Electric soldering iron light prompt and temperature control circuit

Electric soldering iron is a commonly used welding tool. It emits heat silently when working. It only generates heat but not light. If the user does not try to check whether it is hot, he will not know whether it is powered on. Sometimes forgetting to unplug the power plug in time will cause unnecessary waste of electricity, and it is easy to burn the soldering iron tip over time, and even cause accidents. Sometimes it is necessary to lower the temperature of the electric soldering iron a little to avoid damaging the components, but the general electric soldering iron cannot be adjusted in temperature, and it is troublesome to plug and unplug it frequently. For the above problems, the circuit shown in the attached figure can be used to improve them.

When the electric soldering iron is powered on, the current in the positive half cycle of the power supply generates a voltage drop on the diodes D2, D3, and D4. The light-emitting tube LED is illuminated through D1 and the current-limiting resistor R; in the negative half cycle (switch K is closed), the current passes through D5. Since the voltage drop of the diode is only 0.7V, it is negligible for a 220V power supply and will not affect the normal use of the electric soldering iron. If the switch K is disconnected, the circuit is in a half-wave power supply state, and the reduction of the current causes the temperature of the electric soldering iron to drop, which not only reduces the consumption of electric energy but also achieves the purpose of temperature regulation. In addition, D1 blocks the reverse voltage of the power supply, thereby protecting the LED. The whole circuit is very simple, the components are cheap and there are no special requirements. It is not difficult for those who are interested to imitate it. D in the circuit is 1N4007. R uses a 1/4W resistor. Since the current of 1N4007 is 1A, the load current cannot exceed this value. Fortunately, the commonly used 20W or 35W electric soldering irons are far from reaching this value. In addition, this circuit is only suitable for electric soldering irons. Even incandescent lamps are not acceptable.

The circuit provides a power-on luminous indication and a temperature adjustment gear, making it more convenient for users.