZigBee standard or some other standard that is applicable for wireless communica- tions over relatively short distances.

The second control input 406 may be used to give lighting control commands to the driver device. For example, if a maximum magnitude of the output cur- rent has been defined on the basis of a resistor cou- pled to the first control input 307, an output current at that maximum magnitude can represent full bright- ness of the light sources 201. A lighting control com- mand received through the second control input 406 may order the driver device to temporarily produce output current at a reduced level, like some percentage of the maximum value. This would make the light sources 201 to dim down, i.e. to emit a smaller amount of light. Many kinds of lighting control commands are known in this technical field, and they do not need to be considered here in more detail. The second control input 406 may also be used for example for programming the control circuit 404. The control circuit 404 may be configured to receive programming commands through the second control input

406. In particular, the control circuit 404 may be configured to respond to some particular, predefined programming commands by assuming a selected one of the x first and second control modes explained earlier in N this text. Such programming to operate in the selected 2 30 control mode can be part of the manufacturing process N of a luminaire manufacturer, when driver devices ac- =E quired from a subcontractor are tailored for use in * particular kinds of luminaires. Programming through N the second control input 406 can be accomplished also o 35 as a part of the manufacturing and/or testing process S of driver devices.

The driver device may be meant to always op- erate in the second control mode, so that no external component should ever be connected to the first con- trol input 307 for defining the maximum output cur- rent. In such a case the maximum output current may be a fixed feature of the driver device, defined for ex- ample by fixed hardware in an output current measure- ment and feedback loop. Another possibility is that programming, through the second control input 406 for example, is used to define the maximum magnitude of the output current.

An alternative way of programming the control circuit 304 or 404 to operate in the first or second control mode may be so-called auto-programming. By ex- amining the electric characteristics of whatever is coupled to the (first) control input 307 the control circuit 304 or 404 may arrive at a conclusion concern- ing whether an external component or an external source of discrete-valued control information is pre- sent. The control circuit 304 or 404 may respond to such a conclusion by selecting to operate in the cor- responding control mode.

Yet another possibility is that the control circuit 304 or 404 has been programmed to first oper- ate in the first control mode and the change to oper- ate in the second control mode. During the initial op- eration in the first control mode the control circuit = 304 or 404 could use an external component temporarily N coupled to the first control input 307 to define a 2 30 maximum magnitude of the output current to be generat- S ed. The control circuit 304 or 404 could store and =E lock this defined maximum value, and then switch to * operate in the second control mode, in which it re- N sponds to discrete-valued control information received o 35 through the first control input 307 by dynamically S controlling the momentary magnitude of the generated output current.

Making a driver device according to fig. 4 respond to both discrete-valued control information received through the first control input 307 and to digital control commands received through the second control input 407 is possible, but it requires that the program to be executed by the control circuit 404 is devised carefully, for example to ensure a deter- ministic way of operating in cases where competing control commands arrive through both routes simultane- ously.

Features that are explained above with refer- ence to figs. 3 and 4 can be mixed together in various ways. For example a driver device without galvanic isolation, like in fig. 3, may have a second control input like the one in fig. 4.

Fig. 5 illustrates an example of some further details of an exemplary control circuit. According to fig. 5 the control circuit comprises a processor 501 that may have a large number of input and output con- nections. For reasons of graphical clarity only one input connection 502 and a ground connection of the processor 501 are shown in fig. 5. In the first con- trol mode the control circuit, a part of which is shown in fig. 5, is configured to define a maximum magnitude of the generated output current in response to an analog potential at the input connection 502 of the processor 501. Potentials in a circuit like this = are measured with reference to the local ground poten- N tial, so alternatively it can be said that the control 2 30 circuit is configured to define the maximum magnitude N of the generated output current in response to an ana- =E log voltage between the input connection 502 of the * processor 501 and local ground. N In the example of fig. 5 the control circuit o 35 comprises an analog potential generation circuit 503 S that is coupled to the input connection 502 of the processor. The task of the analog potential generationcircuit 503 is to generate an analog potential that acts as the analog control information that was ex- plained above to play a role in the first control mode. The control input 307 provides a connection to the analog potential generation circuit 503 for making the external component (when one is coupled to the control input 307) affect the generation of the analog potential in the analog potential generation circuit

503.

