Variable frequency current-mode control for switched step up-step down regulators

A regulator circuit for step-up and step down operation having an input connectable to a power source and an output connectable to a load, the regulator circuit comprising:

• an inductor;
• a first switch connected between a first inductor terminal and an input terminal;
• a second switch connected between the first inductor terminal and a common connection;
• a third switch connected between the second inductor terminal and the common connection;
• a fourth switch connected between the second inductor terminal and an output terminal;
• and
• a control circuit responsive to current in the inductor for controlling activation and deactivation of at least one of the switches for a constant time to regulate voltage at the output to a preset voltage.

In a circuit comprising an inductor having first and second terminals, a first switch connected between the first inductor terminal and an input terminal, a second switch connected between the second inductor terminal and a common connection, a first rectifying device connected between the first inductor terminal and the common connection, and a second rectifying device connected between the second inductor terminal and an output terminal, a method for regulating the voltage at the output terminal approximately the same as, the voltage at the input terminal, the method comprising the steps of:

• sensing current in the inductor;
• with both switches in an off state at a beginning portion of each cycle, in response to the sensed current falling to a first threshold level, turning the first switch on;
• maintaining the first switch on for a fixed time period thereafter;
• turning the second switch on at the expiration of the fixed time period;
• in response to the sensed current rising to a second threshold level thereafter, turning the second switch off;
• maintaining the second switch off a fixed time to the end of the cycle;
• and
• turning the first switch off at the end of the cycle.

In a circuit comprising an inductor having first and second terminals, a first switch connected between the first inductor terminal and an input terminal, a second switch connected between the second inductor terminal and a common connection, a first rectifying device connected between the first inductor terminal and the common connection, and a second rectifying device connected between the second inductor terminal and an output terminal, a method for regulating the voltage at the output terminal approximately the same as, the voltage at the input terminal, the method comprising the steps of:

• sensing current in the inductor;
• with both switches in an on state at a beginning portion of each cycle, in response to the sensed current falling to a first threshold level, turning the second switch off;
• maintaining the second switch off for a fixed time period thereafter;
• turning the first switch off at the expiration of the fixed time period;
• in response to the sensed current falling to a second threshold level thereafter, turning the first switch on;
• maintaining the first switch on for a fixed time to the end of the cycle;
• and
• turning the second switch on at the end of the cycle.

In a circuit comprising an inductor having first and second terminals, a first switch connected between the first inductor terminal and an input terminal, a second switch connected between the first inductor terminal and a common connection, a third switch connected between the second inductor terminal and the common connection, and a fourth switch connected between the second inductor terminal and an output terminal, a method for regulating the voltage at the output terminal at a level approximately the same as, the voltage at the input terminal, the method comprising the steps of:

• sensing current in the inductor;
• setting the first and third switches to an off state and the second and fourth switches to an on state at the beginning portion of each cycle;
• in response to the sensed current falling to a first threshold level, setting the first and fourth switches on and the second and third switches off;
• maintaining the first switch on for a first fixed time period thereafter;
• setting the third switch on and the fourth switch off at the expiration of the fixed time period;
• in response to the sensed current rising to a second threshold level, turning the third switch off and the fourth switch on for a second fixed time period to the end of the cycle.

In a circuit comprising an inductor having first and second terminals, a first switch connected between the first inductor terminal and an input terminal, a second switch connected between the first inductor terminal and a common connection, a third switch connected between the second inductor terminal and the common connection, and

• a fourth switch connected between the second inductor terminal and an output terminal, a method for regulating the voltage at the output terminal approximately the same as, the voltage at the input terminal, the method comprising the steps of
• sensing current in the inductor;
• setting the first and third switches to an on state and the second and fourth switches to an off state at the beginning portion of each cycle;
• in response to the sensed current rising to a first threshold level, turning the third switch off and the fourth switch on;
• maintaining the third switch off for a first fixed time period thereafter;
• turning the first switch off and the second switch on at the expiration of the fixed time period;
• in response to the sensed current falling to a second threshold level, turning the first switch on and the second switch off for a second fixed time period to the end of the cycle.