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I see in buck converter examples that they have fixed/regulated input voltage and a fixed output.

I'm planning to build or buy a for example 9V to 5V buck converter but the 9V side will be composed of parallel batteries. This means the input voltage will not be regulated. And since the battery voltage will drop by time output voltage will be affected proportionally if I use a buck converter.

Is there a DC DC converter or a type of buck converter which both steps down the input voltage and also regulates it to a reference value? Like in my case the input voltage is not regulated(batteries) but the output voltage must regulated to a fixed voltage.

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I see in buck converter examples that they have fixed/regulated input voltage and a fixed output.

Well, a buck regulator will work fine with a range of input voltages after all, it wouldn't be much of a regulator if it required a constant input voltage.

And since the battery voltage will drop by time output voltage will be affected proportionally if I use a buck converter.

No, it's a regulator and produces a regulated output. There are some caveats but generally I think your research into buck regulators is flawed.

Is there a DC DC converter or a type of buck converter which both steps down the input voltage and also regulates it to a reference value?

Yes, pretty much all of them. Here's an example: -

enter image description here

It will produce 5 volts (at up to 1 amp) at the output with input voltages ranging from 6.5 volts to 100 volts.

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  • \$\begingroup\$ There is no feedback in buck converter examples how would they regulate? See this example i.stack.imgur.com/VBLN4.png Is "buck regulator" you mentioned a different thing than a "buck converter"? \$\endgroup\$ – GNZ Mar 14 '18 at 10:07
  • \$\begingroup\$ A proper regulator uses feedback to maintain the output voltage within prescribed limits. What your picture shows is the basic circuit mechansim that is used to efficiently reduce voltage with minimal power loss. \$\endgroup\$ – Andy aka Mar 14 '18 at 10:10
  • \$\begingroup\$ I see now. Thanks for this example. Seems I can build it myself, for battery to 5V conversion. \$\endgroup\$ – GNZ Mar 14 '18 at 10:11
  • \$\begingroup\$ There are plenty of devices out there to do what you want. \$\endgroup\$ – Andy aka Mar 14 '18 at 10:12
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You can use an 7805 Voltage Regulator IC, which converts anything from (max) 40 (I believe) V to 5 V.

It will dissipate heat, so if the difference is too high (like 9 to 5 V) AND you are using a lot of current, you need a heat sink.

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    \$\begingroup\$ The thing is I dont want to use a linear regulator. Because they are not efficient. \$\endgroup\$ – GNZ Mar 14 '18 at 10:03
  • \$\begingroup\$ Is there a regulated output DC DC converter? \$\endgroup\$ – GNZ Mar 14 '18 at 10:03
  • \$\begingroup\$ Understandable (since you use batteries), maybe good to add in your question as a requirement. \$\endgroup\$ – Michel Keijzers Mar 14 '18 at 10:04
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    \$\begingroup\$ It is already written two times \$\endgroup\$ – GNZ Mar 14 '18 at 10:04

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