Boost converter help...

[moesciphish]

lm3578 leds

Ok, so if anyone had read my post about needing a buck or DC-DC converter to power some 20-40ma 3.6v LED's:

then they know my dilema... however, I figured I may be going about it all wrong and actually want to use a boost converter. The ones I've seen are the Badboy and the Wizard2. Would they be capable of a Vin of 1.2v or 2.4v and a steady Vout of say around 3.6-3.8v? Did I miss something with these? There is not much info on them. Any help would be greatly appreciated! Thanks! Or making something myself would be nice.. I guess I need a step-up/boost converter circuit..?

Thanks again!

 

[IanP]

If you go for constant current boost converter, such as Badboy, you will need to connect ≈10 parallel circuits cosisting of 3 diodes connected in series.
The total current will be 10 *30mA = 300mA (Badboy specification) and the voltage accross the dides will adjust itself (current control), and no additional resistors are required ..
If you want to experiment a little bit you can try this step-up dc-dc converter (only descrete component: transistors, resistors, diodes and caps):
https://www.aaroncake.net/circuits/6-12conv.htm
The supply voltage can go as low as ≈2.5Vdc, ZD3 sets the output voltage ..
Regards,
IanP

 

[moesciphish]

Ok.. that makes sense.. I thought they had a 1000ma badboy though now. I'm just curious as to battery effeciency with such a device and if it would be feasible to use say 2 1.2v NiMH to run them... Again, if there is a way to do this and build it myself, I will. I like the idea you had off the photoresistor on/off switch with the lm3578. I looked at step-up boost converters briefly and found the microsemi lx1994.. though it looks a bit complicated, it sounds like what I need maybe.. https://www.microsemi.com/catalog/part.asp?ID=70562

Or maybe the LX1993? Since it says up to 25ma current, I would have to have the LEDS in a series correct? and then basically since it has a max load voltage of 25V i could do safely about 5 3.6v's in a series... then if I had say 30 total led's I would have to get about 6 of these circuits or could I run 6 parallel LED strings off this one circuit? I'm sorry.. its been a long day and I might not be thinking straight. Or could I run 6 of these circuits off one 2.4v or 3.7 volt power supply in parallel?

I really appreciate all the help you have given. Hopefully it may help someone else too. I know I have alot of questions, but I am eager to learn and find this stuff very interesting.

Thanks!

 

[IanP]

Check out my previous post; I added a circuit that you can try to build by yourself ..
The LX1993 looks pretty efficient, and if you set current to 25mA per string you will have 6 strings ( of 5 leds) + 6 ICs .. and you can run the,as you said, from the same battery (or batteries).

Regards,
IanP

 

[moesciphish]

What about something like this **broken link removed**
that uses pulsed current for battery life? EDIT: Oh Wait, I do see where this is just used to control an external NPN transistor...it lost me after that

Or something else with a PWM.. or maybe like 4 or 3 ZXSC410/420's would be best.. with say 2.4v NiMH's, but they are still used to drive an external transistor, so how exactly is it a boost converter???

Thanks

I think I may have found what I need... the MadMax sandwich uses this IC:
**broken link removed**

I think everything would work nicely with say 2.4v (2 nimh), the only think I'm worried about is the 600ma load I'd be pulling, and the start-up voltage needed also at that load... other than that I think that's basically what I would need?

Also the LM2621 seems like it may work well...

 

[moesciphish]

Ok.. I got both the MAX1674 and LM2623, boy are they tiny.. I'm not even sure I'd be able to put them in a circuitboard...do I need a socket and where would I find one for such a little surface mount, any advice on this? Also.. I may need some help with the LM2623 and the capacitators and all I would need. I know I'd like probably almost a 100% duty... This will probably prove to be quite a challenge for an electronics noob like myself.. but I'd like to try it.

Thanks