Do I need an additional diode in this use case - Page 1
Forum section: electronics / beginners

author: littlebill
author_rank: Regular Contributor
timestamp: December 22, 2024, 07:28:16 pm
content: I am using 2 of the attach designs in parallel. I am going to use droop resistors, but was also going to add another set of diodes for reverse protection, but I am correct in assuming the diagram indicates there is already a diode here to protect against that and another one is not needed?

author: littlebill
author_rank: Regular Contributor
timestamp: December 22, 2024, 07:49:02 pm
content: after additional studying it does appear I need them since PIN5 feedback is not protected I also assume voltage current here can make things go haywire. it appears the D1 is used to offload the current of the internal Diode in the xl6009 module. ( was getting conflicting information)would love some confirmation

author: Konkedout
author_rank: Frequent Contributor
timestamp: December 22, 2024, 07:56:25 pm
content: First of all, you really ought to post a datasheet link. Is this it?https://www.haoyuelectronics.com/Attachment/XL6009/XL6009-DC-DC-Converter-Datasheet.pdfSecondly, I cannot think of any good way to "connect two boost converters (or two boost converter ICs) in parallel" unless they have specific features to allow that. Malfunctions are almost definitely going to result.

author: tooki
author_rank: Super Contributor
timestamp: December 22, 2024, 08:02:16 pm
content: Quote from: littlebill on December 22, 2024, 07:49:02 pmUmmm, assuming that by “module”, you mean the little boost converter boards commonly found on AliExpress and co, then no, D1isthe diode in the module. The module contains the circuit shown. The XL6009 IC doesn’t contain a diode.I highly suggest reading up on how boost converters work, so that you find out what each component does.Why do you want to parallel them anyway? If you need more current, just get a boost converter that can supply what you need. If you want two for redundancy (i.e. each converter alone is capable of fully supplying your load), then you could use diodes to do it. There are special load switch chips that do it better though.I wouldn’t just parallel the outputs through resistors, you don’t know how the converters will react. As Konkedout said, converters that are safe to parallel typically have special features to synchronize the chips. But usually you just use a beefier converter (or one that uses an external MOSFET so that you can select it to whatever current you need).

author: littlebill
author_rank: Regular Contributor
timestamp: December 22, 2024, 08:11:19 pm
content: I have done more reading than you can imagine. I am not strong here. I did not expect to go down this path.I have a size and efficiency limitation at this point, another module would almost make me start over. I am not doing , it can burn to the ground at this point.https://soldered.com/productdata/2016/12/Soldered_XL6009_datasheet.pdfbased on this. there is an internal diode, unless I am not understanding the function block on page 4. unless those symbols don't mean diodes?in regards to the resistors, i have read the theory on it, im using .1ohm. I don't really care if its not perfectly balanced. I just need a bit more capacity to get the thermals down to a normal level.

author: Vovk_Z
author_rank: Super Contributor
timestamp: December 22, 2024, 08:29:29 pm
content: Quote from: Konkedout on December 22, 2024, 07:56:25 pm+1 to this. I am almost sure they want work togther in parallel, or with a battery at it's output.

author: littlebill
author_rank: Regular Contributor
timestamp: December 22, 2024, 08:35:07 pm
content: well I guess were going to find out. with diodes on the output . I am not entirely sure why it won't, the load just takes from the highest voltage. This is no different then in a rv where there are multiple chargers in line sometimes up to 4 at once, and I have never seen the magic smoke.

