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Lets assume we have a 12V source (i.e. an external PSU). We need to go down to 1V8 to supply some load. Leaving the costs behind and using only synchronous buck converters, what are the advantages and disadvantages of the options a) and b)?

a) Cascaded solution with intermediate 3V3 converter

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b) Direct solution with no intermediate converter

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Of course we assume that input voltage is within the spec for every converter etc. This is just an overall example, but I am trying to point out the differences. I would for instance say that solution a) is less effective, since each converter has a < 100% efficiency, so each additional converter in chain introduces more power losses. But for some reason I see this kind of solutions- this made me wonder whether there are some additional advantages here, or maybe disadvantages with option b)?

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    \$\begingroup\$ You would need to check the actual specs for the devices you are intending to use to make a final choice but generally one conversion is going to be more efficient than two sequential conversions. \$\endgroup\$
    – jwh20
    Commented Oct 15, 2020 at 19:29
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    \$\begingroup\$ Also conversion where the ratio Vout/Vin is large (12 V / 1.8 V) is generally more efficient than where that ratio is less (3.3 V / 1.8 V). If you see solution a) but the 3.3 V isn't used for anything else than feeding the 1.8 V regulator look closer because that doesn't make sense so maybe you missed something. \$\endgroup\$ Commented Oct 15, 2020 at 19:34
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    \$\begingroup\$ @Bimpelrekkie for the applications I have seen, the scenario is the following:12V -> 3V3 -> here to many different parallel converters (i.e. 1V8, 1V5 etc.). Because of the architecture, the lower voltage converters had low VIN. But a similar application I have seen without the immediate 3V3 converter (then the converters for 1V8 and 1V5 have higher VIN to handle 12 V). \$\endgroup\$ Commented Oct 15, 2020 at 19:45
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    \$\begingroup\$ Research how CPU’s use nearby onboard regulators from MOBO and you will find your answer. \$\endgroup\$ Commented Oct 15, 2020 at 21:34
  • \$\begingroup\$ Could you make the answer more clear? \$\endgroup\$ Commented Oct 16, 2020 at 3:10

2 Answers 2

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a) Advantage is if you need 3.3V too and the 1.8V cannot handle 12V input. Also any 1.8V converter can be used as it does not need to handle 12V input. Disadvantage is more power losses and heat production in each conversion, and the 3.3V converted needs to be larger to support also the power for 1.8V converter.

b) Advantage is usually that there are less conversion losses and less heat production. Disadvantage is the 1.8V converter needs to handle 12V input, so it might limit your choices but not a lot. If the voltage difference would be larger, it would be more difficult to find a suitable chip that works with given input voltage and is capable of low enough duty cycle.

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  • \$\begingroup\$ (a) applies even more if the 12V is nominal and can go quite a bit higher (e.g. automotive 12V) \$\endgroup\$
    – Chris H
    Commented Oct 16, 2020 at 9:48
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With less, smaller external parts, Buck-Boost converters provide a more powerful solution. You can use this minimum number of components for either step-up or step-down voltages and deliver a shorter operating time and a higher performance over a wide range of input and output voltages. Buck boost converters are also much cheaper than other converters.

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