## Transformer Utilization Factor of bridge rectifier

Determination of transformer rating becomes, necessary while designing a power supply. For this transformer utilization factor (TUF), which is defined as the ration of power delivered to the load and ac rating of the transformer secondary, should be known.

So TUF = dc power delivered to the load/ac rating of transformer secondary

= Pdc /Pac . rated

= Pdc/Pin.rated

At first sight it might appear as if the above ratio is the same as the conversion efficiency. Actually, it is not so because the rating of the transformer secondary is different from the actual power delivered by the secondary.

Pdc = VL(dc).IL(dc)

= VLM/π . VLM/RL

= VLM2 /πRL

= Vsm2 /πRL     - if drop over R0 is neglected

Now, the rated voltage of transformer secondary is Vsm/√2 but actual current flowing through the secondary is IL = ILM/2 (and not ILM /√2) since it is a Half-Wave rectifier current.

Pac.rated = Vsm/√2 .ILM/2

= Vsm/√2 . VLM/2RL

= Vsm/2√2RL

Its value is found by considering the primary and secondary winding of the transformer separately. Its value is 0.812 (as compared to 0.287 for a half-wave rectifier). In such a rectifier, there is no problem due to dc saturation of flux in the core because the dc current in the two halves of the secondary flow in opposite directions.