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The power transformers in set-top box PDF Print E-mail

The set-top box power transformers has been seen the heart of the set-top box power supply, the main function is to transmit power, voltage transform and insulation isolation. Transformer power in general about 30 W, working principle is based on the principle of electromagnetic induction, which not only emphasizes power transmission, but also emphasize insulation isolation high voltage. Using transformer conditions includes two parts: the reliability and the electromagnetic compatibility. Shielding is a good solution to prevent electromagnetic interference, increase high frequency electromagnetic compatibility power transformer.

 

There are two modes for the power of suitch transformer. The first transmit way is to add the voltage in primary winding, produce magnetic cores in magnetic flux change, and make the vice winding induced voltage, then let the electric power from the original side transmits to vice edge. In the power transfer process, magnetic cores divided into the magnetic flux single direction changes and both sides changes work patterns. The second is inductor power transmission way, the original windings input electric power, make magnetic core excitation,and become magnetic energy stored up, and then through the demagnetising make vice winding induced voltage, become electrical energy release to load. Transmit power decided in inductance magnetic core energy storage and energy storage and decided to the original winding inductance. Inductance and magnetic cores on the magnetic permeability, high magnetic permeability, large inductance amount, energy storage, while not directly related to magnetic flux density. Winding circle number and high frequency power transformer leakage are relevant. The leakage size is proportional to original winding circle number. Because leak feeling is bigger, stored energy is also big, in the power switch sudden release, it can produce peak voltage, and increase the voltage switching devices under peak, it's not good for switch tube insulation adverse, also produce additional loss and electromagnetic interference. Factory production in order to reduce  leakage inductance, the designer should pay attention to the following control method:
(1) Reduce winding circle number, choose high saturation magnetic induction intensity, low loss of magnetic materials;
(2) Reduce the thickness of the winding, increase the height of the winding;
(3) As far as possible to reduce insulation thickness between in the winding;
(4) The primary and secondary windings adopt stratified around the system;
(5) The primary and secondary winding should adopt double and around.

 
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