ebay buck boost controllers.  CC CV fail safe?? - Page 1
Forum section: electronics / beginners

author: user1235423643
author_rank: Regular Contributor
timestamp: April 30, 2016, 08:30:18 pm
content: hello, just a quick question about ebay buck boost controllers.i have had my fair share of blowing them up one way or another. a short on the output will do it..PROBLEM is, is you set it to 5v and have a 12v input when it blows it will feed 12v to the output..any ideas how to protect the load on the output in a basic waythanks

author: jeroen79
author_rank: Frequent Contributor
timestamp: April 30, 2016, 08:54:27 pm
content: A crowbar (thyristor and fuse) on the input side triggered by an overvoltage comparator on the output side.

author: Jeroen3
author_rank: Super Contributor
timestamp: April 30, 2016, 08:56:49 pm
content: Most basic way is a big 1500 W TVS diode (SMCJ5.0A) and a fuse (or PTC).

author: uncle_bob
author_rank: Unknown
timestamp: April 30, 2016, 11:44:54 pm
content: HiThe old school approach is to put a monster SCR on the beast and fire that when the output goes above 5.5V. Hopefully it is rated for enough of a surge to take out the up stream fuse. Circuits range from a dead simple two resistors on the SCR gate to far more elaborate approaches. They still create a mess. Since it's a race between the fuse and the surge current rating on the SCR, you more or less are finding out which supplier was lying to you about their part.Bob

author: user1235423643
author_rank: Regular Contributor
timestamp: May 01, 2016, 07:35:46 am
content: the output (UBS )5v needs to start around 5v while the current will be anywhere from 100ma to 2.5athanks

author: uncle_bob
author_rank: Unknown
timestamp: May 01, 2016, 01:02:03 pm
content: Quote from: user1235423643 on May 01, 2016, 07:35:46 amHiIt's the "interesting" current at startup on some of these low cost switchers (not much of a soft start) that drives you to a pretty big fuse on the input. That fuse might be 4X larger than you would first guess. Your OVP scheme needs to pop that fuse ... thus it can get pretty big. Yes, there are a lot of variables and they all get into this. Since you don't have much design control over an eBay regulator board, you live with what you get.Bob

author: user1235423643
author_rank: Regular Contributor
timestamp: May 01, 2016, 03:31:29 pm
content: this is what we are talking abouti dont think fuses will work to protect voltage spike in a blow condition.http://www.ebay.com.au/itm/CC-CV-Voltage-Regulator-Automatic-Boost-Buck-Converter-4-35V-to-1-25-25V-LM2577-/141658672421?hash=item20fb83cd25:g:LxcAAOSwv0tU8XPp

author: uncle_bob
author_rank: Unknown
timestamp: May 01, 2016, 03:40:52 pm
content: Quote from: user1235423643 on May 01, 2016, 03:31:29 pmHiA brute force approach will indeed protect the load with that sort of board. Consider a 20A fuse on the input and a > 20A SCR on the output (parallel with the load). The SCR fires when the output hits (say) 5.5V. While it's on, the output is pulled to near zero volts. The board may catch fire. The fuse may or may not blow. The output will go to zero ....Bob

author: user1235423643
author_rank: Regular Contributor
timestamp: May 02, 2016, 03:11:54 pm
content: not sure i understand? 20a fuses?

author: macboy
author_rank: Super Contributor
timestamp: May 02, 2016, 03:57:47 pm
content: Quote from: uncle_bob on May 01, 2016, 03:40:52 pm20A ?!?! With a 12 V input, that's 240 W input capability. With 5 V on the output, and a maximum current of 2.0 A, that's 10 W of output power. Re-examine your fuse choice.

author: uncle_bob
author_rank: Unknown
timestamp: May 03, 2016, 01:02:30 am
content: Quote from: user1235423643 on May 02, 2016, 03:11:54 pmHiTake a look at how these beasts pull current at startup. It's not at all pretty.Bob

author: Dave
author_rank: Super Contributor
timestamp: May 03, 2016, 05:09:37 am
content: No. No no no.You don't pick the ampacity of a fuse for the turn-on surges. You pick a fuse that is slow enough not to burst immediately on the inrush surge (dive into the datasheet and look at the I2t ratings). 20A fuses would be absolutely insane for a circuit that draws 1-2A when operational.

