Any transformer there is leakage inductance, but the leakage inductance of the SMPS transformers on the switching power supply performance indicators is particularly important. Due to the existence of switching transformer leakage inductance, when the control switch off the moment will produce back electromotive force, easy to switch the device over-voltage breakdown; leakage inductance and the circuit can be distributed in the capacitor and the transformer coil distributed capacitor oscillation circuit The circuit generates oscillations and radiates radiated energy, causing electromagnetic interference. Therefore, the analysis of leakage inductance generated by the principle and reduce the leakage inductance is also one of the important components of the design of switching transformers.

SMPS transformers manufacturer said, there is a leakage inductance between the switch transformer coils because of the leakage flux between the coils. Therefore, the value of the leakage inductance can be calculated by calculating the leakage flux between the coils. To calculate the leakage flux between the transformer coil, the first is to know the magnetic field distribution between the two coils. We know that the magnetic field distribution in the spiral coil is similar to the distribution of the electric field in the two plates, that is, the magnetic field intensity distribution in the spiral coil is substantially uniform and the magnetic field energy is concentrated in the helical coil. In addition, when calculating the distribution of the magnetic field intensity inside or outside the spiral coil, the more complex case can be used Maxwell's theorem or Bi-sand theorem, and the simpler case can be given by the Ampere loop law or the Kirchhoff law of the magnetic circuit.

The magnetic flux? 1 generated by the transformer primary coil N1 passes through the transformer secondary coil N2, and there should be no leakage flux therebetween; however, the direction of the magnetic flux? 1 generated in the area S1 in the area S1 and the magnetic energy generated in the area Sd2 The direction of the ¦Õ1, just opposite to each other; therefore, the transformer primary coil N1 in the area Sd2 generated in the magnetic flux ¦Õ1, still known as the transformer primary coil N1 transformer secondary coil N2 leakage flux, the equivalent inductance is also known as Leakage.

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