HACKED!: Adding a Current Limit Feature to a Buck/Boost Converter

[@kristiandelchev7362]

To make full CV (constant voltage)/ CC (constant current) operation - the voltage and current feed-backs are to be combined into the FB pin. Whoever is higher will take control. Most commonly people use a resistor divider (to FB pin) for the voltage feedback and current sense amp for the current feedback. How to combine them? The simplest is to connect the current feedback signal to FB pin via diode. The drawback? - diodes have voltage drop changing with temperature *by 2mV/deg C). The most accurate solution is to "idealize" the diode by op amp. The current feedback signal is applied to the non inverting input of an op amp. Its output drives an NPN emitter follower, whose emitter is connected to the op amp inverting input. The circuit can only pull up, but not down i.e. does affect the voltage control in normal operation. Should the current limit be exceeded, the current feedback will take over

[@llama1917]

Software Engineer. Always have to remind myself that with circuits and hardware in general you cannot just "get started and refactor when you know what what you're doing more" 😎

[@yashsvidixit7169]

And that's where simulation enters the chat.

[@gizmoguyar]

There's sort of a mechanical/electrical equivalent to refactoring. It's cost-down. You comb over your design and figure out if there's a better/cheaper/more efficient way to achieve the same thing.

[@epiendless1128]

The issue I have with differential amplifiers for current sense is that they are very sensitive to errors in the resistor values. A 1% resistor error will give an output error of 1% of the _supply voltage,_ which is comparable to the thing you're trying to measure. Alternative is to use a current sense amplifier. Silicon Labs SI8540-B-FWR is just one example.

[@SayanMitraepicstuff]

The two main ways Scott starts his video: -Recently... -In ze previous video...

[@greatscottlab]

But not this time

[@DarkSlayer-xk3fb]

XD lol

[@pablobski]

totally!

[@fertilizerspike]

"let's find it out!"

[@nullerrno]

“A while ago”

[@anugrahkorambeth431]

eventhough I donot understand anything, I still watch your videos and I like them. Please keep em coming 👍👌✌

[@Trancelebration]

Good idea is to add a bit integration to comparator circuit. Something around 10nF between output and inverting input does the trick. Much cleaner output voltage and less hissing sound from inductor.

[@tommihommi1]

Another advantage of lab PSUs is a much, much cleaner voltage. Try to power a radio with a circuit like this and you'll see what I mean

[@greatscottlab]

True

[@mattimhiyasmith]

You should be able to reduce the ripple by loading the buck/boost converter with high load but kinda makes the current limiting in this video pointless :P or use a LDO or RC in series to from the converter

[@vaguedirector_7342]

I'd just add an LC filter to the output for lower noise operation.

[@TheOswald42]

I see, LDO, RC or LC filter.....is there more solution for cleaner voltage?

[@brucefox6580]

A linear PSU perhaps.

[@ReagueOfRegends]

I'm always left wondering, how many people watching here are electrical engineers vs. hobbyists? :)

[@philxcskier]

I'm sure there are a ton engineering students.. I happen to be studying mechanical engineering, and it's nice to be able to check these out whenever I have no idea what a circuit does.

[@Lovreli]

Spurdo Sparde both lol

[@vaguedirector_7342]

ECSE student here, binge watching all the good electronics channels

[@aunreza]

Electrical engineering student here. I watch these videos for fun but i might build this circuit for a project.

[@spudhead169]

Hobbyists are 100x smarter.

[@rainbowspeedy]

Ich don't understand what Scott is talking about. But I love his voice. That's why I watch his videos.

[@extrims70]

Hope somebody has already caught electrical schenatic typo at 05:49 - differential amplifier IC1A won't work the way it shown :( Non-inverting pin.3 should be connected to junction between R2 and R3. Anyway - that's is great work, Great Scott!

[@jensschroder8214]

You can also switch off a buck converter by introducing a feedback voltage greater than the reference voltage. In the case of a boost, the output voltage would then roughly correspond to the input voltage.

[@jayzo]

I've learned more _useful_ information about electronic circuits with the likes of GreatScott than I did in school.

