Soldering iron light reminder and temperature adjustment circuit

The electric soldering iron is a commonly used welding tool. It emits heat silently when working. It only emits heat but does not emit light. If the user does not try whether it is hot or not, he will not know whether it is working with electricity. Sometimes he forgets to unplug the power plug in time, which will cause electric energy. Unnecessary waste can easily burn out the soldering iron tip over time and even cause accidents. Sometimes it is necessary to lower the temperature of the soldering iron a little to avoid damaging the components, but generally the temperature of the soldering iron cannot be adjusted, and it is often troublesome to plug in and unplug it. For the above problems, the circuit shown in the attached figure can be used to improve it.

When the soldering iron is powered on, the current in the positive half cycle of the power supply causes a voltage drop on the diodes D2, D3, and D4. The light-emitting tube LED emits light 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 insignificant for a 220v power supply. It will not affect the normal use of the soldering iron. If the switch K is turned off, the circuit is in a half-wave power supply state, and the reduction in current causes the temperature of the soldering iron to drop, which not only reduces the power consumption but also achieves the purpose of temperature regulation. In addition, D1 blocks the reverse voltage of the power supply, thus protecting the LED. The whole circuit is very simple, and the components are cheap and have no special requirements. It is not difficult for those who are interested to imitate it. D in the circuit is all 1N4007.R with 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 soldering iron is far from reaching this value. Also, please note that this circuit is only suitable for electric soldering irons. Even incandescent lamps cannot be used.

This circuit provides power-on light-emitting indication and one-stop temperature adjustment, making it more convenient for users.