I am using the LM3445 in accordance with the application note SNVS570M
At low dim levels the buck converter transitions from regulating the current to constant on state of the switching transistor.
From the application note:
As the TRIAC fires beyond 135°, the DIM decoder no longer controls the dimming. At this point the LEDs will dim gradually for one of two reasons:
1. The voltage at VBUCK decreases and the buck converter runs out of headroom and causes LED current to decrease as VBUCK decreases.
2. Minimum on-time is reached which fixes the duty-cycle and therefore reduces the voltage at VBUCK. The transition from dimming with the DIM decoder to headroom or minimum on-time dimming is seamless. LED currents from full load to as low as 0.5 mA can be easily achieved.
The problem is that the output of the LED is not smooth between these two states.The result is that when dimming from full off slowly up there is a noticeable "pop" or "flash"
The brightness steps down noticeably when the buck converter takes over.
Is there a way to adjust this point to achieve a smoother transition.
I believe this would require altering the input voltage to FLTR1 or adding a bias voltage.
The schematic page 29 of the application note there is a resistor R14 between C3 and D11.
I assume this R14 adds a small voltage bias or?
Thanks in advance for any advice