FI128766B - Method and circuit for detecting characteristics of supply voltage, and connecting device for one or more light sources - Google Patents

Abstract

A connecting device for light sources (101) is equipped for detecting characteristics of a supply voltage received at a supply voltage input (102). A switching regulator (204, 304) produces a first voltage, and an output stage (206, 306) produces an output voltage of the connecting device. A PFC controller (208, 308, 605, 705) makes the switching regulator (204, 304) perform power factor correction. The PFC controller (208, 308) provides switching pulses to a first switch (603) in said switching regulator (204, 304). A signal coupling (210, 310) exists from the switching regulator (204, 304) to a second controller (209, 309, 409, 618, 718, 818), configured to convey a signal indicative of the switching pulses. The second controller (209, 309, 409, 618, 718, 818) detects said characteristics of the supply voltage on the basis of at least said signal.

Description

METHOD AND CIRCUIT FOR DETECTING CHARACTERISTICS OF

SUPPLY VOLTAGE, AND CONNECTING DEVICE FOR ONE OR MORE

LIGHT SOURCES

FIELD OF THE INVENTION

The invention is related to the technical field of detecting the characteristics of a supply voltage to an electric circuit. In particular the in- vention is related to such detecting in an apparatus in which direct monitoring of the supply voltage is not possible or not preferable.

BACKGROUND OF THE INVENTION

Many electronic devices may benefit from in- ternally detecting characteristics of their supply voltage, such as the voltage value, frequency (in case of AC supply voltage), changes between AC and DC sup- ply voltage, interruptions in supply voltage, and the like. As an example of such an electronic device a connecting device for one or more light sources is de- scribed in the following. The connecting device may be for example a LED driver, a ballast of an electric discharge lamp, or the like.

Fig. 1 illustrates a known connecting device for light sources 101. A supply voltage coupled to a = supply voltage input 102 goes first to a rectifying

N and filtering circuit 103, from which the rectified 3 and filtered voltage goes to a primary converter 104 © 30 that produces what is often called the bus voltage. A

I transformer 105 may actually be part of the primary + converter 104 but it is drawn here separately to em-

R phasize its role in implementing galvanic isolation 3 between the primary converter 104 and a secondary con-

S 35 verter 106, which produces the output voltage and cur- rent of desired magnitude at the output 107, to which the light sources 101 are coupled. Any or both of the primary 104 and secondary 106 converters may comprise two or more converter stages in series or (particular- ly on the secondary side) in parallel.

A primary controller 108 controls the opera- tion of the primary converter 104, and a secondary controller 109 controls the operation of the secondary converter 106. As the primary 104 and secondary 106 converters both typically comprise a switching regula- tor, a major task of each corresponding controller is to form the switching control pulses for the switch (es) in the corresponding switching regulator.

Each controller may set the frequency and/or duty cy- cle of the switching control pulses based on feedback signals from the corresponding converter. As the pri- mary converter 104 should also implement power factor correction, the primary controller 108 may use also information about the supply voltage to set the fre- quency and/or duty cycle of the switching control pulses it forms.

The primary 108 and secondary 109 controllers may exchange control information in one direction or in both directions. In order to maintain the galvanic isolation between the primary and secondary sides there is an isolating interface 110 that may be based on any known components such as optoisolators for ex- ample. If the connecting device is to be controlled > externally, to controllably dim the light sources 101

N for example, there may be an external control inter- 3 30 face 111 and a control input/output connection 112. In © the embodiment of fig. 1 the external control inter-

Ek face 111 and the control input/output connection 112 * are on the secondary side of the galvanic isolation.

R The manufacturer of a connecting device like 3 35 that in fig. 1 want to keep the manufacturing costs at

S minimum, which essentially means using as simple and inexpensive components as possible, and using as few of them as possible. At the same time the device should be versatile for use and offer many functional- ities, which as an aim works in the opposite direc- tion. There may be even regulatory reguirements about functionality. As an example, a new version of the DA-

LI standard (Digital Addressable Lighting Interface) requires that the connecting device must be able to detect the voltage level and frequency of its supply voltage. In a device like that in fig. 1 this means that the appropriate information must be extracted on the primary side and conveyed to the secondary side.

If the primary controller 108 includes suffi- ciently versatile functionality, it can be made to de- tect the required characteristics of the supply volt- age and transmit the corresponding information across the isolating interface 110. However, this means that a relatively expensive circuit like a programmable mi- crocontroller must be used as the primary controller 108.

SUMMARY

It is an objective of the present invention to present a method and a circuit for detecting char- acteristics of a supply voltage with a simple piece of circuitry that is adaptable for use in a variety of applications, mainly in connecting devices for light o sources. The detection of the characteristics should > be possible in particular in connection devices that & include a switching regulator for doing power factor 2 30 correction, as well as a controller that is not di-

TY rectly connected to the switching regulator but sepa-

E rate therefrom, possibly with a galvanic isolation in

O between. 5 The objectives of the invention are achieved 2 35 by considering switching pulses that go to a power

N switch in the switching regulator as a digital signal,

characteristics of which reveal important information about the supply voltage.

According to a first aspect there is provided a connecting device for one or more light sources. The connecting device is equipped for detecting character- istics of a supply voltage to the connecting device and comprises a supply voltage input for receiving said supply voltage and a switching regulator coupled to said supply voltage input and configured to produce a first voltage. An output stage is coupled to receive sald first voltage or another voltage derived from said first voltage, and configured to produce an out- put voltage of the connecting device. A PFC controller is configured to make said switching regulator perform power factor correction in producing said first volt- age. In particular said PFC controller is configured to provide switching pulses to a first switch in said switching regulator. The connecting device comprises a second controller and a signal coupling from said switching regulator to said second controller for con- veying to said second controller a signal indicative of said switching pulses. The second controller is configured to detect said characteristics of said sup- ply voltage on the basis of at least said signal.

