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Project Notes

#232 555 PWM LED Dimmer

Test a PWM LED dimmer circuit using a 555 timer.

The Build


This circuit uses a 555 Timer-based PWM circuit to dim a LED strip.

Steering diodes in the 555 timing circuit allow adjustment of the duty cycle with little change to the ~1kHz frequency.

The 555 Timer signal is used to switch the LED strip with a low-side n-channel MOSFET.

I’m using a 1m (60 LED) stretch of a 12V LED strip, and the maximum current draw is 133mA. Since this is quite low power, I’m using a 2N7000 MOSFET which is rated for 200mA continuous/500mA pulsed.


At maximum duty cycle (almost 100%), LED current measures 133mA and the voltage drop over the FET drain-source is 0.71 V.

The minimum duty cycle of ~1.25% does not completely turn off the LEDs. At this point the LED current measures 3.2mA and the voltage drop over the FET drain-source is 4.45 V.


At midpoint of the pot, duty cycle is ~50%:


LED Strip Specifications

I’m using this (very) cheap 3014 Led Strip Light. According to the seller specs:

Attribute Specification
Length 5m
LED Density 60 LED/m
Color cold white
View angle 120°
Working Voltage 12V DC
Power consumption 20W, 4W/m, ~67mW/LED
Working Temperature -40 to 70°
Luminous Flux 880-1080 Lumens/Meter
Size L500cm (5M) x W0.5cm x T0.20cm
lifespan >100,000 hours



The Schematic

The Build

Credits and References

About LEAP#232 LEDPower555 Timer
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