GB2507982A

GB2507982A - Converter module and method for dimming at least one LED

Info

Publication number: GB2507982A
Application number: GB1220555.5A
Authority: GB
Inventors: Phillip Jermyn
Original assignee: Tridonic GmbH and Co KG
Current assignee: Tridonic GmbH and Co KG
Priority date: 2012-11-15
Filing date: 2012-11-15
Publication date: 2014-05-21
Also published as: GB201220555D0

Abstract

A converter module for dimming of at least one LED, comprises a switching converter supplying power to the at least one LED, the converter being operated in a borderline mode, the converter having connected on its input side a passive bleed circuit R10, C10 to generate a holding current for a dimmer, and wherein the converter module is configured to be controlled by a phase controlled/triac dimmer. An arrangement is also claimed in which a detection means is provided for detecting a current/voltage input to the converter and a control unit is provided, the control unit being adapted to modify a switch-off threshold of the converter switch depending on the current/voltage detected at the detection means.

Description

Method for dimmin2 at least one LED The invention relates to converter modules for allowing dimmable operation of LEDs, which are dimmable by a phase control dimmer (Triac). Triacs are still widely used as infrastructure for dimming of lighting bulbs.

It is a known fact that lighting bulbs directly convert the leading phase angle to a corresponding light output, The operation of a dimmable converter module is different as the leading phase angle cannot be converted directly to a corresponding variable light output in a typical LED operating device.

The converter module can be configured for operating of at least one LED bulb. e.g-. a LED retrofit lamp, which may show a limited dimming functionality. Alternatively or additionally, the converter module may also he part of an LED bulb or LED retrofit lamp, e.g. as a module integrated into the bulb/lamp.

The converter module according to the invention includes a control unit.1convertcr driver, which either controls a flyback converter with a galvanic scparatcd primary and secondary side, which e.g. is operated in borderline mode, or a buck converter. Other converter topologies are also possible to he used with the inventive concepts presented.

The switch-on time (T0) of a switch of the flyback converter may be kept on a constant level during on halfcycle/-pcriod of the supply voltage supplied to the converter module. The switch-off time (T)fl) can then he detennined, or results from, the currcnt value of the supply current/voltage. Typically. the supply current'voltagc is a mains current/voltage. but may also he a different input voltage.

In operation. a variation or fluctuation of the supply current voltage, e.g. resulting from a phase cutting dimming action, may result in a variation or fluctuation of the LED input voltage.

Power control methods and apparatuses in which a switching power supply provides power factor correction and an output voltage to a load via control of a single switch, without requii-ing any feedback information associated with the load al-c known from W0200/8 137460 A2. There, a single switch may be controlled without monitoring either the output voltage across the load or a current drawn by the load, without regulating either thc output voltage across the load or the current drawn by the load.

The RMS value of an AC input voltage to the switching power supply may be varied via a conventional AC dimmer to in turn control the output voltage. The switching power comprises a flyback converter configuration, a buck converter configuration, or a boost converter configuration, and the load may comprise an LED-based light source.

There arc dimmable also known control units, which show a variety of approaches to the problem of controlling Triac behavior/phase control dimming and converting the phase angle into an LED current. A disadvantage of these approaches is that they require a high bill of materials (BUM) and, e.g. require double-sided printed circuit boards (PCB5) It is hence a goal of the invention, to provide a LED operating device that allows dimming of LEDs connected thercto to bc dimmable by a phase control/phase-cutting leading-edge/Triac dimmer, while keeping the additional costs as low as possible.

This problem is solved with a device, method and system acccrding to the independent claims. Further aspects of the invention are addressed in the dependent claims.

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In a first aspect, the invention provides a converter module for dimming of al least one LED. comprising a switched/clocked converter supplying power to the at least one [El). the converter being operated in a borderline mode, the converter having connected on its input side a passive bleed circuit to generate a holding current for a dimmer, and wherein the converter module being configured to he controlled by a phase controlleditriae dimmer.

In another aspect, the invention provides a converter module for dimming of at least one LED, comprising a switched/clocked converter supplying power to the at least one LED, the converter being operated in a borderline mode, a detection means for detecting a current/voltage input to the converter, in particular on its primary side, and a control unit adapted to modify a switch-off threshold of the converter switch depending on the current/voltage detected at the detection means.

The passive bleed circuit may consist of a capacitor (C 10) and/or a resistor (RIO) connected in series. Damping resistors (RI, R9) can he conductively connected in input current/voltage paths of the converter. e.g. a live and a neutral wire, respectively.