[@vaseemmehrancp9372]

Real blend of creativity , fundamentals and hacking

[@PropaneTreeFiddy]

0:45 That NOISE!!! You can literally see the LED flickering in the footage. If you want to use a buck-boost converter for anything that requires a fairly stable voltage, I highly suggest adding a good amount of filtering!

[@jeffreygoodson2563]

I LOVE the way you explained this! You're a great teacher. Thank You!

[@Jones12ax7]

I used an ATX power supply with one of these buck modules to make a crude powersupply. It worked so well that I plan to increment that and this circuit will be very handy! Thanks!

[@fmdj]

When Great Scott has a video on the exact thing I'm trying to do... AWESOME! thanks!

[@ritvikaneesh5980]

I just started electronics a few months ago and I have learned so much from these videos. I have recently made my own power supply, no current limit feature though this video should help

[@phrankus2009]

The beauty of Scott not glossing over the finer details is that it inspires me to "really" study the circuit or concept intensively, by consulting MANY sources (including the Wiki, even) until I have a truly intuitive (deep) understanding of the FLOW, the LOGIC, and the MATH. .. I do not care how long it takes. .. I resent being rushed through anything that I do not yet "fully own". .. Scott seems to OWN the knowledge, which he shares, and his uncompromised, comprehensive and detailed presentation illuminates the degree of my shortcomings. .. This allows me to fully remediate my deficiencies, however frustrating.

[@kshysztof9649]

Yes, absolutely ! When I first watched the Nixie tube video, I didn't knew what was going on, but after few hours of research, I came back to the video, and could clearly see what problems and solution he has used.

[@nosafetyswitch9378]

Without really noticing, everyone here is being taught/shown basic control theory principles under their noses! Well done! Usually its scary shit!

[@shariqzaman2834]

I was searching for this type of project for a long time :D ..Thanks GreatScott :)

[@pankajroy5124]

Great Scott YOU ROCK!!!!!. Another great video. You are helping and motivating youngsters to learn electronic. Good work. Keep it up.

[@apeman9001]

Spoken like a true politician! I take it you belong neither to the EE group nor the hobbyist group, but the bureaucrat group. Just kidding!

[@aniketshinde6743]

greetings from India.. great Scott luv ur all videos keep going..

[@greatscottlab]

Thanks mate :-)

[@kulde3pverma160]

Aniket Shinde hi aniket

[@vishal01mehra]

one more from India.😊

[@pardeepk21]

Count Me In Too :P

[@sumit_kashyap..]

One more Indian ;)

[@JKnight89]

This video helps me. I have a junk benchtop power supply that eventually I wish to rebuild, so this gives me a place to start looking for possible starting point. Thanks!!

[@marlonmartins82]

This is exactly what a was trying to learn this week. add current limiting to my power supplies. thanks!

[@BlackXeno]

Just to be sure if I have understood the feedback as you have explained: when you see the output voltage swinging a bit on the scope, that is the switching noise, not the error direction of the control feedback.

[@rtesimpson]

Very neat handwriting and schematics!

[@engician7620]

I don't understand any thing !!! But I love watching your videos It gives me a kind of satisfaction.😌🙏💁

[@TheOleHermit]

This is exactly what I needed to know/do! Thanks! While using buck/boost converters to build a DIY solar charger on a LiPo power pack (w/o mfr's circuitry), I've fried my rework station's internal 15 VDC PSU, a buck/boost converter, a buck converter, a boost converter, and a solar tracker... so far.🥴 Unfortunately, I was unable to keep up with the video. So, I'll watch it about a dozen more times and head to your project info links. Ha! just noticed a link to your DIY LiPo solar charger video. (How did you know?) See ya. 😎

[@damascenoalisson]

You can easily buy current-limiting converters from eBay... But DIY is so much better haha Great project btw! :-)

[@chrysoulakefalopoulou736]

Nice video.A small error thought at 6:20,I think the diff. Ampl circui5 is not correct at the point where you have shown the ground. The non inverting input should be connected after the 3.3k and then the 100k from the non inverting to ground?