author: Zero999
author_rank: Super Contributor
timestamp: May 03, 2016, 07:50:46 am
content: Quote from: Dave on May 03, 2016, 05:09:37 amIndeed. I'd recommend a PTC resistor because it's resetable and takes a long time to blow.

author: uncle_bob
author_rank: Unknown
timestamp: May 07, 2016, 01:19:08 am
content: Quote from: Dave on May 03, 2016, 05:09:37 amHiPut a slow blow fuse in series with a crowbar limiter and see what happens sometime ... it's not pretty.Bob

author: user1235423643
author_rank: Regular Contributor
timestamp: May 07, 2016, 12:53:27 pm
content: ok, so im still unsure why we are talking about fuses.i want to protect the output from going to input voltage in the chance of failurethe output is USB 5v anywhere between 100mah to 3a ampwhat i want to protect is VOLTAGE spike over 5v if the reg fails

author: uncle_bob
author_rank: Unknown
timestamp: May 07, 2016, 01:38:52 pm
content: Quote from: user1235423643 on May 07, 2016, 12:53:27 pmHiThe way you get a spike is when the regulator fails.When the regulator fails, the only solution is to clamp the output to ground.When you clamp the output to ground. You need a fuse to separate the input from the power source.Bob

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: May 07, 2016, 04:43:59 pm
content: Quote from: uncle_bob on May 07, 2016, 01:38:52 pmWithout the fuse whatever you are using to clamp the output to ground (e.g. a Zener) will burn out rapidly, and become open, thus no longer clamping anything to ground.

author: ez24
author_rank: Super Contributor
timestamp: May 08, 2016, 04:31:27 am
content: Quote from: Jeroen3 on April 30, 2016, 08:56:49 pmI do not see one at the OP desired output voltage ?? but I could be not seeing right(hope the 1500 w filter gets through this link)http://www.mouser.com/Circuit-Protection/TVS-Diodes/_/N-axfz1?P=1yw7wqm&gclid=CjwKEAjwpLa5BRCTwcXS6_rpvC4SJACTDQMMFKek5vE1DEn883Roz71pYX0ulss3uIlWX-JEFYs-MBoCft3w_wcB

author: uncle_bob
author_rank: Unknown
timestamp: May 08, 2016, 11:51:36 am
content: Quote from: FlyingHacker on May 07, 2016, 04:43:59 pmHi.... and ...If you want the regulator to run fine at 5.25V, but kill the spike completely at 5.5V, there is no zener that will do that. Either you use one that is to low in voltage (and pulls current all the time) or one that is to high voltage (and starts at 5.6V, but does not fully clamp 6.0V).Bob

author: user1235423643
author_rank: Regular Contributor
timestamp: May 08, 2016, 03:06:44 pm
content: so can someone confirm the best way and simple to keep the voltage at 5v in the case the reg blows or failshttp://www.ebay.com.au/itm/CC-CV-Voltage-Regulator-Automatic-Boost-Buck-Converter-4-35V-to-1-25-25V-LM2577-/141658672421?hash=item20fb83cd25:g:LxcAAOSwv0tU8XPp

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: May 08, 2016, 03:51:35 pm
content: This PDF is the manual, with schematic, for the old Lambda Overvoltage Protectors from Lambda power supplies. Lambda is one of the best names in power supplies, producing supplies for the likes of Agilent/Keysight/HP and others.This schematic uses some older transistors, but the idea is the same. Of course it still needs a fuse upstream...https://www.surplussales.com/Semiconductors/pdf/ps-lmov-2.pdfEdit: file was too big, link included.

author: ez24
author_rank: Super Contributor
timestamp: May 08, 2016, 07:53:04 pm
content: Since the OP keeps saying "simple" how about a linear regulator at the end of the buck?Seems that the buck can be set to give 5v at the output of the LDO and then it would stay there if the buck goes to 12v ??I think there are LDOs designed to reduce ripple from bucks so it would be a win win (I think)

author: uncle_bob
author_rank: Unknown
timestamp: May 08, 2016, 09:08:56 pm
content: Quote from: user1235423643 on May 08, 2016, 03:06:44 pmHiSCR + 2 resistors + fuse. The fuse is not optionalBob

author: user1235423643
author_rank: Regular Contributor
timestamp: May 12, 2016, 08:41:18 am
content: so far the most simple idea is to use a 5v reg. after the buck. remember its a $3 unitif the buck goes high and feeds 12v in to the 5v reg it will get hot and cook but it should then break the circuit before letting more then 5v in.??

