LM3445: About 1% low current LED control

Hello Tao_2199,

The LM3445 using angle sense to detect the rectified AC waveform from 45 degrees cut to 135 degrees cut, this results in a reference to the current sense comparator.  There is a minimum on-time for the LM3445 so the minimum output will depend on the inductor value, off-time and conduction time (duty cycle of the rectified AC).   What topology are they planning on using (valley fill buck, buck, flyback or?).  What is the input voltage and range?  What is the output voltage and current?

2)  It can be modified by what is sent to the angle sense, why do they want to control it more than 135 degrees?

Best Regards,

Hello Irwin,

Sorry for delay.

1) My customer will use valley fill buck as topology.

The input voltage is AC90-110V@50/60Hz.

The output voltage and current are following. (Four pattern.)

2) I’m asking them about more than 135° TRIAC output..

If I get information, I will inform to you soon.

Regards,

Tao_2199

Hello,

The idea of the valley fill is to run from 1/2 of rectified AC when below the peak rectified AC voltage from the Valley fill capacitors.  Also at 135 degrees 90 VAC 1/2 of the rectified AC is 0.707 * 90 * 1.414 = 90V peak.  1/2 of this is 45V (minus some diode drops) which is above the LED stack voltages they want to run, this is how the valley fill design is supposed to work.  Also, even if the range ends at 135 degrees the LM3445 will still put out a minimum light output due to the minimum on-time.

Best Regards,