According to an embodiment said signal cou- pling is a coupling from a switching pulses line to a signal input of said second controller, wherein said > switching pulses line is a coupling from a switching

N pulses output of said PFC controller to a control in- 3 30 put of said first switch. This involves the advantage © that the indicative signal can be made to accurately =E represent the switching pulses. * According to an embodiment the connecting de-

R vice comprises a primary side and a secondary side 3 35 with galvanic isolation between said primary and sec-

S ondary sides, so that said switching regulator is on said primary side, said output stage and said second controller are on said secondary side, and said signal coupling crosses said galvanic isolation through a galvanically isolating interface. This involves the advantage that the relatively simple principle ex- 5 plained above can be effectively utilized also in gal- vanically isolated connection devices.

According to an embodiment the second con- troller comprises a programmable circuit. This in- volves the advantage that advanced calculational meth- ods can be utilized to derive valuable information concerning the supply voltage from the indicative sig- nal.

According to an embodiment the connecting de- vice comprises an external control interface coupled to said programmable circuit, and said programmable circuit is configured to transmit information indica- tive of said detected characteristics of said supply voltage through said external control interface to- wards a remote receiver. This involves the advantage that the relatively simple way of detecting character- istics of supply voltage can be harnessed for the pur- poses reguired by many modern lighting control stand- ards.

According to an embodiment said second con- troller is configured to detect at least one of an in- put power and an output power of the connecting de- vice, and said programmable circuit is programmed to = derive a representative voltage value of said supply

N voltage on the basis of said signal and the detected 3 30 input and/or output power. This involves the advantage © that the voltage value of the supply voltage can be =E found out and communicated further or otherwise uti- * lized even if there is no easy direct way of measuring

R it in the connecting device. 3 35 According to an embodiment said second con-

S troller is configured to detect a cycle frequency of said supply voltage on the basis of said signal. This involves the advantage that the cycle frequency of the supply voltage can be found out and communicated fur- ther or otherwise utilized even if there is no easy direct way of measuring it in the connecting device.

According to an embodiment said second con- troller is configured to detect an interruption in said supply voltage on the basis of said signal. This involves the advantage that the second controller may react appropriately and in good time to such an inter- ruption.

According to a second aspect there is provid- ed a method for detecting characteristics of a supply voltage to an connecting device for one or more light sources. The method comprises using a switching regu- lator to perform power factor correction as a part of converting the supply voltage into a first voltage, deriving an output voltage from said first voltage for delivering to said one or more light sources, and us- ing a signal indicative of switching pulses to a switch of said switching regulator to detect charac- teristics of said supply voltage.

According to an embodiment said detecting of said characteristics of said supply voltage comprises detecting at least one of: a cycle frequency of said supply voltage, a representative voltage value of said supply voltage, an interruption of said supply volt- age. This involves the advantage that quantities that = may reveal important information can be detected with

N a relatively simple circuit and without having to 3 30 measure them directly. © According to an embodiment the method com- =E prises transmitting information indicative of said de- * tected characteristics of said supply voltage towards

R a remote receiver. This involves the advantage that 3 35 conformity with certain lighting control standards can

S be achieved.

According to an embodiment the method com- prises measuring at least one of an output power or input power of the connecting device, and using the measured output and/or input power to derive a repre- sentative voltage value of said supply voltage. This involves the advantage that the voltage value of the supply voltage can be found out and communicated fur- ther or otherwise utilized even if there is no easy direct way of measuring it in the connecting device.

According to an embodiment the method com- prises, as a response to detecting an occurred inter- ruption of said supply voltage, initiating an excep- tional-situations-seguence of operations in said con- necting device, wherein said exceptional-situations- sequence of operations comprises at least one of: re- porting to an external device of the interruption, storing at least one piece of information into nonvol- atile memory within the connecting device, switching sald connecting device to use an alternative power source. This involves the advantage that advanced ways of operating can be implemented while only having to take relatively simple action for detecting the trig- gering features.

According to an embodiment the method com- prises, as a response to detecting an occurred change from AC to DC in said supply voltage, making said con- necting device produce output power at an exceptional- > situations-level of power. This involves the advantage

N that sufficient responsiveness to exceptional situa- 3 30 tions can be achieved with only relatively simple and © cheap circuitry.

Ek Further advantages, aspects, and viewpoints * of the invention are apparent to the reader in the de-

R tailed description given below, when read in associa- 3 35 tion with the accompanying drawings. o

N

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 connecting de- vice, figure 2 illustrates a connecting device ac- cording to an embodiment, figure 3 illustrates a connecting device ac- cording to an embodiment, figure 4 illustrates a connecting device ac- cording to an embodiment, figure 5 illustrates a connecting device ac- cording to an embodiment, figure 6 illustrates a connecting device ac- cording to an embodiment, figure 7 illustrates a connecting device ac- cording to an embodiment, figure 8 illustrates a connecting device ac- cording to an embodiment, figure 9 illustrates a method according to an embodiment, figure 10 illustrates a method according to o an embodiment,

DO figure 11 illustrates a method according to

N an embodiment, 2 30 figure 12 illustrates examples of relation-

T ships between supply voltage and switching pulses, and

E figure 13 illustrates the dependency between

Oo supply voltage and duty cycle of switching pulses at a

N variety of output power levels. 2 35

N

DETAILED DESCRIPTION

Fig. 2 illustrates an exemplary connecting device for one or more light sources 101. The connect- ing device comprises a supply voltage input 102 for receiving a supply voltage, the characteristics of which are not necessarily known beforehand but may vary from device to device (depending on what kind of a system the device is installed in) and also during the operation of an individual device.

