Transient suppression for boost regulator

Abstract

A circuit for generating an output voltage to a top node of a plurality of LED strings. The circuit includes an inductor having a load current flowing therethrough and a switching transistor responsive to a switching control signal. An integrator generates a compensation voltage responsive to a voltage at a bottom node of the LED string and a reference voltage. Circuitry for combining an a correction offset with the compensation voltage is responsive to the compensation voltage and the load current through the inductor. The offset is generated only during a step load change of the load current and substantially reduces voltage transients from the compensation voltage and the output voltage. A summation circuit sums the compensation voltage including the correction offset with at least the voltage at the bottom node of the LED string to generate a first control signal. A latch generates the switching control signal responsive to the first control signal and a leading edge blanking signal.

What is claimed is: 
     
       1. A circuit for generating an output voltage to a top node of a plurality of LED strings, comprising:
 an inductor having a load current flowing therethrough; 
 a switching transistor responsive to a switching control signal; 
 an integrator for generating a compensation voltage responsive to a voltage at a bottom node of an LED string and a reference voltage; 
 circuitry for combining an offset with the compensation voltage responsive to the compensation voltage and the load current through the inductor, wherein the offset is created only during a step load change of the load current and substantially reduces voltage transients from the compensation voltage and the output voltage; 
 a summation circuit for summing the compensation voltage including the offset with at least the voltage at the bottom node of the LED string to generate a first control signal; 
 a latch for generating the switching control signal responsive to the first control signal and a leading edge blanking signal. 
 
     
     
       2. The circuit of  claim 1 , wherein the circuitry for combining further comprises:
 control logic for generating the offset responsive to the compensation voltage and the step load change of the load current; and 
 an adder circuit for adding the offset to the compensation voltage to substantially reduce the voltage transients. 
 
     
     
       3. The circuit of  claim 2 , wherein the control logic further comprises:
 circuitry for implementing a control algorithm for generating a digital value of the offset responsive to the compensation voltage and the step load change of the load current; and 
 a digital to analog converter for generating the offset in analog format responsive to the digital value of the offset. 
 
     
     
       4. The circuit of  claim 1 , wherein the summation circuit further sums the compensation value, the voltage at the bottom node of the LED string, a slope compensation ramp signal and a current sense signal to generate the first control signal. 
     
     
       5. The circuit of  claim 1 , wherein basic loop properties of the circuit remain unchanged in each load condition. 
     
     
       6. The circuit of  claim 1  further including a sample and hold circuit between the integrator and the bottom node of the LED string. 
     
     
       7. A circuit for generating an output voltage to a top node of a plurality of LED strings, comprising:
 an inductor having a load current flowing therethrough; 
 a switching transistor responsive to a switching control signal; 
 an integrator for generating a compensation voltage responsive to a voltage at a bottom node of the an LED string and a reference voltage; 
 circuitry for implementing a control algorithm for generating a digital value of an offset responsive to the compensation voltage and a step load change of the load current; 
 a digital to analog converter for generating the offset in analog format responsive to the digital value of the offset; 
 an adder circuit for adding the offset to the compensation voltage to substantial reduce the voltage transients from the compensation voltage and the output voltage; 
 a summation circuit for summing the compensation voltage including the offset with at least the voltage at the bottom node of the LED string to generate a first control signal; and 
 a latch for generating the switching control signal responsive to the first control signal and a leading edge blanking signal. 
 
     
     
       8. The circuit of  claim 7 , wherein the summation circuit further sums the compensation value, the voltage at the bottom node of the LED string, a slope compensation ramp signal and a current sense signal to generate the first control signal. 
     
     
       9. The circuit of  claim 7 , wherein the basic loop properties of the boost regulator remain unchanged in each load condition. 
     
     
       10. The circuit of  claim 7  further including a sample and hold circuit between the integrator and the bottom node of the LED string. 
     
     
       11. A method for generating an output voltage to a top node of a plurality of LED strings, comprising the steps of:
 generating a compensation voltage responsive to a voltage at a bottom node of an LED string and a reference voltage; 
 generating an offset voltage only during a step load change of the load current; 
 combining the offset voltage with the compensation voltage, wherein the offset voltage substantially reduces voltage transients from the compensation voltage and the output voltage; 
 summing the compensation voltage including the offset voltage with at least the voltage at the bottom node of the LED string to generate a first control signal; 
 generating a switching control signal responsive to the first control signal and a leading edge blanking signal; and 
 generating the output voltage responsive to an input voltage and the switching control signal. 
 
     
     
       12. The method of  claim 11 , wherein the step of combining further comprises the step of adding the offset voltage to the compensation voltage to substantially reduce the voltage transients. 
     
     
       13. The method of  claim 11 , wherein the step of generating an offset voltage further comprises the steps of:
 generating a digital value of the offset voltage responsive to the compensation voltage and the step load change of the load current with a control algorithm; and 
 converting the digital value of the offset voltage into the offset in an analog format. 
 
     
     
       14. The method of  claim 11 , wherein the step of summing further comprises the step of summing the compensation value, the voltage at the bottom node of the LED string, a slope compensation ramp signal and a current sense signal to generate the first control signal. 
     
     
       15. The method of  claim 11  further including the step of maintaining the basic loop properties of a boost regulator unchanged in each load condition. 
     
     
       16. The method of  claim 11  further including the step of sampling and holding the voltage at the bottom node of the LED string used to generate the compensation voltage. 
     
