Question

why is the voltage in the secondary coil 17V not 12V? have i built the circuit in LTspice wrong or am i misunderstanding transformers?

Thank you

- 22x Open with Preview Mon 8:52 pm a V21 04.0400m Vert More 17031SAV 20 Our Cursor 240 50 0 0 0 10) 0 200m

Answer 1

in the LTspice , we need to add transient analysis to see the voltage levels at the primary and secondary. The frequency is 60Hz and it means 1 cycle time will be 1/60.Since you have not specified the question completely,look at the example shown below:

We are going to design a step down transformer using LTspice with Vp=170V and frequency=60Hz. ( all your other steps are correct and you only need to add the transient analysis.)

K Lp Ls 11 2 Lp Ls RI 100u 4u SINE(O 170 60 Rser=0.0001 .Ulan UU.10.UU; ii tran 0 0.1 0.001 i

this represents the transformer. As told above you must add transient analysis in order to get the voltage levels. The voltage levels according to this circuit is shown below.

Drafs Win0011 Vin002 100V 15044 12017 90- ААААААА 30V 3014 -691 - 12014 150 180 1 ms 20 ms 30ms 40ms 50ms Sms 70s m s 0ms Draft3 Cursor 1 Vin001) Horz 19.9222 Vert: 169.129/ Cursor 2 Vn002] Horz 69.8845ms | Vert: 33.8016V Diff Cursor2 - Cursorl) Horz 50.061ms Vert: 135.328V Freq 19.9753Hz Slope: -2703.21

As seen above, the cursor has 2 positions and hence the primary voltage= 169.129V and secondary voltage=33.0816V.

so Vp/Vs= 5/1

i.e the turns ratio between them is 5:1.

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