Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

transformer constantly steps down in LTSPICE

Status
Not open for further replies.
Z

Zak28

Advanced Member level 2
Advanced Member level 2
Joined
Aug 19, 2016
Messages
579
Helped
6
Reputation
12
Reaction score
6
Trophy points
18
Activity points
4,681
Regardless of inductance of either winding the transformer always steps down, there is hardly a load on the secendary also and the primary voltage source has no series resistance. How are transformers properly utilized in LTSPICE?

Screenshot_20180716_213816.png
 

Hi,

I didn't check the series resistances.

But with a L1/L2 ratio of 30/300, I expect a coupling factor of sqrt(300/30)...which is about 3.16.

Klaus
 
  • Like
Reactions: Zak28

    Z

    Zak28

    Points: 2
    Helpful Answer Positive Rating
KlausST said:
Hi,

I didn't check the series resistances.

But with a L1/L2 ratio of 30/300, I expect a coupling factor of sqrt(300/30)...which is about 3.16.

Klaus
Click to expand...

Resistances are 1 ohm per coil and it does not matter what values the coils are, even extremely far in inductance still yeilds lower voltage on secondary.
 

Resistances are 1 ohm per coil and it does not matter what values the coils are, even extremely far in inductance still yeilds lower voltage on secondary.
Click to expand...

It matters well. Problem is that you apparently never calculated the 20 Hz reactance of your transformer magnetizing inductance settings, otherwise you won't use ridiculous small µH values. Try again with 30 and 300H.
 
  • Like
Reactions: Zak28

    Z

    Zak28

    Points: 2
    Helpful Answer Positive Rating
Agree with FVM. You have to consider impedance as well as voltage. The impedance of the coils at 20 Hz is far higher than the 1K you are trying to drive.

Bob
 
  • Like
Reactions: Zak28

    Z

    Zak28

    Points: 2
    Helpful Answer Positive Rating
FvM said:
It matters well. Problem is that you apparently never calculated the 20 Hz reactance of your transformer magnetizing inductance settings, otherwise you won't use ridiculous small µH values. Try again with 30 and 300H.
Click to expand...

Yes, an ideal transformer has infinitely high inductance and therefore draws zero current on its own (all current is due to the secondary load).

I'm willing to put some blame on basic transformer resources which do a poor job of articulating this fact and explaining magnetizing inductance in general.


Ltspice is actually great at teaching this because it models transformers as they are: two coupled inductors and forces you to grapple with the inductance values from the start. I recall having this same confusion.
 
  • Like
Reactions: Zak28

    Z

    Zak28

    Points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top