Test a PWM LED dimmer circuit using a 555 timer.
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%:
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 |
