I did some Googling and found a thread over at eevblog.com where they discuss these chips; it seems there are a lot of counterfeits which use a 52-57kHz switching frequency (instead of 150kHz) and as a result have 200mV+ ripple.
it seems there are a lot of counterfeits which use a 52-57kHz switching frequency (instead of 150kHz) and as a result have 200mV+ ripple.
That's what this one does
Such low freq internal switching could be a rumour. Several expensive/genuine and cheap/fake LM2596 based adjustable boards appear to be using same value inductor.
Discontinuous mode operation may be responsible for the ripple - it is described in detail on page 22 of TI manual.
Can you kindly post a clear photo of your board? I am curious about the inductor and output capacitor. You probably have a clone of this board shown in another of Julian's video.
The apparent 1/3rd rate switching is quite puzzling. Assuming Chinese fab(s) copied LM2596 masks, the internal switching frequency should not deviate that much from 150Khz.
The inductor is only 33uH, same as many 150Khz applications, and should not work well at 1A+ output current or low voltage difference. But these boards are used widely in such applications.
Just wanted to post this since this thread could eventually become the original "proof" of apparent 55Khz switching of some Chinese LM2596.
Above formula is from appnote snva038b which also shows an example calculation. Estimate same 100 mOhm for their cap (it is probably much higher) and plug in 200mV ripple and 1.5A output current.
If internal switching frequency was really just 55Khz, that 33uH inductance is too low for many voltage/current settings where such boards are actually proven to be working.
As mentioned in the thread I linked to, they're probably actually LM2576's as those are much cheaper.
I was just pointing out that even if they copied the masks and made zillions of clones in a local fab, the frequency is unlikely to have become 1/3 of original during the process. But if they are recycled or surplus stock, the internal "fixed frequency" oscillator will still be in 150Khz ballpark.
These PCB designers are copying TI appnote schematics for all these boards. But the inductor/ripple calculations do not match 55Khz operation for many proven working setups with higher voltage differential and higher output current. That is why I am puzzled.
Nothing puzzling here. A Chinese vendor acquired a lot of reclaimed LM2576s, had them marked as lm2596, sold them to board stuffers selling ln2596 app note boards.
Nothing puzzling here. A Chinese vendor acquired a lot of reclaimed LM2576s, had them marked as lm2596, sold them to board stuffers selling ln2596 app note boards.
There is a major flaw with such innuendo ... an LM2576 switching at 52Khz could not use a small 33uH inductor to provide 1.5A output with just 200mV ripple. That is what shdesign reported when I was first puzzled.
an LM2576 switching at 52Khz could not use a small 33uH inductor to provide 1.5A output with just 200mV ripple.
That simply does not interest the sellers. Decapping the part with nitric acid will confirm this.
The reason it is impossible to argue any point with you is that you are unwilling to apply simple reasoning such as:
- module is providing 1.5A output with only 200mV ripple - the inductor appears to be only 33uH therefore, - the simple switcher IC can't be either LM2576 or a cloned LM2596 running at only 50-55Khz
One could argue that they are using a compact 330uH inductor. But it makes no sense to spend a lot more on the inductor than what they supposedly saved by substituting a LM2576 with false marking.
The reason it is impossible to argue any point with you is that you are unwilling to apply simple reasoning such as:
- module is providing 1.5A output with only 200mV ripple - the inductor appears to be only 33uH therefore, - the simple switcher IC can't be either LM2576 or a cloned LM2596 running at only 50-55Khz
One could argue that they are using a compact 330uH inductor. But it makes no sense to spend a lot more on the inductor than what they supposedly saved by substituting a LM2576 with false marking.
You are not making any sense. You pointed out the 50kHz, and the pic confirms that. 200mV ripple is with low Vin-Vout, and small LC.
Can you please clarify the input and output voltage settings for above test? Kindly do a few controlled experiments with (output-input) difference greater than 12V and load current higher than 1A.
I asked around and dozens of people have such applications working fine with various ultra-cheap "LM2596" DC-DC boards with 33uH inductor. Unfortunately they do not the have tools to measure ripple or apparent switching frequency.
But their DMMs show very steady output (4.99-5.01V for 5V etc). Youtube guys also have posted such videos, some with much higher voltage difference and current.
If i remember right, 12V in and 8.4V out. I had it set up for charging LiIon batts.
I would not go with more than 1.5 amps with these. It got real hot and there is no heat sink. I was dissipointed there is no provision to add a heat sink. Others have glued a heat sink to the plastic case of the chip.
I have another running the power feed on my lathe. 1.5-28V with 36V in. Works well but the motor is less than 0.2A.
