FI20176078A1

FI20176078A1 - Setting the output current of a led driver

Info

Publication number: FI20176078A1
Application number: FI20176078A
Authority: FI
Inventors: Hannu Vihinen
Original assignee: Helvar Oy Ab
Priority date: 2017-11-30
Filing date: 2017-11-30
Publication date: 2019-05-31
Also published as: DE102018220341B4; FI127981B; DE102018220341A1

Abstract

A driver (301) for semiconductor light sources (104) comprises a controllable current source (701) for producing output current for semiconductor light sources (104), a control circuit (702, 704, 707), and an output connector (302) that comprises at least four poles. A first pole (LED+) is a first output current pole for providing output current to the semiconductor light sources (104). At least two current poles (LED-, Iset+, Iset-), other than said first pole (LED+), are configured for mutually alternative use as a second output current pole for providing the output current to the semiconductor light sources (104). At least two control poles (LED-, Iset+, Iset-), other than said first pole (LED+), are each connected to different points in said control circuit (702, 704, 707), for selectably changing operation of the control circuit by coupling a selectable control component (203, Rset) between the control poles.

Description

SETTING THE OUTPUT CURRENT OF A LED DRIVER

20176078 prh 30 -11- 2017

FIELD OF THE INVENTION

The invention is related to the field of LED drivers. In particular the invention is related to ways in which the output current of a LED driver can be set with simple external measures.

BACKGROUND OF THE INVENTION

Semiconductor light-emitting devices that are used for lighting, signaling, background illumination, and similar purposes, are typically fed with current coming from an operating device, commonly called a 15 driver for short. Similarly the short expression LED is typically used to cover all kinds of semiconductor light-emitting devices.

The LED driver can be made to produce a constant output current for steady-state lighting or con20 trollable output current for dimmable lighting. In constant current drivers it is advantageous if the luminaire manufacturer or other user of the LED driver can set the magnitude of the output current to some desired value. In controllable current drivers the user may want 25 to select the maximum output current, or current range in which the driver may control the current during operation .

Fig. 1 illustrates schematically a known constant current LED driver 101 that can be connected to 30 AC mains. It has an input connector 102 with three poles: one for the phase line L and another for the neutral line N of the AC mains, and one for the protective earth PE. The driver has an output connector 103 with three poles. The anode end of the LED chain 104 is coupled to 35 the topmost pole, while the cathode end can be coupled to either of the two other poles. Each of these goes to

20176078 prh 30 -11- 2017 a different point in an internal current-sensing resistor chain 105 that forms a part of the current feedback circuit of the LED driver 101. The gain of the current feedback circuit - and consequently the magnitude of the 5 constant output current Iload - depends on the pole to which the cathode end is connected.

There can be more than two possible connection points for the cathode end, respectively coupled to more than two different points in the resistor chain. How10 ever, the selection of possible output current values remains very limited, because it is not feasible to equip the LED driver with an output connector with a large number of poles.

Fig. 2 illustrates another known solution. The 15 driver 201 of fig. 2 has an output connector 202 with four poles: two for the anode and cathode ends of the LED chain 104, and two so-called Iset poles. The user may set the magnitude of the output current Iload by connecting an external resistor 203 of selected magni20 tude across the Iset poles. Once connected, the external resistor 203 becomes part of a current feedback circuit 204 of the LED driver 201. The allowable resistance range of the external resistor 203 depends on the manufacturer and design of the LED driver 201. For example, 25 the LEDset specification created by Osram GmbH assumes the external resistor 203 to be part of a LED module and range from about 1000 ohms to about 50,000 ohms.

A conventional current setting arrangement like that in fig. 1 or fig. 2 can be used also to set 30 the maximum output current of a controllable LED driver.

Although flexible and generally accepted, the conventional current setting arrangement of fig. 2 has its drawbacks. The luminaire manufacturer may want to streamline the manufacturing process as much as possi35 ble, so that even the relatively simple steps of selecting an external resistor and connecting it to the Iset poles is considered cumbersome. Stocking suitable

20176078 prh 30 -11- 2017 external resistors and having them always available at right locations in appropriate quantities is an additional requirement for the luminaire manufacturing process. Some luminaire manufacturers may prefer LED driv5 ers that can be simply set to one of only few available values, while others may want much more flexibility, and yet for both of them - and for the driver manufacturer - it would be easiest if only a relatively small number of different driver versions would need to be manufac10 tured, distributed, and stocked.

