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Current/voltage limiting of a large array of LEDs ... without LED driver ICs?

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Ian.M:
Add as many chokes as your LED matrix has anode lines, and PWM the currently active cathode line in your multiplexing sequence, and you can maintain a constant If (averaged over the multiplex time slot) by reducing the duty cycle proportionally by excess Vcc above Vf, without the usual series resistor for current limiting, so with *MUCH* lower I2R losses at higher Vcc.   Here's a LTspice proof of concept. 

N.B. you *NEED* the 10K resistors across the chokes for damping + you also need some blanking time with all anode lines off before selecting a new cathode line.   

Zero999:

--- Quote from: blueskull on February 07, 2020, 01:58:26 pm ---What is your LED color? GaN-based ones (true green, amber, blue, white) require 2.6V+, most likely 3V+, so you won't reliably drive them at 3V.

Get a boost converter, set voltage to 5V, then drive the LEDs with constant 5V.

Most logic chips with (LV)TTL input can be driven with 3V logic regardless of supply voltage.

Driving a LED array with resistive ballast under low voltage (close to Vf) is bound to give inconsistent result. Bump voltage up to 5V wastes some power, but gives a much better brightness uniformity.

--- End quote ---
Not all amber LEDs are GaN based. Only the phosphor converted type and confusingly some yellow and grass green LEDs are really deep blue/violet dies, with a phosphor.

Here's one with a forward voltage of under 2.4V
http://www.farnell.com/datasheets/2343228.pdf

Here's a lime green one with a forward voltage of 3V and will be a deep blue/violet die with a phosphor.
https://www.tme.eu/Document/59786a08ee3140c896513dd43bcadf0b/osc64l5111a.pdf

And a nice bright yellow LED, with a forward voltage of 3V.
https://static.rapidonline.com/pdf/55-9182.pdf

If the LED has a clear lens you might be able to see the phosphor, so if the die appears to be the same colour as the emitted light, it's probably a deep blue/violet LED plus phosphor, but it's better to check by connecting it to a power supply, via a suitable current limiting resistor.

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