HI Manu, The design shown at the link you provided appears to be a flyback design. You are correct that in flyback converters, the turns ratio does not define the input voltage to output voltage ratio. Flybacks work by building-up a large magnetic field in the core of a "transformer" by putting current through the primary and then suddenly shutting off the current in the primary. The result is an inductive "kick" or "spike" because of V=3DL * di/dt. This spike occurs across both the primary and secondary since they are magnetically-coupled. The turns ratio determines the ratio of the *spike* voltage but not the absolute magnitude of the spike - which is instead determined by the inductance of the windings, the current which was built-up before being shut off, and the impedance of the load on the output. I put transformer in quotes above because usually transformers are designed so that the coupling between primary and secondary is so tight that the current flow in each of them causes nearly equal and opposite magnetic flux so the total magnetic field in the core is minimized. Flyback transformers are in some sense not true transformers because they are designed to allow a significant magnetic field to build up in the core during each cycle. This results in a larger amount of leakage inductance than in a normal transformer, so they are perhaps more properly called coupled-inductors. For SMPS designs based on true transformers (like half-bridge, full-bridge, and forward converter topologies), the voltage ratio is indeed nearly equal to the turns ratio. Sean On Fri, Feb 22, 2013 at 7:37 AM, Manu Abraham wrot= e: > Came across this site: > http://www.danyk.wz.cz/dcdc_en.html > It seems the turns ratio doesn't apply at all here ?? > > V1/V2 =3D N1/N2 > V1=3D325V > V2=3D12V > V1/V2=3D27.08 > N1=3D80 > N2=3D6 > N1/N2=3D13.3 > > In many of the SMPS designs that I am finding that the turns ratio do not= match > the voltage ratio ? > > Regards, > Manu > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .