1
\$\begingroup\$

Most quality COB LEDs are driven with around 35V. Are there any quality constant current step-up drivers available that allow a 3.7V Li-Ion battery to be used?

Or would I have to use TI's WEBENCH POWER DESIGNER to obtain a circuit, source the components, and solder it myself?

I am not a circuit designer, so any help would be much appreciated.

EDIT 1

I think I want to attempt building the circuit myself, so hopefully that re-validates the question. I have found the IC LT3477 from Analog Devices that seems to accept 3.7V Li-Ion input and can step up/boost to 35V. I hope I understood the data sheet correctly. Please see a sample schematic below.

Which components would I need to change to obtain 180mA or 360mA constant current? I saw from https://electronics.stackexchange.com/a/335325/207467 that there is a "feedback" or "sense" resistor that apparently needs to change with respect to the IC's reference voltage.

enter image description here

Edit 2

Another alternative I found to devise my own circuit is the TPS61169 http://www.ti.com/product/tps61169?qgpn=tps61169 with max. 400mA, where the current is adjusted via an "external sensor resistor". How would I calculate that resistor's value to drive a 90mA, 180mA or 360mA LED? If I knew how that is to be done, I could build my circuit with that part.

Edit 3

An even better solution turned out to be the TI LM3410 as a SEPIC device, as shown in the documentation under 8.1.2. That works well with a 3.7V Li-Ion battery as it discharges from 4.2V down to 2.9V with the LED Vf in between - and that little inexpensive IC also boosts 3.7V well to 9V without too much heat, so many other LEDs come into range.

\$\endgroup\$
  • \$\begingroup\$ Unfortunately, questions about off-the-shelf product recommendations is off-topic here. If you want to ask about designing the circuit, that is fine but you should edit your question. \$\endgroup\$ – DoxyLover Dec 16 '18 at 20:41
  • \$\begingroup\$ Yeah, that's why the second part of my question was about using TI's WEBENCH, but I am no circuit designer; for many decades, I assembled luminaires from off-the-shelf components, but I am not sure if I should attempt designing the component in question, although I'd like to. The problem is where to start ; ) \$\endgroup\$ – Systembolaget Dec 16 '18 at 21:58
  • \$\begingroup\$ This question can be salvaged if you ask specific questions about the DESIGN of a suitable converter. Please do NOT ask for recommendations of any particular device - this will cause the question to be closed. \$\endgroup\$ – Dwayne Reid Dec 17 '18 at 5:40
  • \$\begingroup\$ That's what the second part of the question and my above comment pertains to. How should I go about designing such a thing? I have put in my parameters (input 3.2-4.2V from a Li-Ion battery, output 32-37V to LED) in TI's WEBENCH and am shown two suggestions; but how about the constant current part of it all? Is there a "reference design" I should start from? Thanks! \$\endgroup\$ – Systembolaget Dec 17 '18 at 9:01
  • \$\begingroup\$ Did you know that (if) 1 battery cell has 10Wh and your LED lamp is 10W then you can expect only 1h operation. \$\endgroup\$ – Sunnyskyguy EE75 Dec 18 '18 at 22:01
1
\$\begingroup\$

I found the answer reg. calculating the "sensing resistor" for such boost ICs. In case of the latter one, it is in the application note "8.3.4 Current Program".

Now I only have to find a suitable inductor and hope that the suggested schematic will work.

\$\endgroup\$

Your Answer

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

Not the answer you're looking for? Browse other questions tagged or ask your own question.