What is Transistor Welding Power Supply?
Since major part of micro-parts to be resistance-welded is low-thermal-resistance metal, faster-rising current, compared with ordinary resistance welding, must be applied. Various resistance welding power supplies such as ac, capacitor, transistor, inverter power supply are available. As shown in Figure 1, transistor and inverter welding power supplies offer controllable and fast-rising current. These two welding power supplies are suited for welding micro-parts that requires delicate current control, better than the other two. Since transistor welding power supply can apply welding current directly to workpiece without transformer, it can flow faster-rising and quicker-responding current than inverter power supply which applies current via welding transformer.
Three selectable power supplies
Standard power supply (MDA)
Has two or more transistors (MOSFET) connected in parallel and fly-wheel diodes. These transistors switch on and off repeatedly to control weld current, while detecting such as weld current, voltage across electrodes (Figure 2). Current is one-directional. This type of power supply is well suited for welding the same kind of metals.
Figure 2. Block diagram of standard power supply.
Polarity-switching power supply
Is composed of 4 blocks of transistor (S1 to S4) as shown in Figure 3. Combination of S1 and S2 and that of S3 and S4 are reversely connected to electrode. When S1 continues switching repeatedly with S3 and S4 are being off and S2 being on, current flows from upper electrode to lower one. When S1 is off in this operation, current flows through fly-wheel diode of S4. Similarly, when S3 continues switching repeatedly with S1 and S2 are being off and S4 being on, current flows from lower electrode to upper one. When S3 is off in this operation, current flows through fly-wheel diode of S2. Therefore, direction of welding current is switched. This type of power supply compensates for disadvantage of standard power supply. In series welding of different kinds of metals, nugget growth is not same by direction of current which is due to Peltier effect, resulting in size of nugget being different in right and left sides. This type of polarity switching can flow current bi-directionally as shown in Figure 4. Furthermore, polarity switching features that it can change weld time and magnitude of current directionally, i.e., control energy supply by polarity.
Figure 3. Block diagram of polarity-switching power supply.
Figure 4. Welding current waveform of polarity-switching power supply
2-channel power supply
It is provided with transistor blocks, employed in standard power supply, connected in parallel; so, this power supply can switch two welding heads. This is like two-in-one power supply, welding two adjacent weld spots successively to improve part cycle time; however, two weld spots cannot be welded at a time.
Three selectable control methods