The damping resistors and/or the bleed circuit may be configured to dampen a ringing of a radio frequency interference inductor of the dimmer.

The converter maybe a flybaek converter. The converter can he controlled by a control unit. In borderline mode, the converter switch may be switched on, when the input current reaches a predefined threshold level. e.g. 0 Ampere.

A detection means can he provided to switch the converter switch dependent on the input current/voltage of the converter.

The detection means can be an auxiliary winding, in particular galvanically separated from a converter winding, especially arranged on the convertefs primary side. The detection means can feed back a parameter indicating indirectly or directly the input current/voltage of the converter.

The control unit may be a PFC fixed controller and/or a PFC fixed output controller.

The control unit can comprise a DC-bus capacitor and/or a shaping circuit adapted to control an input current/voltage drawn from a supply voltage source during a half-cycle.

A PFC, in particular a passive PFC circuit, can he comprised in the control unit and/or in the converter module. The contr& unit may comprise a switch of the flyback converter.

A feedback signal can be supplied to the control unit from the detection means.

The detection means may be provided on the primary side of a flyback converter and preferably feeds back, directly or indirectly, a parameter to the control unit indicative of the current/voltage through the primary side of the flyback converter, 1 0 The detection means can feed back a current/voltage dependent on the input current/voltage to the module as a negative current/voltage to the control unit, the fed back current/voltage being indicative of the current/voltage through a shunt resistor arranged in series with the flyhack converter switch, e.g. internal to the control unit.

The control unit may generate a current/voltage, and wherein the control unit can he adapted to modify the input current/voltage supplied to the converter, in particular on the converter's primary side, preferably as a fimction of the generated current/voltage.

The control unit can influence the input current/voltage supplied to the converter as a function o[ a phase cutting by modi ving the peak current. i.e. the current/voltage that changes on switching-off the flyback converter, and in particular by modifying the peak current/voltage to be substantially proportional to the currently applied amplitude of the input current:voltage.

An energy storage unit is provided, can he particular on the primary side of the flyback converter.

In particular on the secondary side of the flyback converter, a storage capacitor can be provided dimensioned to compensate ripple on the input current/voltage supplied to the converter module.

The switch-off threshold of the control unit and/or the Ilyback switch can he adaptively set as a thnction of the input current/voltage of the converter to facilitate PFC functionality.

In the feedback path from the detecting means to the control unit, a Zener diode may be connected to clamp the negative current/voltage fed back to the control unit to a maximal value. The clamping may he additionally or alternatively performed internally in the control unit and/or by software of the control unit.

The converter can he a buck converter. The auxiliary winding may only have a few windings, e.g. 1-7, especially at least two windings. adapted to reduce the current/voltage supplied to the control unit and/or to reduce the power loss at the control unit.

In another aspect, a method for dimming at least one LED is provided, comprising the steps of supplying a converter module with an input current/voltage controlled by a phase controlled/triae dimmer, supplying power to the at least one LED by a switched/clocked converter, the converter being operated in a borderline mode, and generating. by a passive Needing circuit, a holding current for the phase controlled/triac dimmer.

In yet another aspeeL a method fr dimming at least one LED is provided, comprising the steps of supplying a converter module with an input current/voltage controlled by a phase controlled/triac dimmer. supplying power to the at least one LED by a switched/clocked converter, the converter being operated in a borderline mode, and detecting, by a detection means, a current/voltage input to the converter, in particular on its primary side. modi'ing a switch-off threshold of the converter switch depending on the current/voltage detected by the detection means through control unit.

In yet a further aspect, a system comprising a phase controllcd/triae dimmer and a converter module as described above is provided.

Further aspects of the invention arc now explained with reference to the drawings. In particular.

Fig. 1 shows an exemplary dimming driver based on a PFC fixed output controller; Fig. 2 shows an exemplary input current waveform; Fig. 3 shows an exemplary power factor corrected buck converter; Fig. 4 shows an existing PFC scheme; Fig. 5 shows an exemplary fixed output driver with PEC; Fig. 6 exemplarily shows converter peak primary cunents without clamping; Fig. 7 exemplarily shows ccnverter peak primary currents with clamping; Fig. 8 exemplarily shows converter mains input currents without clamping; Fig. 9 exemplarily shows converter mains input currents with clamping; Single-stage fixed output flyback driver control units (IC) with build-in power factor correction arc known, however, it turns out that this control unit type can be used to make a simple and elegant dimming solution, with very good performance, as described herein.

