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LM3447 - Data sheet queries

Atul Bhakay
Genius 3205 points
Other Parts Discussed in Thread: LM3447

Hi, Kindly clarify the following points, regarding LM3447 data sheet:- 1) What is meant by Over 50:1 Dimming Range:

2) Angle Decoding Circuit & Dimming, Fig. 29 (Page No. 19,20 of LM3447 datasheet): It seems that below 30Deg phase angle, the graph saturates to below 0.3V, in this situation, what will happen for 0 Deg to 30Deg conduction angle. I think there is no change even if the power is dimmed below 30 Deg, then what will happen when customer needs to set the 5%, 15%, 25% intensities, will it not vary according to set value and when customer needs to set 0% will it not go to blackout? Pl clarify.

Regards Atul Bhakay

  • 0
    TI__Expert 5130 points

    Hello Atul,

    1)      The ratio 50:1 means the output current ratio between maximum dimmer conduction angle and minimum dimmer conduction angle is 50:1.

    For example, if you have a maximum output current of 500mA, you can dim it down to less than 10mA. Normally, the LM3447 can achieve over 50:1 dimming ratio.

    2)       The Figure 29 aims more at phase dimmer (TRIAC dimmer). Those words can be summarized as…

    1. Dimmer conduction angel 180° to 150°, the output current will not change.
    2. Dimmer conduction angel 30° to 0°, the output current will remain same as it is at 30° (for some dimmers, they will just turn off).
    3. From 150° to 30°, you can dim the LED from maximum current to minimum current. The ratio can be 50:1.

    So if your customer wants to set the 5% intensities, the ratio is about 20:1. I think it’s not difficult for LM3447 to achieve that ratio.

    The last thing I want to point out is that the ratio and conduction angle may vary a little bit and it would be affected by what dimmer you are using.

    Regards,

    Victor