Toroid or EE Ferrite core, which is Best for 240V mains SMPS

[jamesrnz]

well,
mostly the caps will see an excessively high level of high frequency pulses which may short, explode and, get really hot, this will cause a chain of events creating high currents backwards through the supply exploding everything else.

Maybe..... well it happened to me.

[odnaizutra]

i´m using push pull topologie and even at full power , we have a quite stable operation.
But there are inductors at almost all regulated smps, but in unregulated
we dont see them very often.
I want to know the practical results of inductor inclusion against a variation in dead time ,like regulated ones.

when i increase dead time in my converter,the edge of square wave becomes a little rounded.
I have no ringing and the performance is good of unregulated but if regulation become a must?
Some people use common mode .Is there any advantage instead a simple inductor per rail?
I have a heating at rect.diodes i will try snubbers.Do you have Eva or N channell or oter smps papa theads about this issues?

[jamesrnz]

ok,

what are the specs of the supply?

the inductor is a choke it is there for smoothing.

as you change the dead time you can enter either discontinuous mode or continuous mode, depending on the current draw of the load.

what does the signal across the rectifiers look like?

[Electrone]

With all this bad talk about my buddy, the ferrite toroid, I just had to put in a good word for it. I find they are good for experimental circuits since the windings can be accessed more easily. I like to wind the primary at one end and the secondary at the other end for zero voltage switching circuits. With that topology, leakage inductance between windings is good to a certain extent.

[odnaizutra]

my smps is fine,but if one day i decide to use it regulated i would like what happen in pratice when inductor is placed.
My actual smps in unregulated dc dc converter very simply using 3525+ 6 irf3205,2.5``diameter ferrite toroid.
Single out 100v .65khz clock .Inductor will be placed afer diodes only that.
At no load ,the 1620 ct become a bit warm, the scope shows a nice square wave at output.
I will try 1640 and snubbers .
Im not happy with that heating at diodes at no load.
Since its unregulated,do you think it is really necessary inductor?

[N-Channel]

Originally posted by odnaizutra
my smps is fine,but if one day i decide to use it regulated i would like what happen in pratice when inductor is placed.
My actual smps in unregulated dc dc converter very simply using 3525+ 6 irf3205,2.5``diameter ferrite toroid.
Single out 100v .65khz clock .Inductor will be placed afer diodes only that.
At no load ,the 1620 ct become a bit warm, the scope shows a nice square wave at output.
I will try 1640 and snubbers .
Im not happy with that heating at diodes at no load.
Since its unregulated,do you think it is really necessary inductor?

First, I would ditch the MUR1620CT for a 100V output. This is a 200PIV diode, and the diodes will see a maximum of 200V across them when not conducting. This leaves no margin for error. I would change immediately to the MUR 1640 or '1660 if you have them.

Second, echoing jamesrnz, if you are running unregualted, you probably won't need an output inductor. However, if you plan on regulating it, the inductor performs the "integrating' function in the buck regulator topology, which, together with the cap(s), smooth out the hi freq ripple seen at the output of the diode. Values for the L&C are chosen by the parameters of the circuit; freq, I(out), V(out), etc.

[odnaizutra]

thanks for answering Steve and James.
I`d changed the diodes and they are not heating anymore.
About the inductor,my curiuos why almost all regulated power supply them and they are not very often in unregulated .

[Electrone]

Originally posted by odnaizutra
thanks for answering Steve and James.
I`d changed the diodes and they are not heating anymore.
About the inductor,my curiuos why almost all regulated power supply them and they are not very often in unregulated .

One thing that happens without an inductor for regulated ones is that the MOSFETs get a lot hotter because they carry much more current while switching on and off. The inductor adds some time delay between the voltage and current peaks.

[odnaizutra]

Hi Electrone.
yes,this is something i want to know.
So , there is no way to get rid of inductor in reulated smps?
Some time ago,i saw i regulated pwm push pull simetrical power supply working without inductor using tl494,bur as this problem never bothered my ,i was not very interested in search this issue.
Since using regulated is not possible for now,i´ll try to decrease voltage variation at heavy loads.
I´ve read one thread about winding technics.
what do you think?
I am using sg 3525 i decreased dead time resistor from 150r to 100 r ,better results.

[N-Channel]

Originally posted by odnaizutra
.......
I am using sg 3525 i decreased dead time resistor from 150r to 100 r ,better results.

Good idea. Reducing the deadtime for a regulated unit w/o output inductors, will allow the MOSFETs to run cooler because they will carry less currents to maintain voltage during the off time.

Originally posted by electrone
The inductor adds some time delay between the voltage and current peaks.

Making things even clearer, the inductor performs this "integrating" function by adding some time delay between the voltage & current peaks, by filling the valleys. For regulation to be efficient and reliable, the inductors play a central part of the process.

That is why the majority of unregulateds have no inductors, while the regulated ones do. (no inductors - less expensive design - higher profits.)