DC-DC Converter - Isolated Power Source Uses

Summary

This video explores the functionality and applications of isolated DC-to-DC converters. It explains how these converters transform DC voltage through an inverter and transformer to provide isolated DC output, which is crucial for safety in medical applications and for eliminating ground loops. The script also discusses the importance of isolation in protecting against ESD, miswiring, and noise propagation. Practical examples include using the converters for creating split rail supplies and boosting voltage levels, showcasing the versatility of these devices in various electronic setups.

Takeaways

• 🔌 Isolated DC-to-DC converters are used to convert DC voltage into an isolated DC output, which can be useful for safety and noise reduction in circuits.
• 🔄 The process involves an inverter converting DC to AC, which is then transformed and rectified back to DC, creating an isolated output.
• 🏥 These converters are particularly useful in applications requiring safety isolation, such as medical devices, to prevent accidental current flow.
• ⚡ They help in minimizing or eliminating ground loops, which can cause noise and interference in electronic systems.
• 💻 Isolation can protect against ESD hits and miswiring, which could otherwise cause damage or system reboots.
• 🔗 The script discusses the use of isolation in USB measurements and DMX lighting applications to protect expensive equipment from harmful surges.
• 📈 The O 5 o 5 converter mentioned in the script converts 5V DC to an isolated 5V DC output, with a current capability up to 200mA.
• 🔍 The efficiency of the converter can range from 76% to 80%, and it requires a minimum load of 20mA to function correctly.
• 🔬 Experiments shown in the script demonstrate how to create various voltage rails (like 10V or 13V) by combining the isolated output with other voltage sources.
• 🛠️ The script provides practical examples of using isolated DC-to-DC converters for creating split rail supplies and for experimenting with voltage combinations.
• 📚 Understanding the datasheet and choosing the right converter based on regulation, efficiency, and output voltage stability is crucial for successful circuit design.

Q & A

What is an isolated DC-to-DC converter and how does it work?

An isolated DC-to-DC converter is a device that takes a DC input voltage, converts it to an AC voltage through an inverter, and then uses a transformer to generate an AC voltage in the secondary winding. This AC voltage is subsequently rectified back into DC, resulting in an isolated DC output. This process allows for the interaction of two separate circuits where grounds may not be at the same potential, preventing direct connection.

Why would you use an isolated DC-to-DC converter?

Isolated DC-to-DC converters are used to provide safety isolation, eliminate ground loops, and protect against ESD hits. They are also used in applications where maintaining separate ground potentials is necessary, such as in medical equipment or systems where different parts may have different ground potentials.

How can isolation help in minimizing or eliminating ground loops?

Isolation can help minimize or eliminate ground loops by preventing the connection of grounds between different sections of a system. This separation prevents the circulation of current between grounds, which can cause noise and interference.

What are some applications where isolated DC-to-DC converters are particularly useful?

Isolated DC-to-DC converters are particularly useful in applications such as medical equipment for safety reasons, in systems prone to ESD hits, and in environments where noise from long cables or inductive loads could interfere with sensitive circuits.

What is the significance of the isolation barrier in the context of the script?

The isolation barrier, represented by a dashed line, separates two sides of a circuit. It ensures that the noise and voltage spikes from one side do not affect the other, keeping the receiver side clean and stable.

How does the O 5 o 5 isolated DC-to-DC converter mentioned in the script work?

The O 5 o 5 converter takes a 5 volts DC input and provides an isolated 5 volts DC output. It can supply up to 200 milliamps and requires a minimum load of 20 milliamps to operate correctly. The efficiency is between 76% to 80%, and the output voltage may fluctuate due to its unregulated nature.

What is the purpose of the load resistor mentioned in the script?

The load resistor is used to ensure that the converter is always drawing at least 20 milliamps, which is the minimum load current required for the converter to function properly.

Can you explain the experiment with the floating 5 volts and the 18 volts supply as described in the script?

In the experiment, the floating 5 volts can be connected in series with the 18 volts supply to create a 23 volts supply by connecting the positive of the floating 5 volts to the positive of the 18 volts. Conversely, by reversing the polarity of the floating 5 volts, it can be used to subtract 5 volts from the 18 volts, resulting in a 13 volts supply.

What is the significance of the floating ground in the isolated DC-to-DC converter?

The floating ground allows for flexibility in how the converter's output can be used. It can be treated as a separate reference point, enabling the creation of split rail supplies or the combination of voltages in series or parallel without being tied to a common ground.

