Most of the Soldering iron Tips or Bits now available are Copper core surrounded by Iron . It is coated with Nickel or Chromium to prevent the sticking of solder. If we are switched on the soldering iron for long period, the excess heat may damage it permanently. If the soldering work is intermittent, it is ideal to keep the tip half warm. This circuit performs this function. It has a switch and if it is in the Off position, the soldering iron tip remains half warm and if the switch is in the On position, within seconds, it will become fully heated. Don’t be confused. Not a large circuit, but a single diode is sufficient.
See how it is working. You know that the 230 volt AC cycles with positive half and negative half cycles. When we give AC to an electric device, it works through both the half cycles of AC. Look the diagram below.
AC switch is there in the Phase line going to the Soldering Iron. It is bypassed by the diode IN4007. The AC switch is doing the trick. When it is in the ON position, the current passes directly to the soldering iron, so it will warm as usual. When the switch is in the Off position, current passes through the diode only and the soldering iron gets only half cycle. So the iron remains half warm.
If you are giving a rest to the soldering job, then keep the switch in the Off position The soldering iron will remain half heated so when the switch is in the On position, it will become fully heated within seconds. By observing the brightness of the LED you can confirm it.
Caution: The circuit uses AC, so there will be lethal shock if any part is touched. So do not try this if you are not experienced in handling AC circuits. You may seek the assistance of a well experienced person to make the arrangement.