LT1932 questions. 9 LED driver

[dat2zip]

Hello,

I've got two LT1932 ICs and I know some of you have used them successfully.

Question on driving 9 LEDs in a 2AA configuration. Will this work??? How much efficiency could I expect?

What if I used two of them. One driving 4 and the other driving 5.

These are 3mm White Nichia LEDs and I'd like to drive them 20+mA. I'd like to get 30mA in the string if possible.

Any help would be greatly appreciated.

I know there are some posts, just too lazy this time of night to search for them.

TIA!!!

 

[remuen]

Hi Wayne

As you know I've worked with the LT1932 and opened a thread some time ago. This is my configuration for this booster:


Cin 4.7uF low ESR ceramic cap
Cout 1.0uF low ESR ceramic cap
L 6.8uH low DCR inductor (0.074 ohms)
Rset 560 ohms (= 38mA output current)
Schottky diode ZETEX ZXCS1000


And here a few results with different numbers of LEDs in one single chain so you can see with which configuration you will get the best results:

As I recently posted in another thread I've got these excellent results with the very first LT1932 booster circuit I have built.

The ones I've made later had not the same outstanding efficiency but with up to 'only' max. 85% at 3 volts input still a very good one. I didn't find out a reason for this different results as I used the same pcb layout and the same SMD parts. I have never updated my excel list with the results of these other converters so I can not give you exact figures.

Btw, using a ZXCS2000 instead the ZXCS1000 would bring you a slight improvement as MrAl once reported in the ZLT thread.

I also did not make a run time test with a lower LED current even I drive my Minimag mods with three and five 5mm Nichias with 'only' 30mA.

Regarding the light conversion efficiency it would be much better to drive the 9 LEDs at nearly 20mA than at 30 or 40 mA.

Looking at my above showed results IMHO to get a steady brightness over a wide input voltage range down to 1.6 volts or lower a two LT1932 boost converter circuit would be better than using only one LT1932 even though you would drive the LEDs with 20mA.

I posted my earlier experiences and results with the LT1932 in this thread: LED driver with the LT1932 from Linear Technology (Page 1)

 

[dat2zip]

Rene,

Thank you very much for the data.

The booster would be to help our Don's 9 LED conversion. The link to his post is:

9 LED flashlight