# Astable Multivibrator Circuit (Flashing LEDs)

Discussion in 'LEDs and Optoelectronics' started by Juan Sanchez, Oct 25, 2017.

1. ### Juan Sanchez

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Oct 25, 2017
Hey, would anyone be kind enough to please help us explain this circuit in detail and what would happen (and why) when you change components and move things around. Really appreciate it, thanks!

2. ### Audioguru

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Sep 24, 2016
It is a very simple transistor circuit. When you learn about transistors then you will see what each part does in the circuit and how to change the timing.

3. ### AnalogKid

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Jun 10, 2015
Harald Kapp likes this.
4. ### duke37

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Jan 9, 2011
Running a mutivibrator on a voltage in excess of the permitted emitter/base voltage, can lead to degradation of the transistors.
Do not supply more than 6V depending on the particular transistors or place diodes in the emitter leads to prevent reverse current.

5. ### AnalogKid

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Jun 10, 2015
Duke is correct. Each transistor is turned off by a negative spike approximately equal to Vcc. If the peak value of the spike is greater than the transistor reverse Vbe rating, repeated applications of the spike will weaken the transistor even if the spike current is limited. One solution is to add a small signal diode (1N914, 1N4148, etc.) in reverse parallel with the each transistor's base-emitter. However, this will alter the timing calculation and increase the oscillation frequency.

ak

6. ### Cannonball

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May 6, 2017
This is a good circuit to play with. Do you have a breadboard? If you do, build the circuit just like the schematic shows and it will work. I won't explain the whole operation of this circuit at this time but I will give you a hint.

The sole purpose of the capacitors is to turn off the transistor that the negative lead of the capacitor is connected to.

7. ### Juan Sanchez

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Oct 25, 2017
Thank you everyone for your responses, it is greatly appreciated! This will help me out a heap.