Alternative solutions have been developed, including the possibility to wirelessly configure a LED driver for a particular output current. However, it introduces additional cost because the LED driver must 15 then be equipped with the appropriate means for wireless communications, which will in most cases be needed only very briefly during the luminaire manufacturing stage.

SUMMARY

It is an objective of the present invention to present a LED driver, the output current of which can be set in a simple way. Another objective of the invention is to provide a LED driver, the output current of 25 which can be set in a flexible way. A further objective of the invention is to provide a LED driver that only has a relatively low number of components, and a relatively simple internal structure, despite its flexibility concerning output current setting. Yet another ob30 jective of the invention is to provide a method for setting the output current of a LED driver in a simple, straightforward, and flexible way.

These and further advantageous objectives of the invention are achieved by equipping the driver with 35 an output connector that has at least four poles. One of them is a first output current pole, while the remaining poles comprise at least two current poles, any of which may be the other output current pole, and at least two control poles for optionally receiving a selectable control component. A pole of said remaining poles may act either as a current pole or as a control pole depending on how the couplings are made.

A driver of semiconductor light sources according to an embodiment is characterized by the features recited in the independent claim directed to a driver .

A method according to an embodiment is characterized by the features recited in the independent claim directed to a method.

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 the de20176078 prh 30 -11- 2017 scription help to explain the principles of the invention. In the drawings:

	Figure Figure Figure	1 2 3	illustrates illustrates illustrates	a known driver, another known driver,
a	driver	according	to	an
25	embodiment,
	Figure	4	illustrates	a	driver	according	to	an
	embodiment,
	Figure	5	illustrates	a	driver	according	to	an
	embodiment,
30	Figure	6	illustrates	a	driver	according	to	an
	embodiment,
	Figure	7	illustrates	a	driver	according	to	an
	embodiment,
	Figure	8	illustrates	a	driver	according	to	an
35	embodiment,
	Figure	9	illustrates	a	driver	according	to	an

embodiment,

Figure	10	illustrates	a	driver	according	to	an
embodiment, Figure	11	illustrates	a	driver	according	to	an
embodiment, Figure	12	illustrates	a	driver	according	to	an
embodiment, Figure	13	illustrates	a	driver	according	to	an
embodiment, Figure	14	illustrates	a	driver	according	to	an
embodiment, Figure	15	illustrates	a	driver	according	to	an
embodiment, and Figure	16	illustrates	a	driver	according	to	an

embodiment.

20176078 prh 30 -11- 2017

DETAILED DESCRIPTION

Figs. 1 and 2 have been described in the description of prior art, so the following description of 20 embodiments will concentrate on figs. 3 to 16.

Fig. 3 illustrates a driver 301 for semiconductor light sources 104. The semiconductor light sources 104 may be called LEDs for short, but throughout this text all kinds of semiconductor light sources are 25 meant. The driver comprises an input connector 102, which in this case has three poles in a similar way as the prior art drivers in figs. 1 and 2. For the present discussion it is not important, whether the driver has actually any input connector at all (because all re30 quired operating power may come e.g. from a battery inside the driver), but the input connector 102 is shown in fig. 3 as an example of how the driver may connect to some supply voltage source.

The driver device 301 comprises an output con35 nector 302 that comprises at least four poles. In fig.

these poles are called the LED+, LED-, Iset+, and Iset- poles. However, these are just names used here to

20176078 prh 30 -11- 2017 unequivocally designate each of said poles in turn. Contrary to driver devices of prior art, the driver 301 in fig. 3 offers more versatile use of said poles than could be deduced by simply looking at said names. Exam5 pies of such versatile use are illustrated in figs. 3,

4, 5, and 6.

