Device and method for controlling current to solid state lighting circuit

Abstract

A device for controlling current to a solid state lighting load includes a capacitor ( 241, 341 ) and a current source ( 245, 345 ). The capacitor is connected in a parallel arrangement with the solid state lighting load ( 260, 360 ). The current source is connected in series with the parallel arrangement of the capacitor and the solid state lighting load. The current source is configured to modulate dynamically an amplitude of an input current provided to the parallel arrangement of the capacitor and the solid state lighting load based on an input voltage.

The invention claimed is:  
     
       1. A device for controlling current to a solid state lighting load, the device comprising:
 a capacitor connected in a parallel arrangement with the solid state lighting load; 
 a current source connected in series with the parallel arrangement of the capacitor and the solid state lighting load, the current source being configured to modulate dynamically an amplitude of an input current provided to the parallel arrangement of the capacitor and the solid state lighting load based on an input voltage; and 
 a diode providing surge protection of the current source, connected in parallel with the current source. 
 
     
     
       2. The device of  claim 1 , wherein the solid state lighting load comprises at least one light-emitting diode (LED). 
     
     
       3. The device of  claim 2 , wherein the modulated amplitude of the input current maximizes operational efficiency of the solid state lighting load and increases a power factor (PF) of the solid state lighting load to at least a minimum PF requirement. 
     
     
       4. The device of  claim 2 , wherein the modulated amplitude of the input current reduces peak power dissipation in the current source. 
     
     
       5. The device of  claim 1 , wherein the solid state lighting load comprises at least two light-emitting diodes (LEDs) connected in series with each other. 
     
     
       6. The device of  claim 1 , wherein the diode comprises a Zener diode. 
     
     
       7. The device of  claim 1 , wherein the current source comprises a metal oxide semiconductor field effect transistor (MOSFET). 
     
     
       8. The device of  claim 1 , wherein the current source comprises a bipolar junction transistor (BJT). 
     
     
       9. The device of  claim 1 , wherein the input voltage is provided by a rectifier supplied from an AC source. 
     
     
       10. The device of  claim 9 , wherein the rectifier is a bridge rectifier and the AC source is a mains voltage source. 
     
     
       11. A device for controlling current to a light emitting diode (LED) load, the device comprising:
 a capacitor connected in parallel with the LED load; 
 a transistor connected in series between the capacitor and a bridge rectifier circuit providing a rectified input voltage; and 
 a modulation control circuit connected in parallel with the capacitor and the transistor and configured to receive the rectified input voltage from the bridge rectifier circuit, the modulation control circuit comprising a current mirror connected to a gate of the transistor, the current mirror being selectively activated and deactivated to downward and upward modulate an amplitude of a current through the capacitor based on an input voltage from the bridge rectifier circuit. 
 
     
     
       12. The device of  claim 11 , wherein the current mirror comprises a plurality of current mirror transistors. 
     
     
       13. The device of  claim 12 , wherein the modulation control circuit comprises:
 a first resistor and a diode connected in series between the bridge rectifier circuit and a first node; 
 a first path connected between the first node and ground, the first path comprising a second resistor and a first one of the current mirror transistors of the current mirror; and 
 a second path connected between the first node and ground, the second path comprising a third resistor and a second one of the current mirror transistors of the current mirror, 
 wherein selection of the first path causes downward modulation of the current through the capacitor, and selection of the second path causes upward modulation of the current through the capacitor. 
 
     
     
       14. The device of  claim 13 , wherein the current through the capacitor is further modulated upward or downward when the input voltage exceeds a voltage threshold defined by the diode. 
     
     
       15. The device of  claim 11 , wherein the transistor comprises a MOSFET. 
     
     
       16. The device of  claim 12 , wherein each of the current mirror transistors comprises a bipolar junction transistor (BJT). 
     
     
       17. The device of  claim 11 , wherein the modulation control circuit further comprises a current shunt resistor connected in series between the transistor and ground, a gate-source-voltage of the transistor and the current shunt resistor determining an upper limit of a current through the transistor. 
     
     
       18. The device of  claim 11 , further comprising:
 at least a second capacitor selectively connectable to the bridge rectifier circuit to alter the input voltage. 
 
     
     
       19. A method for controlling current to a solid state lighting load, the method comprising:
 receiving an input voltage (Urect) having a waveform; and 
 adjusting an amplitude modulation of a capacitor current of a capacitor connected in parallel with the solid state lighting load and further connected in series with a transistor, in response to at least one of the waveform of the received input voltage and a time delay in the waveform of the received input voltage, by a modulation control circuit comprising a current mirror connected to a gate of the transistor, the current mirror being selectively activated and deactivated to downward and upward modulate an amplitude of the current through the capacitor based on the input voltage, wherein adjusting the amplitude modulation of the capacitor current changes at least one of a power factor and operation efficiency of the solid state lighting load. 
 
     
     
       20. The method of  claim 19 , wherein the input voltage comprises a rectified voltage received from a bridge rectifier circuit.