Having problems with a step up converter - Page 1
Forum section: electronics / beginners

author: Moriambar
author_rank: Unknown
timestamp: October 07, 2018, 08:50:55 pm
content: Hi there.I bought some adjustable boost converters and, while trying them out, I found out that the out voltage is always ≤ than the input voltage. Since the purchase was done on the internet (chinese market), I then tried and bought the item somewhere else, but also from china.Well, guess what… I had a different product but the same result. I inspected both products and it had it all: schottky diodes, IC, capacitors, inductor…So what I am saying is: have I been bamboozled twice or, in order to make a step up converter work, do I need to provide it some kind of load?Thanks

author: hsn93
author_rank: Regular Contributor
timestamp: October 08, 2018, 07:19:34 am
content: there is no enough information, picture, drawings, or product name at least?

author: Moriambar
author_rank: Unknown
timestamp: October 08, 2018, 07:24:18 am
content: Quote from: hsn93 on October 08, 2018, 07:19:34 amHi.Yes, sorry;thisis the ebay one (which I've thrown away thinking it was faulty)whilethisis the other one.Thanks

author: mariush
author_rank: Super Contributor
timestamp: October 08, 2018, 07:38:41 am
content: We can't see the second one since you're linking to the order page, and only you can see that. Plus, we may need an AliExpress account to see that anyway, and not everyone feels like creating an account just to help you.As for the first link, it should be genuine step up dc converter. It uses a MT3608 IC (as it says on the pcb) which is a step-up regulator IC. You can see the datashet here:https://www.olimex.com/Products/Breadboarding/BB-PWR-3608/resources/MT3608.pdfMaybe you wired it wrong. Input voltage (up to 24v) was supposed to go on VN+, ground on VN- , you adjust the output voltage using the trim potentiometer, it's not rocket science.

author: Moriambar
author_rank: Unknown
timestamp: October 08, 2018, 07:43:23 am
content: Quote from: mariush on October 08, 2018, 07:38:41 amThat's what I did, but got what I said, namely an out voltage lower than the input.Here is thegenuinelink to the aliexpress product. If you can help me there too, I'd be grateful, otherwise no problem, I'll try search around for other components. Perhaps I've been unlucky with a defective component (ebay) and bought something shady (aliexpress). I'll try again thenCheers!

author: mariush
author_rank: Super Contributor
timestamp: October 08, 2018, 08:00:23 am
content: Same story, only that board is supposed to use a SX1308 chip, datasheet is here:https://www.sunrom.com/get/364610(it's probably same chip as MT1308, or rebranded or something)In worst case scenario, you should get same voltage as input voltage minus some losses (less than 1v) or if everything's right, a higher voltage (as configured by the potentiometer)My advice is to check the datasheet, you have there the example circuit (typical application) on the first page. Then, compare that circuit with what you have on your board, make sure all the connections are right. One of the resistors in the typical application example is the potentiometer (R2 if it's like in your picture) on your board, everything else should be pretty much like the example circuit.Make sure the potentiometer isn't faulty, measure the resistance using a multimeter , measure the other resistor (R1, looks like 1000 ohm in your picture)The output voltage is always Vout = Vref x ( 1 + r1 / r2) where Vref is 0.6v on these chips (see page 6 of datasheet) <--- on your board, R1 and R2 may be numbered the other way, you may hve R2/R1)In the pictures, the fixed resistor has 102 written on it (10 with 2 zeroes after it, so 1000 ohm ) and your potentiometer is 103 so 10 with 3 zeroes, or 10 kOhm so at the highest potentiometer value you should have Vout = 0.6 x ( 1 + 10000/1000) = 0.6 x (1 + 11) = 0.6 x 12 = 7.2vDid you try powering such board from let's say 2 AA batteries (~ 3v) and see if that gets boosted to around 5-7v or did you try only with some higher voltages like 12v? if the potentiometer and resistor are like in the pictures it could explain why you see low voltages, since the maximum output seems to be around 7v.So maybe they used the wrong resistor value or a potentiometer that's too low in value (they used10 kohm instead of using let's say 50kohm potentiometer)Check the circuit and try to figure out the maximum voltage using that formula ... ratio between resistance value + 1 , and everything multiplied by 0.6 gives you the output voltage.ps. Oh , do keep in mind that these chips are not magical and capable of doing what the text says.I mean those things can be accomplished but not under any condition.for example the chip will run with input voltage between 2v and 24v and will output up to 28v and up to 2A but not all at the same time. It probably won't output 24v if the input voltage is only 3v, or if it actually does that, the maximum current will probably be much lower than 2A, maybe 100mA or something like that.The maximum of 2A is more like .... give it 16v input voltage, set the output voltage to 20-24v and you'll get 2A of current.Also the maximum current and how wide, how big the difference between the input voltage and output voltage will depend on the inductor chosen, which can be between 4.7uH and 22uH ... in the pictures i see it as 4.7uH .... in theory that makes it more efficient but may not make it capable of outputting a lot of current. Depending on input and output voltage difference and current desired, bigger inductor may be required for the chip to actually do what it advertises.Also these boards don't use exactly the best components, there's other parameters parts need like "low DCR" and saturaton for inductors... i doubt the guys making these 1-2$ boards really picked the most suitable inductor for a wide range of output voltage and current. Most likely they picked whatever satisfied the minimum requirements and had the best price when bought in 10k pcs quantity.

