The detection method of the quality of the switching power supply transformer - the detection of no-load current.
a, direct measurement method. Open all secondary windings, put the multimeter in the AC current block (500mA, and connect the primary winding in series. When the plug of the primary winding is inserted into the 220V AC mains, the multimeter indicates the no-load current value. This value should not be More than 10% to 20% of the full load current of the transformer.
Generally, the normal no-load current of the power transformer of common electronic equipment should be about 100mA. If it exceeds too much, the transformer has a short-circuit fault.
b, indirect measurement method. A 10?/5W resistor is connected in series with the primary winding of the transformer, and the secondary is still fully unloaded. Set the multimeter to AC voltage.
After power-on, use two test pens to measure the voltage drop U across the resistor 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 commercial power, and use a multimeter to connect the AC voltage to measure the no-load voltage value of each winding (U21, U22, U23, U24) in turn, which should meet the required value. The allowable error range is generally: high-voltage winding ≤±10 %, the low-voltage winding is ≤±5%, and the voltage difference between the two sets of symmetrical windings with center taps should be ≤±2%.