How can the isolated DC-to-DC converter be used to create a split rail supply as mentioned in the script?

By connecting the negative output of the isolated converter to the positive input of the same converter, a split rail supply can be created. This setup allows for both positive and negative voltages relative to a common ground, which can be useful for certain circuit applications like op-amps.

Outlines

00:00

🔌 Introduction to Isolated DC-to-DC Converters

This paragraph introduces isolated DC-to-DC converters, explaining their function and applications. An isolated DC-to-DC converter accepts a DC voltage, converts it to an AC pulse through an inverter, and then transforms it to an isolated AC voltage. This AC voltage is subsequently rectified back to DC, resulting in an isolated output. The technology is particularly useful for applications where grounds may not be at the same potential, such as in safety-critical environments like medical equipment, to prevent accidental current flow. It also helps in minimizing ground loops, which can introduce noise into a system. The paragraph references data from a USB measurement case study, highlighting the importance of isolation to prevent ESD events and voltage mishaps that could damage connected devices. The benefits of isolation in preventing ground loops and noise propagation are also discussed, with examples from DMX lighting applications where isolation is necessary to protect expensive equipment from current surges.

05:01

🔬 Experiments with Isolated DC-to-DC Converters

The second paragraph delves into practical experiments with isolated DC-to-DC converters. It discusses the use of an unregulated 5V-to-5V converter to create an isolated 5V supply, which can be further regulated to 3.3V using a low voltage output (LVO) converter for stable output. The setup includes a test configuration with three double A batteries providing power to two boost converters, one set to output 5V and the other 18V. The isolated converter is used to generate a floating 5V output, which can be manipulated in various ways, such as being connected in series with the input to create a 10V supply or used to create a split rail supply. The paragraph also covers the importance of load requirements for the converter to operate correctly and the use of filter capacitors as recommended by the datasheet. Practical demonstrations include connecting the isolated output in series or parallel with other voltage sources to achieve different voltage levels, showcasing the versatility of isolated DC-to-DC converters in circuit design.

10:03

📊 Analyzing Converter Performance and Applications

The final paragraph focuses on the performance analysis and creative applications of isolated DC-to-DC converters. It discusses the use of oscilloscope measurements to evaluate the AC ripple and noise in the input and output of the converter, comparing the noise levels to determine the effectiveness of the isolation. The paragraph also explores the concept of a floating ground, where the isolated output can be used flexibly, independent of a common ground reference. Practical demonstrations include creating a higher voltage by connecting the floating 5V in series with another voltage source, or subtracting voltage by reversing the polarity of the floating output. The versatility of the isolated converter is highlighted through experiments that show how it can be used to create both higher and lower voltage supplies, and how it can be used to create split rail supplies for specific applications. The paragraph concludes with an invitation for viewers to share their experiences and ideas on using such converters.

Keywords

💡DC-to-DC Converter

A DC-to-DC converter is a type of power converter that converts a source of direct current (DC) from one voltage level to another. In the video, it is used to transform a DC voltage into an isolated DC output, which is essential for applications requiring galvanic isolation between input and output circuits. The script describes how an isolated DC-to-DC converter can take a DC voltage, convert it to AC, transform it using a transformer, and then rectify it back to DC, resulting in an isolated output.

💡Isolation

Isolation in the context of the video refers to the separation of two electrical circuits to prevent the flow of current between them, which can be crucial for safety and noise reduction. The video explains that an isolated DC-to-DC converter can prevent ground loops and provide safety isolation, such as in medical applications where it's important to prevent accidental current flow to a patient.

💡Ground Loops

Ground loops are unwanted electrical loops that can cause noise and interference in a circuit. The video discusses how using an isolated DC-to-DC converter can help minimize or eliminate ground loops by not tying grounds together between sections of a circuit, thus reducing noise and interference.

💡ESD (Electrostatic Discharge)

Electrostatic Discharge (ESD) refers to the sudden flow of electricity due to the buildup of static electricity. In the video, ESD is mentioned as a reason for providing isolation in a circuit, as it can cause damage or reboots in connected equipment. The script gives an example of a test setup where ESD events from a device under test led to the implementation of opto-isolation to protect the system.

💡Opto-Isolation

Opto-isolation is a method of isolating electrical signals using optical coupling, such as light emitting diodes (LEDs) and phototransistors. The video script describes how opto-isolation can be used to protect a system from ESD hits and voltage spikes, ensuring that damage is limited to one side of the isolation barrier.

