| 摘要 |
A timer circuit for connecting a DC voltage source to an electric device, such as a small portable radio, comprises a switching device, such as a switching transistor, connected between the source and the device and having conductive and non-conductive states; a drive circuit operative to selectively establish the states of the switching device in response to a control voltage; a timing circuit for holding a voltage level that initially decays at a first decay rate from a first voltage related to the voltage of the source of a second voltage, and subsequently decays at a second, different decay rate from the second voltage to a third voltage; and a control device, which may be a thyristor, such as, a programmable unijunction transistor, or a thyristor-like circuit, for providing the control voltage to a drive circuit to cause the latter to establish one of the states of the switching device when the voltage level of the timing circuit is above the third voltage, and to establish the other of the states when the voltage level has decayed to the third voltage. |
