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I have a DC-DC converter that with a Vin of 4.75V-14V and a Vout of 18V.

Unfortunately I have a Vsupply of 24V.

Should I use another DC-DC converter with a Vin capable of 24V and a Vout between 4.75V and 14V or should I just use a voltage divider to to step 24V down to an acceptable voltage.

Are there advantages or disadvantages for either?

Is there a problem with using too many DC-DC converters in series?

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  • \$\begingroup\$ How much current? /// Anyway, that DC/DC is no good for you. Get one that takes 28V or 32V or something like that. Or if it's <100mA, go linear and simplify your life in exchange for a heat sink. \$\endgroup\$
    – Pete W
    Mar 12, 2021 at 0:09

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It depends on how much current the Vo (18v) will require.

Typically a divider circuit uses resistors that are least 10x smaller than the load impedence. Example, for a 1Mega-Ohm input that needs to be set to a specific voltage, the divider resistors should be no larger than 100k.

  • Nearly free
  • Easy
  • Has no ability to regulate the output.
  • Horribly effeciency.
  • Use only for driving <1mA load typically
  • Use only when Vin is constant
  • Use only when the load is constant.

A linear regulator acts like a variable resistor that maintains a constant output voltage. It's efficency is dependent on the ratio of Vin/Vout and the load impedence. It can range from 0% to 100% efficient (theroretically) depending on these critea.

  • 0% to 100% efficient (theroretically)
  • Cheap
  • Simple
  • Clean output voltage
  • for current range <10A typically. Typically you don't want to use these if your sourcing a lot of current because they can be ineffecient.

Below is a simulation of the effiency of a divider circuit vs a linear regulator. The load is swept from 1 to 1Meg Ohm. The load value is time(s)*10 on the Xaxis. The linear regulator effeciency ranges from ~%75 to %20, while the divider circuit stays at %6.6 effeciency (using divider resitors <(Rload/10)) enter image description here

DCDC uses a totally different principle. I'm not going to explain how they work but here are the highlights.

  • %80-90 efficient (%70 minimum)
  • Can step voltage both up & down
  • Almost any current & voltage range if you have enough $$$
  • Output voltage can be noisy.
  • produces EM noise.
  • Can be expensize
  • Takes up more board space.

You can put DC-DC converts in series, as many as you want. But, if your only doing it just to get to the right output voltage there are better options: Adjustable Linear-Regulators, Adjustable DCDC converters.

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Are you asking how to regulate 24V to 18V? What kind of current do you need? The easiest way to get a few dozen-to-hundred mA would be to use a linear regulator.

A voltage divider will consume a TON of power and murder your efficiency. And its output will vary depending on the load. IMO, it's really only an option if you're looking to get a reference voltage, driving a very high impedance load

I wouldn't use multiple DCDC converters. Its wasteful and inefficient (why spend dollars when you can spend a few cents?). I'd source a single buck converter with the specs I need, or use a linear regulator if I only needed a few watts of output

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The best choice would be a DC-DC converter that will accept 24 V and output 18 V. Second choice would be a 24 V -> 12 V (or less) to feed your existing converter.

A voltage divider is a Very Poor choice where any sort of power delivery is concerned, as the output voltage will depend on the current you draw from the voltage divider, and you will have to waste a lot of power in the divider in an attempt to keep the output voltage stable.

A voltage divider should only be used to provide very low, preferably constant, current.

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