| 摘要 |
<p>PURPOSE:To obtain a DC voltage detecting circuit which has a constant working speed regardless of the input voltage and can be applied to various types of apparatus with no adjustment, by using the comparator, the time constant circuit and the working level setting circuit each. CONSTITUTION:In case positive DC voltage A is supplied to input terminal 1 due to an unexpected accident such as the fault of the parts or the like, transistor Q1 of comparator 2 is turned on. And collector output B of a high level is lowered to a low level. Output B is also turned to a low level in case the negative DC voltage is supplied. Transistor Q4 in time constant circuit 3 is turned on and off by the high and low levels of output B to give the short circuit or charging to capacitor C. When output C of circuit 3 reaches the voltage of Zener diode ZD2 in working level setting circuit 4, circuit 4 generates output D. Output D drives, e.g., the relay the contact of which is inserted between the output ternimal of the power amplifier circuit and the speaker, and then cuts off the DC voltage to be supplied to the speaker to cut off the speaker.</p> |
