Lighting system, electronic device for a lighting system and method for operating the electronic device

1. An electronic device for a lighting system, wherein the lighting system comprises a TRIAC dimmer and is configured to receive a mains supply voltage and to provide a phase cut voltage to the electronic device, wherein the electronic device comprises:

a control loop that is configured to control a duty cycle of a switched voltage converter that receives a rectified phase cut voltage as an input voltage and provides a drive current to a light emitting semiconductor device,

the control loop comprises an error amplifier that is coupled to receive a sense voltage that is indicative to a current through the light emitting semiconductor device,

the error amplifier being configured to provide a feedback signal to a pulse width modulation logic that is configured to control the duty cycle of the switched voltage converter so as to provide a constant drive current to the light emitting semiconductor device in response to the sense voltage and

the error amplifier being coupled to receive a reference voltage that is a function of the input voltage, wherein a DC path is present between the inverting input of the error amplifier that is coupled to the reference voltage and an output terminal of the error amplifier.

2. The electronic device according to claim 1 , wherein a non-inverting input of the error amplifier is coupled to the reference voltage and the inverting input is coupled to the sense voltage.

3. The electronic device according to claim 1 , wherein the function between the input voltage and the reference voltage is defined by a voltage divider.

4. The electronic device according to claim 1 , wherein the current through the light emitting semiconductor device is sensed by a fixed shunt resistor and the sense voltage is a voltage across the shunt resistor.

5. The electronic device according to claim 1 , wherein the input voltage that is coupled to the non-inverting input of the error amplifier as a reference voltage is filtered by a low-pass filter and is limited to a predetermined maximum voltage.

6. The electronic device according to claim 1 , wherein an output terminal of the error amplifier that is providing the feedback signal is coupled to a load.

7. The electronic device according to claim 1 , wherein the error amplifier is an operational amplifier.

8. The electronic device according to claim 1 , wherein the error amplifier is a rail-to-rail type operational amplifier.

9. An electronic device for a lighting system, wherein the lighting system comprises a TRIAC dimmer and is configured to receive a mains supply voltage and to provide a phase cut voltage to the electronic device, wherein the electronic device comprises:

a control loop that is configured to control a duty cycle of a switched voltage converter that receives a rectified phase cut voltage as an input voltage and provides a drive current to a light emitting semiconductor device,

the control loop comprises an error amplifier that is coupled to receive a sense voltage that is indicative to a current through the light emitting semiconductor device,

the error amplifier being configured to provide a feedback signal to a pulse width modulation logic that is configured to control the duty cycle of the switched voltage converter so as to provide a constant drive current to the light emitting semiconductor device in response to the sense voltage and

the error amplifier being coupled to receive a reference voltage that is a function of the input voltage, further comprising a compensation network that is configured to define a bandwidth of the electronic device that is substantially lower than 2 Hz.

10. A method for operating a an electronic device for a lighting system, wherein the lighting system comprises a TRIAC dimmer and is configured to receive a mains supply voltage and to provide a phase cut output voltage to the electronic device, the method comprising:

receiving a phase cut voltage from the TRIAC dimmer;

rectifying the phase cut voltage to provide a rectified input voltage;

converting the input voltage with a switched voltage converter so as to provide a drive current to a light emitting semiconductor device;

receiving a sense voltage that is indicative to a current through the light emitting semiconductor device at an error amplifier;

coupling an output signal of the error amplifier as a feedback signal to a pulse width modulation logic that is a part of a control loop of the electronic device and that is configured to control a duty cycle of the switched voltage converter so as to provide a constant drive current to the light emitting semiconductor device in response to the sense voltage;

coupling a reference voltage that is a function of the input voltage to the error amplifier;

providing a DC path between the inverting input of the error amplifier that is coupled to the reference voltage and an output terminal of the error amplifier; and

providing an updated feedback signal to the pulse width modulation logic to vary a duty cycle of the switched voltage converter so as to provide an updated constant drive current to the light emitting semiconductor device in response to the sense voltage and the reference voltage.

11. A lighting system comprising a TRIAC dimmer that is configured to receive a mains supply voltage and to provide a phase cut voltage to an electronic device for providing a drive current to a light emitting semiconductor device, wherein the electronic device comprises:

a control loop that is configured to control a duty cycle of a switched voltage converter that receives the rectified input voltage and provides a drive

current to the light emitting semiconductor device;

the control loop comprises an error amplifier that is coupled to receive a sense voltage that is indicative to the drive current through the light emitting semiconductor device;

the error amplifier is configured to couple a feedback signal to a pulse width modulation logic that is configured to control the duty cycle of the switched voltage converter so as to provide a constant drive current to the light emitting semiconductor device in response to the sense voltage;

the error amplifier is coupled to receive a reference voltage that is a function of the input voltage provided to the electronic device; and

further comprising a compensation network that is configured to define a bandwidth of the electronic device that is substantially lower than 2 Hz.