Issue link: https://resources.mouser.com/i/1442856
| 7 | Better Insulation The Bourns® Model HCTSM8 has reinforced insulation, which, according to standards, must consist of either triple insulated wire (three separate layers of insulation on the wire) on one winding or insulation on both windings (double insulation). Double insulation is not efficient from an electrical point of view. The time to strip the insulation from the start of the coil during the winding process will be twice that of a triple insulated transformer. The effective space for conductors is reduced in a double insulated system as both coils have at least 0.08mm of insulation compared to 0.02mm for pure magnet wire with enamel. The time required to wind a toroid with insulated wire is higher compared to enamel coated wire. Therefore, double insulation is less efficient and more expensive. However, to some customers, double insulation has the advantage of offering real redundant insulation compared with triple insulated wire. Using the HCTSM8 series transformer example, the secondary winding consists of FIW (fully insulated wire), which is considered as strong as triple insulated wire but without safety agency recognition (for many types). This is particularly relevant in a transformer with a toroidal core. The concern is the effect of triple insulated wire which could degrade and cause a short to the core and also from the core to the non-insulated wire. This risk can be mitigated using FIW wire on the secondary side. Figure 3 Illustrates the construction of the Bourns® Model HCTSM8 transformer with a toroidal core showing the lid and primary wire wrapped around the housing to extend the distance from the pins to the core Maximum Creepage/Clearance The Bourns® HCTSM8 push-pull transformer makes full use of the enclosure around the ferrite core to maximize creepage and minimize the footprint. The core is not visible from the pins of the design so the clearance pin to core will be measured up the wall of the device and down the joint between the lid and the side wall. The effective tracking distance over the insulated wire from pin to core is maximized by running the insulated wire around the outside of the component. By using this breakthrough design that features a press fit of the lid against the sidewall and the wraparound insulated wire, the Model HCTSM8 series can obtain a creepage and clearance of 8.0mm despite having a nominal height of just 6.5mm and a distance from pad to pad on the PCB of 11mm max. In addition, the Model HCTSM8 uses plastic material classified as Class I, which means it is the least conductive of all plastics to High Voltages. It features triple insulated wire on one winding (primary). Consequently, by taking 8.0mm as creepage and clearance distance and consulting table F.4 of IEC 60664, this transformer offers a working voltage of 800V rms . As a result, inverters and battery packs with rms voltages of up to 800V rms requiring reinforced insulation could use the HCTSM8 for the following two energy storage applications: A) Isolated DC voltages for a gate driver for an IGBT or SiC MOSFET B) Isolated DC power for a microcontroller or voltage monitoring IC or transceiver