The characteristics of a supply voltage com- prise quantities measurable in magnitude such as a representative voltage value and a cycle frequency, but also the mere existence or absence of the supply voltage. If the supply voltage comes in the form of

AC, it has some relatively constant cycle frequency like 50 Hz or 60 Hz, whereas if the supply voltage is

DC its cycle freguency is 0 Hz and all detected oscil- lations are just unwanted ripple. For a DC supply voltage the representative voltage is directly the constant DC voltage value, while for an AC supply voltage the rms (root mean square) voltage is typical- ly considered as representative. Detecting the exist- ence/absence characteristic of a supply voltage may mean e.g. detecting short interruptions caused by ir- regular operation of a supply voltage source, and/or detecting that a supply voltage diminishes or disap- o pears as in a brownout or blackout situation. Further

Oo characteristics of a supply voltage may include e.g.

N first or second order derivatives that tell, how a 2 30 certain basic characteristic like representative volt-

A age is changing.

E The connecting device shown in fig. 2 com-

Oo prises a switching regulator 204, a main functional

N part of which is called the primary converter in fig. 2 35 2. The switching regulator 204 is coupled to the sup-

N ply voltage input 102. In fig. 2 the coupling goes through a filter and rectifier block 203, so that what the switching regulator 204 actually receives 1s a filtered and rectified form of the supply voltage. On this technical field it is, however, commonplace to say that the switching regulator 204 receives the sup- ply voltage, unless there is some specific need to un- derline the role of filtering and/or rectification therebetween.

The switching regulator 204 is configured to produce a voltage that is called here the first volt- age, where the definition “first” is only used to ena- ble unequivocal reference without defining any num- bered order of voltages. The switching regulator 204 produces the first voltage through its operation, which means that a switch (not specifically shown in fig. 2) in the switching regulator 204 alternates be- tween conductive and non-conductive states, causing electric energy to repeatedly become stored in and discharged from the field of an inductive, capacitive, or inductive-capacitive energy storage. The switch is typically a semiconductor switch such as a transistor, and it has a control input, like the gate of a MOSFET (metal oxide semiconductor field-effect transistor).

Switching pulses conducted to the control input of the switch cause said alternating between conductive and non-conductive states.

The connecting device of fig. 2 comprises an output stage 206 that is coupled to receive the first > voltage. There may be further voltage conversion stag-

N es therebetween, in which case the output stage 206 3 30 would receive some other voltage derived from the © first voltage, but the simplest case of conducting the =E first voltage directly to the output stage 206 is con- * sidered here. The output stage 206 is configured to

R produce an output voltage that will appear at an out- 3 35 put 107 of the connecting device.

S Few requirements need to be placed to the output stage 206, and examples of various output stag-

es will be described later in this text. A very simple output stage may require little more than suitable connections from the first voltage to an output of the circuit, possibly with some filtering to block the propagation of unwanted electromagnetic interference.

A more elaborate output stage may comprise for example measuring functionalities, and an output stage may al- so comprise voltage regulation and/or voltage conver- sions accomplished with a linear regulator and/or a switching regulator for example.

The connecting device comprises a PFC con- troller 208 configured to make the switching regulator 204 perform power factor correction in producing the first voltage. In the structural organization of the connecting device the PFC controller 208 may actually be a part of the switching regulator 204. However, it is also possible that the switching regulator 204 and the PFC controller 208 are clearly distinct parts of the connecting device. As a general term, power factor correction covers all functions that aim at drawing current from an AC voltage source in phase with the voltage, with the effect of the relation between real power and reactive power drawn by the connecting de- vice becoming as large as possible. The power factor as a quantity is also called cosine phi or cos(phi), and its value is between zero and one. Power factor correction is the better the closer the power factor = is to one.

N The way in which the PFC controller 208 makes 3 30 the switching regulator 204 perform power factor cor- © rection involves providing switching pulses to the

Ek switch in the switching regulator. According to known + aspects of power factor correction the PFC controller

R 208 may vary certain aspects of the switching pulses, 3 35 for example their duty cycle and/or pulse frequency,

S so that as a result the desired degree of power factor correction is achieved. Further in accordance with known principles of power factor correction, in form- ing the switching pulses the PFC controller 208 may utilize input information like detected zero crossings in the supply voltage, measured voltage and/or current values in the switching regulator 204, and the like.

The connecting device comprises a second con- troller 209, which is a different component than the

PFC controller 208. The difference is at least func- tional, meaning that signals available for operation within one of these two components are not directly available for operation within the other, but must be conveyed thereto through a dedicated coupling. The difference may be also physical, meaning that the PFC controller 208 and the second controller 209 are phys- ically separate components located at different loca- tions on a circuit board or other support structure of the connecting device.

The connecting device comprises a signal cou- pling 210 from what is here called the switching regu- lator 204 to the second controller 209. Here it must be remembered that the concept of a switching regula- tor 204 may or may not comprise also the PFC control- ler 208, so the signal coupling 210 may come either from that part of the switching regulator that ex- cludes the PFC controller, or from the PFC controller, or from somewhere between. The signal coupling 210 is configured to convey to the second controller 209 a > signal indicative of the switching pulses that the PFC

N controller 208 provides to the switch in the switching 3 30 regulator 204. The signal being indicative of the © switching pulses means that it conveys the switching =E pulses themselves, or some modified (like scaled, de- * layed, etc.) version of the switching pulses, or some

R other information that has an unequivocal correspond- 3 35 ence to an essential characteristic (like duty cycle,

S and/or frequency, or the like) of the switching puls- es.

The second controller 209 is configured to detect the desired characteristic(is) of the supply voltage on the basis of at least the signal that it receives through the signal coupling 210. A number of possible ways exist for the second controller 209 to implement such detecting of the characteristics of the supply voltage. Examples will be given later in this text.

The signal coupling 210 may be for example a coupling from a switching pulses line to a signal in- put of the second controller 209. Here the switching pulses line means a coupling from a switching pulses output of the PFC controller 208 to a control input (such as the gate of a MOSFET for example) of the switch in the switching regulator 204. As fast and ef- fective switching is important in all kinds of switch- ing regulators, a coupling from a switching pulses line to a signal input of the second controller 209 should be designed so that it does not inappropriately load the switching pulses line or otherwise interfere with the delivery of the switching pulses to their original intended destination.

