Primary side switched converter for providing a voltage supply to an LED load
The invention relates to a method ( 100 ) for operating an isolated primary side switched converter ( 300 ) for providing a voltage supply to an LED load ( 401 ), wherein the converter comprises a galvanic isolation stage ( 301 ), the method comprising the steps of: detecting ( 101 ) a feedback signal at a primary side of the galvanic isolation stage ( 301 ), wherein the feedback signal corresponds to a secondary side voltage, determining ( 103 ) an LED supply voltage based on the feedback signal, calculating ( 105 ) a threshold value based on a constant reference voltage and an adjustment factor, wherein the adjustment factor is a dynamic factor whose absolute value increases with increasing LED current, and interrupting ( 107 ) the voltage supply to the LED load ( 401 ) if the determined LED supply voltage exceeds the threshold value.
1. A method ( 100 ) for operating an isolated primary side switched converter ( 300 ) for providing a voltage supply to an LED load ( 401 ), wherein the converter comprises a galvanic isolation stage ( 301 ), the method comprising the steps of:
detecting ( 101 ) a feedback signal at a primary side of the galvanic isolation stage ( 301 ),
wherein the feedback signal corresponds to a secondary side voltage,
determining ( 103 ) an LED supply voltage based on the feedback signal,
detecting an LED current,
calculating ( 105 ) a threshold value based on a constant reference voltage and an adjustment factor,
wherein the adjustment factor is a dynamic factor that is repeatedly calculated based on the detected LED current while the converter is operating and whose absolute value increases with increasing LED current, and
interrupting ( 107 ) the voltage supply to the LED load ( 401 ) if the determined LED supply voltage exceeds the threshold value.
2. The method ( 100 ) of claim 1 , wherein the adjustment factor comprises a linear function of the LED current.
3. The method ( 100 ) of claim 2 , wherein the linear function is determined by performing at least two calibration measurements at different LED currents.
4. The method ( 100 ) of claim 1 , wherein the adjustment factor comprises a temperature dependent part.
5. The method ( 100 ) of claim 4 , wherein the temperature dependent part is a linear or higher order function of the temperature, or wherein the temperature dependent part is determined based on a look-up-table.
6. An isolated primary side switched converter ( 300 ) for providing a voltage supply to an LED load ( 401 ), comprising:
a galvanic isolation stage ( 301 ),
a first auxiliary winding (L 51 c ) on the primary side of the galvanic isolation stage which is magnetically coupled to at least one secondary side winding (L 51 a , L 51 b ),
wherein the first auxiliary winding (L 51 c ) is configured to receive a feedback signal corresponding to a secondary side voltage,
a current sensor unit configured to detect the LED current,
a control unit ( 303 ) configured to determine an LED supply voltage based on the feedback signal,
a processing unit ( 305 ) configured to calculate a threshold value based on a constant reference voltage and an adjustment factor,
wherein the adjustment factor is a dynamic factor that is repeatedly calculated based on the detected LED current while the converter is operating and whose absolute value increases with increasing LED current, and
wherein the converter ( 300 ) is configured to interrupt the voltage supply to the LED load if the determined LED supply voltage exceeds the threshold value.
7. The converter ( 300 ) of claim 6 , wherein the current sensing unit ( 309 ) comprises a further auxiliary winding (L 52 a ) on the primary side of the galvanic isolation stage ( 301 ), which is magnetically coupled to at least one further secondary side winding (L 52 c , L 52 b ).
8. The converter ( 300 ) of claim 6 , wherein the converter ( 300 ) comprises a temperature sensing unit ( 311 , 409 ) for sensing an ambient temperature, wherein the adjustment factor comprises a temperature dependent part.
9. The converter ( 300 ) of claim 8 , wherein the temperature sensing unit ( 311 , 409 ) is arranged at the LED load ( 401 ) and is connected to the processing unit ( 305 ) via a communication interface, in particular a DALI or a Bluetooth interface.
10. The converter ( 300 ) of claim 6 , wherein the control unit ( 303 ) is configured to control at least one primary side switch (M 40 , M 41 ) of the converter.
11. The converter ( 300 ) of claim 6 , wherein the control unit is configured to interrupt the voltage supply to the LED load ( 401 ) if the calculated output voltage exceeds the threshold value.
12. The converter ( 300 ) of claim 10 , wherein the control unit ( 303 ) comprises an ASIC and/or wherein the processing unit ( 305 ) comprises a microcontroller.
13. A driver ( 400 ) for light sources, in particular LEDs, comprising the isolated primary side switched converter ( 300 ) according to claim 7 .