Electronic circuits often require a transformer for direct current isolation, voltage conversion, or as a filter element. These transformers generally are formed by a magnetic core member and a bobbin member, although the core member is not essential. Around the bobbin there are wound one or more windings. One winding would be sufficient to form an inductance element. Two or more windings as the primary and secondary result in a transformer. The voltage difference between the primary and secondary windings can be relatively large, more than a thousand volts. Therefore, it is important that the wire leads of the primary winding be well insulated from those of any secondary winding. To this end, it is the present practice to first fasten the lead wires of the primary winding to terminals and to hold them against the inside surface of the flange of the bobbin with adhesive backed insulating tape before beginning the process of forming the secondary winding. This keeps the leads out of the way of the winding process and provides extra insulation between the leads and the turns of the secondary, which would otherwise press directly against the lead wires at the flange.
The winding and terminating process is done automatically. The taping process, however, is done manually, and is a significant aspect of the total labor content of the transformer. Moreover, the taped leads of the first winding tend to get somewhat in the way of the winding process for the second winding, which is also carried out automatically. Further, it is not readily feasible to tape the leads close enough to the wire termination to provide the desired isolation of the first winding lead from the winding turns of the second winding, which end up in contact with it.