A, leakage inductance (hereinafter referred to as the leakage inductance of the)
Ideal (fully coupled transformer primary side of transformer winding should all through the vice of toroidal flux produced by the winding, no damage and leakage. But in fact regular transform transformer cannot be achieved without any damage and leakage. Flux produced by the original winding cannot all through the winding. The coupling part of magnetic flux in the winding conductor or has its own inductance, storage of energy in this "inductive" coupled with the main power transformer circuit. The inductance is what we call "the leakage inductance. Ideal transformer to requirements and of the insulation in order to get a very low electromagnetic interference (EMI) and need a very tight electromagnetic coupling to minimize the leakage inductance of the request, is contradictory.
When transformer without power () during the shift from power supply or switch is shut off, the leakage inductance energy storage to release form obvious noise. On the oscilloscope can see the high frequency noise spike pulse waveform. High frequency peak pulse waveform amplitude Uspike and the leakage inductance of the Lleak is proportional to the current relative time rate of change of the product. That is:
When the working frequency increases, the current relative time rate is increased. The influence of the leakage inductance will be more serious. The influence of the leakage inductance and is directly proportional to the switching speed of the converter. The leakage inductance of the produce high peak pulse can damage the power converter device and forming obvious electromagnetic interference (EMI). In order to reduce the leakage inductance of the spike pulse amplitude Uspike, buffer network must be added in the converter circuit. But the buffer network, will increase the wastage of the converter circuit. As working frequency converter circuit, loss increase, the efficiency is lower.
(1) high voltage transformer winding capacitance
When the transformer winding is a multi-layer winding, it is the potential difference between the top and bottom windings. Have a potential difference between the two conductors, there is a capacitance. The capacitor is referred to as "winding capacitance. When working in high frequency, the capacitor will charge and discharge at an alarming rate. Capacitor charging and discharging process will produce loss. In a given period of time, it is the more the number of charging and discharging, loss is big.
(2) the proximity effect
(3) the skin effect
(4) local hot spot
Regular transformation work in the high frequency transformer, magnetic core there will be local hot spot in central. Therefore, in order to reduce the thermal effect, the conventional transformation when the working frequency of transformer to improve, must be correspondingly reduced its magnetic flux density, increase its volume. This makes the can't use it to do the high power density of power supply.
For the low output voltage ideal type converter, its step-down ratio is very high. With conventional commutation transformer, usually 1 output winding coils, it takes about 32 turns the original winding. Multilayer is needed so that the original winding arrangement, and thus the leakage inductance and capacitance between windings, skin effect and proximity effect seriously adverse factors exist in the commutation transformer.