Abstract: A DC supply for an electronic signalling device that is connected to a signal transmission line. The device comprises a plurality of circuit units each of which must be supplied with a DC-supply current. Feeding the circuit units in series has the advantage that the DC-supply current in each of the circuit units can be utilized to the full. A drawback is that the different supply voltages add up. A practical requirement may be that the total supply voltage does not exceed a certain value at a certain value of the supply current. In order to satisfy this requirement means are present which cause the supply voltage of one of the circuit units to decrease more than proportionally to the DC-supply current when the DC-supply current decreases to below a certain value.The invention is suitable for use in loud-speaking telephone sets.