How to Dim!!!

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Bonjour,

I've read the application note for LinkSwitch-PH family and some its design examples but I didn't get how to dim the loaded LEDs? (I mean changing which element will decrease/increase the LED brightness? Since I couldn't find any variable element!)

Another question, I am supposed to design a LED driver and expected dimmable range is 10%-100% (i.e. 10:1). Is it right to configure the device with non-dimming mode (i.e. setting R resistor to 24.9 Kohm and ...) ?

 

Quoting from AN-49, page 2:

"The normal (non-dimming) mode provides input line voltage compensation that maintains output current regulation within narrow limits (<±10%) across universal input voltage ranges (e.g. 90 VAC – 265 VAC). This mode does not prevent the device from being used with AC phase dimmers however dimming range is reduced (10:1)." 

 

Kindly, explain your answer by this application note:

http://www.powerint.com/sites/default/files/product-docs/an49.pdf

Best, 

Hi,

LinkSwitch-PH LED drivers are designed for phase dimmers such as TRIACs and trailing edge dimmers.  It mimics the characteristic of a bulb during dimming. As the conduction of the AC cycle is reduced the output current will be reduced. The dimming is a natural phenomenon for this controller, there is no direct variable element that controls the output current during phase dimming.

For a PWM dimming, you can control the output current through controlling the IFB current.  Refer to DER-363 as example. http://www.powerint.com/sites/default/files/PDFFiles/der263.pdf

LNK403-410 are optimized for dimming application. The output current is proportional to the AC input voltage in order to optimize the damper and bleeder of the circuit. LNK413-420 are designed to achieved good CC tolerance specially for wide range input application.

Non-dimming mode can be used in TRIAC dimming but the dimming curve will be slightly different.  But then, if the characteristic is acceptable to your application then it should be okay. Refer to figure 2 of AN-49 for comparison.

Regards,

PI-Jono