EveryCircuit - Buck design test

9 years ago

Niki, before you drive your output filter digital, you have to understand what its characteristic is! http://everycircuit.com/circuit/5179278979497984

nikisalli

9 years ago

and what do i do after i know the characteristics of the output filter? Do i have to drive it at its resonant frequency?

hurz

9 years ago

No, the resonace is your enemy and does cause ringing and overshoots and hard to regulate switching power supplies!

nikisalli

9 years ago

So what do i have to do?

hurz

9 years ago

Understanding how LC lowpass works, or going back to a linear regulators.

nikisalli

9 years ago

Let's go for the LC low pass filters

hurz

9 years ago

What do you know about RC lowpass?

nikisalli

9 years ago

That they make frequencies under a certain level pass and higher frequency not pass

hurz

9 years ago

Math?

nikisalli

9 years ago

I know how to calculate them

hurz

9 years ago

Lets see how far you are. http://everycircuit.com/circuit/5260709344837632

nikisalli

9 years ago

Now i have to go to school. I'll make this exercise later :)

hurz

9 years ago

Post your answers one by one and I will guide you into the right direction.

nikisalli

9 years ago

Ok

nikisalli

9 years ago

http://everycircuit.com/circuit/6219343763603456

nikisalli

9 years ago

Here you are all my answers

hurz

9 years ago

ok, http://everycircuit.com/circuit/5260709344837632

nikisalli

9 years ago

http://everycircuit.com/circuit/5988736634716160

nikisalli

9 years ago

Lot of tests there!!

hurz

9 years ago

Ok, forget the PWM part and play with this setup. As I said earlier, resonance is your Enemy. Try to find R load were the resonance is gone but the filter still gives "enough" amplitude/power. http://everycircuit.com/circuit/5260709344837632

nikisalli

9 years ago

Resonance stops at 165mohm load and the maximum output power is still with 30mohm

nikisalli

9 years ago

What's next? I want to build this buck converter!

hurz

9 years ago

165 is close but from math its 111.8 mOhm read a little wikipedia about "dampening" critical dampening and try to come back with a formula for parallel and serial dampening!

nikisalli

9 years ago

I'm still not studying trigonometry because i'm 15 years old and i don't know how to solve those equations

nikisalli

9 years ago

Those sin / cos things there

hurz

9 years ago

No sin and cos needed

nikisalli

9 years ago

(√L/C)/2

nikisalli

9 years ago

(√0,00005/0,001)/2 = (√0.05)/2 = 0,223/2 = 111,8mohm

nikisalli

9 years ago

What's next

hurz

9 years ago

This is for parallel dampening. For serial?

nikisalli

9 years ago

1/R = ( √L/C)/2 i think

hurz

9 years ago

R=2/√L/C or easier (√L/C)*2 for serial and (√L/C)/2 for parallel

hurz

9 years ago

Next http://everycircuit.com/circuit/5710660453531648

nikisalli

9 years ago

I don't know why i have to calculate that resistor when i will put small and big loads om the regulator at the end

nikisalli

9 years ago

I want to design something that will work with a zvs taking 20A from the psu or a simple LED taking something like 20mA so why do i have to calcukate the load when it will be variable?

hurz

9 years ago

Hey hoo lets go, 20mA to 20A load, what is R L and C for the filter only?????

nikisalli

9 years ago

http://everycircuit.com/circuit/4637166395457536

hurz

9 years ago

nicely ringing http://everycircuit.com/circuit/5731889403133952

hurz

9 years ago

You are to quick back in digital with PWM. Forget that tick tack, flip flop.. power on off HURRY.... Take a simple switch and simulate the worste case always power on or always power ground, and see how the filterout behaves with different loads. In frequency domain its already promised that it will not be stable for any regulator. Resonace is your "Enemy!" Again forget the digital part.

nikisalli

9 years ago

Meh ok

nikisalli

9 years ago

What about this http://everycircuit.com/circuit/5453641825910784

hurz

9 years ago

This is the right direction. Tomorrow or late today I will do some practical tests. Maybe a video for you.

nikisalli

9 years ago

Oooook can we work on the digital part after that? I want to do the digital part!

hurz

9 years ago

Yes, you can start to think about the driver. Emitter follower, half bridge, common emitter with your power mitsubishi?,.. read somethink about different buck converter. Syncro is probably not needed. But forget PWM for today and tomorrow 😆