DC-DC Boost converter tutorial


In a previous video I showed you how to
make a dc-dc converter that can step down voltage. Today I’m going to show you a new circuit
that can step up voltage. It’s kind of like a joule thief except a
million times better! It’s called a boost converter and this
one can take input voltages as low as 4 volts and step it up to 30 volts. And you can adjust the output to
whatever you want. This video builds upon material that I covered in my buck
converter and inductor tutorials so make sure you watch those first if
you have any questions. Let’s begin with the classic boost converter schematic. Normally you’d use a transistor for the
switch here but let’s keep it simple with a switch symbol. If we start with the switch open, current
from our 10 volt source will flow through the inductor, through the diode, and charge up the
output capacitor. There’ll be a small voltage drop across the diode (let’s say half a volt) so the output
capacitor gets charged to 9.5 volts. So far we are dropping voltage but that’s
going to change soon. Next let’s close the switch. The diode
prevents the capacitor from discharging so the output stays at 9.5 volts. But now
we have a current path from the input through the inductor straight to ground.
If we keep the switch closed like this we’d basically be short-circuiting the
input through the inductor. Inductors don’t like it when you do
that. So we’re not going to do that! We’re only going to close the switch for a
fraction of a second. We’re going to close the switch just long
enough for some current to start flowing through the inductor. When we do this we’re storing energy in
the inductor in the form of a magnetic field. Now that we have some current flowing
through the inductor, and therefore we have some energy stored
in the inductor, we’re going to quickly open the switch. Since current in inductors can’t instantly
change current has to flow through the inductor,
through the diode, and into the output capacitor. So energy gets transferred from the
inductor to the output capacitor and the voltage increases! Our boost
converter has now boosted the voltage. Now as I said earlier we don’t want to
be closing the switch for very long. we want to be controlling the switch
with a high frequency pulse width modulated square wave. And from watching previous videos you
can guess that by increasing the pulse width we can increase the output voltage. But
how do you predict what the output voltage will be? Well in textbooks you will often see
this equation. But this equation will only work for
very low currents. In the real world the output voltage you
get will be a function of your duty cycle,
your inductance value, your switching frequency, your output current and many
more things. So just like with our buck converter, if
we want to build a real-life boost converter we need a controller
chip that will adjust the pulse width to make sure we have a constantly
regulated output voltage. Let’s use the LT1370HV from Linear
Technology. And as usual I’ll put links in the video
description section. The input and output of the supply have
a combination of electrolytic and ceramic capacitance to help deal with
the high-frequency currents. You’re going to see this in nearly every
switch mode power supply. We’re going to use a schottky diode with
as low forward voltage as possible to keep things efficient. And here we’ve
got our feedback resistor network that I calculated to give you guys a
maximum output of around 30 volts. Depending on the tolerances of your
resistors and potentiometer you may get a slightly different maximum.
Now here’s something new… these components are used for control
loop frequency compensation. Basically they help the controller
adapt to small changes in the output voltage, giving you a cleaner DC output. Learning
how to design compensation circuits requires a lot of complicated math and knowledge of control theory which
is beyond the scope of this tutorial. But here are a few links to some
information. The good news is that most of the time you can just use the
recommended values in your controller’s datasheet and your circuit will work. Alright
let’s build this thing! Start by soldering the heatsinked
controller chip onto some perfboard or make your own PCB. Leave plenty of
space for the other components. Keep component leads short and your solder
traces thick. Add the inductor, the diode, and the
capacitors. Next add the feedback resistors keeping
things as short as possible. Finally solder the frequency
compensation components near the input and leave pins 3 and 6 unconnected. Let’s look at the bottom side of the
board. Notice how I arranged the components so that I could have a simple
continuous ground from the input to the output. And I have
soldered the ceramic input capacitor directly across the controller’s input
pins. And the output ceramic is in parallel with the output electrolytic. Now if we power it up we can take our
input voltage and step it up to 30 volts! Now let’s talk about the limitations of
this design. It can only deliver about 50 watts
before things get uncomfortably hot. You should also be
aware that it has an input current limit of 5 amps.
Notice how I said input current limit, not output current
limit. Check this out. Let’s say our converter has an output
voltage of 12 volts and output current of 1 ampere. So we’re
delivering 12 watts of power. When I power it from a 5 volt source
it’s drawing 2.78 amperes. So the input current is higher than the
output current and this is because we can’t just create power out of nowhere. In order to get the extra voltage on the
output we’re drawing more current on the input. Overall our boost converter is roughly
86% efficient. Finally, BE CAREFUL! For safety reasons
I’ve limited the design of the circuit to a 30 volt output and even just 30 volts
from a large capacitor can do some damage. If you build a boost converter
incorrectly, or you handle it carelessly, you could electrocute yourself! Don’t do
that! With great power electronics comes great
responsibility. Thanks for watching and if you enjoyed
this video please check out the video description section to see how you can support the channel!

