I use NE555 & MC34063 to build a LED driver with dimmer function. The crcuit of NE555 , MC34063 & LED are bridged by a IRF640N NMOSFET. NE555 is responsible for adjusting the brightness and MC34063 is responsible for light up the LED.
Under 90% duty cycle, everything is fine. However, the LED start to flicker under 10% duty cycle.
Here are plot charts of 10% & 90% duty cycle & the circuit of MC34063. (The values in both charts are sampled by 10X probe, please multiple them by 10.)
I guess that the root cause might be the MC34063 entered DCM.
There are some triangles in 10% duty cycle snapshot. Are these evidence of DCM or just big ripple? Should I replace the inductor in MC34063 circuit with bigger one? What if I just replace the output capacitor?