Improved fading LED on off using NPN BJT 2N3904 and astable mode 555 timer electronics circuit
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- เผยแพร่เมื่อ 26 พ.ค. 2020
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Fading an LED on and off using a capacitor directly while switch by a 555 timer didn't work out as nicely as I thought it would. So in this video I improve the circuit by using a much lower value capacitor to control how much current a 2N3904 bipolar junction transistor (BJT) lets pass through the LED.
#electronics #BJT #2N3904 - วิทยาศาสตร์และเทคโนโลยี
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So I was trying this out and I worked out in some scratch paper that the frequency in this situation is 1 hertz. The on time and off time are equal thanks to the diode on the left side of that circuit.
The PWM output goes through a low pass filter, and at 100,000 ohms with 10uF capacitor, This will give us a nice triangle wave right at the signal connected to that capacitor. So when the PWM signal is at the end of its high pulse, the capacitor will be barley fully change, then when it is at the end of the low cycle, the capacitor will be barely fully discharged, but for it to discharge at the right rate the resistor going into the transistor has to be the same value to discharge at the same rate it charges.
The value of the resistor before the capacitor determines brightening time and the value of the resistor after the capacitor determines the dimming time.
Love any video with 555 timers, caps and LEDs !!!
They are fun 🙂
@@Electronzap Can I use 12v on this circuit to use on a 12v led strip?
@@fernandojunior9393check the datasheet of the 555 timer you use. You will probably need to regulate the voltage to the 555 timer, but you can connect the LED strip to the 12V and terminate at the collector of the transistor
Probably not any help 2 years later