100 thoughts on “DC-DC Boost converter tutorial

  1. Ok, here's hoping I might get a reply on an old video! I'm trying to make a nice light box for my shop out of some salvaged LCD TV LED backlights. Based on information from the circuit board, the total array of LEDs in the backlight is getting 118v, and all 32 LEDs are in series (oddly…) There are 4 strips, each with 8 LEDs on them, and each LED consumes around 150mA. 118/32 = ~3.7v. I plan on modifying the bus board that the 4 strips connect to to make them parallel instead of series, meaning that I would only need to provide enough voltage for 8 LEDs, but more current. At ~3.7v each, I'd need about 29.6v, and with the 4 strips in parallel I'd need at least 600mA. Is something like this capable of stepping up, say 12v 2A input to 30v 1A? Please pardon my lack of knowledge on this subject, I'm good with electronics, but usually mess with bigger stuff that makes a lot more sense to me, I have trouble wrapping my head around this smaller stuff.

  2. What will happen when your power requirement will be higher than input ? For ex I want to power LED, which need 30V and 1A, from a powerbank, 5V and 1A.. So power bank can give 15W, and we need 30W. It will not work. It can only give 30V on 0.5A. But what will happen to power bank when you get over 15W, it will burn ?

  3. If I use 6V, 7amp battery, will I be able to draw more current on the output at 30V? And is the variable resistor on the output to adjust the voltage output?

  4. Would these switching boost converters at 500 kHz (or 72 kHz) cause a lot of noise that would affect nearby analog audio circuits? What about the inductor? How would I design a circuit to match LT1111CN8-PBF? Would a 120 kHz IC be better than a lower frequency IC like I mentioned?

  5. question sir… what if i put a load at the output.. does the converter give enough voltage to the load with minimal voltage drop

  6. Please l have a mini generator that generates up to 50v and I want to use this circuit on it so it can power my refrigerator, can this circuit work for the purpose ?

  7. Nice tutorial. But I have question.. For how long can I keep the "switch closed"?? suppose I am using an inductor with 560uH Inductance and the applied voltage across it is 12v….

  8. can we hack ltc7380 buck boost converter and put high current transistor instead of default once and pass high current at same voltages?

  9. Has anyone tried those step up modules you can buy on a certain Chinese website for less than a dollar? I'd like to get more 12V pixies from a 22A 5V rail on a PSU. I need to feed 4x 2A 12V to power up four HDDs for a few seconds, after that the current draw drops significantly. Instead of having one, beefy converter that can handle a lot of watts, can you just put several smaller ones like the Chinese ones in parallel on a single power source or will they interfere with each other?

  10. Has anyone tried those step up modules you can buy on a certain Chinese website for less than a dollar? I'd like to get more 12V pixies from a 22A 5V rail on a PSU. I need to feed 4x 2A 12V to power up four HDDs for a few seconds, after that the current draw drops significantly. Instead of having one, beefy converter that can handle a lot of watts, can you just put several smaller ones like the Chinese ones in parallel on a single power source or will they interfere with each other?

  11. Nice video with a clear explanation. Thank You. The car charger I'm using now uses nominal 12V from the vehicle electrical system and boosts it to 19V. Except when first turned on, then the output will be 22.5 volts. Over the next second or so it drops back to 19V. Putting a 30W load on it makes no difference. What does the output voltage of your circuit look like when first powered on?

