Fading LEDs Circuit

The following diagram is the schematic diagram of fading LEDs circuit. This kind of circuit runs two LED strips in pulsing mode, i.e. one LED strip goes from off state, lights up gradually, then dims little by little, and so on. while one other LED strip does the contrary.

Fading LEDs Circuit diagram

Components part:

R1, R2 = 4K7
R3 = 22K
R4 = 1M *
R5 = 2M2 *
R6, R10, R11, R14, R15 = 10K
R7, R8 = 47K Trimpot *
R9, R13 = 27K
R12, R16 = 56R
C1 = 1µF
C2 = 100µF/25V
D1-D4 etc = 5 or 3mm LEDs *
IC1 = LM358
Q1, Q2 ,Q4 = BC327
Q3, Q5, Q6 = BC337
SW1 = SPST miniature Slider Switch
B1 = 9V PP3 Battery

Circuit Works:
The IC1 contains two Op-Amps circuit which will be used to generate triangular wave form.. The rising and falling voltage obtained at pin #7 of IC1 drives two complementary circuits formed by a 10mA continual current source (Q1, Q2 and Q5, Q6) and driver transistor (Q3 and Q6).
R4, R5 & C1 are the timing components: the total period can be varied changing their values. R7 & R8 vary the LEDs brightness.

Fading LEDs Circuit Notes:

  • For those whishing to avoid the use of trimmers, suggested values for 9V supply are: R4=3M9, R9 & R13=47K and trimmers replaced by a short.
  • Whishing to use a wall-plug adapter instead of a 9V battery, you can supply the circuit at 12V, allowing the use of up to 6 LEDs per strip, or at 15V, allowing the use of up to 7 LEDs per strip.
  • In this case, the value of the trimmers R7 & R8 should be changed to 100K.

Fading LEDs Circuit Source: RedCircuits