ELECTRICAL POWER TRANSFORMER AND INDUCTOR
DESIGN PRINCIPLES, CALCULATION, THEORY, TUTORIALS,
AND OTHER INFORMATION
Transformer is a passive device which transforms alternating (AC) electric energy from one circuit into another through electromagnetic induction. It normally consists of a ferromagnetic core and two or more coils (windings). A changing current in the primary winding creates an alternating magnetic field in the core. The core multiplies this field and couples the most of the flux through the secondary windings. This in turn induces alternating voltage (electromotive force, or emf) in each of the secondary coil according to Faraday's law.
An SMPS power transformer is used to change amplitude of high-frequency pulses by the turns ratio and to provide isolation between circuits. Note that it can't transfer a DC component of the pulses: in a steady state mode net volt-seconds across each winding should be zero, otherwise the core will saturate. DC output voltage is obtained only by using rectifiers. Note that an average voltage across a real coil's terminals can be non-zero due to non-zero coil's resistance. This DC voltage can be used for lossless sensing of an average current across an inductor or a transformer winding: in an RC network parallel to the coil the voltage across the capacitor is proportional to the coil's average current. For better thermal stability the wire can be made of low TCR material, such as a copper alloy.
In general, ideal SMPS transformers need to transfer all energy instantaneously from one winding to another while storing no or little energy in the process (although some topologies do need some energy stored in magnetizing inductance for proper operation). Conversely, a power inductor is used in SMPS as an energy storage device. It accumulates energy in the magnetic field as current flows through it and then transfers all or portion of this energy into another circuit during the alternate part of the switching cycle. In power supplies inductors are also used for filtering high frequency ripple (in which case they are often called chokes).
| Home |
| Tutorial |
| Topologies |
| SMPS design |
| Software |
| PCB design |
| Computer PSU |
| UPS |
| Circuit |
| Magnetics |
| Formulas |
| EE reference |
| Inverters |
| Thermal design |
| Generators |
| Solar power |
