Switching power supply transformers are transformers that incorporate switches in addition to the voltage transformation function of ordinary transformers. They are commonly used in high-frequency circuits such as switching power supplies, providing both insulation and power transmission. However, determining the quality of switching power supply transformers requires careful inspection of various factors. Let's explore the common inspection methods below.
Insulation Testing: Using a multimeter set to the R×10k range, measure the resistance between the core and the primary winding, primary and each secondary winding, core and each secondary winding, as well as between the static shielding layer and each secondary winding. The multimeter reading should remain infinite. Any deviation indicates poor insulation performance.
Identification of Same-Polarity Terminals: To ensure proper functionality, it is crucial to correctly identify the same-polarity terminals of the various windings when utilizing multiple secondary windings. Incorrect connections can disrupt the transformer's operation.
Measurement of No-load Current:
a. Direct Measurement Method: Open all secondary windings and connect the multimeter in series with the primary winding. When the primary winding is plugged into a 220V AC power source, the multimeter reading indicates the no-load current value. This value should not exceed 10%-20% of the transformer's full load current. Typically, the normal no-load current of electronic power supply transformers should be around 100mA. Excessive values suggest a short circuit fault.
b. Indirect Measurement Method: Connect a 10Ω/5W resistor in series with the primary winding and keep all secondary windings unloaded. Set the multimeter to AC voltage mode. Measure the voltage drop U across the resistor R. Then calculate the no-load current I_no-load using Ohm's law: I_no-load = U/R.
Measurement of No-load Voltage: Connect the primary winding of the power supply transformer to a 220V AC power source. Use the multimeter to measure the no-load voltage values (U21, U22, U23, U24) of each winding. These values should be within the allowed tolerance range, usually: high-voltage winding ≤±10%, low-voltage winding ≤±5%, and the voltage difference between symmetrical windings with a center tap should be ≤±2%.
Comprehensive Detection of Short Circuit Faults: Short circuit faults in power supply transformers are typically characterized by severe heating and abnormal output voltage of the secondary winding. The more internal short circuit points in the coil, the greater the short circuit current and the more pronounced the transformer heating.
To detect short circuit faults, measuring the no-load current (as explained earlier) is a simple method. Transformers with short circuit faults will exhibit a no-load current significantly higher than 10% of the full load current. In severe cases, the transformer will rapidly heat up shortly after being energized without load, and the iron core may become hot to the touch. No-load current measurement is unnecessary to confirm the presence of short circuit points in such cases.
Testing of Winding Continuity: Set the multimeter to the R×1 range and check the resistance values of each winding. If the resistance reading for a particular winding is infinite, it indicates a break in that particular winding.
Identification of Primary and Secondary Windings: Primary and secondary terminals of power supply transformers are typically led out from separate sides. The primary winding is often labeled as 220V, while the secondary winding is specified with its rated voltage (e.g., 15V, 24V, 35V). Identification can also be done based on these markings.
Proper inspection and testing of switching power supply transformers are essential to ensure their quality and reliable performance. For high-quality switching power supply transformers, customers can rely on Dezhou Sanhe Electric Co., Ltd., a leading manufacturer in the industry that prioritizes stringent quality control measures and excellent product performance.
Post time: Jul-02-2023