| 摘要 |
PURPOSE:To reset an electronic circuit surely even when power supply and cut- off are repeated by forming a reset signal of the electronic circuit with an operation state signal of a constant voltage circuit provided in the succeeding stage of a power source circuit. CONSTITUTION:When a power source switch 12 is closed, smoothing voltage VC rises, and output voltage of a constant voltage circuit 28 becomes a fixed value which is larger than certified operation voltage V1 of an electronic circuit 20. A transistor TR34 of a resetting circuit 30 is made conducting by conduction of a Zener diode, and a TR40 is made conducting by this, and voltage level of a reset terminal R of the circuit 20 changes from low to high. The circuit 20 is reset by a low level signal of the terminal R when feed voltage exceeds voltage V1. When the switch 12 is opened, output voltage of the circuit 28 lowers and the TR34 tends to become off. However, conduction of the TR34, TR40 is maintained by feedback current that passed a ZD44, a resistance 46 from the terminal R, and unprepared resetting is prevented. When voltage of the terminal R becomes lower than breakdown voltage of the ZD44, the TR34, 40 become off. |
