# Non-Isolated Switching Power Supplies — Topologies & Use Cases

**URL:** <https://forum.digikey.com/t/non-isolated-switching-power-supplies-topologies-use-cases/53641>\
**Category:** Power\
**Tags:** engineering-briefs, power\
**Created:** [April 15, 2025, 9:40am UTC](https://forum.digikey.com/t/non-isolated-switching-power-supplies-topologies-use-cases/53641 "2025-04-15T09:40:29Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![aayushi.nainwal](https://sea2.discourse-cdn.com/digikey/user_avatar/forum.digikey.com/aayushi.nainwal/32/62803_2.png) [@aayushi.nainwal](https://forum.digikey.com/u/aayushi.nainwal)\
**Post date:** [April 15, 2025, 9:40am UTC](https://forum.digikey.com/t/non-isolated-switching-power-supplies-topologies-use-cases/53641/1 "2025-04-15T09:40:29Z")

</div>

## Introduction

In our previous article, we explored the fundamentals of power conversion in **[An Insight into Power Topologies and Design Considerations](https://forum.digikey.com/t/an-insight-into-power-topologies-and-design-considerations/53296)**, where we covered the core concepts behind switching power supplies.  
Building on that foundation, this article will discuss the **further classification of Switching Mode Power Supplies (SMPS)**. Based on the **method of energy flow** , SMPS topologies are categorized into various types — each designed to suit specific application needs, performance goals, and design constraints.

In this section, we focus on **Non-Isolated Switching Power Supplies** , which are widely used in scenarios where input and output share a common ground. These topologies — including **Buck, Boost, Buck-Boost, Cuk, and SEPIC** — offer flexible solutions for efficient DC-DC conversion across a wide range of voltage requirements.

## Non-Isolated switching power supplies

Non-isolated switching power supplies **do not use transformers** and are ideal for application when **input and output share a common ground**.

These are classified into several **topologies** based on the desired voltage conversion:

### 1. [Buck Converter](https://www.digikey.com/en/products/result?s=N4IgTCBcDaIEIFcDGBrABAYQPYDsBuApgE4AuxIAugL5A) (Step-Down)

- **Function:** only step-down voltage **(output voltage is lower than input voltage)** and are used in DC-DC conversion
- **Typical Use:** Converting 12V to 5V to power microcontrollers.
- **Key Components:**
  - Inductor and capacitor at the output.

- **Current Behavior:**
  - Input current is **discontinuous** since the switch is in series with the input.
  - When the input current is discontinuous, an **input capacitor** is required to handle:
    - Compensation for line inductance.
    - High-frequency components of the input current.

 ![image](https://global.discourse-cdn.com/digikey/original/3X/7/5/75d7bfc7a0aacf66a60dc83a254ca0bdab92a134.png)

### 2. [Boost Converter](https://www.digikey.com/en/products/result?s=N4IgTCBcDaIEIHsEGcAuACAwggdgNwFMAnVYkAXQF8g) (Step-Up)

- **Function:** Boost topologies, on the other hand, only step-up voltage **(output voltage is higher than input voltage)**
- **Typical Use:** Boosting 3.7V from Li-ion battery to 5V for USB power.
- **Key Components:**
  - Inductor at the input, capacitor at the output.

- **Current Behavior:**
  - Since the **inductor is in series** with the input, the **input current is continuous** over most of the operating range.
  - The output current is **discontinuous** , so the output capacitor must:
    - Handle worst-case **ripple current**.
    - Meet **hold-up time** and stability needs.

 ![image](https://global.discourse-cdn.com/digikey/original/3X/4/5/45fc93e344a5f9336341651bd82d8a1f546eef0e.png)

### 3. [Buck-Boost Converter](https://www.digikey.com/en/products/result?s=N4IgTCBcDaIEIFcDGBrABHA9pgzgFzQGFMA7ANwFMAnPakAXQF8g) (Step-Up / Step-Down)

- **Function:** can both step-down and step-up voltage, allowing the output voltage to be either higher or lower than the input voltage.
- **Typical Use:** Stabilizing output (e.g., 5V) from a **variable input** (e.g., 3V–12V).
- **Design Note:**
  - The Buck-Boost converter is a DC-DC converter that is equivalent to a **flyback converter** but uses a **single inductor** instead of a **transformer**.

 ![image](https://global.discourse-cdn.com/digikey/original/3X/1/d/1d00225900d60540a0a92b606c1a004bc45f8155.png)

### 4. [Cuk Converter](https://www.digikey.com/en/products/filter/voltage-regulators-dc-dc-switching-regulators/739?s=N4IgTCBcDaIMIFcDWACOB7AdgNwKYCcAXAkAXQF8g)

- **Function:** Cuk converters can both step-down and step-up voltage.
- **Unique Feature:** Output polarity is **reversed** compared to input.
- **Typical Use:**
  - Bipolar supplies, e.g., **audio amplifiers**.

### 5. [SEPIC](https://www.digikey.com/en/products/result?s=N4IgTCBcDaIMoFEAKBJAwgAhAXQL5A) (Single-Ended Primary Inductor Converter)

- **Function:** The SEPIC allows the output voltage to be equal to, lower than, or higher than the input voltage without polarity reversal
- **Typical Use:**
  - **Battery-powered devices** such as **LED drivers**.

For more on different Switching Power Supply topologies, please check out our next article.

### Related Article

[An Insight into Power Topologies and Design Considerations](https://forum.digikey.com/t/an-insight-into-power-topologies-and-design-considerations/53296)