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WARNING! Cheap step up / down converter - surprise ... XL6009

SylwekK 27498 56
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  • WARNING! Cheap step up / down converter - surprise ... XL6009

    I would like to share a fact related to the popular converter based on the XL6009, as in the attached photo. Its basic parameters are:

    - input voltage 3.8-30V,
    - adjustable output voltage 1.25-35V,
    - output current 3A (heater option :D ).

    I do not know if I came across such a series (I once bought a dozen) or if all of them have it, but there is a very dangerous problem associated with it. Theoretically, everything works beautifully, when I set the output voltage, e.g. 12V, it is quite solidly maintained, regardless of whether the input is higher or lower ... Well, is it really ok with the lower one?
    When operating with the voltage range given above, in fact everything is ok, but if we go even lower, we will be surprised ... I found it by accident, playing with the power supply with the mentioned converter connected. Well, when the supply voltage drops below 3.5V (I do not give hundredths on purpose, because there may be a dispersion of parameters depending on the copy), the system for a moment starts to oscillate (very low frequency), which lasts for about 2-3 hundredths volt then at 3.4V ... hop ... and we have a little over 54V at the output !!! The converter when idle took some single milliamperes, yes now consumes 400mA (!) . We lower the voltage further and at some point it begins to slowly drop at the output, to finish the work with an input voltage of about 2.7V (also preceded by oscillations).
    Another test - I loaded the output with a 1k resistor. The maximum voltage with it was just over 20V, and the resistor turned into a heater.

    Is there anything to be afraid of? Probably yes, but ... what I noticed ... In normal operation, when we disconnect the power from it and the inverter is still running on the energy stored in the capacitor, the problem does not occur at all, so when should you be afraid? And then, if someone connects, for example, a Li-Ion battery (3.7V) under it, and it discharges during operation, or if someone tries to power it from 2-3 batteries of sticks, which may also be a little bit here when discharged make trouble (actually they are not to blame ;) ). Just the converter "hangs" only when the input voltage remains within 2.7V-3.5V and it is so efficient that it allows the converter to "bounce".
    I think that this little info may be useful to someone if he suddenly finds that his device has gone up in smoke, and the inverter, after a quick inspection, will not admit that it is guilty. ;)

    Cool? Ranking DIY
    About Author
    SylwekK
    Level 32  
    Offline 
    SylwekK wrote 2753 posts with rating 2743, helped 82 times. Live in city Lipsko. Been with us since 2007 year.
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  • #2 17038019
    excray
    Level 41  
    Badly made project. Do not turn to the minimum values because the inverter will be damaged.
  • #3 17038193
    hv222
    Level 16  
    It is possible that a similar problem occurs in other converters. Many applications from the catalog notes suggest switching off the inverter when the input voltage is too low (Under voltage shut down), if such an input exists in the system. Once a similar Chinese module in buck configuration and with output current control broke the metallization of the plates a few times, giving me the maximum current. Since then, I avoid this type of modules, I prefer to pay extra and build something on the chips of well-known manufacturers.
  • #4 17038990
    krzysiek_krm
    Level 40  
    Presumably the manufacturer of the integrated circuit "forgot" to implement the UVLO function, the circuits of decent manufacturers have this function built in as standard, there is no need to use any external circuits.
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  • #5 17039036
    abart64
    Level 33  
    I checked the converter I also have on the XL6009, only a different PCB, blue and there is only one choke. There are no such symptoms. 12V set, to 3.5V Uz holds 12V, 3V is about 8V and then drops to voltage equal to Uz
  • #6 17039131
    SylwekK
    Level 32  
    @ abart64, isn't yours just a step-up by accident?
  • #7 17039135
    abart64
    Level 33  
    Well, it is by chance ... :)
  • #8 17039153
    SylwekK
    Level 32  
    Exactly. I did not notice a similar disadvantage in these, too. I wonder if the blue step up / down has the same or only the solder color of the mask changed.
  • #9 17039184
    abart64
    Level 33  
    And did you check it on another power supply or on a different power source? See how it is on short power cables.
  • #10 17039275
    SylwekK
    Level 32  
    One linear power supply, the second digital one, some cables around 40cm, the other around 70cm. I bet a design defect, because no other converter (I tested different) behaves like this.
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  • #11 17039296
    Urgon
    Level 38  
    AVE ...

