LM334 Constant Current Source Test - Part 1/5 (Small current (7mA) RGBYW indicator LED)

Introduction

This test uses a constant current source (CCS), instead of a voltage source, to control a RGBYW LED's brightness.  

LM334 is used to test small current ( < 20mA) indicator and large current (< 350mA, 1W) power LEDs.  RGBYW

The circuit used in this test is the most basic one, with a current limit of 10mA.  

Now I am setting up the CCS test circuit with the following parameters:

1. Vcc ~= 5V

2. CCS = LM334Z

3. Measuring equipment, 2 dirt cheap multi-meters, one for voltage, another for current.

4. Rset resistor = 10Ω (30Ω x 3 in parallel)

5. LED samples to test = as shown below.

Now I have tested the ordinary and power LEDs shown below.  I found that the CCS circuits works very well, ALL the samples have a very "constant" value for 5V in the range of 6.80mA to 6.85mA.

Next step is repeat the test without using the CCS, to compare results to show that if CCS is that effective.

I tested RGBYW LEDs, and found that for RED LED, the average difference between series resistor and CCS is around 8%, as shown in the table below.

Conclusion

This test shows that CCS indeed regulates LED current and thus brightness substantially.

This test is for small current, using a pilot case study of 7mA.  Next step is to test high current, up to 350mA.

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