| 摘要 |
A dc-dc converter comprises first (5) and second (6) transistor switches connected in series between a dc input (1) and ground (4). The converter includes an inductor connecting the junction (8) of the two switches to a dc output and also a capacitor connecting the dc output to ground. The switches are closed alternately in response to a switching signal applied to a switching signal input (3), thereby alternately charging the capacitor from the dc input through the first switch and the inductor and discharging the energy stored in the inductor into the capacitor via the second switch. The coupling (12) from the switching signal input to the control input (25) of the second switch is provided with a threshold-responsive disable signal input (13) which is connected to the junction (8) between the two switches, for preventing the second switch from being controlled to a closed state at any time that the voltage on the junction is above a predetermined threshold. This threshold is set to be substantially zero by means of a comparator (28). Thus the second switch is prevented from being closed both when the first switch is conducting and also should the capacitor attempt to discharge through it. The latter would otherwise occur should the converter enter sleep mode, when the switching signal would be absent.
|