[@plamenpetkov6958]

There are ready made CC, CV Buck Boost converters, with additional trim pot for current limit adjustment. They typically use low side current sense resistor (shunt), making it easier to process the current feedback signal. Typically the current feedback signal after non inverting amplification is fed to the FB pin via diode. The FB pin is controlled by the higher of of voltage and current feedback signals. Nothing wrong using high side current sensing...but the accuracy of the simplest 4 resistor diff amp even with 0.1% resistors could exceed 2% due to unwanted sensitivity to voltage due to resistor mismatch. TI and AD have an extensive range of tiny current sense amplifiers, more suitable for this role than a general op amp (comparable on size and cost).

[@micah2936]

The ground at pin3 of the IC is really throwing me off. Why is the non-inverting pin grounded? I’m so confused 5:55 Edit: Since the inverting pin is connected on the lower potential of the shunt resistor, I suppose it means it is negative, and the gain is actually -R2/R1 which means if he wants 333mA, he sets the potentiometer to 1V, and the first op-amp will stabilize to 1V output, or otherwise, the inverting pin will receive -33mV (333mA*0.1ohm) which will receive a gain of -30, which will output 0.99V. And it stays stable because when the current gets too low, it will output less than 1V which will be compared and set the feedback to low, which makes the converter output more energy, and when it is more than 1V, the feedback will tell the converter to output less energy. This took me so many other videos to understand 😅 I still don’t understand the purpose of R2 and R3

[@thecombatengineer7069]

This is very clever and I have enjoyed watching your skills and experiments progress. Thanks for the dedication mate!

[@kristiandelchev7362]

It is better to use dedicated current sense amplifier like INA193. The proposed op amp base design has two main deficiencies:first, with gain of 30 the op amp inputs get too close to the power rail. Many op amps have limited common mode range on the upper side. The second problem is the effect of tolerances between the paired resistors. This results in sensitivity to voltage, not just current. Laser trimmed resistor quad IC like LM5400 can help, but it is easier to use dedicated current sense amp.

[@fuzzy1dk]

using a pot to set output voltage like shown at 4:11 is usually a bad idea, a bad connection in the pot will result in maximum output voltage. Have you looked at the output on scope when the current limit is in effect? I suspect using a comparator rather linearly adding to the feedback node will cause it to rapidly turn on and off rather than lower the output voltage

[@galacticgamers8705]

I'm only 10 and I love these vids.

[@asasif7]

Greeting from PAKISTAN.. Greatscott you always do a great job. You are a great teacher for me. i learnt using arduino totally from you.

[@dave_dennis]

I've done this many times. The problem I've sometimes had was that the high side of the feedback resistor would sometimes exceed the common mode input capability of the opamp. This has often forced a careful selection of a high voltage capable opamp.

[@greenman2262]

GREAT Scott a well thought out and worth while doing little project thanks.

[@45llamas]

I love your videos and how you explain it function so clearly !!

[@vaioskaliakoudas6388]

After this explaination, make sure to make the successor of your DIY Buck/Boost Converter, which will feature that as well. Also, the horsepower of an electric motor, depends by how much current/voltage flows form the battery packs into

[@houseofelectronics5869]

Great video @GreatScott. Your channel is a perfect guideline for any electronics beginner. I learn a lot from each of ur videos. Thanks man :)

[@greatscottlab]

You're welcome

[@jimthvac100]

This is cool knowing how to do this, but I would probably just buy one of the many buck converters that include an adjustable current limiter in the design.

[@miniwarrior7]

Zero challenge or understanding of the components you're using means when they don't work you just buy more

[@Roy_Tellason]

That's exactly what I did, only the board has _three_ trimpots on it, not the two that you'd expect. And it doesn't seem to want to work properly to drive a 10W LED. I'm in the process of trying to figure out why...

[@fmdj]

Yeah but you have to wait for it to arrive from China or wherever. I like to be able to build things with the stuff I have lying around. As a programmer I find there is a lot of beauty in creating complex things from a limited number of primitives. So as an electronics hobbyist endlessly buying new components doesn't satisfy me. If I were building a commercial product that would be another story.

[@matejhusek6855]

Thanks!!! I Made it and with dome changes i Made my super Power supply!!!! Very good video.

[@TheJay6621]

Awesome.. Thanks for your time and efforts.. love from INDIA.

[@TheJay6621]

mrco74 flush it.

[@mja2239]

lol

[@navjotsingh0006]

I enjoyed it alot and you created what i wanted to have in my little electronic project but its not easy for me to build just like you did it but great video its always fun to watch your videos.

