LED Driver 110Vac input

[gilbertomaldito]

led from 110v ac

I just have a question regarding the Vbuck which is drived into the LED from the AC input of 110Vac. I know AC input will pass Bridge Rectifier and then a large capacitor, to make this dc. Because driving LED must be DC. but since AC peak will be 155V (110 x sqrt(2)), does this mean DC will have a maximum value of 155V?

Is my understanding right?

If yes, how can you possibly make the current constant?

reference - National Semiconductor Triac Dimmable LED Driver

 

[erikl]

driving leds 110vac

... since AC peak will be 155V (110 x sqrt(2)), does this mean DC will have a maximum value of 155V?
Is my understanding right?

In principle, yes. The US standard now is 115Vac, which results in a peak voltage of 163Vdc, and with a tolerance of +10%, it can nearly go up to 180Vdc !

If yes, how can you possibly make the current constant?

An AC capacitor in front of the bridge rectifier limits the current. An additional series resistor is necessary to limit the inrush current following switching-on.
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BTW: Such questions (which have nothing to do with Analog IC Design & Layout) should better be asked .