0

I'm struggling with this simple schematic in LTspice. I just want to made a 1:1 insulation transformer but probably I'm missing something. In theory it should works, the inductor are identical and the voltage is imposed from the primary V1. The power should be converted so V1 * I1 should be equal V2 * I2, but it doesn't happen. What am I missing?

Thanks!

LTspice simulation

Simone Santonoceto
  • 1
  • 1
  • Which code is hidden in the subcircuit x_trafo? Ideally it should only consist of inductors (L) and mutual couplings (M). – Ricardo Erckert Nov 12 '21 at 10:30
  • x_trafo is only a parameter of 30mH inductance and there is perfect coupling k1 x1 x2 1 – Simone Santonoceto Nov 13 '21 at 17:40
  • Are you sure your source impedance is 129K Ohm? Your transformer is almost a short at 50Hz. – Ricardo Erckert Nov 16 '21 at 22:27
  • Lower cut off frequency is fg=129K/(6.28*0.03)=684kHz. – Ricardo Erckert Nov 16 '21 at 22:31
  • Thanks Ricardo, I've made the circuit and tested it, all works as expected. I also made the simulation with PLECS and there the simulation works as expected. I've found a suggtion to change the inductor value to 1H to make the 1:1 transformer works, and it works, but I don't understand why. – Simone Santonoceto Nov 19 '21 at 13:12
  • at 50Hz the abs(Z) of the 30mH primary side of the transformer is about 9.4 Ohm. This makes the signal at Vin collapse. Compared to 129K this is almost a short. – Ricardo Erckert Nov 23 '21 at 11:43
  • I agree on that but why the voltage isn't transferred 1:1 between the two side of the transformer? Also the power isn't preserved – Simone Santonoceto Nov 24 '21 at 13:18
  • Simulators work nummerical, not analytic. Your input voltage is 230Veff or about 600Vpp. So the nummerical resulution is a few mV. – Ricardo Erckert Nov 25 '21 at 09:42
  • A simulator always does an itteration. The number of itterations are defined by parameters itl0 to itl6. In addition trtol defines error tolerances. If these limits are too relaxed the simulator simply truncates low voltages (compared to the 600Vpp) to 0. Best check which limits your simulator uses. – Ricardo Erckert Nov 25 '21 at 09:57

1 Answers1

0

Thanks Ricardo, I've made the circuit and tested it, all works as expected. I also made the simulation with PLECS and there the simulation works as expected. I've found on electronics stackexchange that as ideal transformer they use a 1000H transformer. I still don't know why but with this modify all is now working.

Simone Santonoceto
  • 1
  • 1
  • As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – MD. RAKIB HASAN Nov 18 '21 at 11:10