A feature common to all figs. 3, 4, 5, and 6 is that one end (or, more generally: one driving current node) of the LEDs 104 is coupled to the topmost pole, 10 which is the LED+ pole. This feature can be generally characterized so that a first pole of the output connector 302 is a first output current pole, for providing output current to the LEDs 104.

The other poles of the output connector 302 can 15 be characterized as current poles or control poles. A particular pole may be exclusively a current pole or exclusively a control pole, but it is also possible that at least one pole of the output connector 302 is both a current pole and a control pole. Which of these roles 20 it takes depends on how the LEDs, and possible external selectable control components, are coupled.

In fig. 3 the LED- pole is a current pole, which is illustrated by the fact that the other end (or, more generally: another driving current node) of the 25 LEDs 104 is coupled to the LED- pole. As a consequence, the output current Iload flows out of the LED+ pole, through the LEDs 104, and in through the LED- pole. An external selectable control component, like a resistor 203, can be coupled between the remaining poles of the 30 output connector 302, i.e. between the Iset+ and Isetpoles. Thus the Iset+ and Iset- poles are control poles in fig. 3.

In fig. 3 the magnitude of the output current Iload depends on the resistance of the resistor 203. The 35 range in which the magnitude of the output current Iload varies depends on how the driver 301 is built. In general it may be assumed that a zero resistance (i.e. short

20176078 prh 30 -11- 2017 circuit) between the Iset+ and Iset- makes the output current Iload assume a first extreme value Iextl, an infinite resistance (i.e. leaving out the resistor 203) makes the output current Iload assume a second extreme 5 value Iext2, and using a resistor 203 of some finite resistance makes the output current Iload assume some value between said first and second extreme values.

By referring to the magnitude of the output current Iload two cases are covered. If the driver 301 10 is a so-called constant current driver, the magnitude of the output current Iload may refer to the fixed value that the output current will have under normal operating conditions. If the driver 301 is a so-called controllable current driver, the magnitude of the output current 15 Iload may refer to an extreme effective value that the output current may achieve during normal operation. These two possible cases are covered by all instances in this text where the magnitude of an output current Iload is considered.

In fig. 4 the current poles (i.e. the poles through which the output current Iload flows) are the LED+ and Iset- poles. The driver 301 is the same as in fig. 3, only the LEDs 104 have been connected in a slightly different way. Comparing to fig. 3 it can be 25 said that the LED- and Iset- poles are configured for mutually alternative use as the second output current pole for providing output current to the LEDs 104. In other words, if one end of the LEDs 104 is coupled to the LED+ pole, the other end of the LEDs 104 may be 30 alternatively coupled to either the LED- pole or the Iset- pole.

The magnitude that the output current Iload assumes in fig. 4 is preferably different from the magnitude it would assume in fig. 3 if the resistor 203 was 35 left out. This means that a user of the driver 301 may select between at least two different magnitudes of output current even without using any external resistors

20176078 prh 30 -11- 2017 or other control components. What is more, even more magnitudes of output current become available by coupling the LEDs across the LED+ and LED- poles as in fig. 3 and using a selectable external control component. Thus the driver 301 is more versatile than the known driver 101 of fig. 1 because a very large number of different output currents can be obtained (by using a selectable external component), but simultaneously easier to use than the known driver 201 of fig. 2 because two (and not only one) different output currents can be obtained even without using any selectable external components at all.

In fig. 5 the current poles (i.e. the poles through which the output current Iload flows) are the LED+ and Iset+ poles. The driver 301 is the same as in figs. 3 and 4, only the LEDs 104 have been again connected in a slightly different way. Comparing to figs. 3 and 4 it can be said that the LED-, Iset+, and Isetpoles are configured for mutually alternative use as the second output current pole for providing output current to the LEDs 104. In other words, if one end of the LEDs 104 is coupled to the LED+ pole, the other end of the LEDs 104 may be alternatively coupled to any of the LEDpole, the Iset+ pole, or the Iset- pole.

The magnitude that the output current Iload assumes in fig. 5 is preferably again different from the magnitude it would assume in fig. 4 or in fig. 3 if the resistor 203 was left out. This means that a user of the driver 301 may select between at least three different magnitudes of output current even without using any external resistors or other control components.