author: ez24
author_rank: Super Contributor
timestamp: May 12, 2016, 08:49:59 pm
content: Quote from: AcHmed99 on May 12, 2016, 04:45:20 pmI searched Aliexpress to see how much a solid state fuse costs and could not find any. Then I did a Google search and came up with this name "Resettable fuse". Aliexpress sells 10,000s of these for about 25 cents apiece. Cheap and simple.But they are current based, right ? The OP does not want 12v, he says nothing about current. I think we are back to a LDO but that is not 100% guaranteed, because if it is "simply" hooked up, there is a chance it could fail and pass through the 12v (per a Google search).You can increase the reliability with lots of external components as seen in the LDO datasheets.But then it is not "simple" anymore.My guess there is NO "simple answer" to the OP's question with great certainty.If I were to do this, I think I would determine the current under normal conditions and insert a resettable fuse. I believe this is "simpler" than a LDO. You just need a set of fuses to use with different circuits.How about use a buck -> LDO -> resettable fuse (seems pretty safe ?)and the LDO should reduce some ripple. Does this meets the OP's requirement?

author: uncle_bob
author_rank: Unknown
timestamp: May 12, 2016, 10:19:55 pm
content: Quote from: ez24 on May 12, 2016, 08:49:59 pmHiIs the LDO cheaper than a SCR? You will need bypass caps on the LDO. A pair of resistors is all you need with the SCR. Both work with the same fuse.Bob

author: uncle_bob
author_rank: Unknown
timestamp: May 13, 2016, 01:23:32 am
content: HiThe problem with an "input cut" without an output clamp is that the regulator has fried. It will try to convert whatever energy there is in the input bypass caps into output voltage in a big hurry. Since at the trip point you already are (by definition) out of spec, the net result is not going to be pretty. That's why just about every "supply protector" out there has used a clamp approach. The expensive part is $0.59 in quantity 10 at Mouser, good to 120A for 10 ms (which is plenty of time) to trip a fuse. Everything can be sized so that a normally operating regulator has no issues, regardless of how awful the soft start or how big the bypassing. A PTC fuse would run just a bit less than the SCR.Bob

author: ez24
author_rank: Super Contributor
timestamp: May 13, 2016, 01:30:02 am
content: Quote from: AcHmed99 on May 13, 2016, 12:07:55 amBet this does not meet the OP's requirement of simple.Simple, best, low cost, mean different things to different people. So for fun I am going to start a vote on the least components needed to protect a buck. I hope there will be no confusion over a number.I tried to find a SCR circuit with 2 resistors and could not.

author: uncle_bob
author_rank: Unknown
timestamp: May 13, 2016, 01:35:39 am
content: Quote from: ez24 on May 13, 2016, 01:30:02 amHiSCR with two resistors:Cathode goes to groundAnode goes to supply outputR1 and R2 are in series. One end to ground, other to supply output.Junction of R1 and R2 goes to the SCR gate.Fiddle R1 and R2 to set the trigger point, it will be around 0.6V for most SCR's.Bob

author: user1235423643
author_rank: Regular Contributor
timestamp: May 14, 2016, 11:13:17 am
content: not sure i understand how a fuse keeps the voltage under 5v???if i have a device they can draw max 100mah 5v, plug into a output that should be able to provide 5v 0-2amphow can a fuse work

author: ez24
author_rank: Super Contributor
timestamp: May 14, 2016, 07:29:46 pm
content: Quote from: user1235423643 on May 14, 2016, 11:13:17 amI think people mean that after the DUT fails (from over voltage) further damage (fire) will be prevented by a fuse.Wish Bob would include a sketch of his idea. I think it would win the OP's question (simple). I could not find an example by a G search.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: May 15, 2016, 02:11:11 am
content: Actual Overvoltage protector commercial product schematic in the last pages of this manual for the Lambda Overvoltage protector I posted earlier:https://www.surplussales.com/Semiconductors/pdf/ps-lmov-2.pdfOf you don't want to build it then just buy one of these off eBay. It will work on any power supply.Then you put a fuse on the line input of course.

author: ez24
author_rank: Super Contributor
timestamp: May 15, 2016, 02:40:38 am
content: Quote from: user1235423643 on April 30, 2016, 08:30:18 pmOP - did someone answer your question ?

