Ballast circuit for led-based lamp including power factor correction with protective isolation

Abstract

A ballast circuit for a light emitting diode (LED) based lamp including power factor correction with protective isolation. The circuit includes a transformer with electrically isolated windings and a power factor correction circuit that receives no feedback from a secondary winding side of the transformer. An LED-based lamp assembly and a method of driving an LED-based light source are also provided.

What is claimed is: 
     
         1 . A method of driving an LED-based light source, the method comprising:
 receiving an AC input signal;   converting the AC input signal into a regulated DC output using a ballast circuit comprising:
 a transformer having a primary winding, a secondary winding and a feedback winding, the secondary winding being electrically isolated from the primary winding and the feedback winding with no electrical path between the primary winding and the secondary winding or the feedback winding and the secondary winding, and 
 a power factor correction circuit receiving no feedback signal coupled from the secondary winding; and 
   coupling the regulated DC output to the LED-based light source.   
     
     
         2 . A method according to  claim 1 , wherein receiving an AC input signal comprises receiving the AC input signal from a dimmer circuit. 
     
     
         3 . A method according to  claim 1 , wherein converting comprises:
 converting the AC input signal into a regulated DC output using a ballast circuit comprising:
 a transformer having a primary winding, a secondary winding and a feedback winding, the secondary winding being electrically isolated from the primary winding and the feedback winding with no electrical path between the primary winding and the secondary winding or the feedback winding and the secondary winding, and 
 a power factor correction circuit receiving no feedback signal coupled from the secondary winding; and 
 a switched bias circuit including a bias circuit switch configured to close to provide a supply voltage to the power factor correction circuit. 
   
     
     
         4 . A method according to  claim 1 , wherein converting comprises:
 converting the AC input signal into a regulated DC output using a ballast circuit comprising:
 a transformer having a primary winding, a secondary winding and a feedback winding, the secondary winding being electrically isolated from the primary winding and the feedback winding with no electrical path between the primary winding and the secondary winding or the feedback winding and the secondary winding, and 
 a power factor correction circuit receiving no feedback signal coupled from the secondary winding; and 
 an over-voltage protection circuit coupled to the power factor correction circuit to disable the power factor controller circuit when a voltage at the transformer exceeds a predetermined level.