The transistor direct current power supplies (also called "Linear DC") produce much the same results as the high frequency inverter by using a high number of power transistors as the direct energy source. This technology provides clean, square wave forms with extremely fast rise time. Used primarily in constant voltage feedback control, transistor DC power supplies are effective in thin foils and fine wire welding applications and for extremely short welds.
Linear DC welders utilize transistor controlled feedback enabling total feedback response times of less than 5 uS. The term Linear DC comes from the waveform that is output from the power supply. No transformer is utilized. The primary limitation to Linear DC technology is the low duty cycles, typically much less than 1 weld per second at less than rated output.
Typically, constant voltage feedback is utilized in conjunction with short weld pulses. Because the feedback response is so rapid, high energy welds with extremely short duration can be used without weld splash or arcing. These short pulses limit the heat stress and the size of the heat affected zone on the weldments. This provdies a stronger more ductile weld joint, along with less part deformation, less discoloration, and significantly longer electrode life.
Constant voltage feedback is chosen for two reasons: its ability to prevent arcing and the provide the optimum weld power distribution based on the part resistance. If for some reason the weldments collapse faster than the weld head can follow up, arcing usually occurs. When constant voltage feedback is applied with the feedback response times capable by Linear DC welding this arcing is minimized.
Transistor DC units tend to be larger and heavier than other resistance welding power supply technologies.