In particular, in fig. 5 the analog potential generation circuit 503 comprises a voltage divider, consisting of resistors 504 and 505, the middle point of which is coupled to the input connection 502 of the processor 501. The connection is made through an RC filter that consists of resistor 506 and capacitor

507. The control input 307 is a two-pole connection. Fach pole of the control input 307 is connected to a different point of the voltage divider.

If nothing is coupled to the control input 307 (in other words: if "an external resistor of infi- nite resistance is coupled” to the control input 307), the potential of the input connection 502 is that pro- portion of the supply voltage +V that can be calculat- ed from the resistances of the resistors 504 and 505.

If the poles of the control input 307 are shorted, the potential of the input connection 502 is the local ground potential, i.e. 0 V. Any external resistor, = with its resistance between these two extremes, that N is coupled across the poles of the control input 307 2 30 will make the potential of the input connection 502 N assume a correspondingly scaled value between said two Ek extreme values.

* In order to measure the potential at the in- N put connection 502 in the first control mode the pro- o 35 cessor 501 should be equipped with an internal A/D S converter, and programmed to use it accordingly.

In the second control mode the processor 501 (or in general: the control circuit of which the pro- cessor 501 is part) is configured to interpret a first potential at the input connection 502 as a first dis- tinct value and a second, different potential as a second distinct value of the discrete-valued control information. These first and second potentials are the same as the two extreme values explained above. Having an open switch coupled across the poles of the control input 307 is the same as not connecting any resistor thereto, and closing such a switch is the same as shorting the poles of the control input 307. Also in this case there may be an internal A/D converter in the processor 501, but it only needs to be made to ex- press the detected potential value with a single bit. In other words the processor 501 is programmed to con- sider the input connection 502 as a discrete-valued (here: two-valued) input in the second control mode. Basically the invention does not restrict the nature or content of discrete-valued control infor- mation that the driver device is made to receive through the control input 307 in the second control mode. One particularly advantageous form of discrete- valued control information may be considered. Accord- ing to this example the control circuit is configured to measure durations of periods during which the po- tential of the input connection 502 remains at one of = the first or second potentials mentioned above.

N In the following example we may assume that a 2 30 switch 309 has been coupled across the control input S 307 for use as the source of discrete-valued control =E information. We may further assume that the switch is * normally open, resulting in a first potential at the N input connection 502, but can be temporarily closed by o 35 the user, resulting in a second potential at the input S connection 502. In the second control mode the control circuit is then configured to change the magnitude ofthe generated output current as a response to periods during which the potential of the input connection 502 is at the second potential. As a response to periods during which the potential of the input connection 502 is at the first potential the control circuit is con- figured to maintain the magnitude of the currently generated output current unchanged.

One advantageous application of such a prin- ciple can be described in more detail as follows. The control circuit may be configured to switch the gener- ation of the output current on or off as a response to periods shorter than a predetermined time limit during which the potential of said input connection 502 is at the second potential. In other words, closing the switch for short moments, like pressing a spring- loaded button switch and then immediately releasing it, makes the lights go on or off depending on whether they were off or on. Additionally the control circuit may be configured to change the magnitude of the out- put current as a response to periods longer than said predetermined time limit during which the potential of the input connection 502 is at the second potential. The extent of such change may be proportional to the length of the period for which the potential of the input connection 502 remains at the second potential. Figs. 6 to 8 illustrate schematically some methods that apply the above-explained principle. The = method comprises responding to the presence of an ex- N ternal component at the control input of the driver 2 30 device by defining a maximum of the output current as N a value determined by an electric characteristic of =E said external component ("first control mode”). Addi- * tionally the method comprises responding to discrete- N valued control information received through the con- o 35 trol input by controlling the magnitude of the gener- S ated output current in accordance with the lengths ofperiods of the received discrete-valued control infor- mation (“second control mode”). Fig. 6 illustrates an example of operation in the first control mode. The method circulates in the loop consisting of steps 601, 602, and 603. The poten- tial of the appropriate input connection of the pro- cessor is read at step 601. If this is the only thing that should affect the magnitude of the output cur- rent, the appropriate maximum value of the output cur- rent (or the value of the control signal that will be used to set the appropriate maximum value of the out- put current) is calculated at step 602, and taken into use as the constant (and maximum) output current value at step 603. If there are other factors that affect the desired magnitude of the output current, these can be taken into account by looping through step 604, in which such other factors (like a dimming command re- ceived through a second control input) can be taken into account.

