Switching converter with improved recovery time
A switching converter, which produces an output voltage, contains a switch operable between a first state for opposing a decrease in the output voltage and a second state for opposing an increase in the output voltage. The converter also contains a circuit adapted to determine a time period during which the output voltage is decreasing, wherein during the time period the switch is in the first state. The circuit also calculates, based on the time period, a time to turn the switch from the first state to the second state to prevent the output voltage increasing above a reference value. Optionally, the time to turn the switch to the second state is based on a duty cycle of the converter.
1. A converter for outputting an output voltage comprising
a switch operable between a first state for opposing a decrease in the output voltage and a second state for opposing an increase in the output voltage; and
a circuit adapted
to determine a time period during which the output voltage keeps decreasing, wherein during the time period the switch is in the first state; and
to calculate a time to turn the switch from the first state to the second state to prevent the output voltage increasing above a reference value;
wherein the converter has a duty cycle, and wherein the time to turn the switch to the second state is based on a product of a square root of the duty cycle and the time period.
2. The converter as claimed in claim 1 , wherein the circuit comprises a memory device coupled to the switch, the memory device having a first input coupled to a first circuit, a second input coupled to a second circuit, and an output to output a signal to turn the switch to the second state.
3. The converter as claimed in claim 2 , wherein the first circuit is adapted to detect a gradient of the output voltage, and to output a first signal proportional to the time period based on the gradient.
4. The converter as claimed in claim 3 , wherein the first circuit comprises
a first comparator adapted to detect a negative gradient of the output voltage;
a second comparator adapted to detect a positive gradient of the output voltage; and
a memory device comprising a first input coupled to an output of the first comparator, a second input coupled to an output of the second comparator, and an output to output a signal proportional to the time period.
5. The converter as claimed in claim 2 , wherein the second circuit comprises an input for receiving a signal proportional to the time period and an output to output a signal proportional to another time period based on the duty cycle of the converter.
6. The converter as claimed in claim 5 , wherein the second circuit comprises
a current generator,
a capacitor coupled to the current generator, and
a comparator having an input coupled to the capacitor and an output coupled to a logic gate;
wherein the current generator is adapted to output a current to control a rate of discharge of the capacitor.
7. The converter as claimed in claim 6 , wherein the current generator is adapted to output a current proportional to a square root of an input current.
8. The converter as claimed in claim 7 , wherein the current generator comprises
an input current generator for generating the input current;
an operational amplifier adapted to control an output switch; and
a current mirror coupled to an input of the operational amplifier.
9. The converter as claimed in claim 8 , wherein the current mirror comprises a first transistor and a second transistor, and wherein a size of the second transistor is four times as large as a size of the first transistor.
10. The converter as claimed in claim 6 , wherein the current generator is adapted to output a current proportional to an inverse of a square root of the duty cycle.
11. The converter as claimed in claim 6 , wherein the current generator comprises a digital circuit adapted to receive a voltage value and to generate a digital value proportional to an inverse of a square root of the voltage value.
12. A method of regulating an output voltage of a converter comprising:
providing a switch operable between a first state for opposing a decrease in the output voltage and a second state for opposing an increase in the output voltage;
determining a time period during which the output voltage keeps decreasing, wherein during the time period the switch is in the first state;
calculating a time to turn the switch from the first state to the second state to prevent the output voltage increasing above a reference value; wherein the converter has a duty cycle, and wherein the time to turn the switch to the second state is based on a product of a square root of the duty cycle and the time period; and
switching the switch to the second state at the calculated time.
13. The method as claimed in claim 12 , wherein detecting the time period comprises detecting a gradient of the output voltage.
14. The method as claimed in claim 13 , wherein detecting a gradient comprises detecting a negative gradient of the output voltage and detecting a positive gradient of the output voltage.
15. The method as claimed in claim 12 , wherein calculating the time comprises generating a current proportional to a square root of an input current.
16. The method as claimed in claim 15 , wherein the current generator comprises
an input current generator for generating the input current;
an operational amplifier adapted to control an output switch; and
a current mirror coupled to an input of the operational amplifier.
17. The method as claimed in claim 16 , wherein the current mirror comprises a first transistor and a second transistor, and wherein a size of the second transistor is four times as large as a size of the first transistor.
18. The method as claimed in claim 12 , wherein calculating the time comprises generating a current proportional to an inverse of the square root of the duty cycle.
19. The method as claimed in claim 12 , wherein calculating the time comprises receiving a voltage value and generating a digital value proportional to an inverse of a square root of the voltage value.
20. The method as claimed in claim 12 , wherein the circuit comprises a memory device coupled to the switch, the memory device having a first input coupled to a first circuit, a second input coupled to a second circuit, and an output to output a signal to turn the switch to the second state.
21. The method as claimed in claim 20 , wherein the second circuit comprises an input for receiving a signal proportional to the time period and an output to output a signal proportional to another time period based on the duty cycle of the converter.
22. The method as claimed in claim 21 , wherein the second circuit comprises
a current generator,
a capacitor coupled to the current generator, and
a comparator having an input coupled to the capacitor and an output coupled to a logic gate;
wherein the current generator is adapted to output a current to control a rate of discharge of the capacitor.