💡RS-485

RS-485 is a standard defining the electrical characteristics of drivers and receivers for use in balanced digital multipoint systems. The video mentions RS-485 in the context of DMX lighting applications, where it is used for communication between controllers and lighting equipment. Isolation is required to protect expensive lighting equipment from harmful current surges.

💡Back EMF (Electromotive Force)

Back EMF, or counter EMF, is a voltage induced in a circuit by the collapsing magnetic field of an inductor when the current through it is switched off. The video script discusses how back EMF spikes can cause noise in a circuit, particularly in systems with inductive loads like motors or solenoids, and how isolation can be used to prevent this noise from affecting other parts of the system.

💡Linear Regulator

A linear regulator is a type of voltage regulator that maintains a stable output voltage by dropping any excess voltage across a resistive element. The video script suggests that after using an isolated DC-to-DC converter, a linear regulator can be added to provide a cleaner, more stable power source.

💡Load Capacitance

Load capacitance refers to the capacitance that is required at the output of a power supply to ensure stable operation. The video script mentions that the load capacitance on the output of the isolated DC-to-DC converter can only go up to 220 microfarads, which is a specification to consider when selecting a converter for a particular application.

💡Boost Converter

A boost converter is a type of DC-to-DC converter that increases the output voltage to a level higher than the input voltage. In the video, the script describes a test setup where a boost converter is used to provide a 5V output to power the isolated DC-to-DC converter, demonstrating how different converters can be combined in a circuit.

💡Floating Output

A floating output is an electrical output that is not referenced to a common ground. The video script explains how the isolated DC-to-DC converter provides a floating 5V output, which can be used creatively to create different voltage levels by connecting it in series or parallel with other voltage sources, or by reversing its polarity.

Highlights

Isolated DC-to-DC converters allow separate circuits to interact without tying grounds together.

These converters can minimize or eliminate ground loops, enhancing system stability.

Isolation is crucial for safety requirements in medical applications to prevent accidental current flow.

Isolation can protect against ESD hits, which can cause system reboots or malfunctions.

Miswiring in testing setups can lead to hazardous voltages, and isolation can limit damage to one side of the system.

Isolated DC-to-DC converters can provide clean power sources by separating noisy environments from sensitive circuits.

RS-485 communication in DMX lighting applications requires isolation to protect expensive equipment from current surges.

An isolated power supply is represented by a dashed line in schematics, indicating a barrier between two separate circuits.

The O 5 o 5 isolated DC-to-DC converter takes 5V DC in and provides an isolated 5V DC out, with a load requirement of at least 20mA.

Efficiency of the O 5 o 5 converter can range from 76% to 80%, and it requires specific input and output filter capacitors.

Unregulated converters can be used in conjunction with an LVO to achieve a stable regulated output voltage.

Experiments with isolated converters can create voltages in series or subtract voltages for creative power supply solutions.

The isolated converter's floating ground allows for flexible voltage referencing, enabling split rail supplies or adjusted voltages.

The versatility of isolated DC-to-DC converters is showcased through experiments with series and subtractive voltage combinations.

Practical demonstrations include connecting a floating 5V in series with an input 5V to create a 10V output.

The isolated converter can also be used to create a split rail supply, useful for op-amp circuits.

Voltage subtraction is possible with a floating isolated converter, allowing for creative voltage adjustments.

Isolated DC-to-DC converters offer noise immunity, safety isolation, and the ability to combine supplies in innovative ways.

