I. Switching Power Supply Transformer Winding
First, using dedicated transformer design software, input the required parameters, such as input voltage range, output voltage requirements, bias voltage, estimated transformer power, power factor, rated load, number of primary winding layers, and number of secondary winding turns. The PI software will then provide reasonable transformer parameters based on the user's input. The designer can then wind the transformer according to these parameters. (This is for switching power supply transformers.)
The software will provide the following parameters: number of layers, number of turns, wire diameter, winding direction, air gap size, number of layers of tape between coils, bobbin model, magnetic core model, and impregnation requirements for the primary coil, feedback coil, and secondary coil.
Secondly, with these parameters, we can begin winding the transformer. Before winding, we need to number the feet of the frame. For example, if we need to wind a transformer with an input voltage of +24V, output 1 of +9V, and output 2 of +15V, and the power of each output terminal is required to be 1.5W, then the winding method for this transformer is as follows:
Primary coil winding method: Starting from pin 2, use 0.19 mm diameter enameled wire to wind 53 turns around the bobbin, estimating two layers. The winding should be as flat as possible. End at pin 1. After winding, wrap two layers of insulating tape.
The method for winding the bias coil is as follows: Starting from pin 5, use 0.13 mm enameled wire to wind 27 turns around the skeleton until pin 4. After winding, wrap it with two layers of insulating tape, and then wrap it with another layer of insulating tape to cover all exposed parts of the coil except for the pin.
Third, the winding method for the 9V terminal coil: Wrap insulating tape around the bottom of pins 7 and 6, using 0.35 mm diameter enameled wire, starting from pin 7 and winding 20 turns to pin 6, then wrap with two layers of insulating tape. Finally, wrap the winding outside pins 7 and 6 with insulating tape.
II. What is a switching power supply transformer?
A switching power supply transformer is a power transformer with a switching transistor added. In addition to the voltage transformation function of a regular transformer, it also has the functions of insulation and power transmission. It is generally used in switching power supplies and other applications involving high-frequency circuits.
The main materials of a switching power supply transformer are magnetic materials, conductor materials, and insulation materials, which form the core of the switching transformer.
Magnetic Materials: The magnetic materials used in switching transformers are soft magnetic ferrites, which can be divided into two main categories according to their composition and application frequency: MnZn-based and NiZn-based. The former has high permeability and high saturation magnetic induction, and exhibits lower losses in the mid-frequency and low-frequency ranges. The magnetic cores come in many shapes, such as EI type, E type, and EC type.
Conductor Material—Enameled Wire: Enameled wires commonly used for winding small electronic transformers come in two types: high-strength polyester enameled wire (QZ) and polyurethane enameled wire (QA). Based on the thickness of the enamel layer, they are classified into Type 1 (thin enamel type) and Type 2 (thick enamel type). The former has a polyester enamel insulation coating, possessing excellent heat resistance and an insulation dielectric strength of up to 60kV/mm; the latter has a polyurethane enamel insulation layer, exhibiting strong self-adhesion and self-soldering properties (380℃), allowing for direct soldering without removing the enamel film.
Pressure-sensitive adhesive tape: Insulating tape with high dielectric strength, easy to use, and good mechanical properties is widely used for interlayer, intergroup, and external insulation of switching transformer coils. It must meet the following requirements: good adhesion, peel resistance, certain tensile strength, good insulation performance, good withstand voltage, flame retardancy, and high temperature resistance.
Frame Material: The frame of a switching transformer differs from that of a general transformer. In addition to serving as insulation and support material for the coils, it also plays a role in the installation, fixing, and positioning of the entire transformer. Therefore, the material used to make the frame must not only meet insulation requirements but also have considerable tensile strength. At the same time, in order to withstand the soldering heat of the pins, the heat distortion temperature of the frame material must be higher than 200℃. The material must be flame retardant and have good machinability, making it easy to process into various shapes.
