# problem with variable voltage circuit development.

#### vinay sv

Joined Nov 16, 2020
11
Hello,
Thanks for your support in this forum.
Currently, I am working on a project in which the operating voltage is 12v 1.5A to be given to the circuit. but, my input power supply varies from 12v to 24v of 2.5A. but I am not getting an idea that how to get constant voltage regulation of 12v of 1.5A to my circuit. and my circuit load will be always constant.

#### crutschow

Joined Mar 14, 2008
27,696
Even low dropout IC regulators typically require a volt or so minimum voltage across them so I don't know of any that will work if you need very near 12V out with 12V in.
What is the minimum voltage you circuit will operate at?

#### vinay sv

Joined Nov 16, 2020
11
thank you for your replay crutschow,
my minimum voltage requirement is 12v of 1.5A, but my internal circuits are at microcontroller level and some buzzers. so, it can also work on 11.5 to 12v for the basic working.

#### DickCappels

Joined Aug 21, 2008
7,689

Is it adjustable from 12V to 24V or is it unregulated

#### Papabravo

Joined Feb 24, 2006
16,773
It is possible to use a SEPIC converter, where the input can be less than , equal to, or greater than the output voltage. They do have disadvantages though.

#### Bordodynov

Joined May 20, 2015
2,906
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#### Papabravo

Joined Feb 24, 2006
16,773
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#### vinay sv

Joined Nov 16, 2020
11

Is it adjustable from 12V to 24V or is it unregulated
Thank you sir for trying to help me out,
the input power supply varies from 12v to 24v based on the user choice which means there might be a chance of the user might choose to give 12v or 24v based on their type of gadget. because I am developing a slave gadget that depends on the master gadget power supply.

#### DickCappels

Joined Aug 21, 2008
7,689
You might find the circuit in this application note to be helpful. With the right parts selected it will hold its output at +12V regardless of where the input voltage wanders between 24V and 12V. It boost the voltage when the input is 12 volts and it buck the voltage down to +12 volts when the input goes about 12V.

With the use of more appropriate transistors it can be made to handle more current

As Papabravo mentioned there is also the SEPIC topology but I have little familiarity with that topology.

@Papabravo, I'm listening to Alice's Restaurant as I type. Thank you.

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#### crutschow

Joined Mar 14, 2008
27,696
I mentioned a linear regulator but that would dissipate 18W with a 24V input and 1.5A output, so a switching regulator is the way to go.
It doesn't require a buck-boost converter, just a buck converter that can go to 100% duty-cycle (most don't).
The LTspice simulation of an example circuit is shown below.
Note that the output voltage (green trace) stays at 12V for an input voltage of 24V to 12V (yellow trace).

A search shows some other similar converters.

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