PAR test of COBs vs Samsung 561 boards

CobKits

CobKits

Well-Known Member
Stephenj37826 said:
Not true.... 4-5 1212s have many more blue diodes. Each Samsung is 1 blue diode btw. As I've said the tj is only 1-2c higher than heat sink temps. This isn't the case with any cob. Think of package size (footprint per watt).
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true but the fact that 4 1212 cobs has twice as many diodes as a QB means that the current per diode is half as much and this works in the other direction of the cobs' thermal limitations. baseline efficacy of the diodes aside, the effect of adding 10 deg of Tj vs running the diode at half the current is probably a wash.

It seems like once you match up the # of cobs to reach the efficacy of a pcb (cobs of a given diode count, again you'd need fewer of the higher-diode count cobs like an 1825 but they would also suffer from thermal dissipation from crowded diodes), that cobs vs pcbs scale nearly identically in current up and down the range.

to say it another way, since PCBs with individual diodes are more efficient per diode at a given current, we need a lot more diodes on cobs to equal them, but then the cobs are running at a really low current so they are in the ultra efficient range for cobs. thermal effects on a 28mm cob are pretty minimal at 25-37W of input power, so there is a thermal component but not major droop territory
 
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