author: Moriambar
author_rank: Unknown
timestamp: October 08, 2018, 09:19:42 am
content: Quote from: mariush on October 08, 2018, 08:00:23 amSo, I get the worst case scenario by nowQuoteThis I will have to check in the evening when I'll be back from workQuoteI used a psu to power it, and tried it on various ranges, from 4 to 12V input, having the output slightly lower than before (as you mentioned in the worst case above)QuoteI will do it.QuoteYes, I know about the fact that not all can be achieved at the same time. My current demands are, nevertheless, small and, anyway, with only my multimeter as a load, I still cannot get a proper voltage.Anyway thank you for your detailed and patient answer, I will get back to this as soon as I get home from work!

author: Moriambar
author_rank: Unknown
timestamp: October 08, 2018, 06:57:57 pm
content: So I analysed the circuit. Basically what I get is that the fixed resistor is 200 Ohms (yes not kilo), while the potentiometer is 10k. The voltage I have on the pot pins is basically my input voltage while the schottky drop of around 0.11V is what I measure on the third pin. My output is exactly the input MINUS the 0.11V drop.Looking at the datasheet and at the circuit there seem to be some missing connections (I cannot have continuity between pin 6 and the diode and pin 3 and gnd).I think this is it.Thanks

author: mariush
author_rank: Super Contributor
timestamp: October 08, 2018, 07:10:25 pm
content: pin 6 of the chip is NC (not connected) so it shoudn't be used for anything.pin 3 is feedback, to that pin goes the voltage between the resistor and the potentiometer ... a trace must go from there to the resistor and to the potentiometer. the other end of the resistor should go either to ground or to the output voltage (which should be connected directly to one end of the diode)can you post a nice clear picture of your board? (if possible use macro mode of a digital camera?)Don't forget there's some traces on the back side also.. well at least in the ebay pictures.

author: Moriambar
author_rank: Unknown
timestamp: October 08, 2018, 07:24:38 pm
content: oh boy, no digital camera and no macro lens. The only thing I have is my magnifying glass I use to inspect soldering, and its embedded led. I tried my best. Unfortunately I had to upload them on a third party website (imgur) since they're too big to be featured here (1.7Mb per photo).Here's teh link to the albumhttps://imgur.com/a/7MPFQKEI hope it is ok.Thanks a lot

author: MarkR42
author_rank: Regular Contributor
timestamp: November 20, 2018, 12:16:45 pm
content: If it is the SX1308 (it looks like it), then they are very good. I've tested them.The small pot has about 20 turns on it, and it doesn't have an easily detectable end-stop.1. Connect the board to a power supply of NO MORE than 5v. If input voltage is >7v and the output is set too low, then something bad happens and the diode often catches fire.2. Connect meter to output3. Turn the pot anti-clockwise - it takes something like 10 turns before the voltage starts to rise significantly, then it starts going up quickly.They are always shipped with the voltage set at minimum, it takes many turns anti-clockwise before the voltage rises. This is normal.Once it is set at the desired voltage, I *think* you can use a higher supply, but always lower than the set voltage.I also tried replacing the pot with a pair of SMD resistors and that worked ok too.Changing the inductor looks possible, the one they ship is quite high (profile).