author: uncle_bob
author_rank: Unknown
timestamp: May 15, 2016, 01:22:17 pm
content: Quote from: AcHmed99 on May 14, 2016, 02:15:15 pmHiThe solution to the fuse / SCR issue is to use a pretty big SCR. Fortunately they aren't really expensive. The heat sinking required is fairly modest as long as the fuse blows quickly. A slow blow fuse is not a good idea in this respect. That's why most designs use a fairly large (current rating) fuse rather than a slow blow. The bigger "fast" fuse still delivers less of a power pulse to the SCR than the lower current slow blow (it's about time ...).Bob

author: Monadnock
author_rank: Contributor
timestamp: May 15, 2016, 01:52:29 pm
content: The ebay listing says that it is short circuit protected. Have you tried turning the current limit pot all the way down to see if it will survive a short under that condition? I realize you may have to sacrifice a unit to do this test. What is the part number of the IC that is used? I couldn't tell from the photos in the listing.

author: ez24
author_rank: Super Contributor
timestamp: May 15, 2016, 06:02:07 pm
content: Quote from: Monadnock on May 15, 2016, 01:52:29 pmSounds like OP has sacrificed many already:QuoteMaybe we have lost the OP since no response on solutions given.Remember the key word: "simple"As someone said "ebay", maybe this (if you can figure it out)http://www.ebay.com/itm/Voltage-Tester-Monitor-Charge-Discharge-Over-Under-Voltage-Overload-Protect-/262339302180?var=&hash=item3d14a41324:m:mavlGfqFqK5EljOd4VbQwngNot the best but maybe the most simple, just hook up wires.Another maybe (anyone can get through this one?)http://www.ebay.com/itm/Voltage-Control-Relay-Timer-Delay-Switch-Overvol-Tage-Under-Voltage-Protection-/351582363815?hash=item51dbf120a7:g:SDgAAOSwsFpWTIK1

author: Monadnock
author_rank: Contributor
timestamp: May 15, 2016, 09:39:23 pm
content: Quote from: ez24 on May 15, 2016, 06:02:07 pmI was just wondering if the unit came with the current limit pot set to max, and if the unit would fail in that condition, but if the current limit was set to something less than max, if it would survive.

author: user1235423643
author_rank: Regular Contributor
timestamp: May 16, 2016, 04:54:27 pm
content: has anyone answering this post every used one of these buck converters? because it does not seem like these answers are directly relevant to the question.SIMPLE way to protect the load from over voltage if the BUCK fails... another inline reg is the best answer so far.i dont understand why people talk about fuses, please dumb it down for me if im missing something. its not current we need to block its voltage over 5vbuck 12v > 5v usb. output 0-2amp.if i plug in a device that can take a MAX 5a 100mah input and the buck dies and feeds 12v... then ... boom

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: May 16, 2016, 06:35:03 pm
content: The reason people keep mentioning fuses is this:First you have your circuit that is supposed to get 5V.The buck converter fails and passes 12V through to your project.You put a overvoltage protector on the output of the buck converter (like the SCR circuits described, or you buy a pre-made Lambda Overvoltage protector off eBay and use it). You set this to trip at 6V.When the voltage goes high the overvoltage protector essentially shorts out the output of the buck converter. This takes the voltage down to practically zero volts. However, at this point the overvoltage protector circuit is now getting the full output coming from the buck converter. Since the converter is not working right the overvoltage protector is now shorting out a 12V source at whatever current the source can put out. So the overvoltage protector will eventually overheat and fail (this could be miliseconds, seconds, or minutes depending on the values). Once the overvoltage protector fails then it is no longer shorting the output from the buck converter, and thus all this power (and the high voltage again) gets dumped into your project.So you put a fuse in line that will blow when the overvoltage protector kicks in. The overvoltage protector, by shorting the output, will draw a lot more current than your project normally would, and this blows the fuse. Once the fuse is blown no current flows and everything is safe (except your fuse).So the overvoltage protector is to protect your circuit from too much voltage. The fuse is to protect the overvoltage protector from too much current (because if the overvoltage protector gets too much current it fails open and your project gets the high voltage again).Hope this helps.

