A regulator circuit for step-up and step down operation having an input (Vin) connectable to a power source and an output (Vout) 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 node; a third switch connected between a second inductor terminal and the node; a fourth switch connected between the second inductor terminal and an output terminal; a sensing element for sensing current in the inductor, the sensing element being coupled between the node and a common connection; and a control circuit responsive to current in the inductor for controlling activation and deactivation of the switches (22, 33, 34, 27) to regulate voltage at the output (Vout) to a preset voltage, characterised in that in buck mode operation: the control circuit is configured to maintain the third switch in an open state and to maintain the fourth switch in a closed state; and after the control circuit detects that the sensed inductor current has fallen to a threshold level in the step down mode, the control circuit is configured to keep the first switch on and the second switch off for a fixed time, wherein the end of the fixed time terminates a cycle, and in that, in boost mode operation: the control circuit is configured to maintain the first switch in a closed state and to maintain the second switch in an open state; and after the control circuit detects that the sensed inductor current has risen to a threshold level in the step up mode, the control circuit is configured to keep the third switch off and the fourth switch on for a fixed time, wherein the end of the fixed time terminates a cycle. 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 node; a third switch connected between a second inductor terminal and the node; a fourth switch connected between the second inductor terminal and an output terminal; a sensing element for sensing current in the inductor, the sensing element being coupled between the node and a common connection; and a control circuit responsive to current in the inductor for controlling activation and deactivation of the switches (22, 33, 34, 27) to regulate voltage at the output (Vout) to a preset voltage, characterised in that in buck mode operation: the control circuit is configured to maintain the third switch in an open state and to maintain the fourth switch in a closed state; and after the control circuit detects that the sensed inductor current has fallen to a threshold level in the step down mode, the control circuit is configured to keep the first switch on and the second switch off for a fixed time, wherein the end of the fixed time terminates a cycle, and the control circuit is configured to maintain the third switch in an open state and to maintain the fourth switch in a closed state; and after the control circuit detects that the sensed inductor current has fallen to a threshold level in the step down mode, the control circuit is configured to keep the first switch on and the second switch off for a fixed time, wherein the end of the fixed time terminates a cycle, and the control circuit is configured to maintain the first switch in a closed state and to maintain the second switch in an open state; and after the control circuit detects that the sensed inductor current has risen to a threshold level in the step up mode, the control circuit is configured to keep the third switch off and the fourth switch on for a fixed time, wherein the end of the fixed time terminates a cycle.