    But this is a normal phenomenon, because this converter does not work in the standard configuration, but as a SEPIC converter. Simply after reaching the limit parameters, the second half of the inverter, i.e. the step lowering the voltage, stops working properly (the second choke is saturated), so the whole thing works again as a boost converter, but with an additional capacitor "on its way" to the diode ...
  • #12 17039394
    SylwekK
    Level 32  
    The phenomenon may be normal, I have never delved into the theory of converters, which does not change the fact that the converter can break the device if certain rules are not followed. It is all the more dangerous that it is rarely mentioned (at least I haven't seen such an effect so far), and converters of this type are very popular and willingly used in various projects.
  • #13 17039425
    Urgon
    Level 38  
    AVE ...

    Therefore, it is written in the parameters that the minimum voltage is 3.8V. The designer assumed that no one would exceed the boundary parameters and that anyone using these modules would ensure proper working conditions. So the whole topic and your claims to the inverter do not make much sense, because it is not the fault of the system, but yours. It's a bit like I have a grudge against the transistor manufacturer that I went beyond SOAR and the transistor chose the pope ...
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  • #14 17039441
    misiek1111
    Level 36  
    Urgon wrote:
    Therefore, it is written in the parameters that the minimum voltage is 3.8V. The designer assumed that no one would exceed the boundary parameters and that anyone using these modules would ensure proper working conditions.

    You are wrong and you contradict yourself. Since the designer assumed that the circuit would not work below 3.8V, then the circuit should be dead below this value, but it is alive and in an extremely entertaining way.
  • #15 17039451
    SylwekK
    Level 32  
    No, no, I have absolutely no complaints :) that's why I gave the basic parameters of work at the beginning. I just wanted to point out something that is not said much about these converters. Electronics are often experiences and combinations, that's why I just wanted to sensitize all combinators, what may end up playing with parameters outside the recommended range :)
    Oh, while browsing the offers, I also came across the exact same model of the converter (identical appearance, so it is highly probable that it is the same), where the seller gives the input voltage range from 3V ... What can it end with? ... I think it is known :)
  • #16 17039458
    Urgon
    Level 38  
    AVE ...
    misiek1111 wrote:
    Urgon wrote:
    Therefore, it is written in the parameters that the minimum voltage is 3.8V. The designer assumed that no one would exceed the boundary parameters and that anyone using these modules would ensure proper working conditions.

    You are wrong and you contradict yourself. Since the designer assumed that the circuit would not work below 3.8V, then the circuit should be dead below this value, but it is alive and in an extremely entertaining way.

    As it says on a gas cylinder that the maximum allowable pressure is 15 atmospheres, do you think it will explode if you try to raise it to 15.1Atm?
    The designer gave the parameters for the converter to work properly. Outside of their borders, it will not work properly, and eventually it will either stop working or elect a pope. The limit is not binary, because the components also have different parameters ...

    SylwekK wrote:
    Oh, while browsing the offers, I also came across exactly the same converter model (identical appearance, so it is highly probable that it is the same), where the seller gives the output voltage range from 3V ... What can it end with? ... I think it is known

    Are you sure? Maybe they changed the operating frequency or the values of the chokes to widen the range?
  • #17 17039461
    SylwekK
    Level 32  
    @ misiek1111, good point. The inverter SHOULD turn off, and why he does not do it and the manufacturer (seller) does not inform about the consequences is another story.
  • #18 17039981
    Bonifacy
    Level 24  
    Urgon, you may be right a little bit - but a little bit in my opinion. I have made a constant voltage (14V) power supply by chance with a 20k uF capacitor pack, for this I needed a regulated line (in total, the range of 5-12V I am interested in) and used a converter (a similar type only step-down) and although I knew about the supply voltage range, I received it this is as the voltage in which the converter works (so nominally 14V to in) but it is disconnected with all the luck - when the transformer is disconnected, the voltage remains on its filtering capacitors - which during discharging will give voltage in the forbidden range.
  • #19 17040211
    error105
    Level 14  
    SylwekK wrote:
    @ misiek1111, good point. The inverter SHOULD turn off, and why he does not do it and the manufacturer (seller) does not inform about the consequences is another story.


