Abstract: The invention relates to switching regulators with at least one inductance and four controllable switches which can be controlled by a control circuit in such a way that the switching regulators may be operated separately in a step-up mode as well as in a step-down mode, whereby in each clock cycle of either of the modes only two switches each are actuated, which in comparison with previous similar switching regulators, where in each clock cycle four switching operations take place, results in current saving effects because of reduced switching losses and lower currents. These are achieved by an element which constantly monitors the duty cycle of one of the switches and, when in the step-down mode the duty cycle approaches 100%, causes a switch-over into the step-up mode, and when in the step-up mode the duty cycle of 0% is approached, causes the switch-over into the step-down mode. Furthermore, the invention relates to methods for operating switching regulators.

Abstract: A line interface circuit sends two-level signals to a line and receives two-level signals from a line. The two levels of the signals are on opposite sides of a threshold range of levels. For testing the circuit the transmitter is connected to the receiver by a switchable path, and a test signal is produced by the transmitter for reception by the receiver for monitoring the functioning of the circuit. The test signal is of a small amplitude so as not to enter the threshold range of levels). The connections of the transmitter and receiver to the line are maintained during testing. During testing the output of the transmitter is limited in amplitude by a voltage clamp so that it can produce only the test signal.