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toked323

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hey i was wonderinf if i bought this circuit for the cree at http://dealextreme.com/details.dx/sku.4451 its rated for 300ma but 1.5 volt can i lower the current and use it as a LD driver? thanks
 



ericab

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well. it would most definitely work; but would kill your diode probably within minutes...
youd have to figure a way out to cut that current down to a more reasonable level. voltage input is 1.5V ~ 3.0V, so that is alright.

im not 100% sure, but maybe you could just add a resistor to the red POS wire going to you LD such as 5 ohm??
anyone know if that would work?
 

ericab

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before you order; wait an see if someone can answer....
im just not sure if it would be as simple as tying a resistor to it... if so, this would be a real winner (i think... :-X )
 

Gazoo

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toked323 said:
yea maybe im gonna order it and try
Honestly I am not familiar with boost circuits but I see no reason why it will not work. You might even be able to use a silicon diode in series with the LD to cut the current/voltage down, and a 1 watt silicon diode is smaller then a half watt resistor. The voltage drop of a silicon diode is appx. .7 of a volt.

However..looking at the reviews and the results of Eproms testing it doesn't appear to regulate very well. Make sure you read the reviews of these circuits before you buy...as I recall DX has better boost/buck drivers with much better reviews.
 

Daedal

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Subject: Measurements (Don't waste your money)
EpRoM Saturday, June 16, 2007 2:53 AM Reply
Here is the results,

Source is a Lab-Design DC Source.

Source Source Emiter
Voltage - Current - Current

1 volt - 530 ma - 110 ma
1.1 Volt - 670 ma - 140 ma
1.2 Volt - 950 ma - 200 ma
1.3 Volt - 1200 ma - 230 ma
1,4 Volt - 1400 ma - 260 ma
1,5 Volt - 1680 ma - 300 ma
1,6 Volt - 2000 ma - 330 ma
1,7 Volt - 2200 ma - 350 ma
1,8 Volt - 2440 ma - 380 ma
1,9 Volt - 2720 ma - 400 ma
2,0 Volt - 2870 ma - 420 ma
2,1 Volt - 3000 ma - 450 ma
2,2 Volt - 3330 ma - 460 ma
2,3 Volt - 3500 ma - 480 ma
2,4 Volt - 3700 ma - 500 ma
2,5 Volt - 4000 ma - 520 ma
2,6 Volt - 4230 ma - 525 ma
2,7 Volt - 4520 ma - 540 ma
2,8 Volt - 4720 ma - 550 ma

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nuhbiwan Saturday, June 16, 2007 3:05 AM Reply
Do I get this right? This thing has an efficiency of approx 18%?

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EpRoM Saturday, June 16, 2007 4:19 AM Reply
Yes, Every measurement is correct, I double checked with 5 of the boards I have... This boards are only mass.

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Kyle @DX Saturday, June 16, 2007 5:32 AM Reply
Thank you EpRoM for your detailed lab test. According to your results efficiency is indeed 18% at 1.5V. Points.

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JSRJSR Saturday, June 16, 2007 11:59 AM Reply
Actually, efficiency is about 40% at 1.5V.

Assume Vf = 3.3V, @ 300mA, that's approx. 1W.
Vin = 1.5V x Iin = 1.68A = 2.52W.

1W/2.52W = 39.7% efficiency.

At Vin = 1.5V, no driver is very efficient. The best I've seen is about 65-70%.

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nuhbiwan Saturday, June 16, 2007 1:18 PM Reply
You are right then, I didn´t know they convert 1.5V to 3.3V.
So in this case, if 3.3V are correct you really have an output of 1W
ergo an efficiency of approximately 40%!

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EpRoM Friday, June 22, 2007 12:15 AM Reply
Here is a TOPMET IC with 73% efficiency at 1.0V and 80% effi. at 2.4V and have an voltage range of 1.0V to 3.3V. Works perfect and gives 350 ma constant current to emiter.

Product page:
http://www.sztopmet.com/en/products.asp?sort_id=28&bigid=14

Datasheet:
ftp://FTP_sztopmet:123456@59.36.99.172/TDU0201E-11-DC Specification.pdf


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nanotech17 Saturday, July 07, 2007 3:30 AM Reply
how do i order the topmet?

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James_C Monday, July 23, 2007 9:13 AM Reply
I hate to question datasheets, but the Topmet driver linked is not likely to be that efficient at 1V. The efficiency graph does something very strange (going against electronic fact?) when it does not dip down in efficiency very fast when it gets to where the diode forward drop voltage is going to be a large percentage of the input voltage. At least, that is how their design seems to operate based on the picture showing a diode just under the inductor, plus a ceramic cap to the left, just before the driver output.






All was at the bottom of the page... This has been tested and a better alternative has been found ;)

--DDL
 

Daedal

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I don't think you need to add anything to that circuit... ;) It's good to go as is :)

--DDL
 

ericab

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buuutttt....

Constant current output: 330mA±5%

what to do it we wanted more like 200mA ?
 

Daedal

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I'm sure that circuit can be modded somewhat with a simple resistor swap. Also, an extra resistor can be added to the LD leg... that could do the trick. I've never really tried it, but it could be very useful.

--DDL
 

Gazoo

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ericab said:
so; your saying with the TDU0201E-11-DC:

http://www.sztopmet.com/en/products.asp?sort_id=28&bigid=14

all one would have to do is add a silicon diode inline?
with a .7 drop what would the resulting current be?
I am going to have to take that back.. :p After looking at how fast current drops with each .1 of a volt drop at the input, I would not even recommend this driver. I know I would not be happy with it.
 







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