It seems that almost all small DC-DC converter modules listed on eBay with LM2577 in the headline actually use the Chinese XL6009 chip which they may or may not state “replaces LM2577”.
But… is it a replacement?
A quick scan reveals that the XL6009 is a cheap pretender, for instance minimum input voltage is specified as 5V.
So, what does it do below 5V in?
You might expect that it operates with degraded performance, but it is more dangerous than that.
Below is a XL6009 module that has been adjusted to 24V out with 12V input, and now running on reduced input voltage (simulating a flat battery source).
Above, the module is now delivering 51.6V which is dangerously high for its intended 24V load. If powered up from cold at 2V input, the output is unstable and jumps to 50V at times, at 3V input it is stable and produces over 50V out.
A second module was tested with identical result.
The module circuit appears to be the application circuit given in the datasheet.
There is no discussion of an undervoltage lockout in the datasheet (as used in the LM2577), and on test, it clearly lacks such a feature which might otherwise make it safe.
Other reviewers have criticized its regulation and current capacity vs datasheet. I did not get to test any of that, the undervoltage problem precludes its use.
The XL6009 is not a replacement for the LM2577 chips, and it produces dangerously high output voltage under some conditions that might well occur in service.
It is cheap Chinese junk and best put in the rubbish bin.