Need Solution for Astable multivibrator circuit for 24V

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satiz

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Hi there,

I have a 12V astable multivibrator circuit but, I need this to operate in 24V what are the changes I have to do?
Without changing the transistor. LED Quantity is not a matte for me I can add more.




Thanks in Advane
Regards
Satiz
 

Hi,

You just need to do a little maths regarding the base resistors and collector resistors. This tutorial called Astable Multivibrator runs you through the circuit operation and calculations needed nicely, it's easy to understand. Rule-of-thumb would be to double the base and collector resistor values as 24V is twice 12V. ...And maybe the trimpot, I haven't seen that before in a multivibrator so I'm not sure what purpose it serves.
 

Hi again satiz,

Doing rough calculations and excluding the trimpot from the circuit and the subsequent values, and assuming LEDs are around 1.3V to 1.5V...

For same as 12V circuit, where ~10mA LED current and t1 = t2 = 0.83 seconds:

R2 = R3 = 22k (if ic/ib = 10), C1 = C2 = 55uF (57uF is 0.865 seconds)
Or
R2 = R3 = 110k (if ic/ib = 50), C1 = C2 = 11uF
R1 = R4 = 2.2k

I guess trimpot 50k + 4.7k is for ic/ib = 55...

Hope that helps, if I'm right.
 

Hi,

what about using a 12V zener in series with the power supply?
Or using a LM7812?

--> no need to change any value of the existing circuit.

Klaus
 

I believe you need to add a diode in series with each transistor base to avoid excess reverse bias on their base-emitter junctions.
 
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