[@jairopolanco2282]

Can you do a nixie tube clock??????

[@greatscottlab]

On my to do list.

[@jairopolanco2282]

😀😗

[@milkhbox]

@GreatScott. Sweeeeeeeeeeeeeeet. I've got a bunch of drivers and tubes collecting dust.

[@electronicguy4550]

Wow this took 3 years

[@electronicdude921]

"this circuit can be used to test LEDs" is a wrong statement if you leave voltage at any level and just set the current to minimum (20 mA for your case). Because although the current is limited, but the output capacitor is still charged to the set voltage value. So when you connect an LED with let's say the voltage set at 12 V and current at 20 mA, the capacitor will supply enough surge current to destroy the LED. I have practically experienced that. So in order to test LEDs, you'll need to replace the output capacitor with a small 10 to 22 uF capacitor. But that will introduce alot of ripple in low impedance loads (high current) so you'll need to add a relay and a larger capacitor so that the relay connects the bigger capacitor to output when set current exceeds a certain limit (e.g 200 mA). But since the larger capacitor is not charged if disconnected, it will cause a huge current surge when connected at once. Which can affect the transient response of the power supply. To address that, connect a diode from output to larger capacitor so it keeps charging with the output voltage but won't discharge through load unless connected by the relay. And here we got into another trouble. What if we had set a higher voltage with larger capacitor connected and then disconnected it (set a lower current value) and then reduced output voltage and again switched the larger capacitor in? It would provide a higher voltage spike that can cause harm to sensitive electronics. To address that problem now, connect a resistor (e.g 6.8K or 10K) parallel to the larger capacitor so it keeps at the set voltage level whether its connected or disconnected. Thank me later!

[@plamenpetkov7132]

op amp pin 2 connected wrongfully to GND instead of the mid point of R2,R3. Also low side current sensing breaks the input ground from output one. This implies that a short circuit towards the input GND bypasses the current sense shunt i.e. eliminates the protection. Also a current sense amp is preferable to common op amp. In this example the 4 resistor diff amp is sensitive to resistor values match i.e. tolerances result to unwanted sensitivity to output voltage, not just current (1 % resistors may result in say 5% error)

[@ruimvp]

Hello GS. In this type of power supplies can i use a big electrolytic capacitor at output, like in a linear power supply, to avoid ripple? Thank you. Keep the good schematics.

[@milanhlavacek6730]

Due to the quite high frequency i thin its better to use film or ceramic caps

[@camarol88]

Your Differential amp configuration is not correct. You have the positive pin is connected to ground.

[@greatscottlab]

Yep, I already corrected it in the instructables article.

[@kevinlivingston9563]

George T nice catch. Both of you!

[@tuttocrafting]

I was just taking my op amp text book. I used to study electronics but that configuration was looking strange to me. Good that my memory is not completly gone :D

[@UnBOXTopicz]

Scott, thanks for the video, qq, on normal power supplies we can short the terminals to set current limit. I am not understanding how we can achieve this with buck being the power supply and IV meter for display. Red wire from display is negative which goes to the load and positive comes from buck. Thiese two terminals are say the two terminals for DIY power supply. Now I want to set the limit before connecting the load so ideally we would shot them but not sure if that would work. Any idea?

[@UnBOXTopicz]

Answering my own question, GS might not even see this since the video is old. 😅 MY CONFUGURARIOB FOR DIY power supply is this, 2 bucks, 1 to reduce main supply voltage, second to power the display alone. Now to achieve CC limit setting and see it happen on display like normal PSU, we can still short the two terminals (negative or thick red from display and positive from main buck). My issue was the current limit was set to low on my display buck which was causing display to shut off, I guess this is due to high current draw and safety measures. I simply cranked up the current limit on my display buck and that did it. Works perfectly just like any other power supply.

[@tungruffel]

If I knew half of what this guy knows, my head would explode!

[@manliomalavolti9640]

Great video, thx! I wonder what could happe if a boost converter designed to boost to 12V, sees an input (from solar panels in full sun) coming @ 16V. Would it fry?

