Voltage regulator tutorial & USB gadget charger circuit

Voltage regulator tutorial & USB gadget charger circuit


In this video I’m going to talk about
linear voltage regulators and show you
how to use one to charge 5 volt USB
devices like phones
and MP3 players.
So what is a voltage regulator?
A voltage regulator is a device that takes
an unregulated input voltage that could
be fluctuating over time, and spits out a
perfectly regulated constant voltage.
For example here I have a twelve volt
battery that will be
13.8 volts fully charged,
and around 11 volts fully discharged.
This 5 volt regulator will ensure that
I get a constant five volts regardless
of the input voltage.
And the capacitors in the circuit will
maximize the stability of the regulator’s output.
I’ll show you the circuit on the bread
board later on.
In the meantime take a look at this. In
an earlier video I showed you how to
make unregulated DC power supplies.
Right now the output of that unregulated
supply is about 16 volts with about
2 volts of ripple on it.
But if I add a 12 volt regulator I
get a constant 12 volts out
regardless of what’s happening on the
input.
Here’s the same thing with a 9 volt regulator…
and a 5 volt regulator.
So you can buy voltage regulators to get
any voltage you want.
And it’s really not much more
complicated than that.
Basically you have a higher input
voltage that could change at any time
and the linear voltage regulator just
clips all of that off
leaving you with a lower but very
precise DC power supply.
Even a terrible linear voltage regulator
will give you an output that is accurate
to within five percent.
And newer voltage regulators have a
thermal shutdown feature which means
I can’t even show you one catching on fire!
Pfft… progress…
Now how do I find a voltage regulator?
Most voltage regulators begin with a few
letters, then “78”, and then they
have two digits indicating output voltage.
So here I have an L7805CV
and the “05” indicates that it’s a
5 volt regulator.
The LM7809 is made by
a different manufacturer
and it’s a 9 volt regulator.
And on the right we have a 12 volt regulator.
You can buy these anywhere that sells
electronics… Radio Shack, Jameco, Maplin
and a million other places because
they’re such a basic component.
Just search for voltage regulator.
You can also salvage them from old
electronics.
Check it out…
I found a 3.3V, 5V, 6V, and 9V regulator
all on one pcb from an old dvd player.
And I’m not going to lie,
I didn’t know these were all voltage
regulators until I Googled the part numbers
written on them.
As always with engineering, Google is
your best friend.
Okay so let’s say you’ve got a voltage
regulator. Let’s say you’ve got an LM7805
for 5 volts and want to wire it up.
Well that’s really easy.
All you need is the regulator and three
capacitors.
10 microfarads on the input,
10 microfarads on the output, and finally
a 0.1 microfarad ceramic capacitor on the output.
These capacitors help ensure the
stability of the voltage output,
and although you don’t always need them,
if you have them on there the circuit is
pretty much guaranteed to work every time.
The values don’t have to be exact so if
you use slightly more or less
capacitance it’ll probably be fine.
So let’s give it 12 volts in and at
5 volts out you can see that it works.
Right now this circuit would be good for
loads of up to 100 milliamps
but since I want to handle more current
I’m going to put a
heatsink on it.
Okay now I promised to show you how to
make a 5 volt USB charger right?
Well first get a USB cable like the one
your device needs.
Get it from a dollar store so you don’t
get ripped off.
Cut the head off the cable and strip
the insulation.
Next, clip off everything but the red and
black wire.
The red wire goes to your +5 volt
line and the black wire goes to your
circuit’s ground.
Double check your regulator is working,
then plug it all in.
That was easy wasn’t it?
Now you can be even more angry when
people sell you car chargers for
thirty dollars.
Just make sure you keep an eye on the
temperature of the heatsink and use a
bigger one if necessary.
Now there’s two more things that you
should know about linear voltage regulators.
1) They’re not very efficient.
2) They have what is called a dropout voltage.
The power wasted in a linear regulator
is given by (Vin – Vout) x output current.
So if I take the 16 volt
unregulated power supply that I built,
use a 5 volt regulator, and draw 300
milliamps it’ll generate
3.3 watts of heat…
which is a lot for a tiny device!
So a big heatsink is important.
Now let’s see what happens when I use
another input voltage that’s closer to
the 5 volt output that I want.
This is a 7.2 volt NiMH battery
and when it’s fully charged it’ll supply
8.4 volts.
If I draw the same 300 milliamp load,
I get a power dissipation of 1 watt,
so I can get away with no heat sink at all.
In general you want to avoid high input
voltages with linear regulators because
the higher the input voltage, the lower
the efficiency.
Now the dropout voltage that I mentioned
earlier is related to the minimum input
voltage they have to feed your regulator
to guarantee a regulated output.
Most of the time your input voltage will
have to be at least a volt or two above
the output voltage of the regulator.
So for a typical 5 volt regulator you’ll
probably need a minimum input of 7 volts.
Check this out…
Here I am dropping the input voltage
from twenty volts all the way down to
7 volts and the output voltage
doesn’t change.
Now watch what happens when I drop it a
little lower…
the output voltage starts to drop,
and your circuit won’t get five volts
anymore.
The exact amount of headroom you need is
called the dropout voltage and it will
always be given in the datasheet.
You can also buy regulators that have a
lower dropout voltage than normal,
for example this is an LM2940 regulator
and it has a dropout voltage of 0.5 volts.
This means that for 5 volts out, your input
can drop as low as 5.5 volts
before you lose regulation.
Low dropout regulators are slightly more
expensive than standard linear regulators,
but they can be useful if your input
voltage drops really close to the output
voltage that you are expecting.
For example if you’re trying to power a
device with batteries,
think very carefully about how low
your battery voltage will go.
So that’s it!
Voltage regulators are easy. Input
voltage, output voltage, a few capacitors
and a heat sink and you’re done.
Thanks for watching!