  12. Why do you use both ceramic and electrolytic capacitors in series? Naively, it seems like the circuit should behave the same regardless of the type of capacitor. Is it something to do with distance from the feedback pins? (i.e. ceramic -> small but close, electrolytic -> bigger but further).

    Btw, thanks so much for your videos. Very clear and well explained!

  13. I bought a Raspberry Pi 3 pi-topCEED that requires a power input of [email protected] – (actual measured load was around ~800mV, but it could call for a bit more at times, e.g. if something is plugged into a Pi USB port).

    Want the option to power it out in the wild from a 20k mAh battery pack (USB) that can supply [email protected] from up to 2 ports (4.2A max pack total).

    1A x 18V = 18W ~~~ 18W / 5V = 3.6A

    So now the crazy idea part… (keeping in mind that this/your design was for boosting to 14Vout max)

    Q1) Would this project build be stable enough to support and drive something as sensitive as a Raspberry Pi board?
    — If yes, … —
    Q2) If I built 2 boosters, set both at 5Vin–>9Vout, and connected the outputs in series (now 18Vout, with more than enough current), would it work?

    Or, would I just end up with Pi on my face? (sorry)

    Feel free to embarrass me with a better solution. Cheers.

  14. Can this type of circuit make a small electric brush-less motor spin faster? I'm trying to make a hovercraft thrust propeller spin faster but I'm limited to either 9 or 18v (two 9v batteries). I think I'm correct that when I boost the voltage, the current decreases? Is there a way to do what I want with light weight electronics?

  15. // connect motor controller pins to Arduino digital pins // motor one int enA = 10; int in1 = 9; int in2 = 8; // motor two int enB = 5; int in3 = 7; int in4 = 6; void setup() { // set all the motor control pins to outputs pinMode(enA, OUTPUT); pinMode(enB, OUTPUT); pinMode(in1, OUTPUT); pinMode(in2, OUTPUT); pinMode(in3, OUTPUT); pinMode(in4, OUTPUT); } void demoOne() { // this function will run the motors in both directions at a fixed speed // turn on motor A digitalWrite(in1, HIGH); digitalWrite(in2, LOW); // set speed to 200 out of possible range 0~255 analogWrite(enA, 200); // turn on motor B digitalWrite(in3, HIGH); digitalWrite(in4, LOW); // set speed to 200 out of possible range 0~255 analogWrite(enB, 200); delay(2000); // now change motor directions digitalWrite(in1, LOW); digitalWrite(in2, HIGH); digitalWrite(in3, LOW); digitalWrite(in4, HIGH); delay(2000); // now turn off motors digitalWrite(in1, LOW); digitalWrite(in2, LOW); digitalWrite(in3, LOW); digitalWrite(in4, LOW); } void demoTwo() { // this function will run the motors across the range of possible speeds // note that maximum speed is determined by the motor itself and the operating voltage // the PWM values sent by analogWrite() are fractions of the maximum speed possible // by your hardware // turn on motors digitalWrite(in1, LOW); digitalWrite(in2, HIGH); digitalWrite(in3, LOW); digitalWrite(in4, HIGH); // accelerate from zero to maximum speed for (int i = 0; i < 256; i++) { analogWrite(enA, i); analogWrite(enB, i); delay(20); } // decelerate from maximum speed to zero for (int i = 255; i >= 0; –i) { analogWrite(enA, i); analogWrite(enB, i); delay(20); } // now turn off motors digitalWrite(in1, LOW); digitalWrite(in2, LOW); digitalWrite(in3, LOW); digitalWrite(in4, LOW); } void loop() { demoOne(); delay(1000); demoTwo(); delay(1000);

  16. Higher efficiency, better phase perhaps and more elegant concept as compared to transformer-transistor-diodes, particularly for wanted D.C. output.

  17. In term of actual application, this is a better circuit. The thing is we need another pulse rather than automatically attached.

  18. great videos ^_^ what can you do if you want to step down like 10A?!! I mean you can't use them in parallel 🙁 and the step downs with that Current are expensive :O

  19. The way you explain how this works is extremely good.

    You can make a SMPS DC->DC fixed voltage converter like you showed us here. However, you should also be able to use one of those to build a constant current SMPS? Can you show us how to do this for all SMPS types (step up, step down, step up/down, flyback, etc)?

