Current Driven LED Circuit

[Veys]

Hello All,

I am currently designing an LED array. It consists of 20 LEDs which will light up one at a time in sequence. The first design looked something like this with the switch array representing logic 0 outputs on micro-controller:

Buffer Resistor Design

IR On.png (151.7 KiB) Viewed 12043 times

I need to ensure that the intensities are controlled however using a constant current method. I have decided upon this design which uses a shunt regulator to maintain required current through LED:

Shunt Regulator Design

TLV431 Single IR LED ON.png (81.85 KiB) Viewed 12043 times

The problem I am having is that I cannot come up with a suitable way of replicating this design x20 times over, short of just using x20 of each components. Any ideas? MUX's are expensive no?

Regards,

VEYS

[pebe]

Why do you need a constant current controller?
I assume you are using a stab 5V source, in which case your simple resistor feed, R1, should be OK.

[Veys]

LED intensities depend on current flow through them. The application requires the LEDs to operate at known wavelengths and so the typical buffer resistor design is not adequate.

[pebe]

The wavelength of a LED is determined during manufacture and stays the same whatever current is used to drive it. I have driven an IR LEDs with pulses of 4us at a current at over 1A to get a range of 30ft, and the wavelength did not change. I would be interested to know your application.

If your application is very fussy on drive current I can give you a simple constant current circuit to replace R1 in your first circuit.

[Veys]

It is the intensity that varies not the wavelength. I ensure uniform
brightness is controlled via current input.

[pebe]

The application requires the LEDs to operate at known wavelengths and so the typical buffer resistor design is not adequate.

I assumed that you thought the wavelength changed.

I ensure uniform brightness is controlled via current input.

In your top circuit, R1 is common to all LEDs, so they should be equally bright.
However, do you want the circuit?

[Veys]

Apologies the wording was ambiguous. The purpose is to emit pre-defined wavelengths at equal intensities. Thus if the current isn't controlled I will have no control over the intensity emited. Any circuit revisions are welcome.

[pebe]

This constant current circuit can replace R1 in your top circuit.