Timeline for How do I drive 12 strings of 12 leds each?
Current License: CC BY-SA 3.0
10 events
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| Mar 4, 2017 at 19:48 | comment | added | Misunderstood | I would never use a voltage source to drive strings of LEDs. When you're pushing an Amp resistors do not work well. For less than $2 I'm going with a buck driver plus 0.50 load balancers (LM3466) for each string. I only use a current source to driver LEDs and I would never use resistors, especially in parallel LED strings, that's too cheap and will look ugly (see #3 in app note). I do not use 20mA LEDs either. I manufacture boards with strings of 16 LEDs. My market is horticulture research, each board has one wavelength and requires a buck dimmer. Different perspective. | |
| Mar 4, 2017 at 18:46 | comment | added | Andy aka | In fact, for a voltage source and fixed current limit resistor you should, if operating close to maximum allowable current in the LED, take into account the minimum operating voltage in case you overdrive to much current. | |
| Mar 4, 2017 at 18:44 | comment | added | Andy aka | @Misunderstood you have misunderstood (coincidentally) this question and the applicability of that application note. Yes, if you are using a buck regulator as a constant current source then you must take into account maximum LED voltages or you might run out of headroom and the current begins to fall-away. In my answer I'm not suggesting a buck current source; I'm talking about a fixed voltage source and a resistor current limiter. So, when you say "never" please consider that this "word" only applies to driving an LED (or string) with a current source. | |
| Mar 4, 2017 at 17:20 | comment | added | Misunderstood | See the TI App Note Design Challenges of Switching LED Drivers, Section Number 2, Output Voltage Changes when LED Current Changes ti.com/litv/pdf/snva253a | |
| Mar 4, 2017 at 17:12 | comment | added | Andy aka | @Misunderstood I don't think that's entirely correct especially when there is a string of LEDs but, please leave an answer and justify why the maximum voltage should always be used. | |
| Mar 4, 2017 at 17:07 | comment | added | Misunderstood | Never use the typical Forward Voltage, use the max, 2.1v in this case. | |
| Jul 13, 2013 at 19:31 | comment | added | Eric Gunnerson | If you want batteries, two 12V batteries in series will work for you. Or 16AAs in series. Note that the values you list are typical for the LEDs; LEDs have a fairly wide manufacturing tolerance and you may see some differences in voltage and therefore current. If you could split the strings in 24 half-strings, you could drive them from a single 12V source, which would be easier. | |
| Jul 13, 2013 at 19:28 | comment | added | Eric Gunnerson | I like Andy's approach. A few notes: | |
| Jul 13, 2013 at 19:22 | history | edited | Andy aka | CC BY-SA 3.0 |
added 310 characters in body
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| Jul 13, 2013 at 19:16 | history | answered | Andy aka | CC BY-SA 3.0 |