In general, the invention aims at providing a smooth and flicker-free dimming, which can be achieved in connection with a great majority of dimmers, decreasing the amounts of parts and bill of material, which at the same time can be adapted to work with diffcrcnt 1(Ts. Also, no high-voltage electrolytic capacitor needs to he present.

To achieve this, the circuit provided in the converter module for controlling the at least one LED. may provide a power thctor correction (PFC) thnctionality, e.g. a "true" PFC circuit, a flyback converter with PFC functionality, etc. In particular, the invention exploits the high power factor of a PFC circuit, If a flyback converter is used, the current/voltage on the secondary side of the flyhack converter, driving the at least one LED. mirrors the dimming performed via phase cutting or phase firing at the input of the primary side of the converter.

In this, the problem exists that the PFC circuit sometimes does not draw enough current, which is needed by the (Triac) dimmer used for phase cutting or phase firing dimming as holding current. Bleeding circuits are known to address this symptom and to guarantee the required holding current through their power loss. Typically these bleeding circuits are formed as conductive pathways that can be selectively activated or deactivated.

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The invention, however, solves the problem by using only passive components for realizing the bleeding circuits, and in particular an ohmic resistor RIO and a capacitor (:10 as shown in the exemplary LED operating device circuit shown in Fig. 1.

Further, two additional ohmic resistors RI. R9 are connected to the input lines of the circuit labeled live/phase wire and neutral wire in Fig. 1, which is advantageous to dampen the ringing generated at the input of the circuit generated by an interaction of the phase control/Triac dimmer with inductive character and a PFC circuit with a capacitive switch.

Fig. 1 shows a setup, with additional passive components to dampen a ringing RI, R9 of the dimmer's radio frequency interference (RFI) inductor with circuit capacitance.

This, in turn, produces smooth, flicker-free dimming. Fig. 1 hence shows a circuit for a converter module including a PFC fixed output controller. The circuit with PFC functionality is realized by using a control unit inteated circuit, e.g. the flyhaek converter driver, with an integrated switch.

The components circled in Fig. 1 are the extra components for dampening the ringing RI, R9 and for forming the passive bleed Rio, cli). However, the circuit shows a very low complexity of the converter itself using the latest fixed output control units.

Further, an auxiliary winding is provided, which is inductively coupled to the converter and in which a current/voltage is generated depending on the supply voltage of the LED operating device. This generated voltage is supplied as negative current/voltage to the control unit. The generated voltage is also indicative of the current/voltage through a shunt resistor, coupled in senes with a control unit internal switch. The switch-off threshold is ol the control unit changed adaptively. i.e.

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depending on the current state of the supply voltage, which results in the PFC functionality.

In order to facilitate dimming operations as function of a leading phase angle of the supply voltage, a feedback signal is fed back to the control unit from a detecting means. e.g. an auxiliary winding AUX of the converter. In particular, the current through the detecting means is measured to detennine the current in the converter, preferably the current through the primary side of a flyhack converter. By this, the control unit directly or indirectly deternunes the current/voltage, for example, through the primary side of the flyback converter. This determined current/voltage is the signal fed back to the control unit. The control unit may be an IC, ASIC or a micro controller.

If the converter is e.g. realized as a flyback converter, the circuitry of the converter module may provide an energy storage (capacitor) on the secondary side of the converter, the flyhack providing a inductive separation between components arrangcd on its primary side and components arranged on its secondary side. The auxiliary winding as e.g. shown in Fig. S may also he located on the secondary side.

A flyback converter with constant on-time (T00) could also realize the PFC lünctionality without a feedback supplied to the driver IC from the auxiliary winding.

However, the power factor would not be as good. An example for a control unit used is HVLED8O5 by ST Microelectronics.

A single stage power factor corrected control unit may also have a small DC-bus capacitor in the region of about I OOnF, A Ilyhack converter therefore receives as its input unsmoothed rectified mains half cycles which may descend all the way to OV.

Application of such a driver IC allows for an excellent dimming performance with the majority of leading and trailing edge dimmers. The circuitry will typically fit onto a single-sided printed circuit hoard, and, since the technique will work with almost any PFC fixed controller, designs can he easily adapted to suit applications using the latest, low-cost ICs.

Also, while Fig. I shows potential output ripple being controlled only by an output capacitor, the simplicity of the circuitry leaves space for a large capacitor, which allows the ripple to be kept below 40% to 60%, especially 50%.

