How to make Simple&low cost Constant Current led tape light circuit?(with Picture)

Firstly we check Constant Current Characteristics of Triodes as below:

From the characteristic curve of the transistor, The IC in the working area is affected by IB, while VCE has little effect on IC.

Therefore, as long as the IB value is fixed, IC can also be fixed.Output current IO is the IC that flows through the load.

Based on the above principle, Greeled‘s engineer added negative feedback circuit to ensure the stability of constant current. 

This new scheme is widely used in our constant current series flexible led tape light. Feedback circuit include Q1 and R2.

Q2 and R1 two components are used to adjust the led strip‘s current. We can keep the current constant at a fixed value

by setting R1 and proper Q1. For example, 30 mA or 40 mA.  

The whole Circuit working conditions:

1. V+ ＞VF*led QTY+0.7V               2. I2*R2＞0.7V           3. IB2*β2≤IC2

Example Greeled‘ SMD2835 white color led strip, LED VF(Forward voltage) is 3V, Total VF is 3V*6=18V,Then DC19V can drive

circuit. IF V+=DC24V. It also can work. only choose proper R1 and R2 to set current and let all parameter meet conditions. 

Constant current led tape Avantages:

1.  LED tape light working current regulation can be achieved, Meeting different requirment.

2. Comparing constant voltage 5m length led tape light, We can connect very long led tape light. For example, 10m/Roll, 15m/Roll,

20m/Roll. And the brightness of the whole led tape is the same. It is not affected by voltage drop.

3.  Prolong led life and saving cost.

Greeled‘s Constant current led tape link: https://www.gree-leds.com/constant-current-led-tape/