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How to improve the DC-DC converter efficiency?

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bluelaser

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Hi, all guys:
I need to design a high efficiency dc-dc converter for mp3 player application. I sort some dc-dc converter from on-semi or maxim website.
such as ncp1410 or max1706. the efficiency parameter in the datasheet is
very high(95%) . but in my actual application , the Vin=1.5v , Vout=2.7V the coil value is 33uH(coilcraft power inductor). the efficiency is just 78%.
why is there so large difference between them . ?

bluelaser
 

Points in general:

Look at the losses in the inductor. You may have a higher voltage drop across it because of too thin conductors. Make sure you have thick enough wires to carry the current that will eliminate voltage drops.

Also switching losses in the diode will be a factor. Make sure diode is fast enough and have the required reverse blocking voltage rating. Sloppy wiring or layout can produce unwanted leakage inductance that together with fast switching currents will produce high voltage spikes.

Layout is very important, short wires with star type ground connections.

Avoid large enclosed loops for currents from output, to load, and back to ground. Keep this areas as small as possible.

Hope it helps!

E

I see that on the maxim site they have a good amount of tips. It is worth reading....here is the section about layout.


From maxim site:

Layout

Component selection is very important in controlling EMI, but the circuit-board layout and interconnects are equally important. Especially for the high-density, multilayer circuit boards often used in switching power supplies, layout and component placement are critical to the circuit's proper operation and interaction. The power switching can cause large dv/dt and di/dt signals in the circuit-board traces, which lead to compatibility problems by coupling to other traces. Compatibility problems and expensive circuit-board revisions can be avoided, however, by taking extra care in the layout of critical paths.

A distinction can be made between radiated and conducted emissions in a system, but the distinction blurs when talking about interference in a circuit board and wiring. Adjacent traces that couple electric fields also conduct currents by means of parasitic capacitance. Likewise, traces that are coupled by magnetic fields act somewhat like transformers. These interactions can be described in terms of lumped components or through field theory. Which approach to take depends on which method more accurately describes the interaction....

**broken link removed**
 

One more suggesion..
Place your filter capacitor as near as possible to Inductor.Also find out the value of inductor from the graph (Provided by the inductor manufaturer) for ur current rating. Use proper value and gauge of inductor an capacitor to reduce the loss.
Regards
NVP[/url]
 

The inductor was mentioned a lot of times. So you see that the correct choice is very important. Take a look at the DC resistance of the inductor. It should be as low as possible. Another point is that you should not run the inductor in saturation. So the inductor should have enough current.

By,
cube007
 

You have to have a capacitor with low ESR!!!!
 

tell the detail way to realize dc to dc
 

Hi Bluelaser

Here is the link for the evaluation kit if you follow the component
values especially the inductor which is 10uH and not 33uH which
is 3 times higher. That IC has a fixed OSC so you cannot adjust
the frequency to match the 33uH, the switching frequency is to
high for it if you just follow the app by the letter and not substitute
any parts with anything else you should be fine, Jochez, Cube007,
E-design and Nvp they are right about losses and ESR.
So good luck
**broken link removed**

Tornado
 

Hi

Here is the dc to dc converter application note how to built the dc to dc converter with application one thing more national semiconductors have a calculator on there web site
Download able which can calculate the charge pumped capacitor and inductor value also
One thing more they have simulator also PC based, which can simulate the all parameters
In side the PC.

If did not find the these two software on there web page so let me know I can upload here
This was available back in 2000 may be it’s still there. So look at national semiconductor
Web page as under.

www.national.com
 

jochez said:
You have to have a capacitor with low ESR!!!!

While too high ESR caps leads to internal heating and other problems, be careful that having too low ESR caps can lead to stability problems which can be realized by studying the bode plots of such a system.

Sometimes the so called "zero ESR" caps can cause this in some applications if their influence are not analyzed properly.

E
 

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