100 Replies to “Voltage regulator tutorial & USB gadget charger circuit”

  1. Why can’t I find a USB charger with a low amps rating? Why would I want to charge my phone at 2.1 amps while I sleep and reduce the life of it? Any ideas how I can reduce the amps?

  2. I have one question about this, when i build this, i want to put an on/off switch on it, would i put it on the input circuit or on the output circuit.

  3. Also You can find linear voltage regulators in old TV´s since 2000 🙂 It´s a basic component like you said , in tv lvr ( linear volt. reg. ) is used with image maker ( horizontal & vertical circuits ) on the very large heatsink sticked together with other circuits needed for display image maker.

  4. thank you! we built one of these things in class today and without explanation of what we were building. thank you for being very clear what it does! 🙂

  5. It would be nice if you consider to show how to rig a step up buck converter.. from like 8V to 12V DC I always have a hard time finding a good quality one that does step down and step up at the same time! Since I have not seen any new work on your channel I do hope you are doing OK and that life is really good for you, This channel have really help me a lot in my work and hobbies in general. Thank you very much for your hard work!

  6. I just unsoldered a voltage regulator from my electronic dumps… so idk how to use it… but i just think that i might need it one day and it looks useful to me

  7. great job. these regulator is all over in electronics. simple good ones have thermal shut down. over current. some I buy are LM340T-XX or LM340K-XX .same as 78XX .

  8. Great explanation. Great production quality. Outstanding contribution for all makers young and old. Why would people downvote this video?

  9. Hello, I have a 36v source and I want to keep it in a side and I want to have 9v in another side. I've put this 7809 and the multimeter show me like 10v but as soon as I connect another circuit (with a 555) the volt go down to 2v and the circuit with the 555 doesnt work. I want to fix those 9 or 8v with a 7808 to make the 555 circuit works. Anyone could help me please ?

  10. Would i need to change the capacitor values to scale this up to handle 10 amps? Also is this a "quiet" design as I am making it for audio equipment.

    TIA

  11. Hi I'm not an electronics expert. All I need to know if it is possible to make something like, I can input one power source and feed 1x 5v DC and 1x 12DC fan at the same time?

  12. OK so I got this to practice .I get 14.5 V unregulated from the car battery > directly to an 12 V light bulb . The light Bulb will light up fast from the 14.5 Volts but if I leave it for to long it will overheat . So I used your example in the video to transform the 14.5 V to 12 V ( regulated ) .But when I connect the light bulb It won light up ! Why ? The light bulb works fine .

  13. Sir Great video. Can I please use this circuit, modify it and make a linear voltage regulator. I want your permission to upload it on you tube with due acknowledgement. Thanks.

  14. question.. if u wanna charge a smartphone with those voltageregulators- dont u need a constant current circuit to safe the smartphone's akku?