Fig. 3 illustrates another, slightly more elaborate connecting device. The connecting device of fig. 3 comprises a primary side and a secondary side, with galvanic isolation between the primary and sec- ondary sides. The switching regulator 304 is on the = primary side and the output stage and the second con-

N troller 309 are on the secondary side. Between the 3 30 switching regulator 304 and the output stage 306 the © galvanic isolation is implemented with a transformer =E 305, which may comprise parts of any or both of the + switching regulator 304 or the output stage 306, hence

R the difference in reference designators compared to 3 35 fig. 2. The signal coupling 310 from the switching

S regulator 304 to the second controller 309, which con- veys to the second controller 309 the signal indica-

tive of the switching pulses, crosses the galvanic isolation through a galvanically isolating interface 311.

Fig. 4 illustrates a connecting device in which the difference to fig. 3 is that the circuit comprises an external control interface 111 coupled to the second controller 409. Like in all other embodi- ments, the second controller 409 may comprise a pro- grammable circuit such as a processor, a microcontrol- ler, or the like. Programmability as a part of the second controller 409 is particularly advantageous if the external control interface 111 is coupled to the programmable circuit so that the programmable circuit is configured to transmit information indicative of detected characteristics of the supply voltage through the external control interface 111 towards a remote receiver. Hardware circuits with no programmability can be used as the second controller in embodiments where less flexibility in operation is needed.

Fig. 5 illustrates a connecting device in which the signal coupling 310 from the switching regu- lator 304 to the second controller 409, which conveys to the second controller 409 the signal indicative of the switching pulses, goes through not only a galvani- cally isolating interface 311 but also a signal con- version unit 501. Many kinds of signal conversions can be performed in the signal conversion unit 501. Exam- > ples include but are not limited to conversions in any

N direction between analog and digital forms, integra- 3 30 tion, derivation, filtering, level shifting, and con- © versions in any direction between voltage and current = signals. + The parts of the connecting device that are

R different from each other in figs. 2, 3, 4, and 5 can 3 35 be combined in various ways. For example a signal con-

S version unit of the kind shown as 501 in fig. 5 may be used in any of the connecting devices, independent of whether there is also a galvanically isolating inter- face or not or what kind of output stage is used. Sim- ilarly an external control interface and a programma- ble circuit as a part of the second controller could appear in any of the connecting devices.

Fig. 6 is a simplified circuit diagram of a connecting device equipped for detecting characteris- tics of a supply voltage to the connecting device. The connecting device of fig. 6 comprises a supply voltage input 102 for receiving a supply voltage, and a boost- type switching regulator that comprises a series in- ductor 601, a switch 603, and a forward diode 604. The switching regulator is coupled to the supply voltage input 102 through a filter and rectifier block 203, and configured to produce a first voltage according to the known principle of boost-type switching regula- tors. A second inductor 60? inductively coupled to the series inductor 601 is used to sample the filtered and rectified supply voltage and to convey the sample to a

PFC controller 605 that is coupled to a control input of the switch 603. The PFC controller 605 is config- ured to make the switching regulator perform power factor correction in producing the first voltage, by providing switching pulses to the switch 603.

In forming the switching pulses the PFC con- troller 605 takes into account the information it re- ceives through the samples of the filtered and recti- = fied supply voltage from the second inductor 602. Oth-

N er inputs to the PFC controller 605 include feedback 3 30 in the form of a switch current measurement from a © current sensing resistor 606 and a sample of the pro- =E duced first voltage taken through a voltage divider * that comprises resistors 607 and 608. The PFC control-

R ler 605 may use current and voltage feedback of this 3 35 kind for example to set a frequency and/or duty cycle

S of the switching pulses, as is well known in the art.

The first voltage constitutes an input volt- age to a further converter stage, which in the con- necting device of fig. 6 is a flyback-type switching regulator. It comprises a transformer with a primary winding 610 and a secondary winding 611, a switch 609 in series with the primary winding 610, a diode 612 in series with the secondary winding 611, and a capacitor 613 across the series coupling of the secondary wind- ing 611 and diode 612. The PFC controller 605 is also responsible for forming the switching pulses conveyed to the control input of the switch 609 in the flyback- type switching regulator, and as an additional input it receives a further switch current measurement from the current sensing resistor 614 connected between the switch 609 and local ground. An example of a PFC con- troller that can be coupled and operated like the PFC controller 605 in fig. 6 is the FL7921R produced and marketed by Fairchild Semiconductors.

According to a first possible viewpoint the boost-type and flyback-type switching regulators of the circuit of fig. 6 are consecutive stages of one larger switching regulator. According to this view- point the output stage of the connecting device of fig. 6 comprises a straightforward coupling from the output of the flyback-type switching regulator to the output 107 of the connecting device of fig. 6. Accord- ing to this viewpoint the output stage is thus coupled > to receive the "other” voltage derived from the first

N voltage through the operation of the flyback-type 3 30 switching regulator. © According to a second possible viewpoint the =E flyback-type switching regulator is a part of the out- + put stage, so that the output stage receives the first

R voltage and produces the output voltage through the 3 35 operation of the flyback-type switching regulator.

S The connecting device of fig. 6 comprises a second controller 618 and a signal coupling from the switching regulator to the second controller 618. This signal coupling begins at the switching pulses line that connects a switching pulses output of the PFC controller 605 to the control input of the first switch 603. The signal coupling goes through resistor 612 and optoisolator 620 to a signal input of the sec- ond controller 618, and is thus configured to convey to the second controller 618 a signal indicative of the switching pulses that the PFC controller 605 pro- vides to the first switch 603. As said signal input of the second controller 618 is directly coupled to the collector of the phototransistor in the optoisolator, the second controller 618 will detect the signal as variations in the conductivity between its signal in- put and local ground. The second controller 618 is configured to detect characteristics of the supply voltage to the connecting device on the basis of at least said signal.

