I have got a T12 soldering iron station already. When I saw there was a promotion on ALIEXPRESS , I bought a new one as a backup. After all, it can be used in case the old one breaks down suddenly. The internal resistance of a conventional T12 soldering iron is 8Ω, and it uses a 24V power supply with a current of 3A.
The power calculation formula is P = IIR = 72W.
I want to modify the power supply to increase the power a bit. I don't care much about the lifespan of the soldering iron tip. If the voltage is changed to 30V, the power can reach 112W.
Of course, ultimately, due to the limitation of the heat conduction speed from the heating core of the soldering iron tip itself, it won't always be in a high-power state.
1. Determine the model of the switching power supply until the position of TL431.
The TL431 is usually nearby the optocoupler. It is a 2.5V reference voltage component. It adjusts the output voltage of the switching power supply through resistor voltage division, it drives the optocoupler, and completes the voltage feedback.
2. Determine the position of the voltage-dividing resistors.
The voltage-dividing resistors of this device are 2260Ω and 20000Ω.
24V = 2.5 * (1 + 200000/2260)
To adjust it to 30V, just need to change the 2260Ω resistor to 1800Ω.
30V = 2.5 * (1 + 200000/1800)
Generally speaking , the transformer is designed with a margin. After confirming that the withstand voltage values of the microcontroller and MOSFET at the rear end are both over 30V, the modification can be carried out. After modification, it is recommended to disconnect the rear-end circuit first and measure it with a multimeter before connecting.
3. Modify the voltage-dividing resistors and test before wiring.
Resistor No.1: 1.8K
Resistor No.2: 20K
Most T12 soldering iron stations can be modified in this way. Compared with the previous 72W station, the average efficiency can be increased by about (112 - 72)/2 = 20W.
4. Reference for rear-end components
There are risks in Modifying , but the difficulty is not so high. The withstand voltage value of 78M05 is close to 30V - 35V. I've modified two stations already , and they both work perfectly. However,i can not make sure that the 78M05 may be broken down, causing the microcontroller at the rear end to be burned out.The withstand voltage of the D413A MOSFET is 40V, which is relatively safe.