author: Moriambar
author_rank: Unknown
timestamp: December 02, 2018, 09:56:49 am
content: Hi. I tried what you suggest, adjusting from the bottom through the top of the range. nothing change, I just have that schottky voltage drop and that's it.

author: spec
author_rank: Frequent Contributor
timestamp: December 02, 2018, 12:44:51 pm
content: Hi Moriambar,Seems like you are having a bad time with the cheap ebay boost switching PSU. Not sure why, because thousands have been sold so they should work OK.Your symptoms sound like the chip is locking out because it is not happy with the input supply characteristics.Can you describe, specifically, what you are supplying the boost converter with, and can you post a picture of your test set up?

author: Moriambar
author_rank: Unknown
timestamp: December 02, 2018, 12:50:55 pm
content: Quote from: spec on December 02, 2018, 12:44:51 pmHey, a problem from my part is why I posted here: I don't believe to bethatunlucky, it's easier I'm clumsy.Anyhow, I directly power it from my PSU, (VN+ or Vin on the… positive terminal, VN- or GND on the negative one) and attach the output terminals to my BM235. I'm not home thus I cannot provide pictures now, but my psu is an old TTi PL601, which I use normally without any problems and whose displayed voltages and current agree with the brymen.Since the connection is direct, do you still need the pictures?Thanks

author: spec
author_rank: Frequent Contributor
timestamp: December 02, 2018, 02:34:45 pm
content: Quote from: Moriambar on December 02, 2018, 12:50:55 pmQuote from: Moriambar on December 02, 2018, 12:50:55 pmAll good!Quote from: Moriambar on December 02, 2018, 12:50:55 pmNo, not needed thanks. You obviously know what is what.Don't be offended by the following basic questions/procedures- I am not trying to tell grandma how to suck eggs, but it is always worth checking/testing.BENCH PSU Are you sure that the current limit on the power supply is set to max? We once has a bench PSU that used to momentarily output 35V at turn on. It blew quite a few units randomly before we found out what was going on. I have experienced strange results with sophisticated PSUs and some equipment. Have you got another simpler PSU or a decent battery: two LiIon batteries in series would be good. There may be something about the lab PSU turn-on voltage profile that the boost converter does not like. Remove the boost module positive lead from the lab PSU. Turn the lab PSU on and set the output voltage to 6V and the current limit to max. If there is a current fold-back selector on the lab PSU turn it to off. While the lab PSU is still on, touch the positive lead of the boost converter positive to the positive terminal of the PSU.NEW BOOST CONVERTER, NEW POWER SOURCE Get a new boost converter, or at least one that definitely has never been connected to the bench PSU Connect a 220 Ohm, or there about, resistor across the output of the boost module. Connect a 2uF or greater low-loss capacitor directly across the input of the boost converter. Connect a 2uF or greater low-loss capacitor directly across the output of the boost converter. Connect the boost converter to a 5V to 9V DC source (not the bench PSU). Two 18650 LiIon batteries in series would be ideal.Let us know how you get on.

author: Moriambar
author_rank: Unknown
timestamp: December 02, 2018, 03:59:08 pm
content: Quote from: spec on December 02, 2018, 02:34:45 pmNever offended by someone genuinely offering to help. ThanksQuote1-> yep.2-> that's not the case, I think: I've been using the PSU for more than a year now (scored it from my boss, long story) and I never noticed anything wrong. It should've blown up something else if that were the case. It's superstable, for my applications, never ever had a problem with it.3-> this is not sophisticated, it's basically three dials. I do not own another PSU, although I wanted to build one of my own, but the project is lagging… long story short it's either that, a 12V transformer or any reasonable (<20) amount of AA. I never used LiIon batteries and I certainly do not plan to buy one just to test the boost converter4-> could be although it feels strange. With oscilloscope I probed a bit the PSU for fun but there's nothing wrong imo5-> ok6-> if I touch the converter the out voltage varies. If I keep it attached long enough (1-2s?) the output voltage flattens at around 0.1V below the PSU, as usual.QuoteI did not try thid because I do not own another PSU as told above.Thanks for your help

author: spec
author_rank: Frequent Contributor
timestamp: December 02, 2018, 04:20:38 pm
content: No probs.

author: dboris
author_rank: Newbie
timestamp: October 18, 2019, 04:45:05 pm
content: I got the same problem on 10 models.FB output is missing :Fix :Fix with new pcb :