Thermostatic soldering iron temperature is out of control Solution
Thermostatic soldering iron temperature out of control solution
The common failure of constant temperature soldering iron is the temperature out of control, which results in the temperature of the soldering iron is too high. On the one hand, it leads to high temperature oxidation of soldering iron head (solder is also oxidised at the same time); on the other hand, it is easy to burn electronic components when soldering at high temperature. When the soldering iron is working under high temperature for a long time, it is also easy to cause damage to its internal circuitry, resulting in permanent loss of control or even can not be used. In the fault check will be found in the temperature control resistor R2 sliding contacts are oxidised to produce poor contact phenomenon, which is equivalent to the temperature is adjusted to the maximum upper limit, and thus the temperature of the iron is high. The root cause of two points: one is the soldering iron work to the iron's handle (circuit built-in) to transfer part of the heat, so that the circuit working environment temperature increases. After a period of time it is easy to cause the oxidation of the dynamic contacts of R2; Secondly, the rectifier filter circuit in the current-limiting resistor R1 dissipation of heat leading to the circuit working environment temperature is also easy to cause the oxidation of the dynamic contacts of R2.
In order to prevent the occurrence of this failure, the following two circuit modification methods are proposed for reference.
(1) Fixed resistor instead of adjustable resistor R2: Firstly, adjust R2, so that the temperature of the soldering iron to reach the optimal temperature point for normal use, and then measure the value of R2 and replace it with a fixed resistor.
(2) Modify the rectifier circuit: the circuit structure is shown in the figure.
Replace R1 with C (C ≈ 0.12 μF) and connect a diode D1 in parallel.
