Constant temperature electric soldering iron design with cooling indication function
Soldering iron is a tool widely used in industries such as electronic product manufacturing and service. along with
With the development of technology, the automatic welding technology of electronic products is also developing continuously, but the use of electric soldering iron
Technologies such as manual soldering and desoldering of components are still essential. ironing now
Iron generally realizes functions such as constant temperature control and leakage protection, and its service life is also greatly increased. exist
After daily use of the electric soldering iron, its residual temperature is still relatively high, and it may be
Burn people, and even cause dangerous accidents such as fire. Many people who use electric irons are accustomed to using
There is also a risk of burns if the hand is close to the tip of the soldering iron to sense the residual temperature of the soldering iron. for
In order to allow users to intuitively understand the cooling state of the electric soldering iron after use, it is avoided to feel the electric current by hand.
Dangers that may be caused by residual temperature of the soldering iron and fire hazards that may be caused, the design has a cooling indicator function
capable soldering iron.
Analysis of the working principle of the original electrical contact iron
The following is the working principle and circuit diagram of a constant temperature electric soldering iron (see Figure 1). electricity
After the AC220V is stepped down by R1, half-wave rectified by D1, filtered by C1 and stabilized by D2, it is used as an integrated operation
The 3582 compares the power supply voltage of the device IC and the thermostat setting voltage source.
The thermocouple is used as a temperature sensor to detect the tip of the soldering iron, and the temperature varies according to the temperature.
electromotive force. During work, the electromotive force is added to pin ③ of IC-A through resistor R3, as
It is the voltage input terminal for thermocouple detection; and the ② pin is the temperature setting voltage. At ②, ③ feet
After the voltage at both ends is compared, it is output by pin ①. Among them, the feedback resistor R5 acts on the input signal
When fluctuating in a small range, its output signal is locked and unchanged. When the thermocouple detects that the temperature is low, ③
The pin level is lower than the ② pin level, so that the output ① pin is low. This in turn makes the IC-B amplifier
The ⑥ pin is relatively low relative to the fixed bias ⑤ pin, so that the output ⑦ pin is high. Since IC－B ⑤
The pin voltage is obtained by dividing the voltage of AC220V through R6 and R7. Therefore, the frequency and phase are completely consistent with
AC220V is the same. After comparing the level of ⑤ pin with the level of ⑥ pin, the AC voltage is output on ⑦ pin. Should
The AC voltage is connected in antiparallel with D3 and D4 through C2 (acting as a trigger voltage of a bidirectional diode).
The circuit controls the bidirectional thyristor, and controls the conduction time of the current applied to the heating wire of the soldering iron, so as to realize
Now the purpose of constant temperature control.
Improvement design of electric iron control circuit
The above-mentioned original constant temperature electric soldering iron is improved, and the thermoelectric effect of the thermocouple in the circuit is used
To realize the residual temperature detection. While disconnecting the heating control main circuit of the electric soldering iron, put the thermocouple
The voltage signal is led to the voltage comparator composed of integrated op amp. When the soldering iron cools down
At the end, the thermocouple output voltage makes the integrated operational amplifier output a high level, and the indicator LED is lit
It means that the soldering iron is cooling; and when the cooling of the soldering iron ends, the output voltage of the thermocouple is very small,
The output terminal of the integrated operational amplifier outputs a low level, and the LED light goes out, indicating that the cooling of the soldering iron is over.
Through the detection of the output voltage of the thermocouple, the LED light can be used to display the temperature state, so that
Make the electric soldering iron have a cooling indicator function.
Specific implementation process
The following is the working principle and circuit diagram of the constant temperature electric soldering iron with cooling indication (see Figure 2). use
The switch SW1 realizes the control of the working and power-off of the electric soldering iron. When switch SW1 is closed, the power
The soldering iron works normally, and its principle is exactly the same as the above circuit principle, the difference is that it is soldering
after the end.
When the switch SW1 is turned on after welding is completed. U2: A ③ pin is disconnected from the thermocouple,
Make U2:A pin ① output high, and then make U2:B amplifier ⑥ pin relative to the fixed bias
U2:B ⑤ pin is high, so that the output U2:B ⑦ pin is always low. Triac is off
state, the heating wire is powered off, and the soldering iron does not work. In U2: A ③ leg branch and thermocouple are disconnected
At the same time, the double-throw switch SW1 connects the thermocouple to U3:A pin ③, and at the same time makes the integrated operational amplifier
Pin ⑧ of U3:A power supply is connected to the power line, U3:A starts to work, and when the cooling of the soldering iron is not completed,
The thermocouple output voltage makes U3:A ③ pin voltage higher than ② pin voltage, making U3:A ① pin
Output high level, light up the LED after passing through the current limiting resistor R10; when the temperature of the soldering iron tip drops to the set
temperature, the thermocouple output voltage makes U3:A pin ③ pin voltage relative to ② pin voltage be
low, so that the U3:A ① pin outputs low level, and the LED light D5 goes out, thus cooling
Indication
