Issue link: https://resources.mouser.com/i/1442856
| 6 | result with the split ferrite core in a flyback transformer where more turns are needed to ensure the current does not saturate the transformer. If there are tight space considerations and restrictions, the DC resistance will inevitably increase with the higher number of turns, resulting in reduced efficiency. It is advised to look for a push-pull transformer with a toroidal core. What makes them a good choice is that there is no need for a gap, and a toroidal core is well known for providing good coupling between windings. This is because the flux has a short distance to travel and there is little dispersion between windings. The relatively high inductance factor of a push-pull transformer with a toroidal core means it is possible to achieve high magnetizing inductances without a high number of turns. Plus, a coil former is not required as the wires are wound directly on the ferrite, which features a high dielectric protective coating. Coil formers add extra space as does the fact that the ferrite split core is exposed on the top and bottom if the transformer is a surface mount device. A toroid core can be enclosed in a housing separating the core from the circuit board. This difference automatically minimizes the footprint on a PCB in High Voltage applications where safety distances (creepage and clearance) are required as defined by the standards for insulation (IEC 60664) and communications equipment (IEC 62368) that mandate a specified distance between the High Voltage hazardous side of the PCB and the low- voltage side. If the core is exposed, the clearance will be significantly reduced which will need to be compensated by additional width or height of the plastic carrier. Figure 2 shows a comparison in terms of dimensions between the Bourns® Model HCTSM8 transformer and a transformer with a split core such as an E13. The figure illustrates that the E13 solution requires 90 percent more room on the PCB in order to meet the same isolation level of the Bourns® HCT series transformer. Furthermore, the leakage inductance of a transformer with an extended bobbin needs at least 200 percent more space on the PCB compared to a transformer with a tightly coupled toroid, even with the primary wrapped around the outside of the housing. Figure 2 Comparison between Bourns® Model HCTSM8 push-pull transformer and a typical split core transformer, both with 8 mm of creepage " " To some customers, double insulation has the advantage of offering real redundant insulation compared with triple insulated wire.