The main materials that make up the switching power transformer are magnetic materials, wire materials, and insulation materials, which are the core of the switching transformer. Magnetic materials: The magnetic materials used in the switching transformer are soft magnetic ferrite, which can be divided into MnZn series and NiZn series according to their composition and application frequency. The former has high permeability and high saturation magnetic induction, and has low losses in the medium and low frequency range. The magnetic core has many shapes, such as EI type and E type, EC type and other wire materials - 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, there are two types: type 1 (thin paint type) and type 2 (thick paint type). The insulation coating of the former is polyester paint, which has excellent heat resistance, and the insulation resistance and electrical strength can reach 60kv/mm; The latter insulation layer is polyurethane paint, which has strong self-adhesion and self soldering performance (380 ℃), and can be directly welded to pressure sensitive tape without removing the paint film. The insulation tape has high electrical strength, convenient use, and good mechanical properties, and is widely used in interlayer, inter group insulation, and external insulation of switch transformer coils. The following requirements must be met: good adhesion, anti stripping, certain tensile strength, good insulation performance, and good pressure resistance, Flame retardant and high-temperature resistant skeleton materials: The switch transformer skeleton is different from the general transformer skeleton. In addition to serving as the insulation and support material for the coil, it also serves as the installation, fixation, and positioning of the entire transformer. Therefore, the materials used to make the skeleton not only meet the insulation requirements, but also have considerable tensile strength. At the same time, in order to withstand the welding heat of the pins, the thermal deformation temperature of the skeleton material is required to be higher than 200 ℃, and the material must achieve flame retardant, And it should also have good processability and be easy to machine into various shapes. Detection method 1: Check whether there are obvious abnormalities by observing the appearance of the transformer. For example, whether the coil leads are broken, desoldered, whether there are burnt marks on the insulation material, whether the fastening screws of the iron core are loose, whether the silicon steel sheet is rusted, and whether the winding coil is exposed. 2. Insulation test. Using a multimeter R × Measure the resistance values between the core and primary, primary and secondary, core and secondary, electrostatic shielding layer and secondary, and secondary windings at 10k gear. The multimeter pointer should be fixed at infinity. Otherwise, it indicates poor insulation performance of the transformer. 3. Detection of coil on/off. Place the multimeter in R × In gear 1, during the test, if the resistance value of a certain winding is infinite, it indicates that there is an open circuit fault in the winding. 4. Distinguish between primary and secondary coils. The primary and secondary pins of the power transformer are generally led out from both sides, and the primary winding is often marked with the word 220V, while the secondary winding is marked with the rated voltage value, such as 15V, 24V, 35V, etc. Then identify based on these markings. 5. Detection of no-load current. a. Direct measurement method. Open all secondary windings, Place the multimeter in the AC current range 500mA, connected in series to the primary winding. When the plug of the primary winding is inserted into a 220V AC mains supply, the multimeter indicates the no-load current value. This value should not be greater than 10% -20% of the transformer's full load current. Generally, the normal no-load current of a common electronic equipment power transformer should be around 100mA. If it exceeds too much, it indicates that the transformer has a short-circuit fault. b. Indirect measurement method. Connect a 10?/5W transformer in series in the primary winding of the transformer Resistance, secondary is still fully unloaded. Set the multimeter to AC voltage. After powering on, use two probes to measure the voltage drop U at both ends of the resistance R, and then use Ohm's law to calculate the no-load current I empty, that is, I empty=U/R. F? Detection of no-load voltage. Connect the primary of the power transformer to 220V mains power, and use a multimeter to measure the no-load voltage values (U21, U22, U23, U24) of each winding in sequence. The required values should be met, and the allowable error range is generally: high-voltage winding ≤ ± 10%, low-voltage winding ≤ ± 5%, and the voltage difference between two sets of symmetrical windings with central tap should be ≤ ± 2%. 6. The allowable temperature rise for general low-power power transformers is between 40 ℃ and 50 ℃. If the insulation material used is of good quality, the allowable temperature rise can also be increased. 7. Detect and distinguish the homonymous ends of each winding. When using a power transformer, sometimes two or more secondary windings can be connected in series to obtain the required secondary voltage. When using the series connection method to use a power transformer, the identical ends of each winding participating in the series connection must be correctly connected and cannot be mistaken. Otherwise, the transformer will not function properly. 8. Comprehensive detection and discrimination of short-circuit faults in power transformers. The main symptoms of short-circuit faults in power transformers are severe heating and abnormal output voltage of the secondary winding. Usually, the more inter turn short-circuit points inside the coil, the greater the short-circuit current, and the more severe the heating of the transformer. The simple method for detecting and judging whether a power transformer has a short-circuit fault is to measure the no-load current (the testing method has been introduced earlier). Transformers with short-circuit faults will have a no-load current value much greater than 10% of the full load current. When the short circuit is severe, the transformer will quickly heat up within a few seconds after no-load power on, and touching the iron core with your hand will feel hot. At this point, it can be concluded that there is a short-circuit point in the transformer without measuring the no-load current