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Driving 48 LEDs from a single cell
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Jon86:
So my project involves driving 48 white LEDs in a grid pattern from a single 3.7V lipo cell.
The LEDs will have about a 3V forward voltage at their rated current, so I'd like to avoid simply using a 48 channel linear driver with current sinks. I don't have much room for thermal losses here. Also routing 48 traces in a grid will be a bit of a nightmare, especially if I want to maintain good thermal transfer across the board.
One option I'm looking at is the LED7707, 16 channels with a boost converter, so I can tie the LEDs together in series strings of 3 or 4, and let the IC boost the voltage up for me.
This might be the optimal solution, but since I don't have much experience in the field I'm asking for some advice.
Literally all I need is PWM dimming of the whole lot at once, and a relatively high efficiency (>85%?).
If I can do it without SPI or I2C that'd make things simpler, but I'm sure that's where I'll end up.
Anyone who's done something similar I'd love to hear your solution!
Also, LEDs are rated for about 65mA, so I'm looking at around 10W for the whole lot.
coromonadalix:
With an buck boost converter you have to take in consideration the loss of your "autonomy" of your "single" cell
Is it a led matrix display ?? you're a little vague, is it put on clothes ???
From a single cell i found this unrealistic, what life expectancy you want ?
Theres Charlieplexing i've read who could help ...
Jon86:
Not sure what you mean by autonomy?
It's literally just 48 white LEDs, in a grid array. Not a matrix as such, I can wire them however I see fit.
Multi/Charlie plexing might be an idea, but I'm keen to run them all constantly at their rated current and reducing flicker as much as possible.
Not too fussed about run time, but I should be able to get roughly an hour from a 5000mAh cell if the efficiency of my driver is good.
SiliconWizard:
The LED7707 would be one of the simplest paths for this.
It has a 4.5V min input voltage though, so a single-cell LiPo battery wouldn't do. You'd need a 2-cell battery, which, if you have an appropriate charger, would be a better solution in terms of efficiency (obviously) than putting an additional step-up converter in front of the LED7707.
Marco:
--- Quote from: Jon86 on May 23, 2020, 03:43:20 pm ---I can tie the LEDs together in series strings of 3 or 4, and let the IC boost the voltage up for me.
--- End quote ---
Why not just make strings, use any old boost converter which can run off a single cell and then use a resistor to limit the current for every string? LED matching and thus current matching will not be ideal, but close enough. You can use a single MOSFET to PWM them all.
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