Refinement of the soldering iron tip temperature stabilizer. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Ham Radio Technologies
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The author has modified his device. As a result, its permissible output power has been increased, reliability has been increased, and the circuit design has been simplified and improved.
The operation of the soldering iron tip temperature stabilizer I developed earlier with different types and designs of soldering irons required the refinement of the circuit solution to increase its reliability and the accuracy of the operation of the thermostat assembly. In addition, the power of the connected soldering irons was limited by the current limit of the KTs407A rectifier bridge (0,5 A) and the MOS3063 optocoupler (1 A). In the modified device, a more powerful rectifier bridge is used, and instead of the heater control element - an opto-simistor - a powerful triac. In addition, the resistive divider R1R2, which sets the reference voltage, and the resistor R6, which does not affect the quality of the stabilizer, are excluded. The discharge current of the capacitor C3 is limited to a safe level for the output of the op-amp D1.2.
The scheme of the modified version of the stabilizer is shown in fig. 1. A detailed description of the original version has already been given earlier, we note only the main differences.
Rice. 1. Scheme of a modified version of the stabilizer
The exemplary voltage is not supplied from a resistive divider, as before, but from a common junction point of the zener diodes VD3, VD4. The cathode of the emitting diode of the U1 MOC3063 optocoupler is connected directly to the timer output of the temperature control unit, which sets the tip heating time interval. This made it possible to guarantee a more precise control of the state of the soldering iron heater even with the smallest change in its resistance. The timer, similar to the previous design, is assembled on the op-amp DA1. 1 included as a comparator.
Let us briefly consider the operation of the temperature control unit and its elements.
When the temperature of the heater drops below the threshold set by the trimmer resistor R3, the voltage at the inverting input of the op-amp DA1.2 becomes less than the exemplary one set by the zener diode VD4 (+5,6 V). A positive voltage drop appears at the output of the op-amp. This difference through the capacitor C2 discharged by this time (its discharge current through the output of the op-amp DA1.2 limits the resistor R5) is fed to the inverting input of the op-amp Da 1.1. The voltage at its inverting input becomes greater than the reference voltage for the time specified by the parameters of the differentiating circuit R4C2. At the output Oy, a voltage close to zero appears and sets. The LED HL1 and the emitting diode of the optotriac U1 light up. The optosimistor opens, which also leads to the opening of a powerful triac VS1 from the mains voltage rectified by the diode bridge VD7, taken from the resistive divider R8R9. The heating element of the soldering iron is connected to the network. After the time specified by the R4C2 circuit (4 ... 6 s), the voltage at the inverting input Oy DA1. 1 again becomes less than the exemplary one and a positive voltage drop appears at the output of the op-amp. The LED goes out, the optosimistor closes, which also leads to the closing of the triac VS1 - the heating element of the soldering iron is disconnected from the mains. Its next connection will occur after cooling to the appropriate temperature set by resistors R1 -R3.
When replacing or choosing a triac VS1 and a diode bridge VD7 of other types, it must be borne in mind that their maximum permissible current must exceed the maximum load current. Replacing the LM358P op amp chip with the LM393P comparator will require the installation of a 1 ... 5 kOhm resistor between its pin 10 (output) and the positive power line of the control unit. The replacement of the remaining elements, the adjustment and design of the stabilizer was described in detail in a previous article.
The device is assembled on a printed circuit board made of fiberglass laminated on one side. The drawing of the board and the elements located on it are shown in fig. 2.
Rice. 2. Drawing of the board and the elements located on it
Author: L. Elizarov
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