     
       17. A method for generating an output voltage to a top node of a plurality of LED strings, comprising the steps of:
 generating a compensation voltage responsive to a voltage at a bottom node of an LED string and a reference voltage; 
 generating an offset voltage only during a step load change of the load current; 
 combining the offset voltage with the compensation voltage, wherein the offset voltage substantially reduces voltage transients from the compensation voltage and the output voltage; 
 summing the compensation voltage including the offset voltage with at least the voltage at the bottom node of the LED string to generate a first control signal, wherein the step of summing further comprises the step of summing the compensation value, the voltage at the bottom node of the LED string, a slope compensation ramp signal and a current sense signal to generate the first control signal; 
 generating a switching control signal responsive to the first control signal and a leading edge blanking signal; and 
 generating the output voltage responsive to an input voltage and the switching control signal. 
 
     
     
       18. A circuit for generating an output voltage to a top node of a plurality of LED strings, comprising:
 an inductor having a load current flowing therethrough;   a switching transistor responsive to a switching control signal;   an integrator for generating a compensation voltage responsive to a voltage at a bottom node of an LED string and a reference voltage;   circuitry for combining a correction offset with the compensation voltage responsive to the compensation voltage and the load current through the inductor, wherein the offset is created only during a step load change of the load current and substantially reduces voltage transients from the compensation voltage and the output voltage;   a summation circuit for summing the compensation voltage including the correction offset with at least the voltage at the bottom node of the LED string to generate a first control signal; and   a latch for generating the switching control signal responsive to the first control signal and a leading edge blanking signal.   
     
     
       19. The circuit of claim 18, wherein the circuitry for combining further comprises:
 control logic for generating the correction offset responsive to the compensation voltage and the step load change of the load current; and   an adder circuit for adding the correction offset to the compensation voltage to substantially reduce voltage transients on the compensation voltage and the output voltage.   
     
     
       20. The circuit of claim 19, wherein the control logic further comprises:
 circuitry for implementing a control algorithm for generating a digital value of the correction offset responsive to the compensation voltage and the step load change of the load current; and   a digital to analog converter for generating the correction offset in analog format responsive to the digital value of the correction offset.   
     
     
       21. The circuit of claim 18, wherein the summation circuit further sums the compensation value, the voltage at the bottom node of the LED string, a slope compensation ramp signal and a current sense signal to generate the first control signal. 
     
     
       22. A circuit for generating an output voltage to a top node of a plurality of LED strings, comprising:
 an inductor having a load current flowing therethrough;   a switching transistor responsive to a switching control signal;   an integrator for generating a compensation voltage responsive to a voltage at a bottom node of an LED string and a reference voltage;   circuitry for implementing a control algorithm for generating a digital value of a correction offset responsive to the compensation voltage and a step load change of the load current;   a digital to analog converter for generating the correction offset in an analog format responsive to the digital value of the correction offset;   an adder circuit for adding the correction offset in the analog format to the compensation voltage to substantially reduce the voltage transients from the compensation voltage and the output voltage;   a summation circuit for summing the compensation voltage including the correction offset with at least the voltage at the bottom node of the LED string to generate a first control signal; and   a latch for generating the switching control signal responsive to the first control signal and a leading edge blanking signal.   
     
     
       23. The circuit of claim 22, wherein the summation circuit further sums the compensation value, the voltage at the bottom node of the LED string, a slope compensation ramp signal and a current sense signal to generate the first control signal. 
     
     
       24. A method for generating an output voltage to a top node of a plurality of LED strings, comprising:
 generating a compensation voltage responsive to a voltage at a bottom node of an LED string and a reference voltage;   generating a correction offset voltage;   combining the correction offset voltage with the compensation voltage, wherein the correction offset voltage substantially reduces voltage transients from the compensation voltage and the output voltage;   summing the compensation voltage including the correction offset voltage with at least the voltage at the bottom node of the LED string to generate a first control signal;   generating a switching control signal responsive to the first control signal and a leading edge blanking signal; and   generating the output voltage responsive to an input voltage and the switching control signal,   wherein the generating a correction offset voltage further comprises:
 generating a digital value of the correction offset voltage responsive to the compensation voltage and a step load change of the load current with a control algorithm; and 
 converting the digital value of the correction offset voltage into an analog format. 
   
     
     
       25. The method of claim 24, wherein the combining further comprises adding the correction offset voltage to the compensation voltage to substantially reduce the voltage transients. 
     
     
       26. The method of claim 24, wherein the summing further comprises summing the compensation value, the voltage at the bottom node of the LED string, a slope compensation ramp signal and a current sense signal to generate the first control signal. 
     
     
       27. A method for generating an output voltage to a top node of a plurality of LED strings, comprising:
 generating a compensation voltage responsive to a voltage at a bottom node of an LED string and a reference voltage;   generating a correction offset voltage only during a step load change of the load current;   combining the correction offset voltage with the compensation voltage, wherein the correction offset voltage substantially reduces voltage transients from the compensation voltage and the output voltage;   summing the compensation voltage including the correction offset voltage with at least the voltage at the bottom node of the LED string to generate a first control signal, wherein the summing further comprises summing the compensation value, the voltage at the bottom node of the LED string, a slope compensation ramp signal and a current sense signal to generate the first control signal;   generating a switching control signal responsive to the first control signal and a leading edge blanking signal; and   generating the output voltage responsive to an input voltage and the switching control signal.