Fig. 7 illustrates another example of opera- tion in the first control mode. Here the method is ex- ecuted only once, for example following a switch-on of the driver device. The potential of the appropriate input connection of the processor is read at step 701.

The maximum value of the output current (or the value of the control signal that will be used to set the maximum value of the output current) is calculated at x step 702, and stored in a memory at step 603. After N step 703 the operation of the method may continue for 2 30 example so that the momentary value of the output cur- S rent is always calculated in accordance with a subse- =E quently received dimming command. > Fig. 8 illustrates an example of the opera- N tion in the second control mode. Looping through steps o 35 801, 802, 803, and 804 involve switching the genera- S tion of the output current on or off as a response to periods shorter than a predetermined time limit duringwhich a conductivity of a first magnitude is observed at the control input.

The processor reads the poten- tial of its input connection at step 801 and checks at step 802 whether it has changed to the second value since last time.

If yes, the processor checks at step 803 whether the potential changes back to the first value before the expiry of the predetermined time lim- it.

If yes, lights go off if they were on, or on if they were off, at step 804 and the method returns to step 801. If the potential] at the input connection of the processor does not change immediately back at step 803, this means that there is a period longer than said predetermined time limit during which a conduc- tivity of the first magnitude is observed at the con- trol input.

In other words, the user keeps the switch closed, wanting the momentary magnitude of the output current to be changed.

A check is made at step 805 whether the change in output current value has reached an endpoint (i.e. minimum or maximum output current). If no, a change is initiated in the output current at step 806, causing the lights to dim up or down depend- ing on the current dimming direction.

If the potential of the input connection of the processor still does not change back at step 807, steps 805 and 806 are re- peated.

If the endpoint was reached at step 805, or x if the potential of the input connection of the pro- N cessor changes back to the first value at step 807, 2 30 the dimming direction is changed at step 808, after S which the method returns to step 801. =E It is obvious to a person skilled in the art * that with the advancement of technology, the basic N idea of the invention may be implemented in various o 35 ways.

The invention and its embodiments are thus not S limited to the examples described above, instead they may vary within the scope of the claims.

Claims (14)

1. A driver device for light sources (201), comprising: - a power input (301) for receiving electric input power, - an output (302) for outputting output current of controlled magnitude to said light sources (201), - between said power input (301) and said output (302) a controllable current source (303, 403) configured to use said electric input power to generate said output current, - a control circuit (304, 404) coupled to said con- trollable current source (303, 403) and configured to control the magnitude of the generated output current, - a control input (307) coupled to said control cir- cuit (304, 404), characterized in that said control circuit (304, 404) is programmable to operate in at least a first control mode and a second control mode, of which: - in said first control mode said control circuit (304, 404) is configured to define a maximum magnitude of the generated output current in response to analog control information generated within said driver de- vice using an external component (308) coupled to said control input (307) and - in said second control mode said control circuit (304, 404) is configured to control the magnitude of = the generated output current in response to discrete- N valued control information received through said con- 2 30 trol input (307).

S r

2. A driver device according to claim 1, i characterized in that: N - the control circuit (304, 404) comprises a processor LO (501), > 35 - in said first control mode said control circuit (304, 404) is configured to define said maximum magni-

tude of the generated output current in response to an analog potential at an input connection (502) of said processor (501), - the control circuit (304, 404) comprises an analog potential generation circuit (503), coupled to said input connection (502) of the processor (501), for generating an analog potential as said analog control information, and - said control input (307) provides a connection to said analog potential generation circuit (503) for making said external component (308) affect the gener- ation of said analog potential in said analog poten- tial generation circuit (503).

