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I have planned to build a variable voltage DC power supply based on the LTC3780 DC-DC 5-32V converter. I guess you are familiar with the converter, but I am attaching and image for illustration:

TZT-LTC3780-DC-DC-5-32V-to-1V-30V-10A-Automatic-Step-Up-Down-Regulator

I used an AC/DC adapter (12V, 4A) on the input. Everything worked, so I replaced the default trimmers with potentiometers. It should have a 500kΩ pot on Vout set and a 200KΩ pot on current limit set.

I tested it and quickly realized that I am getting just 13V output max. (with 12V input). I made a stupid mistake - I switched the pots, so 500kΩ was on current set and 200kΩ on Vout set.

So I connected the potentiometers as they should be and everything worked fine, for a while. Then I saw the green "OK" LED was randomly blinking from bright to nearly off (which indicates high and low Vout). I disconnected the input, connected it again and realized that the red FAULT diode is on and the LTC3780 IC is geting REALLY HOT.

I desoldered the potentiometers and replaced them back with original trimmers, just to be sure there is no additional failure there. But nothing changed - FAULT is still on and the IC gets hot in a second.

Is there anything I could inspect to identify the problem, or did I just fry the LTC3780 by using the wrong pots? I will be happy for every suggestion how to possibly fix it, as I already made nice wooden box for it... :(

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    \$\begingroup\$ What is your circuit? what does your layout look like? What load were you testing it at? Is there a decent specification for the part you copied? Is the part you copied from a reputable supplier or did you copy some ebay/amazon trash? \$\endgroup\$
    – Andy aka
    Commented Apr 29, 2020 at 16:28
  • \$\begingroup\$ @Andyaka I testet it wit no load, just multimeter on output. So there is no need to draw a circuit. Just 12V input and voltemter on output. I do not have any datasheet for that particular device. And regarding the "supplier" as you suspect, it is "aliexpress trash". Beside that, it worked properly quite a while unless I started my modifications, so I believe the device itself is not a problem here. I count on experience of community with this device, maybe someone had the same problem... \$\endgroup\$
    – Oki
    Commented Apr 29, 2020 at 16:37
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    \$\begingroup\$ Ah you count on experience eh? My experience is this: only copy designs that have a proven pedigree and make sure you can justify the design based on what you find in the data sheets for the parts used in the design you copy. As for the circuit - I presume you do not know what the circuit is because you are evading the question. If someone else has the same problem then it's more likely to be because the original design is suspect. \$\endgroup\$
    – Andy aka
    Commented Apr 29, 2020 at 16:45
  • \$\begingroup\$ Welcome to the site. Please can you edit your question and add the schematic for your board. Without that, it's impossible to answer the question. The schematic editor here is very easy to use. Thanks. \$\endgroup\$
    – TonyM
    Commented Apr 29, 2020 at 17:07
  • \$\begingroup\$ @TonyM I am afraid I am really not able to re-draw the schematic for whole board as it has "ton" of components. I have not even found a schematic for that particular product, just "typical application" circuit in LTC3780 datasheet, which obviously differs. So I guess this question will remain unanswered. \$\endgroup\$
    – Oki
    Commented Apr 29, 2020 at 17:42

2 Answers 2

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It's unlikely that just mixing up the pots blew up your supply. Mixing up the connections might have done so but is more likely to have done so straight away rather than working for a while.

Looking on my local Amazon site one listing for this device (under a different part number) has 7 reviews. 3 owners reported their devices failed completely and 2 more reported failure to fully meet the claimed specification. So your device may have just failed because of marginal design, rather than anything you did.

If you want to try repairing it yourself you can try tracing the circuitry back from the pcb. It is likely to be based on the circuit in the datasheet (which you seem to have found) with the addition of some pots to adjust the voltage and current limits.

Alternatively you could buy a replacement module offering favourable reviews from a site in your country. It won't be as cheap but it will be more likely to work. You could run the module on load for a few days to a week to confirm it works before making any changes to it.

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  • \$\begingroup\$ The board I bought had tens of positive reviews. The most of the "FAULT"cases I googled is because undervoltage trimmer is set that the device shows FAULT by default. It has to be adjusted and then it works fine. Unfortunately, I have not found such a device in some local store. So I am considering buying the same device and LTC3780 ICs for replacement of old one. With my "skills" in electronics, the new device will arrive faster then I would trace the circuit from the PCB (which would solve nothing I guess). But I am afraid I will fry it again, as I do not know what was the prior error... \$\endgroup\$
    – Oki
    Commented Apr 29, 2020 at 18:14
  • \$\begingroup\$ "tens of positive reviews" Better online vendors will make some attempt to ensure reviews are posted by genuine purchasers, rather than by the seller. \$\endgroup\$
    – Graham Nye
    Commented Apr 29, 2020 at 18:23
  • \$\begingroup\$ "I am considering buying the same device" As you wish but note that my local Amazon site is offering odds of 2 good ones out of 7 purchases. \$\endgroup\$
    – Graham Nye
    Commented Apr 29, 2020 at 20:07
  • \$\begingroup\$ Well, I also found one, on local arduino shop. It is the same device (probbably from the same source) only 5x more expensive... So I will give it a try witch cheap one again, I believe the device is OK as "everybody" is doing low-cost lab bench power supply using this. I have found many projects, linking the same device from amazon/eaby/aliexpress, so I refuse to believe the design itself is faulty. I have also checked amazon and the low-rating reviews mentioned physical damage of the board, or FAULT led because of under-voltage trimmer. \$\endgroup\$
    – Oki
    Commented Apr 30, 2020 at 4:23
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I also messed up with this module and I found below link with a user-made schematic and explanation of how it all fits together. Just paying it forward...

https://wiki.beyondlogic.org/index.php?title=WD2002SJ_LTC3780_Synchronous_Buck_Boost_Converter_Ebay_Automatic_lifting_pressure

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  • \$\begingroup\$ Can you expand this angle put the rolling information in the post? \$\endgroup\$
    – Voltage Spike ♦
    Commented Feb 8, 2021 at 14:20

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