S As a control factor, the control unit generates a current/voltage, which is used to modify the current of the flyback converter on its primary input side, In particular, a dimming operation depends on the phase cutting as the peak current, i.e. the current at the flyback converter switch-off is modified, and the peak current is controlled to he basically proportional of the amplitude of the input voltage present at the moment.

In result, depending on the phase cut, a current characteristic as exemplarily shown in Fig. 2 might be generated.

It should be noted that the converter module circuit also may be implemented with IS other converters, such as buck converter topologies. Also, the control unit may comprise power factor correction (PFC) hut this is not mandatory. However, improving the power factor of the converter module circuit is desirable and hence in the following a method to add power I actor conection to any control unit is described.

especially for control units with an external peak current sense resistor.

Specifically, when a control unit with only source input is used (e.g. NXP SSL21083, which in contrast. e.g. T-IVLED8 15 has only one source input) to deteniuine a current/voltage at the shunt resistor, a different approach may be used. In Fig. 3 such a control unit is shown in a setup with a buck converter.

At the source input of the control unit as shown in Fig. 3, a relatively low impedance of e.g. about 1 to 5 0. preferably 2,7 12, is connected. In case a relatively high negative current/voltage would be detected at this input delivered from the detecting means, the power loss would be improperly high.

Hence, the power loss is limited by significantly reducing voltage at the detecting means. This is achieved by reducing the turns of e.g. the auxiliary winding to only a few turns, e.g. to 1 to 5 turns, especially about two turns. In result the current/voltage

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at the detecting means can be reduced and also with lower impedance the power toss can be reduced.

In more detail, the control unit contains a control system which includes a current sense resistor to measure a peak inductor current during the time that the main switch is on, In a non-PFC device, the switch generally gets switched-off when the voltage drop across the current sense resistor reaches a pre-detcrmincd value, The peak current flowing through the inductor represents a known amount of energy, and, in combination with a known switching frequency, this provides the basis for power output control or current control.

The power factor associated with such a scheme tends to he poor, even if a bulk IS storage capacitor is small. This is because the switch-on time might be relatively long when the supply voltage is low (during the mains values). This is because it takes longer for the inductor current to ramp up to the required peak value. Consequently, the mean input current is high during these periods and low during the mains voltage peaks. This is the exact opposite of the current waveform required for high power factor.

In order to correct this, the detecting means can he added to the inductor. This is to provide a negative current/voltage while the main switch is on. This current/voltage then is applied to the control unit's current sense CS input via a second resistor. Fig. 3 shows an example in which the technique has been applied to an inexpensive buck converter. Hence. this Fig. 3 shows a powcr factor corrected buck converter.

The negative current/vollage provided by the auxiliary winding will vary depending on the supply voltage at the moment. When the main switch is on, a current will flow through resistor R3 and owing to the varying negative current/voltage, the current/voltage will be raised when the input current/voltage is at its peak and greatly reduced during supply voltage valleys. The currents through resistor 1(3 shunts current away from the sense resistor R4, increasing the final peak current by an amount which depends upon the input voltage at this instant. The result is an input current which is fairly constant over the majority of each half-cycle of the supply voltage providing a greatly improved power factor.

Again, the resulting typical cun-ent waveform is shown in Fig. 2, in this case a typical input current waveform with power factor correction.

However existing implementations require that the control unit's current sense input is separate from the pin carrying the actual current as shown in Fig. 4. which is a typical I 0 example for an existing PFC scheme.

In Fig. 1, the sense resistor R5 is not connected directly to the control unit's current sense (S input. Instead, is connected wire resistor R7. This raises the impedance sufficiently to allow the method to work using the standard auxiliary winding present in a typical fly-back converter, By providing a separate winding as shown in Fig. 3, comprising a small number of turns, thc technique can he generalized to work with any driver IC having an external current sense resistor.

F his solution is particularly relevant for applications with buck converters, because the turns of the auxiliary winding can simply be wrapped around a standard drum inductor.

En summary, the setup shown in Fig. 3 exhibits a very low cost and widely applicable power factor correction method providing power Factors of 80% to 90%, in particular around 85%. and a total harmonic distortion (THD) of around 25-45%, in particular 3O%-4O%, Also, this setup can be easily adapted for control units and may also be combined with the setup as shown in Fig. I. Another example for an inventive circuitry is shown in Fig. 5, showing a schematic for a modified PFC scheme. While there are a number of ways in which a PFC can he achieved, one common method is to feed contribution from an detecting means into the control unit's peak current detection circuit via an external resistor, as previously outlined.

