The present invention relates to a solder heating appliance with variable duty
cycle. Rather than applying power continuously to the heating element, the element
power is intermittently switched over to a variable duty cycle. Savings are gained
in three areas: extended life of the element; less heat lost to thermal radiation;
and less solder waste due to dripping and overheating. The variable duty cycle
may be adjusted manually or automatically based on the temperature of the heating
element, or tip. Additionally, the voltage and/or current to the heating element
may be adjusted, either manually or automatically, for more rapid recovery during
high usage periods. Higher throughput is achieved by sensing the temperature, comparing
the temperature to a desired temperature, and then increasing the variable duty
cycle by either or both one of increasing the frequency of duty pulses and/or lengthening
the duration of the variable duty cycle.