Buck converter calculation does not match with LTspice results

[Electric1]

The below is the problem

The formulas as per the textbook are




I followed the above formulae and the calculations are as below

To verify i did the LTspice simulation but the values are different the current is getting discontinuous, the output voltage is only 11V. What is the reason?

 

[Alec_t]

The crystal ball is cloudy this morning. Without seeing Fig 6-3a we can't tell if your LTspice circuit is correct.

 

[Electric1]

The crystal ball is cloudy this morning. Without seeing Fig 6-3a we can't tell if your LTspice circuit is correct.

The above is the circuit.

 

[Electric1]

Sorry i think i missed the diode in my ltspice circuit.

 

[Electric1]

But the simulation does not run now i mean it takes lot of time and simulation does not stop.

 

[Electric1]

Ok it works now if i replace the diode with 1N914 and the results are as expected of output voltage 15V and inductor currents.

 

[danadak]

A 1N914 is a small signal diode, so validity of your results would be in question in this
type of application.

 

[Electric1]

A 1N914 is a small signal diode, so validity of your results would be in question in this
type of application.

Ok, which diode i can use to verify the result?

 

[Harald Kapp]

1. Using a component in (LT)SPICE requires the definition of the component's parameters. The generic "D" model is practically useless for simulations. Always use a model for a real diode from the dropdown menu.
   That is why a 1N4148 gives more or less meaningful results here.
2. use a power schottky diode rated for the current and voltage in your application. Schottky type will minimize the losses.

 

[bertus]

Hello,

The 1N914 and 1N4148 are small signal diodes.
Better try a ultra fast diode like the UF4007 or an other high current fast diode.

Bertus

 

[Alec_t]

the simulation does not run now i mean it takes lot of time and simulation does not stop.

If a sim is running extremely slowly and taking forever, it can be because any default circuit components in it are ideal ones, e.g. an inductor or voltage source with zero resistance, a diode with infinite cut-off function, a capacitor with no leakage. Adding some parasitic resistance etc to the ideal component parameters can often cure the problem.

 

[Electric1]

Thank you all for the support, i have to perform the analysis on the interleaved buck converter, did not start new thread, it is pretty tough circuit for me to analyze, as of now i have the following issue the sw2 output is not proper. Why? Please help and thank you once again for your time.

 

[Alec_t]

It is good practice to adding meaningful labels to significant nodes on your schematics. 'n005' is not helpful unless the reader can actually run your sim and hunt for it.
What is the blue trace?

 

[Electric1]

It is good practice to adding meaningful labels to significant nodes on your schematics. 'n005' is not helpful unless the reader can actually run your sim and hunt for it.
What is the blue trace?

Sorry i was not clear i have updated with nodes, the plots are switch outputs which i expect to be On/Off PWM signals.

 

[crutschow]

Your switching signals are not interleaved as the test circuit shows, they are just the same signal with inverted polarity.
Why?

Also why are you using a small-signal, 200mA diode which is carrying over 1A peak current?

Modified circuit below:

 

[Electric1]

Your switching signals are not interleaved as the test circuit shows, they are just the same signal with inverted polarity.
Why?

Also why are you using a small-signal, 200mA diode which is carrying over 1A peak current?

Modified circuit below:


I followed Interleaved as per the text book

It is asking to operate the switches at 180Degrees out of phase. Yes i updated with S24 diode, but i still face the same problem.

 

[crutschow]

It is asking to operate the switches at 180Degrees out of phase.

Yes, but you are misinterpreting the meaning of "180 degrees out of phase", (although I think that's technically a questionable use of the term for those signals here).
Look at the Fig. 6-17 control signals in post #12.
They are the same signal, but are separated in time (i.e. interleaved), not just a simple inversion between the two.

Make sense?

 

[Electric1]

Can you please share me the .asc file? i still get errors.

 

[crutschow]

Can you please share me the .asc file? i still get errors.

What errors?

File below:

 

[Electric1]

What errors?

File below:

I was probing at different place sorry my mistake