While the converter's switching transistor is on, the output from the detecting means is negative and proportional to the mains input voltage at that moment. The feed from the detecting means has the effect of increasing the peak cutTent reached through the S primary winding by an amount proportional to the instantaneous supply voltage. The contribution to the peak current actually dominates, with a result that the current drawn by the converter becomes roughly sinusoidal, providing high power factor.

In summary. the wiring to the control unit is changed to compensate fin changes or tluctuations in the supply voltage resulting in changes in the light output emitted by the at least one lID.

For this reason, a Zener diode shown in Fig. 5 is provided in the feedback path from the detecting means at the converter to the control unit to clamp the negative current/voltage fed back to the control unit to a maximal and/or predetincd value.

Above this value, the voltage remains clamped and hence constant and changes or fluctuations out of the clamping range are disregarded. instead of a Zener diode, the clamping can also he facilitated by internal means of the control unit and/or control unit software.

This improves the regulation properties in respect to stability of the output current/voltage of the converter, taking into account a slight declinc of the power factor as described in the following.

A drawback to the described method can be seen in that the converter output becomes dependent upon the mains supply voltage. The output regulation with respect to the input voltage fluctuations is poor. Ho\vevcr, this can he improved by regulating with only minor degradation of power factor as shown below.

As shown in Fig. 5, the original PFC was achieved by resistor RS, which was connected directly between the auxiliary winding and the control unit's current sense input and the higher potential side of resistor R7. Fig. 5 now shows some additional component enclosed in the box shown. In particular, a shunt reference U2 of the control unit (e.g. a 2,5V) clamps the voltage at the lower potential side of resistor R8 to a maximum magnitude of a negative voltage, e.g. I to SV. especially 2.5V negative.

This voltage is then applied to the driver IC's current sense input via resistor R27.

Power factor correction is still provided but the maximum amount is limited by the claimed voltage. Hence, increases in the supply voltage can 110 longer increase the maximum peak current.

Figs. 6 and 7 show peak currents envelope wavefonns with and without modification.

hO The positive envelope shows the peak current variation. In particular, Fig. 6 shows the peak current envelope without clamping while Fig. 7 shows the peak current envelope hay with clamping.

In this example, the output regulation with respect to the input voltage is improved by a factor of about 3. while the power factor slightly declines about 1%-4°A, e.g. from 88% to e.g. 84%.

Further, Figs. 8 and 9 show input current waveforms with aid without modification.

As can he seen from Figs. 8 and 9. there is only very little diflèrence in the converter mains input currents. In particular, Fig. 8 exemplarily shows the converter main's input currents without clamping and a power factor of e.g. 88%, while Fig. 9 exemplarily shows converter mains currents with clamping and a power factor of e.g. 84%.

Hence, the regulation is improved to better than about -1-5% across the mains voltage range. while the method can easily be adapted to different control units.