Fig. 6 illustrates the driver 301 coupled to the LEDs 104 in the same way as in fig. 4, but with a resistor 203 (or, more generally, an external selectable control component) coupled between the LED- and Iset+ poles of the output connector 302. Depending on the resistance of the resistor 203 (or, on some electric

20176078 prh 30 -11- 2017 characteristic of an external selectable control component coupled in its place) the output current Iload would assume some other values than that in fig. 4. In this respect one of the teachings of figs. 3 to 6 can 5 be summarized so that among the at least four poles of the output connector 302 there are at least two control poles, other than the first output current pole (i.e. other than the LED+ pole), for selectably changing the magnitude of the output current Iload by coupling a 10 selectable control component between the control poles.

Fig. 7 illustrates schematically an internal structure of a driver that can be used to realize the features explained above with reference to figs. 3 to 6. In order to maintain graphical clarity and ease of 15 understanding, only those parts of the driver are shown in fig. 7 that take part in making the driver operate in the way explained above. For example, no parts of the input side of the driver are shown in fig. 7, but a person skilled in the art can easily understand how an 20 input part of some known kind will be there and support the general operation of the driver and the functions explained in the following.

The driver of fig. 7 comprises a controllable current source 701 for producing output current for sem25 iconductor light sources. The controllable current source 701 may comprise for example one or more switched-mode power supplies that have been configured to generate a current in a controlled manner. Here the terms controllable and controlled are used in gen30 eral sense to say that some control or regulation can be exercised regarding the magnitude of the current. The description is not limited to e.g. LED drivers that allow dimming the LEDs. In a simple embodiment controllability means that the controllable current source 701 35 can be made to output a constant current, i.e. limit the magnitude of the current to a constant value even if,

20176078 prh 30 -11- 2017 as such, the load coupled to consume said current could draw more if allowed.

The driver of fig. 7 comprises also an output connector that comprises at least four poles. In the 5 embodiment of fig. 7 there are exactly four poles, and they are named in the same way as in figs. 3 to 6. In particular, a first pole (the LED+ pole) of the output connector is a first output current pole for providing the output current from the controllable current source 10 701 to the LEDs. The other poles in fig. 7 are the LED-,

Iset+, and Iset- poles, and they may take the roles of current poles and control poles in various ways as will be described later.

The other components shown in fig. 7 belong to 15 a control circuit for the controllable current source 701. In principle, the control circuit comprises a current feedback circuit for producing a control signal for controlling the controllable current source 701 depending on a magnitude of the output current. This way the 20 magnitude of the output current can be kept constant, for example.

For this purpose the control circuit comprises a measurement circuit 702 that is configured to produce an indicator signal 703 indicative of the magnitude of 25 the output current. In fig. 7 two inputs of the measurement circuit 702 are coupled to the LED- pole and the Iset- pole respectively. The measurement circuit 702 is coupled between these inputs and the internal reference potential (the internal ground potential) of the driver. 30 If the LEDs (not shown in fig. 7) are coupled for example between the LED+ and LED- poles, the output current flows out of the LED+ pole and in through the LED- pole. The magnitude of the output current is measured when it flows through the measurement circuit 702.

The control circuit comprises also a controllable reference signal source 704 that is configured to

20176078 prh 30 -11- 2017 produce a reference signal 705. In particular, the reference signal 705 is produced depending on an electric characteristic of a selectable control component (if any) coupled to those poles of the output connector that 5 act as control poles. In fig. 7 the controllable reference signal source comprises a controllable voltage source 706, and the produced reference signal is the potential of its upper end with reference to the internal ground potential.

A further part of the control circuit is an error amplifier 707 that is configured to compare the indicator signal 703 coming from the measurement circuit and the reference signal 705 coming from the controllable reference signal source 704, and to produce the 15 control signal for the controllable current source 701 based on said comparison. Operating voltage connections and feedback components of the error amplifier 707 are not shown in the drawings for graphical clarity, but it can be assumed that the error amplifier 707 is equipped 20 with a predominantly capacitive feedback coupling from its output to its inverting input. This makes the error amplifier 707 to have infinite gain at DC and a decreasing gain in proportion to increasing signal frequency.

