| 摘要 |
<p>An input device for a Programmable Logic Controller is taught. Briefly stated, an incoming input voltage is rectified with an input impedance being principally capacitive in order to avoid heat dissipation. This rectified power in turn cooperates with a current source such that once a set point is reached the current source current does not increase with increasing input voltage. The current source is also utilized to prevent off-state leakage current from turning on an input optocoupler by allowing most of the input current to be drawn through the current source until a turn-on threshold which is set by a zener diode is met.</p> |
