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
).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.
SylwekK wrote 2753 posts with
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Comments
Badly made project. Do not turn to the minimum values because the inverter will be damaged. [Read more]
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),... [Read more]
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... [Read more]
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... [Read more]
@ abart64, isn't yours just a step-up by accident? [Read more]
Well, it is by chance ... :) [Read more]
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. [Read more]
And did you check it on another power supply or on a different power source? See how it is on short power cables. [Read more]
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. [Read more]
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... [Read more]
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... [Read more]
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... [Read more]
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... [Read more]
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... [Read more]
AVE ... 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... [Read more]
@ 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. [Read more]
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,... [Read more]
There is also no information on my LPG cylinder that something will explode, does it mean that I can freely change the pressure inside? :) [Read more]
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... [Read more]