    There is also no information on my LPG cylinder that something will explode, does it mean that I can freely change the pressure inside? :)
  • #20 17040284
    Urgon
    Level 38  
    AVE ...

    Two notes from Bonifacy:
    1. With a buck converter, the output voltage will never be higher than the input voltage, so your circuit is safe.
    2. Assuming you have a SEPIC inverter instead of a boot, and it is loaded, if you use more than a few mA, the primary capacitance will be discharged below the inverter operating voltage before the secondary voltage increases dangerously.

    Also note the jump in current consumption to 400mA without load when the voltage is too low. The boost controller increases the PWM signal duty cycle as the difference between the output and input voltage increases, but in the SEPIC converter, an excessive increase will saturate the second choke, thus stopping it working like a choke in this system.

    It gets more interesting when we look at the XL6009 datasheet. This circuit works in the range of 5-32V. In addition, the voltage jump in the SEPIC configuration is also explained by the fact that the maximum filling is 90%, which means that at the moment of voltage regulation failure in the module tested by SylwekK, this module has already achieved this filling and ceases further regulation until the ULVO system is activated, which turns off the entire inverter.
  • #21 17040400
    Bonifacy
    Level 24  
    error105 wrote:

    There is also no information on my LPG cylinder that something will explode, does it mean that I can freely change the pressure inside? :)


    Nobody writes that you can connect whatever you want. A parameter that is too low should be secured, and too high should not be admitted to the system. Nobody wants to test this converter on 230AC.

    For your favorite example, LPG cylinders should also not be completely emptied, most controllers do not allow this to happen - but in the first and second generations it often happened, and now imagine that in 30% of cases where the gas is completely empty, it explodes? would such solutions be allowed for use?


    Urgon wrote:
    AVE ...

    Two notes from Bonifacy:
    1. With a buck converter, the output voltage will never be higher than the input voltage, so your circuit is safe.
    2. Assuming you have a SEPIC inverter instead of a boot, and it is loaded, if you use more than a few mA, the primary capacitance will be discharged below the inverter operating voltage before the secondary voltage increases dangerously.

    Also note the jump in current consumption to 400mA without load when the voltage is too low. The boost controller increases the PWM signal duty cycle as the difference between the output and input voltage increases, but in the SEPIC converter, an excessive increase will saturate the second choke, thus stopping it working like a choke in this system.

    It gets more interesting when we look at the XL6009 datasheet. This circuit works in the range of 5-32V. In addition, the voltage jump in the SEPIC configuration is also explained by the fact that the maximum filling is 90%, which means that at the moment of voltage regulation failure in the module tested by SylwekK, this module has already achieved this filling and ceases further regulation until the ULVO system is activated, which turns off the entire inverter.


    1.I know that I am not in danger of a different type of converter, but I also have a system plugged in for the regulated line only at the time of operation and using the main line (I have never had to turn off the power supply with the regulated line connected) - but this is a side topic

    2.In my opinion, such systems as XL6009 should be internally secured with the ULVO system or the converter module is already equipped with it (but from what I see, the price corresponds to the quality)
  • #22 17041591
    amator2
    Level 17  
    Good morning
    Please be very careful with cheap Chinese power supplies, I got a very similar one in an identical housing and also could not be loaded with 1A current. I was more scared when I found the video of his autopsy:
    https://www.youtube.com/watch?v=2DyejSzCEW0&t=335s
    Virtually any such power supply should be opened before plugging it in. I threw mine away and used the old company one.
    It is safer
    best regards
    Slawek



