Solution for the loss of temperature of the soldering iron at a constant temperature
A common failure of a constant-temperature soldering iron is that the temperature is out of control, which results in the temperature of the soldering iron being too high. On the one hand, it causes high-temperature oxidation of the soldering iron tip (the solder is also oxidized at the same time); on the other hand, soldering at high temperatures can easily burn out electronic components. When a soldering iron works at high temperatures for a long time, it can easily cause damage to its internal circuit, causing it to become permanently out of control or even unusable. During the fault inspection, it will be found that the sliding contact of the temperature regulating resistor R2 is oxidized and causes poor contact. This is equivalent to the temperature being adjusted to the maximum upper limit, so the temperature of the soldering iron is too high. There are two fundamental reasons: First, when the soldering iron is working, it transfers part of the heat to the handle of the soldering iron (built-in circuit), which increases the temperature of the circuit working environment. After a period of time, it is easy to cause the movable contact of R2 to oxidize; secondly, the current limiting resistor R1 in the rectifier and filter circuit dissipates heat, causing the circuit working environment temperature to rise, which also easily causes the oxidation of the moving contact of R2.
In order to prevent this kind of failure from happening, the following two methods of modifying the circuit are proposed for reference.
(1) Replace the adjustable resistor R2 with a fixed resistor: first adjust R2 to make the temperature of the soldering iron reach the optimal temperature point for normal use, then measure the value of R2 and replace it with a fixed resistor.
(2) Modify the rectifier circuit: replace R1 with C (C≈0.12μF), and connect a diode D1 in parallel.
