LED arrangement with over-current protection
An LED board comprises an arrangement of LEDs, a current sensor for sensing a current flowing through the arrangement of LEDs and a cut-off switch in series with the arrangement of LEDs. The cut-off switch is controlled in dependence on the sensed current. In this way, over-current protection is provided at the LED board level, without needing any signal communication between the LED board and the LED driver.
1. An LED board adapted to be wire-connected to a separate LED driver, comprising:
a circuit board which carries:
an arrangement (D 1 , D 2 , D 3 , D 4 ) of LEDs;
a current sensor for sensing a current flowing through the arrangement of LEDs;
a cut-off switch (W 1 ) in series with the arrangement of LEDs;
a switch control circuit which is adapted to control the cut-off switch in dependence on the sensed current;
wherein the switch control circuit comprises a reference voltage unit and a comparison circuit for comparing the current sensor signal with a voltage reference set by the reference voltage unit; and
wherein the reference voltage unit comprises a resistor-diode circuit (R 1 , C 1 , D 5 ) for generating an internal supply voltage and a resistor divider (R 3 , R 4 ) for generating the reference voltage from the internal supply voltage.
2. An LED board as claimed in claim 1 , wherein the switch control circuit comprises a timing circuit.
3. An LED board as claimed in claim 1 , wherein the switch control circuit ( 26 ) comprises a latch circuit (Q 1 , M 2 , R 8 , R 9 ).
4. An LED board as claimed in claim 3 , wherein the latch circuit comprises a transistor circuit (Q 1 , M 2 ) coupled to a control input of the cut-off switch (W 1 ).
5. A luminaire comprising: a configurable LED driver; and
an LED board as claimed in claim 1 .
6. An LED board adapted to be wire-connected to a separate LED driver, comprising:
a circuit board which carries:
an arrangement (D 1 , D 2 , D 3 , D 4 ) of LEDs; a current sensor for sensing a current flowing through the arrangement of LEDs; a cut-off switch (W 1 ) in series with the arrangement of LEDs; and
a switch control circuit which is adapted to control the cut-off switch in dependence on the sensed current;
wherein the switch control circuit comprises a timing circuit;
wherein the switch control circuit comprises a reference voltage unit and a comparison circuit for comparing the current sensor signal with a voltage reference set by the reference voltage unit; and
wherein the timing circuit comprises a feedback circuit between the comparison circuit output and input, which comprises a capacitor (C 3 ) adapted to charge when the cut-off switch is closed and to discharge when the cut-off switch is open.
7. An LED board as claimed in claim 6 , wherein the timing circuit comprises a resistor (R 6 ) and diode (D 6 ) in parallel and the capacitor (C 3 ) in series with the parallel resistor-diode.