[@nitinnahar7713]

Really I would say the video is very excellent. You are really Great Scott

[@MrBreak745]

if any one had difficulties understanding the concept behind this circuit you can watch Dave johns 's portable lab power supply playlist

[@sersheva]

Please, I have a doubt about the connection in the feedback pin of the IC. Did you connect the new feedback signal from the current limiter with the same feedback that is used for voltage measure? How does the circuit will control the output voltage if there are two signals in the same pin? Thank you!!

[@Se7enAte]

What kind of power supply would I use if I wanted to hook up some LED off road light bars (say 180 watts) as outdoor lights? So taking mains and converting to 12v while supplying enough power. And isn't too expensive

[@ergindemir7366]

It might be a good idea to use a pot for the feedback resistor to calibrate the opamp for the precise current measurement.

[@JohnWayne99999a]

Wonderful! Is there any way to miniaturize this?

[@electroumit]

Thank you. Your voice and speech is great. I very like.

[@matuga92]

Hi, great video as always. Can this be used to power a super capacitor bank? Thank you.

[@owalkmachinemaishitechdobr3674]

Your videos are amazing! Thanks to share knowledge and your experiences!

[@32_gurjotsingh82]

i FINALLY understand all of the circuit, and started to build my own, but still the current calculations, i do not understand at 7:12, can anyone just give me a little hint? thanks

[@h.tronics]

Can I change the shunt value according to the capacity of my circuit?? For example for a circuit which can output maximum of 9A , the value of shunt should change right? 😓😓

[@briannielsbergh]

Your videos are just so cool, thanks for sharing your knowledege :P

[@osamaalhamwi1662]

Very good If Iwant to increase the current with transistor LM7805 how conect it with 2n3055.....thanks

[@utkuserin9750]

Hi. This is the video that I am searching for. Is there any cheaper solution? For example which opamp I can use instead of mcp602? I cannot reach it currently. Unavailable. How I can decide the compınents?

[@imnotbeluga007]

In theory, you should be able to make a simple circuit to hack SMPS power supplies too, to regulate the voltage and current accurately. Just make a circuit that activates the optocoupler when the output voltage or current is too high, with current control having priority. That decreases the switching circuits duty cycle, decreasing current and voltage with it. It's actually possible that this exact circuit will be able to do that, but I (and probably you as well) want voltage regulation down to lower voltages than 3-4V. And because buck converters work like switching power supplies, it has to work, right?

[@bobibobi3063]

Hi Great, why you don't use your JBC? 😃

[@Andratos95]

Can I use this as a laser diode driver for a 3A laser such as the NUBM08 without damaging it?

[@harys6382]

can we create free energy using boost converter, lamp, and solar panel? 😅 just asking. i dont knw it will work or not

[@maxximumb]

Thanks for posting this.It's exactly what I'm looking for.

[@brainpoweredelectronics3351]

Very useful hack. I was looking into doing something as elegant for a a linear regulated power supply. Perhaps you could could think of a similar way to Implement current limiting using an Lm317?

[@blackbrayn]

Brainpowered Electronics i just burned a lm317 with overvoltage , i was lucky to have a spare lm338 , this reminds me to buy some more.

[@michaelumenyi6907]

Your videos always exists me!!

[@ameliabuns4058]

wouldn't the sudden 3.3v to regular voltage create a very spikey and uneven power output (current fluctuating as a result) when the current limit is activated?

[@TveshajKumarSubudhi]

Hey, great video. Really informative. I have a small doubt, can we take the output from the buck/boost converter and use a LM317 in a current regulator configuration?

[@AlphaTroniks]

Yes but it will not be efficient

[@TveshajKumarSubudhi]

@@AlphaTroniks thanks a lot.

[@AlphaTroniks]

@@TveshajKumarSubudhi you can reach me at [e-mail] I can help you

[@mrmega328]

Comparing this method to a mosfet doing the current limiting with an op-amp, which one would be the better option to go for? I guess the mosfet way is separated from the DC-DC but it also means the mosfet would drop the voltage when current limiting so it could get quite hot for high current. But if you had both voltage and current controlled by an MCU, you could lower the voltage that way.

[@shapshooter7769]

It would be great until the MCU locks up (and you haven't provided a proper watchdog timer to check the status of the chip). The added complexity in this case is not going to outweigh the features it brings unless you do it correctly.

