Anatomy of a 7135 board, some links added, more would be nice. Any suggestions?

[Rufusbduck]

@kramer5150

@Rufusbduck

Don’t know about Field effect transistors. I thought 7135’s are constant current sinks that turn excess voltage into heat. The reference to transistors was comparing the Vdd pin to the “gate” of a transistor. Just looking at similarity to what it does as opposed to what it is. For perspective only.

The bolded statement is correct. 7135 chips DEFINITELY run hot pushing low Vf emitters with 4.2Vin. They generate enough heat to be “painfully” hot to the touch after ~.5-1 second of gentile touch pressure…. IMHO hot enough to require additional cooling methods.

Agreed. The data sheets seem to indicate the possibility of handling up to 4V excess(see dropout voltage vs output current graph) which translates to ~ 1.5W PER CHIP. Also indicated is the heat sink area at various thermal resistances. Up to 1000mm^2 of copper trace area to sink each chip. WAY more than is present on a 17mm board. I have often wondered how much better the chips would do if they were not backed up against another high heat source like the LEDs. I have always tried to separate the led and the driver as much as possible even though it adds some extra wire.