Pre-Regulator

Overclocked said:

I have a unregulated power supply from a transformer that gives out a peak voltage of 61V after the rectifier (unloaded). With a 1A load the voltage goes down to 41.5V peak. I am powering a very large LED, 32V @1A and will be using A NCL30160 to do so, but its max input voltage is 40V (lower would be better). What kind of pre-regulator should I use? A series pass transistor or a LM317HV? I dont care what happens after the 40V, its just so the chip wont fry. Adding on another SMPS in front of the LED regulator would be too costly.

To re-iterate:
Vin Min:41.5V Peak DC (1A Load)
Vin Max: 61V Peak DC (no Load)
Iout Max:1A
Voltage needed: 40V (lower would be better since I wouldnt stress the chip out).

I know there are other solutions (ie TI) but I would rather not spend $2.50 a chip.

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zahwi said:

Voltage of LED to draw specific current is very critical because of the sharp knee. It also vary with temperature and variations in production.
The right way to drive LED is with current source. It insures constant power on the LED.
It is enough to have only current source using LM317 and one resistor, you don't need voltage regulator.

Your transformer could be made of rice, it could also be that it was made to European standards. In EC the isolation voltage is 4KV and the winding must be on split bobbin, this gives regulation that is similar to what you get. In Europe old transformers that the secondary winding was on top of primary we got better regulation.

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Overclocked said:

Thats what I plan on using. The NCL30160 is a buck constant current source. My problem (which has been solved) was that its Vmax is 40V.

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