    ----
    Separated from the topic: Artificial load 150W (200W) - a review
    by gulson on 16 Feb 2018 22:13:25
  • #23 17043740
    redstonefire
    User under supervision  
    My step up converter behaves similar to the one described at the beginning of the topic. I give a voltage of about 3V (i.e. the one that is below the operating range of the converter) to the input and the output is 40V.
  • #24 17043861
    SylwekK
    Level 32  
    You will have the highest voltage on the edge of the transition from about 3.5 to 3.4V
  • #25 17049697
    mailover
    Level 11  
    Therefore, the seller should post the official text "This equipment is not intended for use by people with reduced physical, sensory and mental capabilities (including children) and by people who do not have adequate knowledge about the device"
  • #26 17337663
    Szyszkownik Kilkujadek
    Level 37  
    Thanks for the warning. It's worth keeping them in mind.

    However, I would like to draw your attention to an important point. Well, the manufacturer gives the nominal:
    SylwekK wrote:
    input voltage 3.8-30V,

    And the author of the topic warns against incorrect operation of the inverter below the rated values:
    SylwekK wrote:
    Well, when the supply voltage drops below 3.5V


    Likewise, Fiat 126p owners can be warned that their cars will be unstable at 200 km / h. ;-)
  • #27 17337685
    krisRaba
    Level 31  
    It does not change the fact that this is why UVLO was invented ...
    The warning is valid if the inverter can damage the output. Hardly anyone expects that when, for example, his inverter power supply is discharged, he will blow up his system ;-)
  • #28 17337736
    Szyszkownik Kilkujadek
    Level 37  
    @krisRaba I fully agree.
    I just want to point out that every designer should know that if the constructed device will operate outside the rated range, check how it will behave.
  • #29 17337746
    SylwekK
    Level 32  
    Szyszkownik Kilkujadek wrote:
    Likewise, Fiat 126p owners can be warned that their cars will be unstable at 200 km / h. ;-)

    I don't understand why all of your examples are over the high end. Every time the "more than" argument. It is understandable that in 99% of devices, whether electrical or mechanical, or even simply overeating donuts, will be harmful. On the other hand, how many situations are there in which it is harmful not to exceed the minimum range? Why was this topic raised? - just for this 1%.
  • #30 17337776
    Szyszkownik Kilkujadek
    Level 37  
    SylwekK wrote:
    Szyszkownik Kilkujadek wrote:
    Likewise, Fiat 126p owners can be warned that their cars will be unstable at 200 km / h. ;-)

    I don't understand why all of your examples are over the high end. Every time the "more than" argument. It is understandable that in 99% of devices, whether electrical or mechanical, or even simply overeating donuts, will be harmful. On the other hand, how many situations are there in which it is harmful not to exceed the minimum range? Why was this topic raised? - just for this 1%.

    But here you are, first person:
    When installing LPG to a car, always have gasoline in the fuel tank. Even if you only drive on gas and the car does not start with LPG immediately. In the absence of gasoline, the fuel pump will seize up.

    Another example? The aircraft manufacturer does not guarantee the correct operation of the engines if there is less than the recommended amount of fuel in the tanks.

    And what will happen if you fill with fuel with a lower octane number than the minimum recommended by the engine manufacturer? Well, it may not work properly.

    Next? If it wasn't, an example from the electrical industry: What will happen if you supply the motor with a voltage below the rated voltage and load it with the rated torque? It will be warm. :-)
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Topic summary

The discussion centers around the XL6009 step-up/down converter, highlighting a critical issue when operating below its specified input voltage range. Users report that while the converter functions well within the nominal parameters (3.8-30V input, 1.25-35V output), unexpected behavior occurs when the input voltage drops below 3.5V, potentially leading to dangerously high output voltages. Several participants note that this could damage connected devices, emphasizing the lack of under-voltage lockout (UVLO) protection in many cheap converters. Some users share their experiences with different models and configurations, suggesting that the design flaw may be common among similar products. Recommendations include using additional protective circuits and being cautious with low-voltage applications.
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