If the circuit of fig. 7 is used for basic 25 current feedback control, the reference signal 705 that comes to the lower input of the error amplifier 707 defines the level to which the voltage indicative of output current can rise before the error amplifier 707 produces a control signal that limits the operation of 30 the controllable current source 701. This operation can be inverted, if required and if better suited for the logic of controlling the controllable current source 701: it may be defined that a control signal is produced as long as the voltage indicative of output current 35 remains below the level of the reference signal.

20176078 prh 30 -11- 2017

In addition to the controllable voltage source 706, the controllable reference signal source 704 comprises a current source 708 and a voltage measurement circuit 709 (or voltmeter 709 for short) . The control input of the controllable reference signal source 704 is the upper end of the current source 706. The idea here is that the higher impedance is coupled to said control input, the higher voltage the voltmeter 709 will measure. The measured voltage makes the voltmeter 709 produce a measurement signal that in turn controls the controllable voltage source 706 and makes it produce a reference signal 705 of particular magnitude.

Fig. 8 illustrates an exemplary circuit that can be used to realize the functions explained above.

Again, only components that have actual significance in understanding the explained functions are shown, while the person skilled in the art will easily understand, what kind of further components would be of advantage.

The controllable current source 701 and the error am20 plifier 707 controlling it are shown in a similar manner as in fig. 7. The measurement circuit 702 comprises a simple resistor network, here consisting of only resistors Rl and R2, between the LED- pole and the internal ground potential. A first node of the resistor network 25 (here: the right-hand end of resistor Rl) is coupled to the error amplifier 707 to convey the indicator signal to the error amplifier 707. Another node of the resistor network (here: the middle point between resistors Rl and R2) is coupled to the Iset- pole, which is thus config30 ured to act (at least) as a current pole.

The controllable reference signal source 704 comprises a controllable shunt regulator 801 configured to produce a regulated voltage Vset between its output and the internal ground potential. A voltage divider, 35 consisting of resistors R5 and R6 coupled between the output of the controllable shunt regulator 801 and the internal ground potential, produces the actual reference signal to be fed to the error amplifier 707, by scaling the regulated voltage Vset. The control input of the controllable shunt regulator 801 is coupled to the Iset+ pole through resistor R3. The potential Vref at the control input is defined in part by the voltage divider consisting of resistors R4 and R7, and in part by any current that might flow through resistor R3 and out of the Iset+ pole.

Fig. 9 illustrates a case in which LEDs 104 are 10 coupled between the LED+ and LED- poles. Thus the LED+ and LED- poles take the role of current poles. A selectable control component, here a resistor of a resistance Rset, can be coupled between the Iset+ and Iset- poles. Thus the Iset+ and Iset- poles take the 15 role of control poles. The resistance of the resistor

Rset can be zero (i.e. short circuit), infinite (i.e. open circuit), or something in between.

The relation of the voltages Vset and Vref can be calculated in fig. 9 for example by noting that Vref 20 is a scaled down version of Vset, and the scaling takes place in a voltage divider, the upper resistor of which is R4 and the lower resistor of which consists of the combination of R7, R3, Rset, and R2. Also it must be noted that the current Iload through the LEDs has an effect on the potential of the node between resistors

Rl and R2. It can be shown, as Equation (1), that

20176078 prh 30 -11- 2017

R4

R3 + Rset

Iload R2 R4

R3 + Rset

Here some simplification has been made by noting that since Rl and R2 are so-called current sensing 30 resistors on the main current path, their resistances are very small in relation to the resistances of the other resistors in the control circuit. Rl and R2 can be omitted from such expressions where the larger resistances dominate anyway.

