Driver device and driving method for driving a load, in particular an LED unit
The present invention relates to a driver device ( 40; 50; 60 ) and a corresponding driving method for driving a load ( 12 ), in particular an LED unit ( 12 ) including one or more LEDs, said driver device comprising a power input unit ( 14 ) for receiving an input voltage (V 10 ) from an external power supply ( 18 ) and for providing a rectified supply voltage (V 12 ), a controllable resistor ( 48 ) for providing a load current (I L) to power the load ( 12 ), a frequency filter ( 42 ) connected to the power input unit ( 14 ) for providing a voltage (V 18 ) to the load ( 12 ), wherein the frequency filter ( 42 ) is partially coupled in parallel to the load ( 12 ) and connected to the controllable resistor ( 48 ) to provide a substantially constant electrical power to the load ( 12 ).
1. A driver device for driving an LED unit including one or more LEDs, the driver comprising:
a power input unit for receiving an input voltage from an external power supply and for providing a rectified supply voltage,
a controllable resistor for providing a load current to power the LED unit,
a frequency filter connected to the power input unit for providing a substantially constant voltage to the LED unit, the frequency filter being connected to the controllable resistor to provide a substantially constant electrical power to the LED unit, wherein the frequency filter is connected to the power input unit to derive a voltage from the rectified supply voltage, wherein the voltage is at least partially applied to a series connection formed by the control input of the controllable resistor and the LED unit, and
a modulator coupled in series to the LED unit for modulating the drive current and for modulating the emitted light output, wherein the substantially constant voltage applied to the LED unit is further applied to the modulator by means of the frequency filter.
2. The driver device as claimed in claim 1 , wherein the frequency filter is a low-pass filter comprising a capacitor and a resistor, wherein the resistor is coupled to the controllable resistor, wherein a substantially constant voltage drops across the capacitor and a second voltage including an AC-component of the rectified supply voltage drops across the resistor.
3. The driver device as claimed in claim 2 , wherein a control contact of the controllable resistor is connected to a node between the resistor and the capacitor.
4. The driver device as claimed in claim 2 , wherein a voltage limiting device is coupled to the controllable resistor to limit the second voltage dropping across the resistor.
5. The driver device as claimed in claim 2 , wherein the controllable resistor comprises a transistor.
6. The driver device as claimed in claim 5 , wherein the controllable resistor comprises a Darlington stage.
7. The driver device as claimed in claim 6 , wherein a resistor is connected in parallel to the capacitor to decrease the voltage dropping across the capacitor.
8. The driver device as claimed in claim 7 , wherein the modulator, which is coupled in series to the LED unit for modulating a drive current driving the LED unit and for modulating the light output emitted from the LED unit, the modulator including a resistor and a controllable switch coupled in parallel to each other to provide two different drive current levels.
9. The driver device as claimed in claim 8 , wherein the controllable switch comprises a transistor controlled by a control unit.
10. The driver device as claimed in claim 8 , wherein the modulator comprises a second controllable switch controlled by the controller and coupled in series to a second resistor, wherein the second controllable switch and the second resistor are coupled in parallel to the first controllable switch to provide at least three different drive current levels.
11. A driver device for driving an LED unit including one or more LEDs, the driver comprising:
a power input unit for receiving an input voltage from an external power supply and for providing a rectified supply voltage,
a controllable resistor for providing a load current to power the LED unit,
a frequency filter connected to the power input unit for providing a substantially constant voltage to the LED unit, the frequency filter being connected to the controllable resistor to provide a substantially constant electrical power to the LED unit, wherein the frequency filter comprises a capacitor coupled to the controllable resistor so that a voltage provided by the capacitor is at least partially applied to a control input of the controllable resistor as a control voltage to drive the controllable resistor, and
a modulator coupled in series to the LED unit for modulating the drive current and for modulating the emitted light output, wherein the substantially constant voltage applied to the LED unit is further applied to the modulator by means of the frequency filter.
12. Method of driving an LED unit including one or more LEDs, comprising the steps of:
receiving an input voltage from an external power supply,
rectifying the input voltage to a rectified supply voltage and providing the rectified supply voltage to a frequency filter,
providing a modulated load current to the LED unit by means of a controllable resistor and a modulator, to power the LED unit, wherein the modulator is coupled in series to the LED unit,
providing a substantially constant voltage to the LED unit and the modulator by means of the frequency filter, and
providing a substantially constant electrical power to the LED unit by means of the frequency filter connected to the controllable resistor, wherein the frequency filter is connected to the power input unit to derive a voltage from the rectified supply voltage, wherein the voltage is at least partially applied to a series connection formed by the control input of the controllable resistor and the LED unit.