Other inputs to the second controller 618 in- clude feedback in the form of an output current meas- urement from a current sensing resistor 617 and a sam- ple of the produced output voltage taken through a voltage divider that comprises resistors 615 and 616.

In the connecting device of fig. 6 the second control- ler is also configured to provide feedback to the PFC controller 605 through an optoisolator 619. Such feed- back can be used for example to inform the PFC con- = troller 605 of actual output power demands, which may

N make the PFC controller 605 drive one or both of the 3 30 switches 603 and 609 accordingly, as is known in the © art.

Ek The transformer of the flyback-type switching * regulator and the optoisolators 619 and 620 divide the

R connecting device of fig. 6 into a primary side and a 3 35 secondary side, with galvanic isolation therebetween.

S Fig. 7 is a simplified circuit diagram of a connecting device equipped for detecting characteris-

tics of its supply voltage. Parts that are similar to those in fig. 6 are marked with the same reference designators, so for their description reference is made to the text above. The connecting device of fig. 7 differs from the one of fig. 6 in that the flyback- type switching regulator is controlled by the second controller 718. The second controller 718 forms the switching pulses for the switch 609 of the flyback- type switching regulator, at least partly based on voltage and current measurements from the voltage di- vider of resistors 607 and 608 and the current sensing resistor 614 respectively. The connecting device could involve output voltage and current measurements simi- lar to those in fig. 6, in which cases those measure- ments could serve as additional inputs to the second controller 718.

The signal coupling from the switching regu- lator (i.e. the boost-type switching regulator) to the second controller 718 is now a direct connection from the switching pulses line between the PFC controller 705 and first switch 603 to a signal input of the sec- ond controller 718. Thus the second controller 718 re- ceives the signal indicative of the switching pulses as a straightforward digital signal that toggles be- tween a higher voltage value and a lower voltage value like the switching pulses do. Also the feedback cou- pling from the second controller 718 to the PFC con- > troller 705 is a direct connection without any optoi-

N solators or other galvanically isolating components. 3 30 Fig. 8 is a simplified circuit diagram of a © connecting device equipped for detecting characteris- =E tics of its supply voltage. Parts that are similar to + those in fig. 6 are marked with the same reference

R designators, so for their description reference is 3 35 made to the text above. The connecting device of fig.

S 8 differs from the one of fig. 6 in three ways. First, the output stage comprises a further, buck-type switching regulator. Second, there is a signal conver- sion unit along the signal coupling from the switching regulator on the primary side to the second controller on the secondary side. Third, the connecting device comprises an external control interface coupled to (a programmable circuit in) the second controller 818.

The buck-type switching regulator in the out- put stage comprises a series inductor 830, a switch 831, and a freewheeling diode 832, as well as a smoothing capacitor 833 coupled across the output 107 of the circuit. The switch 831 is between the free- wheeling current loop and local ground, which makes the coupling a buck-type switching regulator with low side switch. Buck-type switching regulators of this kind are well known and widely used in the art. The second controller 818 forms the switching pulses to the switch 831 of the buck-type switching regulator.

In forming the switching pulses it may take into ac- count the sensed sample of the output voltage it re- ceives from the voltage divider consisting of resis- tors 615 and 616, and/or the sensed output current it receives from the current sensing resistor 617.

The signal conversion unit comprises the pull-up resistor 834 and the capacitor 835. A current path exists from a positive potential (here: the posi- tive node of the operating voltage of the second con- troller 818) through the pull-up resistor 834 and the = capacitor 835 to local ground. The phototransistor in

N optoisolator 620 constitutes a controllable short- 3 30 circuit path from between the pull-up resistor 834 and © the capacitor 835 to local ground. The coupling from =E the positive potential through the pull-up resistor * 834 tends to charge the capacitor 835 with a constant

R current, whereas whenever the phototransistor in the 3 35 optoisolator 620 is conductive it tends the discharge

S the capacitor 835. As a result the signal conversion unit operates essentially as an integrator, so that the voltage across the capacitor 835 depends on (the frequency and) the duty cycle of light pulses produced by the light-emitting diode in the optoisolator 620.

These in turn appear at the same frequency and duty cycle as the switching pulses to switch 603 in the switching regulator on the primary side, so the volt- age across the capacitor 835 is a signal indicative of said switching pulses. A signal input of the second controller 818 is coupled to sense the voltage across the capacitor 818.

There are also control connections between the second controller 818 of the connecting device in fig. 8 and the external control interface that is schematically shown as block 836, separated from the second controller 818 with optoisolators 837 and 838.

External control interfaces of this kind are well known from for example DALI-controlled connection de- vices for light sources.

A feature common to all simplified circuit diagrams above is that a number of additional compo- nents that would typically appear in a practical con- necting device are not drawn, in order to maintain graphical clarity by omitting components that have little significance to understanding how the invention works. Examples of such components include but are not limited to filtering components that are used to smoothen various voltages and to filter out high- = frequency components; overcurrent and/or overvoltage

N protector elements that are used as safety devices 3 30 against exceptional conditions; reference voltage © sources that are used to produce reference voltage =E levels; level shifters that are used to shift voltage * values to a more practical range of magnitude; startup

R circuitry that ensures smooth and predictable opera- 3 35 tion when the circuit is switched on; and so on.

