---
title: "SIMO converters"
question: "Can one inductor feed three rails?"
url: "https://nearfieldnotes.com/videos/simo/"
site: "Near Field Notes"
video: "https://nearfieldnotes.com/media/simo/full.mp4"
duration: "0:44"
date: "2026-11-01"
note: "https://nearfieldnotes.com/notes/simo/"
---

# SIMO converters (video)

Can one inductor feed three rails?

0:44, with sound. [Read Note 22](https://nearfieldnotes.com/notes/simo/) for the full answer, with figures, conditions and sources.

## Transcript

A smartwatch needs three rails from one battery.

Which is best?

LDOs take the least room, but turn over half the battery into heat.

Three bucks double the battery life, but need three inductors.

A SIMO converter nearly matches them, with one inductor.

How does one inductor feed three rails?

Each rail has a comparator.

When its voltage drops below the line, it asks for energy.

The battery charges the inductor up to a set current.

Then it empties into that rail, until the current is back to zero.

When several rails ask, they take turns.

When none ask, it rests.

Every packet starts from zero, so a heavy load on one rail just asks more often.

---

Source: https://nearfieldnotes.com/videos/simo/