Transformer is a device to transform AC voltage, current and impedance, when the primary coil through the AC current, the iron core
(or magnetic core) will produce AC flux, so that the secondary coi induced voltage (or current). The transformer is composed of an iron core (or a magnetic core) and a coil. The coil has two or more windings, among which the windings connected to the power supply are called primary coils, and the remaining windings are called secondary coils.
Design principle of high frequency transformer:
In the high frequency transformer design, the leakage inductance and distribution capacitance of the transformer must be minimized, because the high frequency transformer in the switching power supply transmission is the high frequency pulse square wave signal. During transmission transients, leakage inductances and distributed capacitances cause surge currents and spikes, as well as top oscillations, resulting in increased losses. Generally, the leakage inductance of transformer is controlled as 1% ~ 3% of the primary inductance.
Leakage inductance of primary coil ---- The leakage inductance of transformer is caused by the fact that the magnetic flux between primary coil and secondary coil, layer to layer, and turn to turn is not completely coupled. Distributed capacitance ---- The capacitance formed between turns of transformer winding lines, between upper and lower layers of the same winding, between different windings, and between windings and shielding layer is called distributed capacitance.
The primary winding ---- The primary winding should be placed in the innermost layer, so that the wire length of each turn of the primary winding of the transformer is the shortest, so that the wire of the whole winding is the least, which effectively reduces the distributed capacitance of the primary winding itself.
Secondary winding ---- After winding the primary winding, (3 ~ 5) layers of insulating pad lining should be added to wind the secondary winding. In this way, the capacitance of the distributed capacitance between the primary winding and the secondary winding can be reduced, and the insulation strength between the primary and secondary windings is increased, which meets the requirements of insulation voltage resistance.
The BIAS winding ---- Whether the bias winding is wound between the primary and secondary or in the outermost layer is related to whether the switching power supply is adjusted according to the secondary or primary voltage. #power transformer#