Gideon Analytical Laboratories received two 144A9111 pulse transformers with the secondary wiring shorting. Transformers are devices that transfer electric energy from one circuit to another, usually with a change in voltage. Pulse transformers are transformers optimized for transmitting rectangular electrical pulses. Ideally, pulse transformer designers try to minimize voltage droop, rise time, and pulse distortion. Small versions called signal types are used in digital logic and telecommunications circuits, often for matching logic drivers to transmission lines. Medium-sized power versions are used in power-control circuits such as camera flash controllers. Larger power versions are used in the electrical power distribution industry to interface low-voltage control circuitry to the high-voltage gates of power semiconductors. Special high voltage pulse transformers are also used to generate high power pulses for radar, particle accelerators, or other high energy pulsed power applications. Of the two144A9111 pulse transformers with the secondary wiring shorting, one was completely exposing the seconding wire and the other was still intact on the printed circuit board (PCB). The goal was to determine the cause of the failure.
Failure analysis was conducted. The devices were electrically tested. The reason for the lower impedance measurement is that the contiguous winds around the bobbin were shorting together as the wire remains within the bobbin. Once they were removed, the short went away, and the wireless resistance per unit length was normal; there were no signs of thermal degradation to either the coating or the copper wire. The short was caused by the removal of the insulation coating from the copper surface. The insulation was either cracked, split, open, or degraded. Or, there might have been enough moisture present to form a contiguous electrical path to the next wire. The film insulation lacked integrity because of the chemical makeup, which allowed the accumulation of moisture. The film then lost adherence and caused shorts on contiguous winds.
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