On the other hand, assuming that the task of the error amplifier 707 is to maintain a constant magnitude of the output current Iload so that the input signals to the error amplifier 707 are equal, the output 5 current can be expressed by Equation (2):

Iload —

R6

R1 + R2 ' R6 + R5 ' ^Vset

Equations (1) and (2) can be combined to find an expression for the output current Iload in cases where Rset is finite. This expression is called here 10 Equation (3) :

Iload — (R3 + Rset) fi6 Vref (1 + _fl3 *⁴ _feet + (Rl + R2) (R6 + R5) (R3 + Rset) + R6 R2 R4

The first extreme value of Iload can be obtained by shorting the Iset+ and Iset- poles, i.e. making Rset=0. This extreme value can be calculated from 15 Equation (4) by replacing Rset with 0:

( R4 R4\

R3 R6- Vref- (1+

Iload extl = ₇------------7--———--(Rl + R2) (R6 + R5) R3 + R6 R2 R4

20176078 prh 30 -11- 2017

If there is no selectable control component coupled between the Iset+ and Iset- poles in fig. 9 (in other words: Rset is infinite), the other extreme value 20 of the output current is obtained, and can be calculated from Equation (5):

Iload_ext2 =

R6 (R4 + R7) Vref (R1 + R2)-(R6 + R5)-R7

Fig. 10 illustrates a case in which the LEDs

104 are coupled between the LED+ and Iset- poles. Thus the LED+ and Iset- poles take the role of current poles.

No selectable control components are coupled between the remaining LED- and Iset+ poles in fig. 10, but one could be coupled. Thus the LED- and Iset+ poles take the role of control poles in Fig. 10.

In this case an expression can be found for the output current Iload by noting that only resistor R2 takes any significant part in producing the indicator signal in the measurement circuit consisting of Rl and R2. The expression of the output current in this case is called Equation (6) :

Iload_interm —

R6 (R4 + R7) Vref

R2 (R6 + R5) R7

The designation interm means that this current value is a kind of intermediate value between the extreme values calculated in Equation (4) and Equation (5). Indeed, comparing Equation (5) with Equation (6) reveals a relation that can be expressed as Equation 15 (7):

Iload_interm =

Iload

20176078 prh 30 -11- 2017

Above it has been shown that the user can obtain two fixed output current values (Iload_ext2 and Iload_interm) from the driver of figs. 7 to 10 without 20 having to use any selectable control components. Additionally the user may get a wide range of selectable other output current values by making the connections as in fig. 9 and using a resistor Rset of desired resistance as a selectable control component. This is a 25 significant advantage over prior art drivers, where the user could only have one fixed output current value without any selectable control components plus a range of output current values with a selectable control component (like in fig. 2), or only a limited number of 30 fixed output current values without any range of selectable values (like in fig. 1).

Fig. 11 shows how a selectable control component, here a resistor of resistance Rset, can be coupled

20176078 prh 30 -11- 2017 also between the LED- and Iset+ poles when the LEDs are coupled between the LED+ and Iset- poles like in fig.

above. The effect here is that the resistance between the control input of the controllable shunt regulator

801 and the internal ground potential becomes the smaller, the smaller is the resistance Rset. Another range of possible output current values are obtained, so that one end of the range is that calculated in Equation (6) above and the other end is obtained by 10 making the analysis of fig. 11 with Rset=0.

Fig. 12 illustrates a LED driver according to another embodiment. In this embodiment the controllable current source 701 and the measurement circuit 702 are similar to those in fig. 7 (note, however, that the 15 order of the poles on the right in the drawing has been changed to improve graphical clarity). Also, there is an error amplifier 707 configured to compare an indicator signal 703 coming from the measurement circuit 702 to a reference signal 705 coming from a controllable 20 reference signal source 704, and to produce a control signal for the controllable current source 701 based on said comparison.

The differences to fig. 7 are evident in the internal structure of the controllable reference signal 25 source 704. It comprises a voltage source 1201 configured to produce a voltage between the Iset+ pole (i.e. one of the control poles that is not a current pole) and the internal reference (i.e. ground) potential of the driver. The controllable reference signal source 704 30 comprises also a current measurement circuit 1202 (or ammeter 1202 for short) that is configured to measure a current flowing through the Iset+ pole. The ammeter 1202 produces a measurement signal based on the measured current, and uses it to control a controllable voltage 35 source 706, the output of which is the reference signal 705. If the measurement signal produced by the ammeter 1202 is of suitable range and impedance as such, it can

20176078 prh 30 -11- 2017 be used directly as the reference signal 705 or even directly as a control signal to the controllable current source 701.

