Feed forward controlled voltage to current source for led driver

Abstract

A DC to DC converter receives a DC input voltage and generates an output DC voltage. A current sensor measures a DC input current. A control circuit is coupled to the current sensor for controlling the DC to DC converter to have a constant DC input current.

1 . A DC to DC converter receiving DC input voltage and generating an output DC voltage, comprising:
 a current sensor for measuring DC input current;   a control circuit coupled to the current sensor for controlling the DC to DC converter to have a constant DC input current.   
     
     
         2 . The DC to DC converter of  claim 1  wherein a load coupled to an output is an LED. 
     
     
         3 . The DC to DC converter of  claim 2  wherein the LED is a string of LEDs. 
     
     
         4 . The DCD to DC converter of  claim 1  wherein an output voltage of the current sensor is compared to a fixed reference voltage for generating a comparison voltage for controlling the DC input current to the converter. 
     
     
         5 . The DC to DC converter of  claim 4  wherein a pulse width modulation (PWM) circuit is coupled to receive the comparison voltage. 
     
     
         6 . The DC to DC converter of  claim 1  wherein an output voltage of the current sensor is compared with a voltage related to the output voltage for generating a comparison voltage for controlling the DC input current to the converter. 
     
     
         7 . The DC to DC converter of  claim 6  wherein a pulse width modulation (PWM) circuit is coupled to receive the comparison voltage. 
     
     
         8 . The DC to DC converter of  claim 6  wherein the load coupled to an output is an LED. 
     
     
         9 . The DC to DC converter of  claim 1  wherein the output voltage of the current sensor is compared with a pulsed reference voltage generating a comparison voltage for controlling the DC input current to the converter. 
     
     
         10 . The DC to DC converter of  claim 9  wherein a pulse width modulation (PWM) circuit is coupled to receive the comparison voltage. 
     
     
         11 . The DC to DC converter of  claim 10  wherein a load coupled to an output is an LED. 
     
     
         12 . The DC to DC converter of  claim 1  wherein an output voltage of the current sensor compared with absolute value of a sinusoidal voltage reference for generating a comparison voltage controlling the DC input current to the converter. 
     
     
         13 . The DC to DC converter of  claim 12  wherein a pulse width modulation (PWM) circuit is coupled to receive the comparison voltage. 
     
     
         14 . The DC to DC converter of  claim 13  wherein a load coupled to an output is LED. 
     
     
         15 . The DC to DC converter of  claim 1  wherein an output voltage of the current sensor is compared with the absolute value of a sinusoidal reference voltage multiplied by value related to the voltage on a load for generating a comparison voltage for controlling DC input current's to the converter. 
     
     
         16 . The DC to DC converter of  claim 15  wherein a pulse width modulation (PWM) circuit is coupled to receive the comparison voltage. 
     
     
         17 . The DC to DC converter of  claim 16  wherein a load coupled to an output is an LED. 
     
     
         18 . A method of driving an LED comprising:
 measuring and input current to it LED driver circuit;   controlling the driver circuit so that output power to drive the LED is proportional to input voltage.   
     
     
         19 . The method of  claim 18  for driving LEDs from a voltage source comprising:
 generating a current signal related to the input current; 
 comparing a signal related to the output voltage of the driver to the current signal to generate a comparison signal; 
 controlling the driver with the comparison signal so that output current is proportional to an input voltage. 
 
     
     
         20 . The method of  claim 19  wherein the comparison step compares the current signal to a fixed reference voltage for generating a comparison voltage for controlling the DC input current to the driver. 
     
     
         21 . The method of  claim 19  wherein the comparison step compares the current signal to a voltage related to the output voltage for generating a comparison voltage for controlling the DC input current to the driver. 
     
     
         22 . The method of  claim 19  wherein the comparison step compares the current signal to a pulsed reference voltage for generating a comparison voltage for controlling the DC input current to the driver. 
     
     
         23 . The method of  claim 19  wherein the comparison step compares the current signal to an absolute value of a sinusoidal voltage reference for generating a comparison voltage for controlling the DC input current to the driver. 
     
     
         24 . The method of  claim 19  wherein the comparison step compares the current signal to an absolute value of a sinusoidal reference voltage multiplied by a value related to the voltage on a load for generating a comparison voltage for controlling the DC input current to the driver. 
     
     
         25 . A voltage to current converter receiving a DC input voltage comprising:
 a current sensor for measuring DC input current;   means for generating an absolute value of a sinusoidal reference voltage;   means for multiplying a value related to an output voltage of the converter by the absolute value of the sinusoidal reference voltage to generate a first reference voltage;   means for comparing an output of the current sensor with the first reference voltage to generate an error signal;   modulation means responsive to the error signal for operating the converter in order to maintain a constant input current whereby an output current of the converter driving an LED load is proportional to the DC input voltage.   
     
     
         26 . A converter circuit comprising:
 a capacitor coupled across an output of the converter;   a controlled DC current source coupled between the converter output and a load output;   an error amplifier having an inverting input coupled to one terminal of the capacitor and a noninverting input coupled to another terminal of the capacitor and an output coupled to a control input of the controlled DC current source;   wherein the error amplifier controls the average voltage across the capacitor so that it is constant.   
     
     
         27 . A converter circuit comprising:
 a controlled DC current source in series between an output of the converter and a load output;   a comparator coupled across the controlled DC current source to measure the voltage across the controlled DC current source and having an output coupled to a control input of the controlled DC current source; wherein the comparator controls the controlled DC current source so the average voltage drop across the controlled DC current source is constant, whereby ripple across the load output is reduced.   
     
     
         28 . The converter circuit of  claim 27  wherein the comparator comprises a current measuring device coupled in series between active switch of the controlled DC current source and a load terminal to measure current going to a load at the terminal, the current measuring device providing a current dependent reference voltage for use by the comparator to control the controlled DC current source. 
     
     
         29 . The DC to DC converter of  claim 10  wherein a load coupled to an output is a DC to AC converter operating an AC load. 
     
     
         30 . The DC to DC converter of  claim 13  wherein a load coupled to an output is a DC to AC converter operating an AC load.