Buck-boost converter using hysteretic control

A hysteretic buck-boost converter system, separating buck and boost pulses, wherein operation regions and buck or boost cycles of the buck-boost converter are controlled based on monitoring an output voltage of the buck-boost converter and a difference between the output voltage of the buck-boost converter and a reference voltage (error voltage) and additionally based on relations of the load current to the coil current and to one or more reference currents or based on the relations of either the load current or the coil current to one or more reference currents, comprising:

• a buck-boost converter configured to provide the output voltage which can be higher or lower than an input voltage of the buck-boost converter, comprising an inductor and separate switches for buck and boost operation where in a given cycle either switches for buck operation or switches for boost operation are configured to switch;
• an input stage configured to monitor the output voltage of the buck-boost converter in relation to reference voltages and to monitor the load current in relation to the coil current and to one or more reference currents or to monitor the coil current in relation to the one or more reference currents, wherein the monitoring is performed either by a number of comparators connected in parallel or by a state machine and wherein the outputs of the input stage are inputs to a logic and timers block;
• an output voltage change monitoring block configured to detect if the output voltage is falling or rising, wherein the output of the output voltage change monitoring block, providing a derivative ∂VOUT/∂t of the output voltage, is an additional input to said logic and timers block;
• and
• said logic and timers block, configured to define an operation region of buck or boost operation modes and buck or boost cycle times, wherein the logic and timers block comprises a number of logic gates and timer blocks, which are configured to set, depending on the outputs of the input stage, buck or boost duty cycles, wherein the buck timer block is configured to set the buck cycle time and a boost timer block is configured to set the boost cycle time, where in a given cycle the logic and timers block is configured to activate the buck or boost switches of the buck-boost converter according to the operation region defined by the logic and timers block.

A hysteretic buck-boost converter system, separating buck and boost pulses, wherein operation regions and buck or boost cycles of the buck-boost converter are controlled based on monitoring an output voltage of the buck-boost converter and a difference between the output voltage of the buck-boost converter and a reference voltage (error voltage) and additionally based on monitoring a ratio of the output voltage to a supply voltage of the buck-boost converter, comprising:

• a buck-boost converter configured to provide the output voltage which can be higher or lower than an input voltage of the buck-boost converter, comprising an inductor and separate switches for buck and boost operation where in a given cycle either switches for buck operation or switches for boost operation are configured to switch;
• an input stage configured to monitor the output voltage of the buck-boost converter in relation to reference voltages and to monitor a relation of the output voltage current in relation to the supply voltage, wherein ranges of the output voltage, limited by threshold voltages, are used, wherein the monitoring is performed either by a number of comparators connected in parallel or by a state machine and wherein the outputs of the input stage are inputs to a logic and timers block;
• an output voltage change monitoring block configured to detect if the output voltage is falling or rising, wherein the output of the output voltage change monitoring block, providing a derivative ∂VOUT/∂t of the output voltage, is an additional input to said logic and timers block;
• and
• said logic and timers block, configured to define an operation region of buck or boost operation modes and buck or boost cycle times, wherein the logic and timers block comprises a number of logic gates and timer blocks, which are configured to set, depending on the outputs of the input stage, buck or boost duty cycles, wherein the buck timer block is configured to set the buck cycle time and a boost timer block is configured to set the boost cycle time, where in a given cycle the logic and timers block is configured to activate the buck or boost switches of the buck-boost converter according to the operation region defined by the logic and timers block.

A method to improve operation of buck-boost converters, comprising the steps of:

• (1) providing a hysteretic buck-boost converter comprising comparators, timer blocks, a hysteretic derivation block to monitor a direction of output voltage by a derivative ∂VOUT/∂t of the output voltage or to monitor a coil current or of a load current or of both coil and load currents or to monitor a ratio of the output voltage to an input voltage of the buck-boost converter, and control logic cells;
• (2) designing the buck-boost converter using separate buck and boost pulses only;
• (3) setting cycle times for both buck mode and boost mode;
• and
• (4) monitoring the output voltage of the buck-boost converter and the derivative ∂VOUT/∂t of the output voltage or to monitor a direction of a coil current or of a load current or of both coil and load currents or to monitor a ratio of the output voltage to an input voltage to define the buck or boost operation mode of the buck-boost converter.