LED desk lamps are cheaper to make with V(LEDs) < 42VDC?

[treez]

Regarding making a LED desk lamp with 16 LEDs (each LED vf = 3V) carrying 0.16 Amps. (Vin = 24V from isolated offline SMPS)
If they are all in series the LED string voltage is 48V.

Is it thus standard practice to avoid series connection and connect them say, 4 strings of 4-in-series, in parallel, in order to get beneath the 42VDC level, (SELV) and thus make the enclosure around the LEDs and the driver much cheaper?

 

[chuckey]

Where did you get 42V from? SELV is set at 60V according to Google.
Frank

 

[treez]

Yes I do believe its 60v, but is it common to deliberately design led strings to be under 60v because its cheaper to make an enclosure for them that meets the safety regulations?

 

[chuckey]

If you design for your LED string to be 48V then you still have 5V or more to operate your current source and still be under the 60V with a bit in hand?
Frank

 

[treez]

Thanks, but supposing we are PWM dimming a 48V string of LEDs....then the current to the LEDs is going on and off, and the voltage across them has a ripple in it in phase with the PWM dimming, so in this case of PWM dimming, does the AC limit apply?, since there is an AC content to the LED current waveform.?

So what I am saying is, 60VDC is the limit of SELV circuits, but does this value of 60V come down when the LEDs are being PWM dimmed? And the SELV limit is lower than 60vdc for the case of PWM dimmed LEDs?

Also, why doesn't the LDH-45B-1050 LED driver, which has a maximum output voltage of 43V, boast of being "SELV" rated?

LDH-45B-1050 LED driver datasheet
http://www.meanwell.com/webapp/product/search.aspx?prod=ldh-45

..I mean surely, if something is SELV rated, then lots of people will buy it because it conforms with SELV regulations, so why are they not bragging of the SELV rating of the LDH-45B-1050 LED driver?

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And once again, the entire family of DLG series LED drivers below all have SELV outputs (<60VDC), so why does their datasheet not boast of this?..surely thay are going to miss out on sales due to not bragging of the SELV output rating? Customers want SELV outputs because it means they don't have to have such an expensive enclosure for their LED product, to protect against the voltage inside it.

DLG50-150 LED drivers
http://amtex.com.au/power_pdf/DLG50-150.pdf

 

[chuckey]

In a word I don't know. Suppose you are marketing a mobile phone charger for use in a car (Vin = 12V, Vout = 3.7V), would you bother to say its SELV compatible?
Frank

 

[D.A.(Tony)Stewart]

I have this nagging feeling you are wasting your time with PWM drivers for this application when they will run nearly perfect on 48Vdc and just require 50mΩ current shunt, Comparator & Mosfet. ..with ESR(FET) < ESR(LEDx1). if they are good LEDs. WHat specs for LEDs (V,I min/max ) and power source V,I min/max

If Vf on 16 LEDs is > 48V, then I suggest you picked poor LEDs