Em 22/02/2013 09:37, Manu Abraham escreveu: > On Fri, Feb 22, 2013 at 5:33 PM, RussellMc wrote: >>> I have been trying to wind a high frequency transformer running at >>> approximately 100kHz, in a push pull configuration with a square >>> wave of about 25% duty cycle in a step up configuration. >> >> General answer. Someone may offer specifics: >> >> Litz wire uses small conductors so that the skin effect uses the >> majority of the copper in each conductor. You then use multiple >> conductors as required. >> >> Power transmission is when wire is being used to carry power between >> points - perhaps in a cable trough or secondary sheath. >> >> Chassis wiring is short distance inside an item of equipment. >> Differences in Imax will affect temperature rise which may be >> reguilated differently on long runs. > > > So: which value do I need to use for calculation ? > > > >> A transformer has the wires adjacent and confined so heat is shared >> and cannot erasily esscape - so you'd tend to go with the lower rating >> - or maybe even lower again. If you are using an eg iron powder core >> (which are commonly used for power handling at 10's to 100's of kHz >> then they often use an organic binder which has a maximum temperatute >> rating. Get them too hot and the binder starts to fail so the losses >> rise so thjey get hotter so ... . Regenerative failure. >> >> SO: >> >> Decide what area per ampere you need designing conservatively. >> Make that area up using eg 38 gauge strands. >> Strands handle skin effect. >> Area handles temperature effects. > > According to the wire gauge table > > 26AWG is sufficient for full penetration at 100kHz > but http://www.litz-wire.com/New%20PDFs/Litz_Designing_Calculations.pdf > states 38AWG is needed. !! ?? > > The more I search, the more confused I am getting. > > 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 ? Turns ratio only applies to sinusoids, because the derivative of a sinusoid is a co-sinusoid (which in turn is just a sinusoid 90 degrees out- of phase). With different waveforms (pulses, square waves, etc.), the derivative is a quite different function. Isaac --=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 .