Doesn't this forum say something about being nice to noobs
jk. appreciate the detail. Not tldr. You gave me greater understanding of how to interpret the specs.
The XL4005 has a current limit, or so it claims, but that doesn't mean the whole board has a useful current limit.
so basically, to extend your summary slightly, "didn't give a shit" means they used a diode that's under-rated (thermally speaking) for this board, right?
Question, would a sufficient heatsink on the diode suffice to allow me to drive it to 5A or 8A?
Assuming (pulled out of my ass) 12V in, 4.2V out: duty cycle is 4.2V/12V = 0.35.
-Actually i'm giving it 19V. Again, with sufficient heatsink on that diode, can i get away with that? Let's see:
-Duty Cycle: 4.2/19 = .22
-Diode Current: 8A*.22 = 1.77A
-Diode power dissipation: 1.77A * .55V = .97W
-Diode temp: 55*.97 = 53.5C
Hmm, that's actually seem cooler. Is my math wrong? Seems counter-intuitive that a higher supply V would run the diode cooler. Which makes it stranger that the diode blew. But hey, i'm a noob.
Assuming 25°C ambient, the diode is at 110°C. This is way too hot, but still under the absolute maximum.
Ok so you're saying there must be another variable that's pushing the diode to hot. I think i'm almost getting this.
Now, to push it higher, all you need to do is:
Drop the input voltage. For example, at 10V input, the diode goes about to the absolute maximum of 125°C.
My V is higher, not lower...
Increase ambient temperature. Is it summer where you are?
SF does get not particularly hot...
Use a cheap, possibly faulty diode. Not unlikely.
Now i'm thinking about replacing that diode with a hotter-rated diode, same board, because i like the price and size of this board. Now trying to figure out how to find a correct replacement part.... Suggestions welcomed!
Not give a sufficient path for heat to exit the diode, causing the thermal resistance to go above 55°C.
Yep, gonna throw a heat-sink on there. Your analysis makes me think this (plus a higher input V), same diode, might actually work.
Have the current limit kick in at greater than 8A due to the fact that it doesn't even specify a tolerance.
This other ebay page (same board) says "Load regulation:±0.5%". Did they pull that out of their ass?
http://r.ebay.com/QRwl6v