I am new to SMPS. How do I calculate switching frequency of a DC-DC step down converter. Example IC : TPS54260 http://www.ti.com/lit/ds/symlink/tps54260.pdf

The datasheet says it is meant to work at 100% efficiency. How do I calculate the exact switching efficiency ?

I have Input, Voltage, Output Voltage, Output Current values.


closed as unclear what you're asking by Andy aka, Voltage Spike, Lior Bilia, Finbarr, Nick Alexeev Feb 24 '18 at 6:35

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    \$\begingroup\$ No such thing as 100% efficiency, though some active rectifier types approach 95% to 98%. Even if it is 99.5% efficient, that is not an irrational claim of 100%. Usually the frequency is 1 MHZ and Vout is 3.3 volts or 1.35 volts. \$\endgroup\$ – Sparky256 Feb 21 '18 at 23:44
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    \$\begingroup\$ It's not 100%, the datasheet shows it never exceeds 90%. Work out the efficiency from the power input divided by power output VinIin / VoutIout \$\endgroup\$ – Jack Creasey Feb 21 '18 at 23:46
  • \$\begingroup\$ The internal MOSFET is 200 mohms. Frequency is up to 2.5 MHZ, so the higher the frequency the less LC filter you need on the output, and the higher Q the inductor is. 4 turns of bifilar 20 awg should work, on a 1/2" diameter toroid. \$\endgroup\$ – Sparky256 Feb 21 '18 at 23:55
  • \$\begingroup\$ Why don’t you use TI.com webbench tools? \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Feb 22 '18 at 0:59
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    \$\begingroup\$ I think you've misread it. It says that the chip is designed to operate at 100% duty cycle, not efficiency (under 7.3.4 at p.13). As you can see from the graph at the 1st page it never reaches to 100% efficiency. If you want to calculate the efficiency by yourself then just use TI webench instead. \$\endgroup\$ – Rohat Kılıç Feb 22 '18 at 4:16

TI's Webench can probably do the rough estimate that you're looking for. Here is a link where you can input parameters on the right hand side of the page.

TPS54260 Webench

If you want to know more, read further.

Dividing the output power by the input power is the quickest way to measure power supply efficiency. One thing to keep in mind is that efficiency is a function of output voltage, input voltage, load current, and many other things. The following are the biggest contributions to losses in power converters.

  1. Conduction losses
  2. Switching losses
  3. Loss in magnetics

Calculating these numbers can get quite involved and aren't worth going into unless your really need to know efficiency ahead of time. The reason this gets really involved is because these losses are influenced by many variables / parameters, all of which need to be known or there is a rough estimate.

There are many good books on power converters that go over this information. One of the best I've seen is Switching Power Supplies A-Z.

edit: updating link


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