Discrete LED Driver Topology
The LED driver is self oscillating which gives a simple lowcost approach. In this case it isn't uncommon to not use a chip for low power stuff because orthodox thinking states that chip cost is relatively more significant . Your circuit is a const current source but its not accurate and doesn't have to be .  In fact any circuit that relies on inductor characteristics wont be accurate .LED currents do not have to be super accurate but VBE based current sense allows inductor changes without suprises . The small neg temp co of VBE can be beneficial to the thermal management of the      LED fitting.        I use self oscillating schemes at high power to give switching regimes that give lower switching losses than orthodox current mode but your circuit relies on some inductor saturation to work so is   less efficient than normal PWM peak current mode     chips anyway.