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Issue Time:2020-04-24

Title:Differences between switching power transformers and ordinary transformers?

For switching power supply, the working principle of switching transformer is different from that of ordinary transformer. The normal transformer input ac voltage or current of the positive, negative half cycle waveform are symmetrical, and the input voltage and current waveform are generally continuous, in a period, the average value of the input voltage and current is equal to 0, this is the basic characteristics of the ordinary transformer working principle; And switch transformer are generally working in switch state, its input voltage or current is generally not sequential, but staccato, the input voltage or current within a period of mean value most of all not equal to zero, therefore, also known as pulse transformer, switch transformer it is a common transformer switch transformer with the biggest difference in terms of working principle.

Through PWM(pulse width modulation) control switch tube, the rectified dc voltage is conducted on the high-frequency switch, so that the high-frequency current flows into the primary side of the high-frequency transformer of the switching power supply, and the secondary side of the transformer generates the induced current. After rectification, the required voltage or multiplex voltage can be obtained.

The switch supply transformer and the switch tube together form a self - excited (or other excited) blocking oscillator to tune the input dc voltage into a high frequency pulse voltage. In flyback circuits, the transformer converts electrical energy into magnetic field energy to be stored when the switch tube is switched on and released when the switch tube is shut off. In a positive excitation circuit, when the switch tube is on, the input voltage is supplied directly to the load and energy is stored in the energy storage inductor. When the switch tube is cut off, the energy storage inductance carries on the continuous flow load transmission.

Switching power transformers are divided into single-excitation switching power transformers and double-excitation switching power transformers. The working principle and structure of the two types of switching power transformers are not the same. The input voltage of a single-excitation switching power transformer is a unipolar pulse, and its output is divided into positive and negative voltage. The input voltage of the double-excited switching power transformer is a bipolar pulse, which is generally a bipolar pulse voltage output.

Switching power transformer parameters

Voltage ratio: refers to the ratio of primary voltage to secondary voltage of a transformer.

Dc resistance: copper resistance.

Efficiency: i.e. output power/input power *100[%]

Insulation resistance: insulation capacity between transformer windings and between cores.

Resistance: the extent to which a transformer can withstand a specified voltage for one second or one minute.

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