[@kishorgoodday276]

Thanks for this great hack bro...i searching for this type of hack...😍

[@luiscarlosmarques3946]

A caligrafia do Scott, é muito bonita. Suas explicações e internações são dignas de muitos elogios. Gratidão Scott.

[@flyingskorpion]

Great project, next one should be "make a li-ion battery charger using a buck-boost converter". Interesting thing would be, how to prevent reverse flow of current.

[@alexnik8334]

Will I loose integrated to converter overcurrent protection using feedback circuit ?

[@micah2936]

Current can be dependent on load resistance, or it can be dependent on voltage. In this case, it is dependent on voltage. What if you need constant voltage and constant current? Can’t you make a current limiter dependent on a variable resistance such as a thermistor which is designed to heat up for a specific resistance, or a photoresistor designed to be exposed to a specific light intensity for a specific resistance?

[@Coastal_Cruzer]

If I were to use a buck converter to drop 12v down to 9v, would the amperage increase? If so by what factor? I am attempting to DIY a guitar pedal power source, and I can't find any suitable inexpensive 9v power supplies

[@MCsCreations]

Fantastic work, man! Do you think it's possible to do the same to a boost buck converter that uses a XL6009? I have one identical to the one you used. BTW, what about short circuit protection? Would it add it too?

[@greatscottlab]

Same theory and my circuit should apply to all buck or boost converters with a feedback pin. And at the end of the video you can see how I short the output of the converter. So yes, this allows a short circuit protection.

[@bbreeuwer4577]

Btw, a proper name for a buck/boost converter is called a SEPIC converter.

[@bbreeuwer4577]

btw, there is an error in the differential amplifier. It's correct in the link in the description!

[@thecombatengineer7069]

Btw, no it's not, a SEPIC is one form of this topology and is different than the original B/B

[@budandbean1]

Man, you are pretty amazing and one heck of an instructor! It's like you make almost everything understandable. Please continue your fine work... :-)

[@greatscottlab]

Thanks for the feedback. I will try my best.

[@tupai62]

is it all this 3 module just can adjust the voltage only, not current?. how about the output current?. is it have overcharge protection?. is it can solar panel to connect to input to charge 6v 7ah SLA battery?.

[@arshamskrenes]

Could you make a video on building a trailing edge AC dimmer? There aren’t any on eBay or Aliexpress that are controllable via a micro controller. Thanks!

[@alirezashiri4506]

Hi You are shorting pin 3 to ground with the schematic you showed on video.but the schematic on instructable is ok.

[@BoomBrush]

nice use of highligher throughout video. @ 7:00 why the use of a shockley diode? D1

[@JuraganLED]

for protection so the voltage at feedback pin is not below 0V. Schottky diode is used because of its low dropout voltage and fast response. Tell me if i'm wrong.

[@babacloanza]

Hi, you should have connected the GND on the other side of the R3 resistor in order to have a differential amplifier.

[@micah2936]

This is what I was looking for, R2 and R3 just form a combined resistance of 103.3K ohms. I don’t understand the purpose.

[@ACupOfDuck]

Can you make a video about converting small solar lanterns for gardens to an option for charging cellphones?

[@animatrix1851]

Is it possibly to modify the shunt on the LTC3780 to make it work with such low currents.

[@jossydornelles7606]

GreatScott! Thank you for the class on this circuitry! I assembled the circuito but, for any reason, I was not able to control the output current. I am using a step down LM2596S-ADJ (yes, the feedback pin is 4), and I would like to know: should I have to disconnect pin 4 from the board? How much current I am able to control?

[@techexplained5725]

Hi nice vid as always. btw. whats the MIC you are using. sound is crystal clear. thanks.

[@strapatser9427]

can you increase the current output if you adjust the feedback system?

[@greatscottlab]

Not above the specs of the buck/boost.

[@MatejVelican]

Try making electronic police/warning light with 4 bit counter, with 16 segments making hexadecagon? It might be better because no moving parts.

[@dzee9481]

Very good video, I have been trying to look for a boost converter that will take a single 18650 Li Ion Cell and boost its voltage from 4.12 Volts to 30 volts. Most of the boost converter go with a min voltage of 5 volts. Is there such a boost converter or could one be made?