# Power Electronics Fundamentals - DC to DC Power - Regulators

Publish Date: Oct 04, 2013 | 1 Ratings | 4.00 out of 5 | Print | Submit your review

## Overview

The National Instruments Power Electronics Fundamentals series series is designed to provide an overview of power electronics concepts used in research and taught throughout worldwide institutions.

Using advanced simulation models and analyses used in industry, but wrapped in an intuitive, pedagogical environment Multisim enables students to characterize power circuits concepts before the laboratory.

The power capabilities of Multisim means that students have access to the same technology that they will use for research and industry to prototype power electronics circuit designs. However in learning power electronics in a simulated environment optimized for education, students have the ability to experiment safely before the laboratory.

## Table of Contents

When considering DC to DC power electronics we are referring mainly to the conversion of one DC voltage to another DC voltage. There are different options for achieving this that vary in complexity and efficiency.

### 1. Potential Divider

A very simple example of regulating voltage is with a potential divider.

However the output across a voltage divider is not constant and varies according to the load. To be effective, changes in the output current must remain small in comparison to the input current. This highlights the inefficiency of this technique as the input current is dissipated as heat.  An example of a potential divider is a potentiometer.

### 2. Zener Diode Regulator

We can improve on the potential divider method by using a zener diode. A zener diode allows current to flow in one direction as well as in the reverse direction when the voltage is above a certain breakdown voltage. The diode is setup so that it operates in reverse bias and conducts when the reverse bias breakdown voltage is met.

In Multisim we can easily measure the regulated output using Virtual Multimeter  Instrument whilst also monitoring the current flow.

### 3. Power Switching

The buck converter is a form of power switch which dramatically increases the  efficiency of the regulator circuit. Its core functionality is built upon switching a voltage to control the output voltage allowing us to step down the input voltage to that needed by the output. A capacitor is required to smooth the output voltage and remove the steps created by the switching.

To achieve this, a Pulse Width Modulated (PWM) signal is used to control the switching of the voltage allowing regulation of the output voltage. When the switch is closed, the inductor will begin to charge and there will be a voltage drop across it causing the output voltage to drop. When the switch is open, the charge within the inductor is released, supplying the output voltage.

Below is an example of a simple Buck Converter. A PWM signal is being used to control the switch, allowing the charge in the inductor to build up. Care needs to be taken when selecting the most suited frequency for the PWM signal in order to maintain the required DC voltage level.

To help with determining the correct frequency and component values, Multisim provides interactive components which are capable of having their parameters changed during execution. The use of interactive components allows us to adjust the duty cycle, impedance and resistance during simulation.

The example above shows an open loop implementation of a buck converter. This can be taken a stage further and translated into a closed loop system by taking the output voltage and comparing it to a reference voltage to produce the appropriate PWM signal for the switch.

This can be fully modelled in Multisim alongside LabVIEW using co simulation.

Multisim gives you the tools to simulate a schematic prior to the circuit creation whilst LabVIEW assists in creation of the FPGA code. Co-simulation allows these two systems to be integrated allowing full testing of the power switch prior to deployment. You can learn more about co-simulation in Simulation Fundamentals: Cosimulation In NI Multisim tutorial.

### 4. Tutorial Questions

What happens to the zener voltage if a minimum value of reverse current is being reached and what if the reverse current exceeds its maximum?

What is the disadvantage of a zener diode regulator?

Here we have an example of a Buck Converter, research and gain an understanding through Multisim of a Boast Converters operation .

Attachments:

dc-dc.zip

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