Posted on Apr 16, 2012 10519
This circuit responds quickly enough to prevent damage from most overloads. C 1 `s input is connected to the output of the LT1088 servo circuit. If the LT1088 circuit`s output exceeds the threshold at Cl`s other input, C1 trips, discharging the 2-!`F capacitor. This causes C2`s output to become low, energize the relay, and break the heater circuit. The 560-KO resistor provides a long recharge for the capacitor, preventing chattering action.
This arrangement"s speed of response is limited by the rrns circuit"s slew rate, about 0.2 V/ms. For reasonable overloads, the LT1088"s temperature increases about 1 Â°C/ms. A 10-V LT1088 output step takes 50 ms, causing a temperature rise of about 50Â°C.