Dimming Driver With Stealer Switch

Abstract

An apparatus for supplying power includes a power input, a load output and a switch connected in series to the power input, a pulse generator comprising a pulse output connected to a control input of the switch, and a stealer switch connected to the control input of the switch. When the switch is closed, electrical current is able to flow from the power input to the load output. When the pulse output is in a low state, the stealer switch is closed.

What is claimed is: 
     
         1 . An apparatus for supplying power, comprising:
 a power input;   a load output and a switch connected in series to the power input, wherein when the switch is closed, electrical current is able to flow from the power input to the load output;   a pulse generator comprising a pulse output connected to a control input of the switch; and   a stealer switch connected to the control input of the switch, wherein when the pulse output is in a low state, the stealer switch is closed.   
     
     
         2 . The apparatus of  claim 1 , wherein the stealer switch is configured to pull the control input of the switch to a ground when the stealer switch is closed. 
     
     
         3 . The apparatus of  claim 1 , wherein the switch comprises a bipolar junction transistor. 
     
     
         4 . The apparatus of  claim 3 , further comprising a diode connected between a base and an emitter of the bipolar junction transistor, configured to assist the base of the bipolar junction transistor to drain when the bipolar junction transistor is off. 
     
     
         5 . The apparatus of  claim 3 , further comprising a diode connected between a base and a collector of the bipolar junction transistor, configured to prevent the bipolar junction transistor from entering a deep saturation state. 
     
     
         6 . The apparatus of  claim 1 , wherein the stealer switch comprises a field effect transistor. 
     
     
         7 . The apparatus of  claim 1 , further comprising an inductor connected in series with the load output and the switch, and a diode connected in parallel with the load output and the inductor, wherein when the switch is open, electrical current circulates through the inductor, the diode and the load output. 
     
     
         8 . The apparatus of  claim 1 , further comprising an inverter having an input connected to the pulse output and an output connected to a control input of the stealer switch. 
     
     
         9 . The apparatus of  claim 1 , further comprising a load current sensor connected in series with the load output. 
     
     
         10 . The apparatus of  claim 9 , further comprising a load current detection circuit connected to the pulse generator, wherein the pulse generator is configured to adjust a pulse width of pulses at the pulse output based at least in part on a control signal from the load current detection circuit. 
     
     
         11 . The apparatus of  claim 10 , further comprising a reference current source connected to the load current detection circuit, wherein the load current detection circuit is configured to compare a first signal from the reference current source with a second signal from the load current sensor. 
     
     
         12 . The apparatus of  claim 10 , further comprising a level shifter connected between the load current detection circuit and the pulse generator. 
     
     
         13 . The apparatus of  claim 10 , further comprising a filter connected between the load current sensor and the load current detection circuit. 
     
     
         14 . The apparatus of  claim 13 , wherein the filter is configured to average the second signal from the load current sensor. 
     
     
         15 . A method of supplying power, comprising:
 regulating current from a power input to an output driver using an output driver control switch;   controlling the output driver control switch with a pulse signal from a pulse generator; and   connecting a control input of the output driver control switch to ground when the pulse signal is in a low state.   
     
     
         16 . The method of  claim 15 , further comprising connecting the control input of the output driver control switch to the ground when an inverted version of the pulse signal is in a high state. 
     
     
         17 . The method of  claim 15 , further comprising powering the pulse generator by drawing power from the output driver via inductive coupling. 
     
     
         18 . The method of  claim 17 , further comprising varying a current through the output driver based on a dimming signal. 
     
     
         19 . The method of  claim 15 , further comprising controlling the pulse generator to vary a pulse width of the pulse signal to regulate a current through the output driver. 
     
     
         20 . The method of  claim 19 , wherein the pulse width is varied based at least in part on a load current through the output driver.