author: uncle_bob
author_rank: Unknown
timestamp: May 16, 2016, 08:11:58 pm
content: Quote from: user1235423643 on May 16, 2016, 04:54:27 pmHiIf a second regulator is the answer then *why* use the buck regulator? When I use the buck regulators (and I use them a lot) it is because I need to. If you don't need the efficiency and lack of giant heat sink that the switcher provides, then why use one at all?Is the efficiency difference between the two devices apparent? Maybe not.If I need 3.3V at 3A and have 12V, a linear regulator will burn off 3 x (12 - 3.3) = 26.1 W. That's a big heatsink.If I use a switcher that is 90% efficient, there is 9.9 W in the load and roughly 1 W in the regulator.If I put in a switcher at 4V and follow it with a linear, that regulator will dump 2.1W. Your efficiency is now down around 70% and the linear needs a heatsink.The linear *and* the switcher both can fail. There is noting magic about it, they can fail. In the above example there is a lot of power in the linear. It gets mighty hot. It can fail. It also costs $$$$. You need bypassing and all the other stuff.Surprisingly there *is* a generic solution. People have been building power supplies for a *long* time. They have been failing for a *long* time. The solution is an output clamp. When the output goes out of range you pull it to ground with something that will handle the maximum power available. The device does nothing except clamp. It does not run power / get hot all the time. Your output protection needs to be *more* reliable than the rest of the circuit not less reliable. If the protection is the hottest part in the circuit, you do not meet this requirement.You *can* simply put a clamp in with no fuse. The output shorts to ground and that does accomplish the task. If you do this, whatever the upstream source is will put maximum current into the clamp. If that is a 12V 100A rectifier, it likely will put about 2,500A into the crowbar. You *can* size the crowbar to handle 1000A on a continuous basis without getting overly hot. The 120V circuit supplying the 12V rectifier would need to handle a 100 A load without blowing. The transformer and other parts in the bulk supply would have to be happy running into a short circuit.Much easier to spend the $0.23 on the fuse....With the fuse, crowbar fires, fuse blows. You have no output and you investigate. With the regulator, nothing much happens. There is no investigation. Everything runs really hot until the next part fails. In one case you have protection, in the other case you have a mess ...Bob

author: user1235423643
author_rank: Regular Contributor
timestamp: June 04, 2016, 04:32:26 pm
content: good explanation, do yo have any links to these items i can start looking at. thanksQuote from: uncle_bob on May 16, 2016, 08:11:58 pm

author: uncle_bob
author_rank: Unknown
timestamp: June 05, 2016, 01:38:29 am
content: Quote from: user1235423643 on June 04, 2016, 04:32:26 pmHiLook for OVP module on the auction sites. Buy a few of them and tear them apart.Bob

author: johnh
author_rank: Regular Contributor
timestamp: June 05, 2016, 03:56:40 am
content: Where all the marking will be erased

author: uncle_bob
author_rank: Unknown
timestamp: June 05, 2016, 11:42:36 am
content: Quote from: johnh on June 05, 2016, 03:56:40 amHiJust like the information on the non-existant schematics ....Why you ask? There's not much to a power supply. Just about all the work in designing one appears to be copying / tracing out somebody else's circuit. Eventually the schematics disappear in order to make that process a bit more difficult.Bob

author: batteksystem
author_rank: Regular Contributor
timestamp: June 05, 2016, 12:16:11 pm
content: Quote from: user1235423643 on May 16, 2016, 04:54:27 pm1.Why use a max. 2A converter to drive a max. 5A load in the first place?2. Another reg. would not help, additional reg. can also die too if something go wrong.My suggestion: Use an adequate rated converter to handle the load in the first place.

author: user1235423643
author_rank: Regular Contributor
timestamp: June 07, 2016, 03:38:24 pm
content: OVP module, nothing comes upany1 have a link to a ebay item?

author: uncle_bob
author_rank: Unknown
timestamp: June 07, 2016, 11:05:28 pm
content: Quote from: user1235423643 on June 07, 2016, 03:38:24 pmHiThird hit on a Google search for "overvoltage protection module":http://www.aeroelectric.com/DIY/DIY_Crowbar_OVP_F.pdfIt is overdone, but it gives you the idea.Bob

author: ez24
author_rank: Super Contributor
timestamp: June 07, 2016, 11:30:50 pm
content: Quote from: user1235423643 on June 07, 2016, 03:38:24 pmTry "Overvoltage Protection" stuff comes up, but not sure if helpful. Maybe a useful book.