What is the purpose of the Switching Regulator Design Calculator?

The calculator helps design DIY switching circuits by calculating critical parameters such as duty cycle, inductor values, diode power dissipation, and current limits. It accepts inputs like Vin, Vout, and switching frequency to generate output values for custom regulator designs.

What types of switching regulators does this tool support?

The tool covers Buck, Boost, and inverter regulator designs. For example, you can calculate step-down (Buck) circuits such as 12V to 5V, or step-up (Boost) configurations using components like MOSFETs, inductors, and diodes.

What should I enter for "Current Sense Resistor" or "Rf1" if unsure?

Use the default values provided: 0.01 ohms for the current sense resistor and 10 kΩ for the top feedback resistor (Rf1). These are safe starting points for most designs.

How does the calculator determine inductor (L) and capacitor (Cout/Cin) values?

It uses input parameters such as maximum Vin, Vout, ripple, and current limits to compute optimal inductor (L) and capacitor (Cin/Cout) values. For instance, higher switching frequencies reduce inductor size, while ripple requirements affect capacitor selection.

Can I use this tool for LM317/LM7805-based designs?

Yes. While focused on switching regulators like the LM25085, the calculator also supports linear regulator components such as the LM317. Input your target voltage, current, and resistor values to generate R1, R2, and output voltage results.

Introduction

5V Regulator Design Tutorial: Switching Regulators & Calculation Guide

Switching Regulator Design Calculator Overview

Glofell Electronic has developed several online calculation tools for electrical designers, including a Switching Regulator Design Calculator. This tool helps calculate the output voltage of a switching regulator to create an ideal switching circuit.

Introduction to Switching Regulators

What is a Switching Regulator?

Unlike a Linear Regulator, a [Switching Regulator] (also known as a Switched Mode Power Supply or SMPS) acts as a DC-to-DC converter. It utilizes a power switch, diode, and inductor to efficiently transfer energy from the source to the output.

Types of Switching Regulators

There are three main types of switching regulators available in the marketplace:

1. Buck Regulator (Step-Down)

A Buck regulator is used to step down a higher input voltage to a lower output voltage.

Example: The MC34063 DC-DC converter IC can be used in Buck mode to convert 12V to 5V.
DIY: You can also create a simple Buck regulator circuit using an N-Channel MOSFET and an Arduino.

2. Boost Regulator (Step-Up)

A Boost converter generates a voltage at the output that is higher than the input voltage.

Example: Boosting a single 3.7V lithium-ion battery to produce 5V or 12V.
Popular ICs: TPS61022, TPS61088, LM5150, and TPS61023.

3. Inverter

Used to reverse the polarity of the input voltage (e.g., generating -5V from +5V).

Core Components of a Switching Regulator

A switch-mode converter typically relies on four main electronic components:

Switches / Transistors: These control the voltage flow and are the reason these devices are called "Switching Regulators."
Inductors: A passive component used to store energy in its magnetic field during the switching cycle.
Capacitors: A 2-terminal passive device used to store energy in an electric field and filter the output voltage.
Diodes: Function as a one-way switch for current, permitting flow in one direction while blocking it in the other.

Design Examples: Switching vs. Linear

1. Switching Example: LM3671 Buck Converter

The LM3671 is a step-down DC-DC converter IC designed for high efficiency. Designing a switching regulator like this is generally more complex than a linear regulator due to the requirement of external inductors and filter capacitors.

Key Design Elements: Inductor selection, Input/Output Capacitor selection.
Resource: Download LM3671 Datasheet.

2. Linear Example: LM317 Voltage Regulator

The LM317 is a classic 3-terminal positive adjustable voltage regulator. Unlike switching regulators, it dissipates excess power as heat but is much simpler to use.

Related ICs: LM350, LM338 (High current versions), and LM337 (Negative regulator).
Calculation: You can use an LM317 calculator to determine the values of R1 (Program Resistor) and R2 (Set Resistor) to achieve the desired output voltage.

!LM317 Pinout Diagram

Key Features of LM317:

Adjustable Output-voltage range: 1.25 V to 37 V
Output current greater than 1.5 A
Internal short-circuit current limiting
Thermal overload protection
Output safe-area compensation

Applications:

Desktop PCs, DVS, and DVRs
Digital Signage and Cameras
Energy Harvesting and Optical Networking