Abstract: The adjustable temperature electric soldering iron is composed of a soldering iron head, a soldering iron frame, a power cord, a soldering iron handle, a temperature controller, etc. The principle of the constant temperature electric soldering iron is to add the heating core through the power line through the voltage of 220V, and the heating core converts the electric energy into Thermal energy passes through the heat transfer, causing the soldering iron tip to reach or exceed the temperature at which the solder melts. The following is a detailed explanation of the adjustable thermostat soldering iron circuit diagram and the thermostatic soldering iron principle.
[Temperature electric soldering iron] adjustable thermostat electric soldering iron circuit diagram thermostat electric iron principle
This article explains how the working principle of constant temperature soldering iron is? At the same time, share the circuit diagram of the homemade constant temperature soldering iron. This circuit diagram uses a thermocouple sensor with a temperature control accuracy of up to ±5%. The control circuit uses a direct current buck, filter, and regulated power supply scheme for AC mains. as the picture shows. The temperature range of the soldering iron is 100 ° C ~ 400 ° C, the temperature adjustment mark indicates low, medium and high position, the temperature control accuracy is nominally ± 5%, and a thermocouple sensor is used. The control circuit adopts the direct current step-down, filtering and regulated power supply scheme of the AC mains.
The mains AC220V is used as the power supply voltage and temperature setting voltage source of the comparison device IC after R1 step-down, D1 half-wave rectification, D2 clipping regulation, and C1 filtering. The IC-A3 pin is the thermocouple detection voltage input terminal (corresponding to the temperature value); the 2 pin is the thermostat setting voltage. After the voltages at both ends of pins 2 and 3 are compared, they are output by pin 1. The role of R5 is to feed back a small part of the input to the non-inverting input pin 3, so that the output lock does not change when the small signal fluctuates. When the thermocouple detects that the temperature is low; the level of the 3 pin is lower than the 2 pin, so that the output pin 1 is also low. Further, the IC-B amplifier 6 pin is lowered relative to the fixed bias 5 pin, so that the output 7 pin is high. Since the voltage of the IC-B5 pin is obtained by dividing the AC220V by R6 and R7, the frequency and phase are completely the same as those of the AC220V. After comparing with 6-pin DC, the AC voltage is output at 7 feet. The AC voltage is reversely connected in parallel with C2, D4, D3 and D4 (acting as a bidirectional diode) to trigger the bidirectional thyristor, so that the corresponding voltage is applied to the soldering iron heating wire to achieve the purpose of constant temperature.
the first time
The iron core burned, but the thermocouple was good, so I bought a 30 watt iron core and placed the thermocouple behind the iron core and used it as usual.
the second time
The thermocouple is broken. Looking at the original circuit, it costs a dollar to buy a resistor with a negative temperature coefficient. It replaces the thermocouple and it takes a long time.
the third time
I saw that the iron core with thermocouples is now sold. It is not very expensive (4 yuan a). The original soldering iron used for too long, it should be changed, so I bought a 40 watt iron core and a soldering iron. The soldering iron handle, according to the following circuit, re-DIY one, used for half a year, the effect is not bad. The warm-up time is slightly longer, nearly 2 minutes.
The physical map is made with the originals already in hand. 
Editor in charge: Zhao Hongli
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