I am trying to wet my feet with switching regulators. Please note I am not an expert on electronics.

Currently, I wish to have an adjustable supply of about 3 - 25 Volts, 5A available across the voltage range. The input to this is 30VDC from a transformer/rectifier at max 7A. The original decision was to use an LM1084 adjustable regulator, and even though it won't be able to supply sufficient power at the lower levels (at Vi-Vo=25V less than 1A), I would know how to use this device. I don't want to switch multiple in parallel.

Now I have looks at the more efficient switching regulators and datasheets on Mouser, but the have a lot of circuitry around them to get right (example circuits for different types of converters), and I'm not sure I understand all the ratings or which circuit I need in the datasheets.

For example, LT's LT1070 datasheet lists the following:

Negative Buck Converter

Positive Buck Converter

Negative Current Boosted Buck Converter

Positive Current Boosted Buck Converter

Negative to Positive Buck/Boost Converter

Positive to Negative Buck/Boost Converter

Voltage Boosted Boost Converter

Current Boosted Boost Converter

Negative Boost Regulator

Negative Input/Negative Output Flyback Converter

Flyback Converter

Totally Isolated Converter

Forward Converter

What would be an "common" adjustable switching regulator that I can control with a potentiometer that would be appropriate for this application, and the appropriate circuit type?

Thank you in advance.


After suggestions of a Prosivite Buck Regulator, I came up with an LM2678. On page 22 of the reference design, there is a reference circuit: Reference Design

There are also long lists of inductors for L and Schottky diodes for D1 to choose from. I think they recommend 47uH for L. What is the use for D1? Is it a flywheel diode??

  • 1
    \$\begingroup\$ Look for "synchronous buck" regulators. \$\endgroup\$
    – Andy aka
    May 5, 2020 at 15:40
  • 2
    \$\begingroup\$ yes, D1 is called a: flywheel, freewheeling, flyback and catch diode. \$\endgroup\$
    – Aaron
    May 5, 2020 at 16:16
  • \$\begingroup\$ @Aaron Ok, just out of curiosity, is it necessary because it's in their reference circuit? Or just in case inductive loads are present? \$\endgroup\$
    – namezero
    May 5, 2020 at 16:18
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    \$\begingroup\$ D1 is a requirement! Look at section 10, fig. 23 of the LM2678 datasheet, and look up how a buck converter works on google. \$\endgroup\$
    – Aaron
    May 5, 2020 at 16:22

1 Answer 1


Your initial description of what you desired is the Positive Buck Converter. To make it adjustable, put a potentiometer in for the feedback (R1 & R2).

Read up about the feedback in the datasheet, and see if maybe you can leave R1 fixed and then only R2 would be variable.

  • \$\begingroup\$ Thank you, I have found the LM2678-ADJ. I have updated the question with a followup. \$\endgroup\$
    – namezero
    May 5, 2020 at 16:10

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