3. A driver device according to claim 2, characterized in that said analog potential generation circuit (503) comprises a voltage divider (504, 505) coupled (506, 507) to said input connection (502), and said control input (307) is a two-pole connection, each pole of which is connected to different point of said voltage divider (504, 505).

4. A driver device according to any of the preceding claims, characterized in that: - the control circuit (304, 404) comprises a processor (501), - an input connection (502) of said processor (501) is © coupled to said control input (307), and > - in said second control mode said control circuit Sd (304, 404) is configured to interpret a first poten- W tial at said input connection (502) as a first dis- © 30 crete value of said discrete-valued control infor- E mation and a second, different potential at said input N connection (502) as a second discrete value of said & discrete-valued control information. 00 2

5. A driver device according to claim 4, characterized in that in said second control mode saidcontrol circuit (304, 404) is configured to measure durations of periods during which the potential of sald input connection (502) remains at one of said first or second potentials.

6. A driver device according to claim 5, characterized in that in said second control mode the control circuit (304, 404) is configured to change the magnitude of said generated output current as a re- sponse to periods during which the potential of said input connection (502) is at the second potential, and maintain the magnitude of said generated output cur- rent unchanged as a response to periods during which the potential of said input connection (502) is at the first potential.

7. A driver device according to claim 6, characterized in that in said second control mode the control circuit (304, 404) is configured to - switch the generation of said output current on or off as a response to periods shorter than a predeter- mined time limit during which the potential of said input connection (502) is at the second potential, and - change the magnitude of said output current as a re- sponse to periods longer than said predetermined time limit during which the potential of said input connec- tion (502) is at the second potential.

= 8. A driver device according to claim 7, N characterized in that in said second control mode the 2 control circuit (304, 404) is configured to change the ON magnitude of said output current as a response to pe- = 30 riods longer than said predetermined time limit during a which the potential of said input connection (502) is S at the second potential, the extent of such change be- o ing proportional to the length of the period for which Q the potential of said input connection (502) remains at the second potential.

9. A driver device according to any of the preceding claims, characterized in that: - the driver device comprises a primary stage (401) coupled to said power input (301) and a secondary stage (403) coupled to said output (302), - the driver device comprises a transformer (402) be- tween said primary (401) and secondary (403) stages for transferring electric energy from said primary stage (401) to said secondary stage (403), and - said control circuit (404) and said control input (307) are on the same side of said transformer (402) as the secondary stage (403).

10. A driver device according to any of the preceding claims, characterized in that: - said control input (307) is a first control input, - the driver device comprises a second control input (406), and - the control circuit (404) is coupled (407) to said second control input (406) and configured to receive digital control commands through said second control input (406).

11. A driver device according to claim 10, characterized in that the control circuit (404) is configured to receive programming commands through said second control input (406), and to respond to © predefined programming commands by assuming a selected > one of said first and second control modes. 2

12. A driver device according to any of the ON preceding claims, characterized in that it is a driver z 30 device for semiconductor light sources. a N

13. A method for controlling an output cur- LO rent of a driver device for light sources (201), char- > acterized in that the method comprises: - responding to the presence of an external component

(308) at a control input (307) of the driver device by defining (601, 602, 603) a maximum of said output cur- rent as a value determined by an electric characteris- tic of said external component (308), and - responding to discrete-valued control information received through said control input (307) by control- ling the magnitude (804, 806) of the generated output current in accordance with the lengths of periods of said received discrete-valued control information.

14. A method according to claim 13, charac- terized in that the method comprises: - switching (804) the generation of said output cur- rent on or off as a response to periods shorter than a predetermined time limit during which a conductivity of a first magnitude is observed at said control in- put, and - changing (806) the magnitude of said output current as a response to periods longer than said predeter- mined time limit during which a conductivity of said first magnitude is observed at said control input. 00

O

N

O

N

O

I jami a

N

N 00

LO 00

O

N