S Fig. 9 illustrates a method for detecting characteristics of a supply voltage to a connecting device for one or more light sources. Step 902 illus- trates how the method comprises using a switching reg- ulator to perform a power factor correction as a part of converting the supply voltage 901 into a first voltage 903. Steps 904 to 906 illustrate how the meth- od comprises deriving an output voltage 907 from the first voltage 903; the word "deriving” underlines how these steps may comprise further voltage conversions, but additionally or alternatively they may comprise other kind of operations like filtering, transient suppression, or the like. Step 910 illustrates how the method comprises using a signal indicative of switch- ing pulses to a switch of the switching regulator to detect characteristics of the supply voltage. Forming the switching pulses at step 909 typically takes into account a (possible) AC waveform of the supply volt- age, which is illustrated in fig. 9 as detecting zero crossings therein at step 908. Other forms of evaluat- ing the nature and behavior of the supply voltage than zero crossing detection can be used in addition to or in place of the detection of zero crossings, as is well known in the art.

The characteristics of the supply voltage that are detected in step 910 may comprise detecting a cycle frequency of the supply voltage, a representa- tive voltage value of the supply voltage, an interrup- tion of the supply voltage, and/or some other charac- > teristic(s) of the supply voltage. Examples of ways in

N which such characteristics can be detected from the 3 30 signal indicative of the switching pulses are de- © scribed in more detail later in this text.

I Steps 911 to 913 illustrate some examples of + what can be done with the detected characteristics of

R the supply voltage. According to step 911 values, 3 35 codes, statistical descriptors, and/or other infor-

S mation representing the detected characteristics can be stored. Simple storing is an option for example in connecting devices like those shown in figs. 2, 3, €, and 7, where no straightforward means are available for transmitting such information further. Stored in- formation may be read later through some special ar- rangement, like a dedicated analyzer device for exam- ple. Information that is stored and only read later at a specific instant may be useful for example in moni- toring how a particular system (such as a lighting system of a building for example) has operated, and/or what operating conditions a particular circuit has been subjected to during its previous use.

Step 912 shows how the method may comprise reporting, i.e. transmitting information indicative of the detected characteristics of the supply voltage to- wards a remote receiver. This kind of reporting may take place for example in a centrally controlled lighting system, where a central controller may inter- rogate individual connection devices concerning the characteristics of supply voltage they have detected.

Communications related to such reporting can take place through a digital lighting control bus or through wireless communications, for example.

Step 913 shows how the method may comprise locally reacting to changes in the detected character- istics of the supply voltage. As an example, there may be detected an interruption that occurred in the sup- ply voltage. Reacting to a detected interruption may = involve e.g. initiating an exceptional-situations-

N sequence of operations in the connecting device that 3 30 is executing the method. Such an exceptional- © situations sequence of operation may involve reporting =E to an external device of the interruption; storing at + least one piece of information into nonvolatile memory

R within the connecting device; switching the connecting 3 35 device to use an alternative power source; and/or the

S like. If the connecting device includes sufficiently large capacitors or other temporary storages of elec-

tric energy, it may happen that even if its supply voltage disappears, the second controller and/or other circuitry may remain operational long enough to per- form some kind of a predefined safe shut-down sequence or even to bridge the gap (i.e. remain operational) until the supply voltage comes back.

One possible way of reacting to changes in step 913 comprises detecting that a change from an AC supply voltage to DC supply voltage has occurred, and as a response thereto making the connecting device in question produce output power at an exceptional- situations-level of power. In lighting systems that normally run on an AC supply voltage a sudden change to a DC supply voltage may mean that unexpected condi- tions like a fire have caused the electricity grid to fail. An emergency DC voltage source packs a limited amount of energy, on which the emergency lighting should remain active at least as long as it takes to evacuate the building. Reducing the output power of connection devices of light sources, i.e. making them assume an exceptional-situations-level of power, may help in ensuring that the emergency lighting remains on long enough. Alternatively the exceptional- situations-level may mean an unusually high level of output power, for example in order to ensure that all lights shine bright enough to ensure safe passage through the evacuation routes. = Fig. 10 illustrates a method in which, in ad-

N dition to what was shown and explained above with ref- 3 30 erence to fig. 9, step 1001 represents performing one © or more signal conversions that eventually convert the =E original switching pulses into the indicative signal * from which the detection of the supply voltage charac-

R teristics is made. Examples of such signal conversions 3 35 have been described above, for example with reference

S to the optoisolator 620 and the pull-up resistor 834 and capacitor 835. In fig. 10 the method also compris-

es detecting an output power of the connecting device, as illustrated by step 1002. The measured output power can be utilized for example to derive a representative voltage value of the supply voltage, as is explained in more detail later in this text. In addition to or as an alternative to output power, other output- related quantities like output current and/or output voltage can be detected and utilized for the same pur- pose.

Fig. 11 illustrates detecting an input power of the connecting device at step 1102. Such a measured input power can also be used to derive a representa- tive voltage value of the supply voltage. In addition to or as an alternative to input power, other input- related auantities like input current can be detected and utilized for the same purpose.

Fig. 12 illustrates examples of relationships between characteristics of supply voltage and switch- ing pulses that the PFC controller may provide to the switch in the switching regulator. Graph 1201 illus- trates a filtered and rectified supply voltage the representative voltage value of which is relatively large, as is seen by the relatively high half-waves in graph 1201. Graph 1202 is a schematic illustration of switching pulses that the PFC controller might provide to the switch in the switching regulator in such a case. It should be noted that the horizontal scale in = graph 1202 is not realistic but selected for the ease

N of illustration; if the cycle frequency of the supply 3 30 voltage is in the order of 50 Hz or 60 Hz, there © should be thousands or tens of thousands of switching

Ek pulses during each half-wave. + As schematically illustrated by graph 1202

R the duty cycle of the switching pulses is largest at 3 35 the smallest absolute values of the supply voltage and

S decreases so that it is smallest when the momentary magnitude of the filtered and rectified supply voltage is the largest. Also the frequency of the switching pulses may change, for example so that the frequency is largest at the smallest momentary absolute values of the supply voltage.

