| 摘要 |
PURPOSE:To discriminate surely a signal without intermission for a prescribed time or over by providing an integration circuit charged/discharged with a sufficiently larger time constant than an on/off time to be identified according to on/off of an open collector driver and a comparator circuit discriminating a capacitor voltage of the said integration circuit. CONSTITUTION:The open collector driver 1 is driven by a pulse signal fed to an input terminal IN, and when the driver 1 is turned off, a capacitor C1 is charged from a power supply Vcc with a time constant of (R1+R2)C1 when the driver 1 is turned off, and the capacitor is discharged with a time constant R2C1 when the driver 1 is turned on. A stable voltage Vc of the capacitor C1 is expressed in equation, where alpha is the on/off ratio of the driver 1. Thus, it is most suitable to match the time constant ratio tau1/tau2 to the on/off ratio of the driver 1 to be detected. The voltage charged in the capacitor C1 is compared with a voltage Vcc.R4/(R2+R4) by a voltage comparator circuit 2. Thus, the discrimination whether or not the on/off ratio of the driver 1 reaches a setting value is outputted at an output terminal OUT. |