Transcripts

let's take a look at isolated dc-to-dc

converters what they are when you would

want to use them and let's try a few

circuit configurations with one an

isolated DC to DC converter will take a

DC voltage in go through a DC to AC

inverter which will send pulses to this

transformer at a certain number of

kilohertz generating an AC voltage in

the secondary winding which is then

rectified back into DC so you end up

with a DC in and an isolated DC out so

this allows two separate circuits to

interact where for example there grounds

may not be at the same potential so you

can't directly connect them this can

also be used to help minimize or

eliminate ground loops because you're

not tying grounds together between

sections it can be used for safety

requirements for example medical

applications or helping maintain a

person's safety from accidental current

flow looking at some apt notes about

isolation we can get some ideas about

when and why we'd want to do it this one

from data translation regarding USB

measurements on a computer they

mentioned several good reasons you may

want to provide isolation at some point

between two parts of a circuit or system

one would be ESD hits which I've

experienced before in a test setup where

the device under test had moving parts

and it was generating static electricity

all the time so there were always ESD

events and it was causing the computer

running the tests to reboot so we

actually had to implement opto isolation

another good reason to isolate

especially if you're doing testing on

multiple units and one could be miswired

you end up with a hazardous voltage or

just a certain voltage that the

circuitry can't tolerate and it will

cause damage the damage should be

limited to one side of an isolation

barrier and not cause the whole system

to get damaged also ground loops can be

eliminated by not having all the grounds

tied together so if you have something

that can pick up noise like long cables

or something else where noise can couple

into

a part of a system it can possibly

propagate over to another part of the

system that you'd like to be clean so

you separate your power connections and

data connections and the noise can only

get so far through your system similarly

if you have common mode noise one good

example in a typical circuit board

design might be a mixed analog and

digital system or anything inductive

you're driving motors or solenoids you

might have back EMF spikes noise

coupling into the power supply

you could get voltage spikes ground

bounce so you can keep all of this noisy

environment on one side of an isolation

barrier you keep the other side isolated

and stable analog devices talks about

the rs-485 communication in DMX lighting

applications DMX is a digital interface

between controllers and lighting

equipment mostly and accessories and

this uses rs45 differential data dmx512

requires isolation to protect expensive

lighting equipment from harmful current

surges here's an example of an isolated

receiver on schematics an isolation

barrier is typically represented by a

dashed line running through two separate

both sides of this barrier at the top

here we would have an isolated power

supply so we have an input voltage some

circuitry to pulse this transformer then

on the other side of the transformer

where it's isolated we rectify it back

to DC and if we wish we can add a linear

regulator and get a more clean power

source and likewise any data coming

across the barrier in either direction

will go through opto isolator x' so if

this right side is some expensive

equipment and the left side has this

communication data cable running for a

long distance and it can pick up all

kinds of noise or even have voltage and

current spikes on it this isolation

barrier helps keep everything clean on

the receiver side and anything harmful

over on the out

Side world this is the dc-to-dc isolated

converter I have on hand it's an O 5 o 5

so it takes 5 volts DC in and gives an

isolated 5 volts DC out it can do up to

200 milliamps and it needs to be loaded

with at least 20 milliamps to run

correctly so either the circuit being

powered has to always draw more than 20

milliamps or else you can put a load

resistor to make sure you're always

drawing at least 20 milliamps the

efficiency on this one can be 76 to 80%

and the load capacitance on the output

can only go up to 220 micro this one is

not regulated so depending on your load

current the output voltage may fluctuate

so you'd have to make sure you look at

the data sheets for various converters

and make sure they can do what you want

so if we wanted maybe an isolated 3.3

volts supply that'd have to be well

regulated we could use this 5 volt in to

5 volt out unregulated converter and

then use that unregulated

to go into a 3.3 volt LVO and get a

stable 3.3 volts out this top circuit is

a representation of the test setup I

have so I have three double A batteries

giving me about 4.5 volts it's actually

a little less because these three double

A batteries aren't so fresh I have two

identical boost converters one is

adjusted to give +5 out the other gives

plus 18 out so I'm taking this plus 5

putting it into this DC to DC isolated

converter getting isolated floating 5

volts out so these bottom circuits

represent a few experiments the way

these boost converters are designed the

minus input from the battery goes to the

minus input of each of these converters

and that minus input on each converter I

represented going straight through to

the minus output terminal with a dotted

line so really this minus on this 5

volts out and the minus on the 18 volts

out it's all connected you could probe

continuity straight through any of these

minus terminals but over here this minus

output on the isolate

Converter this does not connect anywhere

else this is isolated fully with a

transformer so I can treat this as if I

have a five volt battery and I can throw

it in series with this input five volts

if I want and give myself 10 volts like

I've drawn here I can get a plus 10 by

connecting my input five volts in series

with my floating output five volts as if

it's just a battery and I stack it in

series with this or if I take that

center junction call it ground relative

