Recommended design PWM-enabled driver for multiple 1W LEDs in series-and-parallel configuration?
FET's need at least 2.5 to 3 times their threshold voltage,Vt or Vgs(th) to be low RdsOn.
uC are usually low voltage &lt;=5 , so Z1 is for inductive line protection, I guess for OVP on Vg.
Since uC could be 3.3V say, then you need a FET that is "Logic Level" type gate voltage such as Vt=1V.
Pd (max) for R3 &amp; Q2 is important to choose components. You can balance for low cost by looking up costs of FETs and power R's.  
Usually current sensors are 50 to 100mV for &lt;&lt;0.25 W  with an Op Amp, but with 0.6=Vbe R needs to 0.35A*.6V=210mW meaning est. 120'C rise on a 1/4W R. ( so use 1/2W)  R3=0.6V/0.35A= 1.7 Ω 1/2W 


Then regulate current with PWM 0 to max and ensure LED's have heatsink designed on copper or alum. substrate with 50 'C /W rise for  each LED or 3.4V*0.35A=1.2W or about 6 sq cm for each LED with conductive radiator. ( do more reading on best practices for LED luminaire design on MCPCB.)