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| Transformer Design for Power Amplifier |
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| Archangel1235:
Hi, I have been tasked with building an Amplifier that will output a 30-150 KHz sine wave with 1KVpp and about 1App.. The sine wave will be a 3-15 pulse burst signal with a repitation rate of about 100-200 Hz.. With this as requirements I came up with a simple design a simple Class AB stage that has a swing of about 50 Vpp and able to provide up to 60 A in bust mode with repitation rate of about 200Hz. This is coupled to custom made push pull transformer (No CT) with primary to secondary turns ratio of 1:21. I have Attached below the transformer design parameters. The Problem I am facing right now the above design works for lower frequencies below 80 KHz but fails above 80KHz with the transformer gain droping to 1:15 or something. I followed this site for transformer design https://www.electrical4u.com/design-of-high-frequency-pulse-transformer/ here are the questions I have about transformer design: * How Does one Design a transformer with a badwidth * What Properties of the Transformer decides the power handling ablility of the Transformer (or more precisely what properties of the core) * What if I want to have a wide input to the primary?? - the site calculates the transformer's primary turns based on input voltage , Is there any other method to create a transformer with wide input range |
| Archangel1235:
Any Help will is appreciated.. I am even happy if someone points me to a good book on transformers design.. Thanks a lot in advance |
| xavier60:
You should tell us what you have tied so far. Although I have successfully made a few SMPS transformers, I don't fully understand what I'm doing. The primary turns are calculated to avoid core saturation at the combination of the lowest expected frequency and highest primary voltage. The core size doesn't directly determine power handling, mainly copper loss does. Larger cores allow for less turns per volt and thicker wire which increases power handling. Because your busts have such a low duty cycle, power handling becomes less of a problem. For a recent project I used an ETD49 with 3C90 cores at 40Khz. Although I utilized the winding window rather inefficiently, it easily handles 600 watts continuously. With your project, minimizing winding capacitance would be important. https://coefs.uncc.edu/mnoras/files/2013/03/Transformer-and-Inductor-Design-Handbook_Chapter_17.pdf |
| fourtytwo42:
I am not surprised at your problems the site is laughable, nowhere does it show or include in calculations the effects of operating frequency!! More specifically skin effect in winding's that reduces the effective area of round wires as frequency increases nor core losses that again increase as frequency increases. I would suggest you find yourself a copy of ExcellentIT7100 (Russian authored freeware) that at least takes these into account. Expect to be using expensive Litz wire and copper foil as a minimum in this design. A 1Kw core able to operate over 30-150Khz is going to be expensive too. But at least you can get some solid idea's using the software I have suggested, it is not perfect BTW but gives a very good starting point for estimating the design parameters. |
| xavier60:
This explains how to reduce inter-layer capacitance with the Foldback winding method. If you then go and add another Primary layer over the top, the capacitance will be increased again. Because you aren't hard switching, leakage inductance isn't as messy. https://books.google.com.au/books?id=JR7OBQAAQBAJ&pg=SA17-PA10&lpg=SA17-PA10&dq=foldback+winding&source=bl&ots=owp6heryl2&sig=Blndd19xuTnG4wyCHHdSTnOFCz8&hl=en&sa=X&ved=2ahUKEwi8rreN6vveAhVKBIgKHRgtACQQ6AEwDnoECAYQAQ#v=onepage&q=foldback%20winding&f=false |
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