Soldering iron that cannot melt solder

I made this temperature-controlled soldering iron completely free of charge using the component vouchers, 3D printing vouchers, and PCB vouchers provided by JLCPCB. The circuit board is very compact and can be used to upgrade an old-fashioned soldering iron to a temperature-controlled type.
 
The circuit board is based on the most common 936 temperature-controlled soldering iron on the market, but the resistor that determines the minimum temperature has been changed. Therefore, when this soldering iron is set to its lowest temperature, it is equivalent to the sleep temperature of a fast-heating soldering iron like the T12, which is around 110 degrees Celsius. Even if it is powered on for a long time, the soldering tip will not burn out.
 
As a result, this soldering iron can be adjusted to and kept at a temperature that prevents solder from melting. This is very useful for some crafts, such as drilling a hole in a plastic board or melting hot glue, without having to worry about burning out like a regular soldering iron.