Graph 1211 illustrates a filtered and recti- fied supply voltage the representative voltage value of which is smaller than that illustrated by graph 1201. Graph 1212 is a schematic illustration of switching pulses that the PFC controller might provide to the switch in the switching regulator in such a case. Compared to the schematic representation given by graph 1202 there may be differences in any of fre- guency and duty cycle of the switching pulses or both, depending on the implementation and designed operation of the PFC controller. Here it is assumed that a smaller representative voltage value of the supply voltage makes the PFC controller provide the switching pulses at a higher frequency but with a duty cycle that does not go as low even at the largest momentary magnitude of the filtered and rectified supply voltage as in the case of larger representative voltage value.

From the viewpoint of conveying to the second controller, the train of switching pulses that is schematically illustrated by graphs 1202 and 1212 is a digital-valued signal in which the information content is encoded into the frequency and/or duty cycle at which changes between high and low values occur. > Concerning the varying freguency and duty cy-

N cle of the switching pulses it must be noted that 3 30 there may be also other factors affecting their varia- © tion than just the representative voltage value of the

Ek supply voltage. Whether such other factors affect also + the detection of the characteristics of the supply

R voltage performed by the second controller, depends on 3 35 what characteristics are to be detected. If for exam-

S ple the zero crossings in the supply voltage cause a pause or other easily detectable effect in the switch-

ing pulses, the second controller can be made to de- tect these and consequently detect the cycle frequency of the supply voltage irrespective of what other fac- tors affect the frequency and/or duty cycle of the switching pulses during their active period in the middle of the half-wave. For example with a signal conversion unit like that in fig. 8 a brief pause in switching pulses results in a corresponding interval during which the phototransistor in optoisolator 620 remains non-conductive, which in turn causes a momen- tary peak in the voltage across the capacitor 835. The second controller 818 may detect the frequency at which such peaks occur and divide it by two to obtain the cycle freguency of the supply voltage.

Another characteristic of the supply voltage that can be detected from the indicative signal with- out having to take into account other affecting fac- tors is the mere existence of a supply voltage. The operating voltage of a PFC controller typically comes rather straightforwardly from the supply voltage, so an interruption in the supply voltage, shown by graph 1221 in fig. 12, switches the PFC controller off and consequently ends the provision of switching pulses essentially instantaneously, as shown by graph 1222.

The second controller may remain operational for a significantly longer time, due to its operating volt- age coming from parts of the circuit that include rel- = atively large capacitors. The second controller may

N notice that the signal indicative of the switching 3 30 pulses assumes a constant value, because for example © in the connecting device of fig. 8 an interruption in

Ek the switching pulses causes the voltage across the ca- + pacitor 835 assume the value +V as quickly as the re-

R quired additional charge can flow through the resistor 3 35 834.

S Detecting a characteristic like the repre- sentative voltage value of the supply voltage may take some more elaborate processing in the second control- ler. The details of such processing may be designed on the basis of the known circuit topology and perfor- mance of the connecting device, and it may take into account for example a known relation between an input power and output power of the connecting device. If the second controller receives measured output voltage and current values as inputs like in figs. 6 and 8 for example, it can calculate the momentary output power.

If it additionally knows the frequency and duty cycle of the switching pulses in the PFC controller, having received a signal indicative thereof, it can use these and its knowledge of the momentary output power (and of the known efficiency of the connecting device) to calculate the representative value of the input volt- age. An example of a signal indicative of the behavior of the freguency and duty cycle of the switching puls- es over each half-wave is the voltage across the ca- pacitor 835 in the connecting device of fig. 8: since a larger representative voltage value of the supply voltage causes a correspondingly larger relative vari- ation of duty cycle during each half-wave (see graphs 1201 and 1202 in fig. 12), the voltage across capaci- tor 835 will exhibit a larger variation during each half-wave than if the representative voltage value was smaller.

Fig. 13 illustrates one possible way of how = the second controller may utilize the information it

N receives to derive a characteristic of the supply 3 30 voltage through calculation. Here it is assumed that © the second controller receives measured output voltage

Ek and current values as inputs, or otherwise becomes * aware of the momentary output (or input) power. Based

R on that it can select one of a number of preprogrammed 3 35 dependency relations, of which graphs 1301, 1302, and

S 1303 are shown as examples in fig. 13. Additionally the second controller is capable of interpreting a re-

ceived signal indicative of the PFC switching pulses as an indication of the smallest duty cycle that is encountered during the half-waves of the filtered and rectified supply voltage. From these pieces of input information the second controller can then calculate the representative voltage value of the supply volt- age. The example shown in fig. 13 concerns a case in which the output power is 17 watts, and the smallest duty cycle of the switching pulses is 17.5%, which makes the second controller derive a representative supply voltage value of approximately 232 volts.

Graph 1231 in fig. 12 illustrates a (filtered and rectified) DC supply voltage. As shown by graph 1232 the frequency and duty cycle of the switching pulses remain constant as long as there are no changes in other affecting factors such as the required output power. For example sending a command to a connecting device to brighten up the light sources is synonymous to requesting more output power, which necessarily means drawing more input power as well. As a result of such a command, if all other aspects remain the same, the duty cycle of the switching pulses in graph 1232 would assume a larger constant value.

Thus if the second controller receives a sig- nal indicative of a constant duty cycle of the switch- ing pulses over a period significantly longer than a typical AC cycle time (which is in the order of 20 > milliseconds in grid AC voltages), it may proceed to

N detecting that the supply voltage is DC. In the exem- 3 30 plary implementation of fig. 8 the second controller © could make such a detection by noting that the voltage =E across capacitor 835 remains constant over a period + significantly longer than a typical AC cycle time

R and/or only changes in response to implemented changes 3 35 in the brightness of the light sources.