Figs. 13 and 14 illustrate two possible cou5 plings of LEDs 104 to a driver of the kind explained above with reference to fig. 12. In fig. 13 the LEDs are coupled between the LED+ and LED- poles, and the user may either leave the Iset+ and Iset- poles open or couple an external selectable control component between them.

Leaving the Iset+ and Iset- poles open means that no current can flow through the Iset+ pole, and the measurement signal from the ammeter 1202 to the controllable voltage source 706 assumes a corresponding first extreme value. Shorting the Iset+ and Iset- poles (i.e. making 15 Rset=0) causes the largest possible current flow through the Iset+ pole, because there is only the resistance of resistor R2 to limit the current. In that case the measurement signal from the ammeter 1202 to the controllable voltage source 706 assumes a corresponding second ex20 treme value.

In fig. 14 the LEDs are coupled between the LED+ and Iset- poles, and the Iset+ and LED- poles are left open. Again, no current flows through the Iset+ pole, and the measurement signal from the ammeter 1202 25 to the controllable voltage source 706 assumes the first extreme value mentioned above. However, since now only the resistance of resistor R2 affects the measurement of the output current, the output current assumes a different value than if the Iset+ and Iset- poles were 30 left open in the case of fig. 13. Thus, also with this embodiment the user may select between two fixed output current values without any external selectable control component, and additionally achieve a range of output current values if such selectable control components are 35 available.

Figs. 15 and 16 illustrate examples of how a user can get more output current values from a LED driver where a resistor network between one current pole and the internal ground potential of the driver offers multiple intermediate nodes for connection. The controllable current source 701 and the error amplifier 707 may 5 resemble those explained above. The measurement circuit comprises a chain of three current sensing resistors RCS1, RCS2, and RCS3. The current path from the LED1pole to the internal ground potential goes through all of them, while the current path from the LED2- pole goes 10 only through resistors RCS2 and RCS3, and the current path from the LED3- pole goes only through resistor

RCS3. The error amplifier 707 compares the current indicator signal to a fixed reference voltage produced by the voltage source 1501.

In fig. 15 a resistor with resistance Rset is coupled between the LED2- and LED3- poles. This has the effect that instead of RCS1 + RCS2 + RCS3, the resistance used for current sensing is RCS1 + RCS3 + (RCS2*Rset/(RCS2+Rset)), which is slightly smaller, and the current Iload may consequently achieve a slightly higher value. In fig. 16 the LEDs 104 are coupled between the LED+ and LED2- poles, and a resistor Rset is coupled between the LED1- and LED3- poles. In such a case it can be shown that the output current assumes the value given by Equation (8):

20176078 prh 30 -11- 2017 , RCS1 + Rset\

Iload = —------———' 1 Ί--—---1' Vfix

Rset + RCS3 \ RCS2 J

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

For example, even if the term output connector is used as if there was a single mechanical 35 connector entity that houses the described poles, it is possible to provide the same functionality in more than one mechanical unit. There may be even a dedicated connector for each pole separately.

Also, even if the resistor network used to measure the output current is shown as a simple chain of two resistors in the embodiments above, it is possible to use more complicated resistor networks. Typically a first node of the resistor network is coupled to an error amplifier, comparator, or some other means, the 10 task of which is to react to the measured output current achieving or exceeding some limit. Typically one of the alternative current poles is coupled to a different node within the resistor network than the first current pole. If there are further alternative current poles, they may 15 be connected to yet other nodes of the resistor network.

The relative magnitudes between said nodes of the resistor network have significant influence upon those values of output current that can be achieved without external selectable control components, and said rela20 five magnitudes can be selected through routine workshop modifications .

