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Project Notes

#232 LEDDimmer/555PWM

Test a PWM LED dimmer circuit using a 555 timer.

The Build

Notes

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.

Performance

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.

scope_min

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

scope_mid

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 Tempreture -40 to 70°
Luminous Flux 880-1080 Lumens/Meter
Size L500cm (5M) x W0.5cm x T0.20cm
lifespan >100,000 hours

Construction

Breadboard

The Schematic

The Build

Credits and References

About LEAP#232 LEDPower555 Timer
Project Source on GitHub Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is my personal collection of electronics projects, usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.