S In those cases where detecting a characteris- tic of the supply voltage requires calculation from measured values, tolerances in component values may cause the calculation to give different results in different connecting devices. One particular component in this respect is the inductor in the switching regu- lator that performs power factor correction (winding 601 in figs. 6 to 8). The inductance of the inductor affects the way in which the representative voltage value of the supply voltage can be calculated from a detected frequency and/or duty cycle of switching pulses. If this dependence on inductance (and/or other component value tolerances in the connecting device) is modest and if the representative voltage value does not need to be detected very accurately, one may just accept it as a fact that the representative voltage values that eventually can be detected will be only approximate. If better accuracy is needed, calibration can be performed for example during testing that typi- cally is performed on the manufacturing line anyway.

Such testing may involve e.g. feeding supply volt- age(s) of known magnitude to the device under test, noting the representative supply voltage value(s) that the device initially detects, and programming the de- vice to apply a correction coefficient in its calcula- tions so that as a result, better fidelity is achieved between actual supply voltage values and detected rep- resentative voltage values.

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 3 30 ways. The invention and its embodiments are thus not © limited to the examples described above, instead they

Ek may vary within the scope of the claims. For example, + even if certain boost-type and flyback-type switching

R regulators have been considered in the circuits of 3 35 figs. 6, 7, and 8, this is not a restriction from the

S viewpoint of the invention. Other types of regulators can be used to perform the power factor correction in producing the first voltage, as well as any possible further conversions between the first voltage and the output voltage. o

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Claims (14)

1. A connecting device for one or more light sources (101), the connecting device being equipped for detecting characteristics of a supply voltage to the connecting device and comprising: - a supply voltage input (102) for receiving said sup- ply voltage, - a switching regulator (204, 304) coupled to said supply voltage input (102) and configured to produce a first voltage, - an output stage (206, 306) coupled to receive said first voltage or another voltage derived from said first voltage, and configured to produce an output voltage of the connecting device, - a PFC controller (208, 308, 605, 705) configured to make said switching regulator (204, 304) perform power factor correction in producing said first voltage, wherein said PFC controller (208, 308) is configured to provide switching pulses to a first switch (603) in said switching regulator (204, 304), and - a second controller (209, 309, 409, 618, 718, 818); characterized in that: - the connecting device comprises a signal coupling (210, 310) from said switching regulator (204, 304) to said second controller (209, 309, 409, 618, 718, 818), configured to convey to said second controller a sig- O nal indicative of said switching pulses, and < - said second controller (209, 309, 409, 618, 718, 2 818) is configured to detect said characteristics of © 30 said supply voltage on the basis of at least said sig- > nal. Ao a

O 2. A connecting device according to claim 1, 5 wherein said signal coupling (210, 310) is a coupling 2 from a switching pulses line to a signal input of said N 35 second controller (209, 309, 409, 618, 718, 818), wherein said switching pulses line is a coupling from a switching pulses output of said PFC controller (208, 308, 605, 705) to a control input of said first switch (603).

3. A connecting device according to any of claims 1 or 2, wherein: - said connecting device comprises a primary side and a secondary side with galvanic isolation between said primary and secondary sides, - said switching regulator (204, 304) is on said pri- mary side, - said output stage (206, 306) and said second con- troller (209, 309, 409, 618, 718, 818) are on said secondary side, and - said signal coupling (210, 310) crosses said galvan- ic isolation through a galvanically isolating inter- face (311, 620).

4. A connecting device according to any of claims 1 to 3, wherein said second controller (209, 309, 409, 618, 718, 818) comprises a programmable cir- cuit.

5. A connecting device according to claim 4, wherein: - said connecting device comprises an external control interface (111) coupled to said programmable circuit, and = - said programmable circuit is configured to transmit N information indicative of said detected characteris- 3 tics of said supply voltage through said external con- © trol interface (111) towards a remote receiver. I E 30 6. A connecting device according to any of C claims 4 or 5, wherein: Lo - said second controller (209, 309, 409, 618, 718, > 818) is configured to detect at least one of an input power and an output power of the connecting device,

and - said programmable circuit is programmed to derive a representative voltage value of said supply voltage on the basis of said signal and the detected input and/or output power.

7. A connecting device according to any of the preceding claims, wherein said second controller (209, 309, 409, 618, 718, 818) is configured to detect a cycle freguency of said supply voltage on the basis of said signal.

8. A connecting device according to any of the preceding claims, wherein said second controller (209, 309, 409, 618, 718, 818) is configured to detect an interruption in said supply voltage on the basis of said signal.

9. A method for detecting characteristics of a supply voltage to an connecting device for one or more light sources, the method comprising: - using a switching regulator to perform power factor correction as a part of converting (902) the supply voltage (901) into a first voltage (903), - deriving an output voltage (907) from said first voltage (903) for delivering to said one or more light sources, and - using a signal indicative of switching pulses to a = switch of said switching regulator to detect (910) N characteristics of said supply voltage. 3 ©

10. A method according to claim 9, wherein said detecting (910) of said characteristics of said E 30 supply voltage comprises detecting at least one of: a C cycle freguency of said supply voltage, a representa- Lo tive voltage value of said supply voltage, an inter- > ruption of said supply voltage.

11. A method according to any of claims 9 or 10, comprising transmitting (912) information indica- tive of said detected characteristics of said supply voltage towards a remote receiver.

12. A method according to any of claims 9 to 11, comprising: - measuring (1002, 1102) at least one of an output power or input power of the connecting device, and - using the measured output and/or input power to de- rive a representative voltage value of said supply voltage.

13. A method according to any of claims 9 to 12, comprising: - as a response to detecting an occurred interruption of said supply voltage, initiating (913) an exception- al-situations-seguence of operations in said connect- ing device, wherein said exceptional-situations- seguence of operations comprises at least one of: re- porting to an external device of the interruption, storing at least one piece of information into nonvol- atile memory within the connecting device, switching said connecting device to use an alternative power source.

14. A method according to any of claims 9 to 13, comprising: = - as a response to detecting an occurred change from N AC to DC in said supply voltage, making (913) said 3 connecting device produce output power at an excep- © tional-situations-level of power. = a R 3 &