DC/DC power converter with feedback control operable in linear and non-linear modes
View Patent ↗A current mode power conversion system and method operates in cycles. Each cycle includes an on time and an off time. The system includes an inductor connected to store energy during the on time of each cycle and use the energy during the off time of each cycle. The system provides a stable output voltage and a maximum-limited output current to a load during constant load conditions. The system comprises a feedback control linearly operable so as to control the output voltage across the load during constant load conditions, and non-linearly operable so as to control the output voltage across the load during certain detected changes in load conditions as a function of the derivative of the current in the inductor so as to speed up the transient response of the power conversion system when a fault condition exists.
1. A current mode power conversion system that operates in cycles, each cycle including an on time and an off time, the system including an inductor having a set point current and a control loop that regulates measured inductor current to equal the set point current and connected to store energy during the on time of each cycle and use the energy during the off time of each cycle, the system providing a stable output voltage and a maximum limited output current to a load during constant load conditions, the system comprising:
a feedback control linearly operable so as to control the output voltage across the load during constant load conditions, and non-linearly operable so as to control the output voltage across the load during certain detected changes in the inductor current set point so as to speed up the transient response of the power conversion system, the feedback control including:
a circuit for producing a first signal as a function of a difference between a reference voltage and a signal proportional to the output voltage, the first signal representing the inductor current set point,
a circuit for producing a derivative signal representing the derivative of the first signal, and a transient detector configured for detecting a change in the set point current of the inductor, wherein the feedback control is responsive to the transient detector for switching from linear operation to nonlinear operation when a threshold detector detects a change in the inductor current set point that has a magnitude that exceeds the threshold.
2. A current mode power conversion system according to claim 1 , wherein the change in load condition includes a load release.
3. A current mode power conversion system according to claim 1 , wherein the change in load condition includes a load step.
4. A current mode power conversion system according to claim 1 , wherein feedback control includes a first amplifier configured to generate a signal representing the current through the inductor, and the transient detector is configured to generate a control signal as a function of the first derivative of the current in the inductor.
5. A current mode power conversion system according to claim 4 , wherein the first amplifier is a transconductance amplifier.
6. A current mode power conversion system according to claim 4 , wherein the first amplifier is a comparator.
7. A current mode power conversion system according to claim 1 , wherein the threshold detector is constructed and arranged so as to detect changes in the derivative signal when it drops below the predetermined threshold.
8. A current mode power conversion system according to claim 1 , wherein the threshold detector is constructed and arranged so as to detect changes in load conditions that rise above the predetermined threshold.