Switching power transformer power transformer switch is added in the circuit, in addition to the ordinary transformer voltage transform function, but also has high frequency circuit involved in switching power supply and other occasions with isolation and power transfer function of insulation. Quality inspection items include switching power transformer insulation test, check the transformer name end, detection of the no-load current, short-circuit fault detection, fault detection coil, etc. the primary and secondary coils, how to detect these items should be? See below for a specific analysis.

Insulation test of switching power supply transformer.

With a multimeter R * 10K block respectively to measure the core and primary, primary and secondary, the core and the secondary electrostatic shielding layer, and a secondary and secondary windings between the resistance value of the pointer multimeter shall refer to the real position at infinity. Otherwise, the transformer insulation performance is not good.

Detect and identify the same ends of each winding.

In the use of a power transformer, sometimes two or more secondary windings are connected together in order to obtain the desired secondary voltage. When the power transformer is used in series, the same ends of each winding in series must be connected properly, and no mistake can be made. Otherwise, the transformer can not work properly.

Detection of no-load current.

A and direct measurement. All the secondary windings are opened, and the multimeter is placed in the AC current block (500mA, series into the primary winding). When the plug of the primary winding is inserted into the AC mains of the 220V, the current value indicated by the meter is the no-load current. This value shall not be greater than 10% to 20% of the full load current of the transformer. General common electronic equipment, power transformer normal no-load current should be about 100mA. If too much is exceeded, the transformer is short circuited.

B and indirect measurement. In the primary winding of the transformer, a resistor of 10 /5W is connected in series, and the secondary is still all no-load. Switch the multimeter to the AC voltage barrier.

After power, voltage resistance R measured at both ends of two pen down U, and then calculate the no-load current by Ohm's law I I =U/R is empty, empty. F detection of no-load voltage. The primary 220V power transformer, AC voltage with a multimeter connected in order to measure the winding no-load voltage value (U21, U22, U23, U24) shall comply with the requirements of value, the allowable error range is generally less than 10%: high voltage winding and the low-voltage winding voltage of less than 5%, two groups of symmetrical winding with center tap the difference should be less than 2%.

Comprehensive detection and discrimination of short circuit fault of power transformer.

The main symptoms of short circuit fault of power transformer are serious fever and abnormal output voltage of secondary winding. Generally, the more winding turns are, the higher the short-circuit current is, and the more serious the transformer is heated.

A simple way to detect and determine whether a power transformer has a short-circuit fault is to measure the no-load current (the test method has been introduced before). A transformer with short circuit fault, its no-load current value will be much greater than 10% of the full load current. When the short-circuit is serious, the transformer in the no-load plus electricity within a few seconds will quickly heat, hand touch the core will have a hot feeling. At this point, it is concluded that the transformer has a short-circuit point without measuring the no-load current.

Detection of winding turn off.

The multimeter is placed in the R * 1 block test, and if the resistance value of a winding is infinite, the winding is shown to have a circuit breaking fault.

Distinguishing primary and secondary coils.

Power transformers, primary pins and secondary pins are generally derived from both sides, and the primary winding is marked with the word "220V", and the secondary winding is marked with the rated voltage values, such as 15V, 24V, 35V and so on. And then identify them based on these tags.