author: tooki
author_rank: Super Contributor
timestamp: December 22, 2024, 08:46:50 pm
content: Quote from: littlebill on December 22, 2024, 08:11:19 pmThe function block (figure 3) is on page 3, and it shows no diodes at all.The typical application schematic (figure 4) is also on page 3, and it shows one diode. It is NOT inside the chip.Again, when you say “module”, do you mean the little boards? Or are you using the word “module” to mean the XL6009 chip itself?Quote from: littlebill on December 22, 2024, 08:11:19 pmSo your problem is that you have one and it’s getting too hot?Quote from: littlebill on December 22, 2024, 08:35:07 pmRight. And since all the current to the load is flowing from the supply with the higher voltage, then the supply with the lower voltage won’t see any load at all, and the higher-voltage supply will continue to get hot.This is why I said diodes might work for redundancy (= power continues even if one converter fails), but not for balancing.Quote from: littlebill on December 22, 2024, 08:35:07 pmWithout knowing how those chargers are designed (and what they are being used for, and how) it’s impossible to draw any conclusions from that.

author: littlebill
author_rank: Regular Contributor
timestamp: December 22, 2024, 08:56:00 pm
content: I am using a module that is identical to the typical application circuit design on page 3. The function block confused me a bit, I am not sure what are the discrete components inside the IC, again didn't expect to have to get to this pointyes its too hot, these are listed at 4amps, obviously with forced cooling after some testing. I can't do active cooling.The resistors are suppose to keep the balance in checkThose chargers are generic battery chargers nothing special, and is done everyday by millions of people. Think solar, generator, converter, and alternator. etc..

author: tooki
author_rank: Super Contributor
timestamp: December 23, 2024, 03:20:45 pm
content: Quote from: littlebill on December 22, 2024, 08:56:00 pmThere are no discrete components inside an IC. “IC” means “integrated circuit”, precisely because it isnotcomposed of discrete components. But in terms of functional blocks, you see a bunch of opamps/comparators and a MOSFET forming the core of it.Quote from: littlebill on December 22, 2024, 08:56:00 pmThe chip is rated for a 4A switching current. First off, the switching current ≠ the maximum output current. The maximum output current is also limited by the choice of external components. Those little modules are often… let’s just say “optimistically marketed” and aren’t capable of their rated specs.The typical application schematic says right on it: output 18.5V/2.5A. Unfortunately the datasheet provides no engineering guidance whatsoever on how to design a whole circuit, so we can’t really calculate what the true output power of your module might be. (It might be possible to use the datasheet for the original part from TI that the XL6009 is a copy of. That happens to be the LM2577. The XL6009 is basically an improved version of the LM2577 with a 4A MOSFET instead of a 3A BJT in the original. Here’s the LM2577 datasheet, which is 4 times as long because it actually has some basic design guidance:https://www.ti.com/lit/ds/symlink/lm2577.pdf)I wouldn’t even bother trying to parallel them. They aren’t designed for that and the behavior might be unpredictable, and almost certainly won’t accomplish what you want.Either buy a converter with the output power you need (plus headroom!), or if your load can be divided, split it up and give part to each module. (E.g. if your load is 100 lamps, divide them into two groups of 50, and put each group onto its own module.)Quote from: littlebill on December 22, 2024, 08:56:00 pmYou might get lucky and it works. Or you may get unlucky and blow up everything. Hard to predict since they’re not designed for it.Quote from: littlebill on December 22, 2024, 08:56:00 pmThat doesn’t tell us any of the information we’d need to know. There’s no such thing, from an engineering standpoint, as a “generic” “nothing special” charger.

author: littlebill
author_rank: Regular Contributor
timestamp: December 24, 2024, 12:49:09 am
content: So to close this out.Tested it out, .56A output on module1 .95A output on module2. 23% different. My calcs were slightly off, prolly could have got it tighter. but the modules are now just warm vs burning. Glad I finished this out. I have several other modules on order, with different chips. but this was an odd ball design which put me in a bad place. the xl6009 are still smaller modules then everything else I looked at, and there was a size limitation that these barely fit, so outside of a TPS61088 which may be a better fit for future stuff. also ordered a LTC3780 sync rectifier board which should also run cooler.I would not have needed droop resistors if i bought boards with Constant Current control, just the diodes, these could have been dialed in much better, but eh we got there.Hope other readers find something useful from this.below thermals were taken at 25 minutes in. they had stabilized.