Hi all,
I’m reverse-engineering a schematic from a PCB — an automotive daylight running light / headlamp LED driver module (Volvo FH). I’ve mapped out the general topology but need help confirming three part numbers from their markings.
1) Q1 — SOT23-3
Marking: 090S1
Circuit: base biased through a 33k/1K divider from VCC/GND, output feeds into the next stage. Looks like a small-signal switching transistor, but I can’t find this marking in any cross-reference database (alldatasheet, s-manuals, smd.yooneed.one).
2) U2 — SOT23-5
Marking: Z8
Pinout: Pin 4 = VCC (100nF decoupled), Pin 5 = input (pulled up via 1K, driven by Q1’s output), Pins 1 & 2 = GND, Pin 3 = output (feeds toward the power IC’s dimming/control input). Looks like it could be a buffer/inverter/comparator, but “Z8” only matches Zener diodes in SOT23-3/SOD-323 packages in every database I’ve checked — doesn’t fit a 5-pin part, so I suspect there’s more to the marking than what I’ve transcribed (a second line or date code, maybe).
3) Main power IC — SOT89-5, exposed thermal pad
Marking: 6663 B40A
Circuit: VCC input with dual 100nF decoupling, drives an inductor → Schottky diode → output cap → LED string, with current-sense resistors (0.68R and 0.22R). Classic hysteretic buck constant-current LED driver topology.
