Temperature controlled soldering iron employing a variable resistance heating element for temperature sensing

摘要

PCT No. PCT/IT87/00091 Sec. 371 Date Jul. 5, 1988 Sec. 102(e) Date Jul. 5, 1988 PCT Filed Nov. 4, 1987 PCT Pub. No. WO88/03455 PCT Pub. Date May 19, 1988.A temperature controlled soldering iron with a heating element having a positive temperature coefficient arranged as one leg of a Wheatstone resistance bridge such that the voltage across the heating element signals the temperature of the soldering iron. A comparator is connected across opposite nodes of the bridge and turns off a switching element to cut current flow through the bridge when the heating element is above the desired temperature. A pulse generator continuously supplies pulses to briefly restart current flow through the bridge and allow the temperature to be sensed. The pulses are short duration and occur regardless of whether the comparator has previously turned off current flow, and independent of the temperature of the heating element. After each pulse the comparator controls current flow by leaving the flow on or turning it off according to the temperature of the heating element as measured by comparison of the voltages on the opposite nodes of the bridge.