| 摘要 |
<p>An I2t monitoring circuit utilizes a multiplier (12) to provide a signal (B) that is representative of the squared value of a monitored current (i). The squared signal (B) minus a DC level (Z¿2?) is provided as an input to a voltage-to-frequency converter (16) and the output (18) of the voltage-to-frequency converter (16) is provided as an input to a down counter (20). The down counter (20) is configured to decrement a stored value in response to the frequency of pulses (82) received from the voltage-to-frequency converter (16) and provide a signal in response to the magnitude of the stored value being decremented to a first predetermined magnitude. Periodically, the magnitude of the stored value in the down counter (20) is refreshed to a second predetermined magnitude. When a signal is received from the down counter (20) to indicate that the magnitude of the stored value has been decremented to the first predetermined magnitude, the signal is latched (24) and a continuing signal (30) is provided to indicate that a trip should occur. The trip signal is provided so that external circuitry can respond by either disconnecting the load from the monitored current or taking steps to reduce the magnitude of the monitored current (i).</p> |
