The role of switch mode power supply transformers
The switching power transformer and switching transistor together form a self-excited (or separately excited) intermittent oscillator, thereby modulating the input DC voltage into a high-frequency pulse voltage
It plays a role in energy transfer and conversion. In a flyback circuit, when the switch is turned on, the transformer converts electrical energy into magnetic field energy for storage, and when the switch is turned off, it is released. In a forward circuit, when the switch is turned on, the input voltage is directly supplied to the load and energy is stored in the energy storage inductor. When the switch is turned off, the energy is further transferred to the load through the energy storage inductor
Classification of Switching Power Transformers
Switching power supply transformers are divided into single excitation switching power supply transformers and double excitation switching power supply transformers. The working principle and structure of the two types of switching power supply transformers are not the same. The input voltage of a single excitation switching power supply transformer is a single polarity pulse, and it also has forward and reverse voltage outputs; The input voltage of a dual excitation switching power supply transformer is a bipolar pulse, usually outputting a bipolar pulse voltage.
Composition of Switching Power Transformers
The main materials of switch mode power transformers are magnetic materials, wire materials, and insulation materials, which are the core of switch mode transformers
Magnetic materials: The magnetic materials used in switch transformers are soft ferrite, which can be divided into two categories based on their composition and application frequency: MnZn series and NiZn series. The former has high permeability and high saturation magnetic induction, and has low losses in the mid and low frequency ranges. The magnetic core has many shapes, such as EI type, E type, EC type, etc
Wire Material - Enamelled Wire: Generally used for winding small electronic transformers, there are two types of enameled wire: high-strength polyester enameled wire (QZ) and polyurethane enameled wire (QA). According to the thickness of the paint layer, they are divided into Type 1 (thin paint type) and Type 2 (thick paint type). The insulation coating of the former is polyester paint, which has superior heat resistance, and the insulation strength can reach 60kv/mm; The latter insulation layer is made of polyurethane paint, which has strong self-adhesiveness and self soldering performance (380 ℃), and can be welded directly without removing the paint film
Pressure sensitive tape: Insulation tape has high electrical strength, is easy to use, and has good mechanical properties. It is widely used in interlayer, inter group insulation, and outer insulation of switch transformer coils. It must meet the following requirements: good adhesion, anti stripping, certain tensile strength, good insulation performance, good pressure resistance, flame retardancy, and high temperature resistance
Skeleton Material: The skeleton of a switch transformer is different from a typical transformer skeleton. In addition to serving as insulation and support material for the coil, it also plays a role in the installation, fixation, and positioning of the entire transformer. Therefore, the material used to make the skeleton should not only meet the insulation requirements, but also have considerable tensile strength. At the same time, in order to withstand the welding heat resistance of the pins, the thermal deformation temperature of the skeleton material is required to be higher than 200 ℃. The material must be flame retardant and have good processability, making it easy to process into various shapes
