I have printed out your response, Sean. It is good information. I do not know about LTSpice. I like the price :-) Is there some way to get it on the net? ----- Original Message ----- From: "Sean Breheny" To: "Microcontroller discussion list - Public." Sent: Monday, August 11, 2008 12:57 AM Subject: Re: EE > Hi Rich, > > Russell is saying that the input impedance should be 16 ohms according > to your spec. As you have since stated, in reality, you have a fairly > fixed OUTPUT load and you do not know for sure what this will > translate to in the primary. > > Note that even though a transformer consists of two inductors, they > don't exactly behave that way when both pri and sec are connected to > reasonably low impedances. Under these circumstances, the current in > one side produces a current in the other side and they partially > cancel each other's magnetic field. They would totally cancel in a > perfect transformer with a very low source and load impedance. In a > real transformer, there is some magnetic flux which "leaks" out and is > not coupled to the other winding. This leads to an inductive component > in the impedance as seen looking into one side of the transformer. > > Skin effect and core loss will also add some resistance to the > impedance so that power is lost to heat in the transformer and the > real part of the impedance is not exactly what is expected from the > ideal transformer formula. > > Have you ever used LTSpice? It is an excellent, free circuit > simulation program which might be very helpful to you. You could make > a model of your circuit and play around with it. > > I've attached a small JPG which shows a model of a non-ideal > transformer which I derived several years ago. I cannot guarantee its > accuracy but I think I did verify it in spice. > > Sean > > > > On Sun, Aug 10, 2008 at 11:39 PM, Rich wrote: >> Hi Russell. The short approximation is Zp=Vp/Ip = 220/13.6 = 16.1 ohms. >> So >> your estimate is pretty close. The more accurate way is: >> Zp=?(R^2+?^2 L^2 ). I think the skin effect at 100 KHz will modify R. >> Even >> a small change can make a big difference. Of course, it would be more >> important if Q was an important consideration. If R increases Q decreases >> because Q = X/R in the approximate. I like to actually measure the >> impedance and compare it to the calculated value. >> >> >> >> ----- Original Message ----- >> From: "Apptech" >> To: "Microcontroller discussion list - Public." >> Sent: Saturday, August 09, 2008 7:20 AM >> Subject: Re: EE >> >> >>>>> I have to drive a transformer primary at 230 VAC @ 14 >>>>> Amps @ 100KHz. I have not yet measured the primary >>>>> impedance, but I will. >>> >>> The impedance you see will be about 16 ohms - ie the load, >>> more or less regardless of the transformer's unloaded >>> impedance. >>> >>> >>> Russell >>> >>> -- >>> http://www.piclist.com PIC/SX FAQ & list archive >>> View/change your membership options at >>> http://mailman.mit.edu/mailman/listinfo/piclist >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > -------------------------------------------------------------------------------- > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist