| 摘要 |
PURPOSE:To make it possible to adjust a detection level with hysteresis width kept constant by varying a comparison reference potential on detecting a drop in level. CONSTITUTION:When a pilot level is normal and an input level is less than detection level VTH, transistor TR2 is OFF and level decrease detection level D' is equal to 20log[VrefR2/(R1+(R8//R9)+R2)]/Vst(Vst is an input voltage at a standard level). On the other hand, when the pilot level lowers abnormally and the input level is greater than the detection level, TR2 turns ON and at this time, hysteresis width H' becomes equal to H'(dB)=20log[1+K(R1+(R8//R9)/R2)]. As a result, equalizing VELto KVref varies the detection level, so that even if Vref is varied in value, the hysteresis width will unconditionally be determined by the value of K. |