  15. So if I made a flashlight with a voltage regulator, it would stay at it's peak brightness until the battery fully drains?

  16. ВЕОМА САМ ЗАХВАЛАН ШТО ИМА ПРЕВОД НА ЈЕЗИК КОЈИ РАЗУМЕМ. ОВОЈЕ ДЕФИНИТИВНО МОЈ КАНАЛ. ХВАЛА И ВЕЛИКИ ПОЗДРАВ!!!.

  17. Just btw, "Jameco Electronics" was originally "James Electronics", the first word pronounced with a long "a" like the common given name. And back in the day when I dealt with them by phone they pronounced their new name the same way, with the "a" in the "Jam" part sounding like the "a" in "fame". not as in "jam" or "fan" or "ran".

  18. I have a problem with an electric scroll saw that would not power back on…i took it to an electronics guy because i knew it wasn't the motor…he told me it's the voltage regulator and would cost 165 Can to have it fixed!!! Is this something i can do myself…i believe he said it was under the circuit board. Do these voltage regulators just pop out like a pin? And what would cause it to fail?. I hardly used the saw but was told that sometimes without using a tool often they just die.

  19. I think the small capacitor (0.1uF) works best for decoupling if placed closest to the regulator. THANKS FOR THE SUPER VIDEO!

  20. I want to charge 8v,4600mah battery pack when I use 7808 it’s burned out in 2 mins it’s dissipate heavy heat can any one suggest a solution for limiting output drawn current of regulator ics

  21. my friend L78xx is for positive voltage and L79xx is for negative voltage. it has nothing to do with manufactors …

  22. If I'm building a 5V power supply that accepts 220V and 110V using a 220V AC to 14V AC Transformer(AC->AC->FWR->VR), @220V what would be the best way to drop down to 5V and avoid 6 watts of heat at 700mA? I'm building something to possibly sell, but at this point I'm thinking of just advertising it at 110v and using a 110v->6V TX.

  23. Because of your tutorials, I have a much better understanding of electronics.
    I'm self-taught out of a desire to modify and improve my cheap Chinese tools.
    However, this has led me down the "rabbit hole".
    Thank you so much for your guidance.

  24. This is a great educational video. I learned a lot from your series on Power Supplies. Thank you for the comprehensive coverage of all the concepts and parameters. That's the proper way to learn instead of people simply demoing their work with inadequate explanation on how it works. You are a great teacher, paying attention to the content you're communicating. It's very fun listening to your videos. Thank you very much again for sharing your knowledge with the world.

  25. really good video, thank you !. Can I ask ( As I'm just starting to learn ) how you came about the capacitor sizes and why you arranged them in the sequence you did, I understand the idea that they are there just to further smooth out the signal, but have no idea why you used the ones you did, thanks

  26. The hell with fixed regulators just use lm317t. Buy in bulk and chose what voltage you want between 1.2v and 35v

  27. hi, wanna ask..im still figuring out v.regulator. im powering 6 servo by using 12v power supply. how many voltage regulator do i need?

  28. So if I have a device that uses two AA batteries that's 3 volts or 2.4 volts depending upon the type and I want to use li-on which output 3.7 volts I'll just need to use one of these from the video that's a 3 volt?

  29. I have a doubt that I have made hand crank generator it give not constant it give 12,30,47,32,30 and so much how to make constant voltage as12v can I use voltage regulator are something else please tell me how to reduce and there must me less drop out current (mah) because I am planning to create a hand crank Power bank.please tell me

  30. Good video… With all due respect, what regulators would you suggest to go from USB 5 volts DC to 3 volts DC?

  31. What's the point/function of those capacitors? Why so many. How do I know when to use and what f value is appropriate?

  32. I've enjoyed playing with electronics for over 45 years & these are great refresher videos. Thanks for sharing.

  33. You could take a 16V power source and run it through a 9V regulator, and then to a 45V regulator, to not have all of that heat on the 5V regulator.

  34. Such a great video. No bs, packed with information. Can you (or someone) explain the function of the .1uF ceramic capacitor? In parallel with the 10uF cap, its capacitiance is a negligible contribution, so what is it adding?

  35. real electronics is simple and easy but when we link it for bussiness it becomes complicated with extra components.best wishes .

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