Claims

Claims I. A converter module for dimming of at east one LED, comprising -a switched/clocked converter supplying power to the at least one LED, the converter being operated in a borderline mode.-the converter having connected on its input side a passive bleed circuit to generate a holding current for a dimmer, and wherein -the converter module being configured to he controlled by a phase controlledrtnac dimmer.ID
2. A converter module for dimming of at least one LED, comprising -a switched/clocked converter supplying power to the at least one LED, the converter being operated in a borderline mode, -a detection means for detecting a current/voltage input to the converter, in IS particular on its primary side, and -a control unit adapted to modify a switch-off threshold of the converter switch depending on the current/voltage detected at the detection means.
3. Converter module of claim 1, wherein the passive bleed circuit consists ot'a capacitor (C 10) and/or a resistor (RED) connected in series, and wherein damping resistors (Ri. R9) arc conductively connected in input current/voltage paths of the converter, eg. a live and a neutral wire, respectively, wherein the damping resistors and/or the bleed circuit are configured to dampen a ringing of an radio frequency interference inductor of the dimmer.
4. Converter module according to clain1 1 or 2. wherein the converter is a flyhaek converter.
5. Converter module according to any one of the preceding claims, wherein the converter is controlled by a control unit.
6. Converter module according to any one of the preceding claims, wherein in borderline mode, the converter switch is switched on, when the input current reaches a predefined threshold level, e.g. 0 Ampere.
7. Converter module according to any one of the preceding claims, wherein a detection means is provided to switch the converter switch dependent on the input current/voltage oithe converter.
8. Converter module according to any one of the preceding claims.wherein the detection means is an auxiliary winding, in particular galvanically separated from a converter winding, especially arranged on the converter's primary side, and wherein the detection means feeds back a parameter indicating indirectly or directly the input current/voltage of the converter.
9. Converter module according to any one of the preceding claims, wherein the control unit is a PFC fixed controller and/or a PFC fixed output controller.
ID. Converter module according to any one of the preceding claims, wherein the control unit comprises a DCbus capacitor and/or a shaping circuit adapted to control an input current/voltage drawn from a supply voltage source during a half-cycle.
11. Converter module according to any one of the preceding claims, wherein a PFC. in particular a passive PFC circuit, is comprised in the control unit, and wherein thc control unit comprises a switch ol'the flyback converter.
12. Converter module according to any one of the preceding claims., wherein a feedback signal is supplied to the control unit from the detection means.
13. Converter module according to any one of the preceding claims, wherein the detection means is provided on the primary side of a flyback converter and preferably feeds back, directly or indirectly, a parameter to the control unit indicative of the current/voltage through the primary side of the flyback converter.
14. Converter module according to any one of the preceding claims, wherein the detection means feeds back a current/voltage dependent on the supply culTent/voltage input to the module as a negative current/voltage to the control unit, the fed back current/voltage being indicative of the current/voltage through a shunt resistor arranged in series with the flyhack converter switch, to e.g. internal to the control unit.
15. Converter module according to any one of the preceding claims, wherein the control unit generates a current/voltage, and wherein the control unit is adapted to modify the input current/voltage supplied to the converter, in particular on the converter's primary side, preferably as a frmnction of the generated current/voltage.
16. Converter module according to any one of the preceding claims, wherein the control unit influences the input current/voltage supplied to the converter as a function of a phase cutting by modifying the peak current. i.e. the current/voltage that changes on switching-off the flyback converter, and in particular by modifying the peak current/voltage to be substantially proportional to the currently applied amplitude of the input currcnt/voltage
17. Converter module according to any one of the preceding claims, wherein an energy storage unit is provided, in particular on the primary side of the tlyhack converter.I. Converter module according to any one of the preceding claims, wherein, in particular on the secondary side of the flyback converter, a storage capacitor is provided dimensioned to compensate ripple on the input current/vohage supplied to the converter module.19. Converter module according to any one of the preceding claims, wherein the switch-off threshold of the control unit and/or the flyback switch is adaptively set as a frmnction of the input current/vohage of the converter to facilitate PEC functionality.20. Converter mod We according to any one of (he preceding claims, wherein in the feedback path from the detecting means to the control unit, a Zener diode is connected to clamp the negative current/voltage fed back to the control unit to a maximal value and/or wherein the clamping is perthrmed internally in the control unit and/or by software of the control unit.2!. Converter module according to any one of the preceding claims, wherein the converter is a buck converter and wherein the auxiliary winding only has a few windings, e.g. 1-7, especially at least two windings, adapted to reduce the current/voltage supplied to the control unit and/or to reduce the power loss at the control unit.22. A method for dimming at least one LED, comprising the steps of -supplying a converter module, according to anyone of the preceding claims, with an input current/voltage controlled by a phase controlled/triac dimmer, -supplying power to the at least one LED by a switched/clocked converter, the converter being operated in a borderline mode, and -generating, by a passive bleeding circuit, a holding current for the phase controlled/triae dimmer.23. A method for dimming at least one LED, comprising the steps of -supplying a converter module, according to anyone of the preceding claims.with an input current/voltage controlled by a phase controlled/triac dimmer.-supplying power to the at least one LED by a switched/clocked converter, the converter being operated in a borderline mode, and -detecting. by a detection means, a eun-ent/voltage input to the converter, in particu'ar on its primary side.-rnodi'ing a switch-off threshold of the converter switch depending on the current/voltage detected by the detection means through control unit.24. A system comprising a phase controlied/triac dimmer and a converter module according to any one of the claims 1-21.25. A converter module substantially as hcreinhefore described with reference to and/or substantially as illustrated in any one of or any combination of the accompanying drawings.26. A method for dimming at least one LED, substantially as hereinbefore described with reference to and/or substantially as illustrated in any one of or any combination of the accompanying drawings.27. A system comprising a phase eontrolled/triac dimmer and a converter module, substantially as hercinbefore described with refcrence to and/or substantiaLly as illustrated in any one of or any combination of the accompanying drawings.