PWM LED Ramping Circuit (Slow Bright, Slow Fade)

PWM LED Ramping Circuit (Slow Bright, Slow Fade) make LED light go bright slowly and with not sudden ON/OFF

This circuit is good for signal, decoration and for soft light.

It uses 2× IC 555, LM393, 2N7000 MOSFET for smooth change.

The circuit works best with 3 to 12V power with 6V is best.

Circuit Working:

Parts List:

IC1 555 make square wave (clock) at Pin 3 and its speed depends on R1 and C1.

IC2 555 make ramp signal and C2 charge/discharge slow and its speed is set by R2, C2.

IC3 LM393 compare ramp with fixed voltage which gives PWM signal.

Q1 2N7000 MOSFET act as switch and control LED brightness

PWM make LED slow bright and slow fade.

Formulas with Calculations:

Formulas with Calculations are mentioned below for PWM LED Ramping Circuit (Slow Bright, Slow Fade):

IC1 555 (square wave):

f = 1.44 / (R1 × C1)

R1 = 47k. C1 = 0.001µF ( = 1 × 10⁻⁹ F).

f = 1.44 / (47000 × 1e-9) = 30,638 Hz = 30.6 kHz.

IC2 555 (ramp time):

t = R2 × C2

R2 = 1M, C2 = 1µF ( = 1 × 10⁻⁶ F).

t = 1,000,000 × 0.000001 = 1 second.

MOSFET LED current:

I_LED = (V_supply − V_MOSFET) / R4

V_supply = 6 V, V_MOSFET = 0.2 V, R4 = 180 Ω.

I = (6 − 0.2) / 180 = 5.8 / 180 = 0.03222 A = 32.2 mA

How to Build:

To build a PWM LED Ramping Circuit (Slow Bright, Slow Fade) following steps should be followed to design our own circuit for connections:

• Take all parts from circuit diagram.
• Connect IC1 pin 1 to GND.
• Connect IC1 pin 2 to IC1 pin 6.
• Connect IC1 pin 3 to IC1 pin 6 through R1.
• Connect IC1 pin 4 and pin 8 to +V.
• Connect C1 between IC1 pin 2 and GND.
• Connect IC2 pin 1 to GND.
• IC2 pin 2 go to IC1 pin 6.
• IC2 pin 3 go to IC2 pin 6 through R2.
• IC2 pin 4 and pin 8 go to +V.
• C2 goes between IC2 pin 2 and GND.
• IC3 pin 1 go to MOSFET Q1 gate.
• IC3 pin 2 go to IC1 pin 6.
• IC3 pin 3 go to IC2 pin 6.
• Connect IC3 pin 4 to GND.
• Connect IC3 pin 8 to +V.
• Connect R3 from IC3 pin 8 to IC3 pin 1.
• MOSFET drain go to LED cathode.
• LED anode connect to one side of R4.
• Other side of R4 connects to +V.
• MOSFET source connects to GND.

Conclusion:

This article for PWM LED Ramping Circuit (Slow Bright, Slow Fade) make LED slow bright, slow fade.

It use 555 timers, comparator, MOSFET for smooth work.

If require we can change R, C values to change fade speed for many projects.

References:

PWM Led Fade out slowly help required!