to this ground I can get a plus five out

or a minus five out another experiment

if I take this 18 volt supply and then

use my floating five volt source I can

take the floating 5 volts put it in

series with the 18 and get plus 23 but I

could also reverse the polarity on here

since it's floating

I can put positive or negative wherever

I want so if I reverse this what I'm

doing is subtracting five volts from 18

and probing here to ground I get 13

volts instead of 23 here's the five volt

in five volt out isolated DC to DC

converter along with the datasheet

recommended input and output filter

capacitors and I have a 200 ohm resistor

loading the output so I can have about

25 milliamps of load current at all

times where the datasheet suggests we

need at least 20 milliamps of load for

this to work properly I have three

double A batteries giving me a 4.5 volt

supply that I'm feeding into a boost

regulator and that's also feeding into a

second boost regulator the main battery

voltage is about 4.2 volts I have it set

to give 5 volts out and that's powering

the isolated DC to DC converter so those

wires come over here here's the output

wires of the DC to DC but I'll just

probe down on the breadboard the input

from the boost converter is 4.99 it's 5

volts then if I move over the output is

also 4.99 5 volts so now I can take

these output

just to confirm everything's plugged in

we got our five volts this is five volts

isolated so there's no common ground

with anything else and I can do some

experiments with this so here there's an

extra pair of wires coming from the

battery source over to this other boost

converter and I have this set for 18

volts out just to do some more

experiments so that's still set for 18

aside from the isolated output all of

these other power sources the batteries

and the two non isolated converters they

all share a common ground so I can probe

this ground on the input of the isolated

converter just as an easy way to probe

over here and I can probe the positive

output of this 18 volts and I have a

complete circuit path so that's what we

mean by it's not isolated the grounds

are common i can probe the positive of

the battery using the same ground and I

get my 4.2 volts for the battery and

obviously I'm using the ground from the

output of this so I can probe its VCC

and get my 5 volts but I can't probe the

+5 out of the isolated and get anything

because it's not common ground you can't

get anything until you actually probe

both positive and minus isolated outputs

as one circuit so this is kind of like a

floating 5 volt battery that I can do

what I want with ground it however I

want

because ground is just a reference it

doesn't mean 0 volts I can take one of

these and connected to plus 18 volts and

just call that my ground if I want

looking at the scope first just looking

at the input we have our 5 volts in

looking at any minor spikes the scope is

showing a couple hundred millivolts so

if I AC couple and zoom in on that

there's all of our stuff coming out of

our switching regulator to give us our 5

volts into the isolated converter just

as a reference for what's going in vs.

what's coming out the battery pack

itself

rage 25 millivolts of little spikes here

and there now I'll hook up to the output

of the DC to DC so on the AC ripple

measurement we still have our same

couple of hundred millivolts spikes if I

go back to DC coupled bring it back on

screen there's our 5 volts out and looks

like around 500 millivolts of spikes

here so if we say this is actual

legitimate noise that would be in our

system and we're not just picking up

stuff from other equipment being on this

may be okay but if you need a more clean

source you would get a DC to DC

converter that's a little higher than

you need and then you would use an L do

to get a more clean linear regulated

voltage supply overall it seems to be

working quite well so to demonstrate

connecting this floating 5 volts in

series with the actual input 5 volts to

create a 10 volt the first 2 pins here

would be ground and plus 5 in then I

have ground and plus 5 floating so I'm

going to consider this input 5 volt

source as my final circuit ground so

I'll take the minus of the 5 volts out

connect it to the plus 5 in put this

overall final ground so now I have

ground and plus 5 in connecting 2 minus

out and my final plus 5 out now I have 2

5 volts in series 9.99 I have 10 volts

out or keeping that same setup if I

simply move what I'm going to consider

my ground over to the junction between

the 5 volts in and the 5 volts out now

relative to this center node I have plus

5 out and I have minus 5 out so I've

created a split rail supply that I could

use for an op amp or or something like

that double checking I still have 18

volts on this boost converter so if I

want to create something a little higher

than 18 volts if I consider the minus of

the 18 as my overall ground then I have

plus 18 well I can add this plus 5

Cirie's so I take this minus terminal of

5 volts and now it says if I took an 18

volt battery and a 5 volt battery stuck

them in series and I'm gonna probe

overall between the ground of 18 and

this floating 5 now I got 23 18 plus 5

volts but you can also turn this

floating 5 volts backwards and you'll

get a subtraction so if I want something

a little less than 18 volts for part of

my circuit I can connect the positive of

my floating 5 to the positive 18

now I've connected a smaller battery

backwards in series with a bigger 18

volt battery so if I probe again from

the main 18 volt ground and my negative

5 out I get 18 minus 5 or a 13 volt

supply I can do this because both the

positive and negative are floating

they're not referenced with any other

part of the circuit there's a few neat

things you can do with a floating

isolate a DC to DC converter

whether you need noise immunity safety

isolation or you just need to combine

supplies in some creative way to give

you plus and minus rails or boost a

little higher or go a little lower than

some other main rail for your system

this is one way to do it any questions

comments or other ideas that you've used

or figure we could use these types of

regulators for comment below see you on

the next video