The scenario
An AC-mains LED bulb must survive line surges and maintain a stable LED current across normal mains variation.
What is in this drawing
Read the decisions behind it.
01
TVS diode after the fuse clamps line transients before the rectifier
02
Bridge rectifier plus bulk capacitor creates the DC bus
03
Discrete NPN transistor with zener reference and emitter sense resistor forms the constant-current sink
Use for small offline LED bulbs or indicator lamps that need basic surge protection and current regulation without an integrated driver IC.
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