#232 555 PWM LED Dimmer

Test a PWM LED dimmer circuit using a 555 timer.

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.

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:

Construction

Credits and References

• LED Dimmer Circuit - reuk.co.uk
• PWM LED Dimmer/ Brightness Control by 555 Timer With Video Simulation
• LM555 Datasheet
• 2N7000 datasheet
• ..as mentioned on my blog