The rectifier bridge is a crucial component in the welding machine, responsible for converting the input alternating current (AC) into the required direct current (DC) for welding, thereby enhancing welding quality and stability.
1. Why does the welding machine need a rectifier bridge?
The welding machine usually directly connects to the alternating current (single-phase or three-phase) from the power grid, but direct current (DC) is more suitable for welding because:
- The arc is more stable, making it less likely to lose arc during the welding process;
- It is easier to strike the arc, improving work efficiency;
- There is less spatter, resulting in a more aesthetically pleasing weld seam (especially for stainless steel, aluminum, etc.);
- It is more adaptable to different types of welding rods, improving welding quality.
The application and key requirements of the rectifier bridge in the welding machine
2. Application scenarios of the rectifier bridge in the welding machine
1. DC manual arc welding machine (ZX series, etc.)
Traditional silicon rectifier welding machine: The rectifier bridge converts the reduced voltage AC from the transformer into DC for the welding clamp and the workpiece.
Inverter welding machine: In the secondary rectification part, the rectifier bridge converts the high-frequency AC into low-voltage DC to ensure welding stability.
2. DC TIG Welding Machine
Requires highly stable DC output. The rectifier bridge ensures a smooth arc and improves welding quality (especially for stainless steel, aluminum, etc.).
3. MIG/MAG Welding Machine
Although the wire feeding and gas control are separate, the core of the welding power supply relies on the rectifier bridge to provide DC (either traditional or inverter structure is applicable).
4. Submerged Arc Welding Machine
Converts AC input to DC output to ensure the stability of large current welding.
5. Spot Welding/Seam Welding Machine
The main welding current may be AC, but the control system or auxiliary power supply may require a small-power rectifier bridge to provide DC.
3. Special Requirements of Welding Machines for Rectifier Bridges
1.High Current Carrying Capacity
The welding current usually reaches several tens to several thousand amperes. The rectifier bridge (such as rectifier bridge stack or diode module) must support continuous operation with large currents.
2. High Surge Current Tolerance
Instantaneous large current surges occur during arc ignition or short circuits. The rectifier bridge must withstand such transient loads without damage.
3. Sufficient Reverse Voltage Rating
Diodes need to be able to withstand the peak voltage of the AC input and leave a safety margin to avoid breakdown.
4. Efficient Heat Dissipation Design
High currents lead to significant heat generation (I²R loss). The rectifier bridge must be equipped with a large heat sink + forced air cooling (such as fans) to prevent overheating and burnout.
5. Industrial Grade Reliability
It needs to adapt to harsh industrial environments such as vibration and dust to ensure long-term stable operation.
4. Key Components of the Rectifier Bridge
Filter Inductor (connected to the output of the rectifier bridge)
- Suppress current fluctuations:Reduce the ripple of direct current, making the output more stable.
- Stabilize the arc: Utilize the inductive characteristic (to suppress current fluctuations), reduce the arc initiation splashing, and improve droplet transition.
Protection circuit
- Fuse/thermal protection switch:Prevents damage to the rectifier bridge due to overcurrent or overheating.
- Buffer circuit (common in inverter welders): Absorbs voltage spikes and protects the rectifier module.
5Design guidelines for rectifier bridge to filter in welding machine circuits
In traditional industrial frequency transformer welding machines:
- Input alternating current
- Industrial frequency transformer (reducing voltage)
- Rectifier bridge (alternating current to pulsating direct current)
- Filter inductor (smoothening voltage)
- Output direct current terminal
- Input alternating current.
- Input rectifier filter (primary rectification, usually a bridge, to obtain high-voltage direct current) .
- Inverter circuit (high-frequency switching, converting direct current to high-frequency alternating current).
- High-frequency transformer (reducing voltage and isolation) .
- Secondary rectifier bridge (converting high-frequency alternating current back to direct current) .
- Output filter inductor.
- Output direct current terminal.
Note: Inverter welding machines have two stages of rectification:
The primary rectification converts the alternating input to high-voltage direct current for the inverter to use; the secondary rectification converts the high-frequency low-voltage alternating current obtained after inversion into the required direct current for welding.
Summary:
The rectifier bridge is one of the key components of a DC welding machine. The welding machine has strict requirements for it, needing to be able to withstand high currents, large surges, and be equipped with powerful heat dissipation. Both traditional AC welding machines and modern inverter welding machines rely on the rectifier bridge to achieve the function of DC welding. Without it, the welding machine will be unable to perform DC welding operations.