Claims

1. A driver for semiconductor light sources, comprising :

5 - a controllable current source (701) for producing output current for said semiconductor light sources,

- a control circuit of said controllable current source, and

- an output connector that comprises at least four

10 poles, wherein a first pole (LED+) of said output connector is a first output current pole for providing said output current to said semiconductor light sources;

characterized in that:

15 - at least two current poles, other than said first pole, of said output connector are configured for mutually alternative use as a second output current pole for providing said output current to said semiconductor light sources, and

20 - at least two control poles, other than said first pole, of said output connector are each connected to different points in said control circuit, for selectably changing operation of said control circuit by coupling a selectable control component between said con25 trol poles.

2. A driver according to claim 1, wherein said control circuit comprises a current feedback circuit for producing a control signal for controlling said controllable current source (701) depending on a

30 magnitude of said output current.

3. A driver circuit according to claim 2, wherein said control circuit comprises:

- a measurement circuit (702) configured to produce an indicator signal (703) indicative of said magnitude of

35 said output current,

20176078 prh 30 -11- 2017

- a controllable reference signal source (704) configured to produce a reference signal (705) depending on an electric characteristic of said selectable control component, and

5 - an error amplifier (707) configured to compare said indicator signal (703) to said reference signal (705) and to produce said control signal based on said comparison .

4. A driver according to claim 3, wherein:

10 - said measurement circuit (702) comprises a resistor network (Rl, R2) between one (LED-) of said current poles and an internal reference potential of said driver,

- a first node of said resistor network is coupled to

15 said error amplifier (707) to convey said indicator signal (703) to said error amplifier (707), and

- another (Iset-) of said current poles is coupled to a different node within said resistor network than said one (LED-) of said current poles.

20 5. A driver according to claim 4, wherein:

- one (Iset+) of said control poles that is not any of said current poles is coupled to a control input of said controllable reference signal source (704) .

6. A driver according to claim 5, wherein:

25 - the controllable reference signal source (704) comprises a current source (708) configured to make a measurement current flow through said one (Iset+) of said control poles that is not any of said current poles,

30 - the controllable reference signal source (704) comprises a voltage measurement circuit (709) configured to measure a voltage between said one (Iset+) of said control poles that is not any of said current poles and the internal reference potential of said driver

35 and to produce a measurement signal based on said

20176078 prh 30 -11- 2017 measured voltage, and

- the controllable reference signal source (704) comprises a controllable voltage source (706) coupled to receive said measurement signal from said voltage

5 measurement circuit (709) and configured to use said measurement signal to produce a voltage that defines said reference signal (705).

7. A driver according to claim 5, wherein:

- the controllable reference signal source (704) com-

10 prises a voltage source (1202) configured to produce a voltage between said one of said control poles that is not any of said current poles and the internal reference potential of said driver,

- the controllable reference signal source (704) com-

15 prises a current measurement circuit (1202) configured to measure a current flowing through said one of said control poles that is not any of said current poles and to produce a measurement signal based on said measured current, and

20 - the controllable reference signal source (704) comprises a controllable voltage source (706) coupled to receive said measurement signal from said current measurement circuit (1202) and configured to use said measurement signal to produce a voltage that defines

25 said reference signal (705).

8. A driver according to any of the preceding claims, wherein at least one pole of said output connector is both a current pole and a control pole.

9. A method for producing output current for

30 semiconductor light sources, the method comprising:

- providing a driver with an output connector that comprises at least four poles,

- producing an output current of a first magnitude in response to receiving a first driving current node of

35 said semiconductor light sources to a first pole of said at least four poles, and receiving a second driving current node of said semiconductor light sources to a second pole of said at least four poles, with no other external components coupled between remaining

5 ones of said at least four poles,

- producing an output current of a second magnitude, different from said first magnitude, in response to receiving said first driving current node of said semiconductor light sources to said first pole of said at 10 least four poles, and receiving said second driving current node of said semiconductor light sources to a third pole of said at least four poles, with no other external components coupled between remaining ones of said at least four poles, and

15 - producing an output current of a third magnitude, different from said first and second magnitudes, in response to receiving said first driving current node of said semiconductor light sources to said first pole of said at least four poles, and receiving said second 20 driving current node of said semiconductor light sources to either of said second and third poles of said at least four poles, and receiving an external component between two remaining ones of said at least four poles.