    Thank you!

  20. How do I re-modify this boost converter such that I can input a voltage as low as 1.5V yet keeping the the output voltage at about 30V?

  21. The link for the input and output ceramic caps says page can not be found? I'm a newbie so I am not yet at a place to be able to figure out from the schematic what size I actually, (10uF)? I ordered everything thru the links you provided, and do not want to stray from what you recommend in order to have the best chance for a project that works, this will lessen all the variables I have control over? I have some ceramic caps from other projects but want to make sure I'm using the correct size.
    Question: Can I use a 470 uF 200V cap in place of a 50V?

  22. I know this sounds like a really stupid question but I don't understand what the trade off for inputting a low voltage and getting a higher voltage in return?

  23. Damn, just the chip costs (in my country) way more then the old laptpop AND tablet AND homemade "sound system" used mostly to annoy neighbours and bragging rights 😉
    which i planned to use it to power them from one "slightly" smashed (ENORMOUS, and tested, has bout 95% nominal cap.) single Li-ion cell from a crashed beyond repair hybrid/electric car
    😉
    Now if that thing, slightly smashed battery, bursts in flames/smoulders in crowded public transport…. DOUBLE BONUS for me 😉

  24. what if you wanted to take say 14 volt and step it up to 348 volts like the dc current coming from a 370 amp Mechman alternator ? I ask cause I would like to be able to use the dc current from the alternator to run an ac motor from a rinehart ac motor controller

  25. your tutorial is very good. I tried mine it boosted 3v to 12v using a 100uH inductors but I got lower ampere than that of my input current. My input current was 0.6amps and I got 0.01 at the output. Pls help

  26. afrotechmods, your my idol!!!.. your the best electrical video tutorials i ever encountered in youtube. today, I was creating a mobile charger using a solar and steam powered generator.. can you suggest a nice type of boost converter which have an input of max 2v 100mah to output 5v 2.1ah (max)????? plssssssss

  27. Im trying to make a 1.5 to 3v booster. Any changes i would need to make to the components. obviously the values depending on my maths but can i still do it with same mofset

  28. I make it with the auto pulse and short protection,and overload protection

    Are im make this right?
    https://youtu.be/YyYFVZ9NTPA

  29. I really like your channel. You tend not to dwell in the theory and do things from a more practical approach

  30. you are the best man in the world …you are the god for me ….you show me how to understand the electronic at in the best way ..i will always watch your video ..from now and don't forget to upload the video….I need the daily doses…..for the medication purpose

  31. You didn't really explain the most important part: how the voltage increases in the capacitor -.-
    Why current flowing through the inductor increases the voltage?

  32. If you increased the inductor to something larger, like 56uH, and a larger 50V cap, would that be the proper way to increase the output voltage, to something capable of 50 V? I would imagine that you'd need active cooling, as the heatsink on the controller wouldn't quite be enough. Would you need to cool the cap as well? Also, since my experience with boost converters is very limited, if you increase the values of the inductor and cap, would the duty cycle on the controller need to be as high to boost the voltage higher? Would the lower switching frequency require less cooling?

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  34. Isn’t current flowing through the inductor even with the switch open? Does it just build a stronger field when it’s the only thing flowing current to ground?

  35. i want to make a boost converter that can go from 1v 8a to 8v 1a but i cant find anything that can take that low input voltage 🙁

  36. How did you do the feedback calculation with the 10K pot? I know in the datasheet it gives formulas to calculate if only using 2 fixed feedback resistors, but nothing about calculations with a pot. I am doing a thesis project on this and would be helpful if I knew how these were calculated. Thanks!

  37. Hello,

    I want an SMPS with 5v USB input and dual output of 12v and 5V for Battery and Ardunio respectively. I would request you to suggest a PCB board or an IC.

    Thanks and Regards

  38. Awesome tutorial! Please, any idea on how can I convert from a 12v car leisure battery to 42v/2A? Noticed your board goes up to 30v. Thanks heaps!

  39. Is there a way to reduce current on input, but the current output is not being reduced too? Or maybe input current as same as output current. I just need the raising voltage, not the raising current consumption.

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