| 摘要 |
PURPOSE:To improve reliability and reduce manufacturing cost by changing the side of the frequency of a reference clock generating circuit for frequency detection, using real system voltage as it is even at inspection, thereby making it as if the frequency of the real system being the detection target changes apparently. CONSTITUTION:The input waveform on the quantity of electricity is insulated in a input circuit 1, and is transformed into the voltage of proper magnitude, and then it is added to a rectangular wave input circuit 2, and is converted into rectangular waves. In this case, the output of a reference clock generating circuit 3b for inspection is connected to a counter circuit 4 by a reference clock changeover switch 5. The counter circuit 4 starts counting from zero when the output of the rectangular wave circuit becomes positive, and continues the counting during the positive period. A comparison circuit 4 compares the count value at the point of time of counting end in each cycle of the counter circuit 7 with the set value of a reference value setting circuit 6, and when the hand of count value is larger, the output comes out of the comparison circuit 7. |
