Help with buck and boost converter

[usuki]

Hi all,

I'm new to power electronics, and somehow I still could not get the impact of switching frequency on voltage gain, output voltage ripple and inductor current.

Additionally, how is the voltage gain affected when increasing load resistance?

Thank you!

 

[Jeff Rosenbury]

I've mostly seen switching converters used as power supplies. While they technically have gain, they are usually specified by voltage output.

As the frequency goes up, it is easier to filter the ripple, though RF noise can couple without careful design. The inductors get smaller as well. I think the current through the inductor is more a function of load than frequency though I could be wrong. Check the data sheet.

Ideally the converter provides a constant voltage. There will of course be some small drop with usage which should go down with less load (i.e. increasing load resistance.) Again, in the data sheet.

The primary change in gain will come with the input voltage since the output voltage is constant. A changing input voltage will affect all the values slightly. Again, it's in the data sheet.

One warning, not all switchers are created equal. I've designed with some high frequency switchers where the data sheets specified impossible to achieve components like large value capacitors on less than 3mm square pads. On the surface higher frequency seems better, but there are limits. I think the sellers often design a chip for a particular application then sell leftovers to all comers. So there are lots of switchers out there that seem to work until you dig into the details. (I'm sure they worked for someone.)

 

[Ronie Bayron]

Hi all,

I'm new to power electronics, and somehow I still could not get the impact of switching frequency on voltage gain, output voltage ripple and inductor current.

Additionally, how is the voltage gain affected when increasing load resistance?

Thank you!

If there is a considerably big difference in voltage beyond operating condition, that can not be handled by capacitors and regulators, you need to tweak transformer by means of switches. Here is a wonderful explanation and demo by Patnaik UC, very helpful.

 

[meBigGuy]

Can you pick one converter topology and ask questions about it? Your general questions are way too open ended.
Start with either of these:
https://en.wikipedia.org/wiki/Boost_converter
https://en.wikipedia.org/wiki/Buck_converter

When you want a constant output voltage, a controller modulates (controls) the period or duty cycle of the switch.

 

[Windadct]

Another good topo reference : TI SMPS Topos

 

[berkeman]

If there is a considerably big difference in voltage beyond operating condition, that can not be handled by capacitors and regulators, you need to tweak transformer by means of switches. Here is a wonderful explanation and demo by Patnaik UC, very helpful.

That is a very confusing video, IMO. And I'm not sure that it will be helpful to the OP...

 

[Ronie Bayron]

That is a very confusing video, IMO. And I'm not sure that it will be helpful to the OP...

Probably. May be this is the appropriate: http://ecee.colorado.edu/copec/book/slides/Ch6slides.pdf