Building a Formidable 90W High-Frequency Soldering Iron

In this comprehensive guide, we delve into the workings of a high-frequency soldering iron, employing the eddy current heating principle, akin to household induction cooktops. This technology is remarkably efficient and cost-effective. We explore its core components, circuitry, and practical aspects, aiming to provide valuable insights for both enthusiasts and professionals in the field.

Section One: Main Circuitry Diagram

1. Transformer T1: Utilizing the ATX power supply's core (optional air gap) - EI33.

· Primary Winding: A direct winding of 34 turns using φ0.7 single-strand wire.

· Secondary Winding: φ0.7 wire wound with 12+7 turns. For 90W, use 12 turns; for 150W, use 19 turns.

· Primary Inductance (L_primary): 0.718mH (100KHz/1.0V).

2. Transformer T2: The core for driving from the ATX power supply (no air gap required).

· Inductance (Ln): 0.516mH (100KHz/1.0V).

· Primary with 30 turns and secondary with 36 turns. Wound with φ0.25 enameled wire meters.

· Note: Ensure same terminals are connected.

3. L1 Inductance: Employing a T106-2 magnetic ring (black and red), wound with 24 turns of φ1.0 wire. Using other colored rings may result in significant heating. This ring serves as a load in case of accidental short circuits in the handle heating coil and can be omitted under normal conditions.

4. Auxiliary Power Supply: An independent switching power supply provides a 12V DC power source for SG3525 and the temperature control board, with a low output current requirement of 12V 1A.

5. PCB Size: Designed for compatibility with a 10555150 aluminum alloy housing. For different housing sizes, custom layout adjustments are necessary.

Section Two: Temperature Control

The temperature control system simplifies the soldering iron's main functions to temperature adjustment, sleep mode, and automatic shutdown. It does not function as a thermometer but rather serves to maintain and indicate the soldering iron's approximate temperature.

Section Three: Physical Construction

1. Housing: An aluminum alloy case measuring 10555150 is recommended. Users may create custom openings in the front and back panels as needed.

2. Mainboard: The circuit boasts a substantial power margin, supporting the use of 203H and 205H handles. Remarkably, the circuit generates no heat, and the two push-pull MOSFETs remain cool throughout operation.

3. Temperature Control: Implemented via PID control, the temperature control system maintains a temperature accuracy within ±3 degrees. It's important to note that the high-frequency soldering iron requires approximately 20 seconds to reach solder-melting temperature, surpassing the capabilities of traditional T12 soldering irons in terms of power margin and reheat capability.

4. Handle: The handle features a pure silver heating core with a measured resistance of 0.7 ohms.

Section Four: Troubleshooting and Optimization

Before connecting the handle, it's advisable to observe the circuit's waveform for initial troubleshooting.

In Conclusion:

This high-frequency soldering iron project incorporates a professionally designed handle and casing, while other components are repurposed from an old ATX power supply and existing inventory. The temperature control section adopts T12 source code, resulting in a cost-effective solution with a highly satisfactory performance profile.