i am wishing to design a symmetrical astable multivibrator circuit (Figure 1) to run at a frequency of about 1 kHz by 4.7 kΩ resistors for the collector loads (RC1, RC2).
How can i choose the resistor values for RB1, RB2, (assume RB1 and Rb2 are equal value) to ensure that the transistors saturate when ON if the minimum current gain of the transistors is 100 in the linear region.
How can i select capacitor values to give a free-running frequency of about 1 kHz (+/- 25%) (assume than i mayy have to reselect the values of RB1, RB2 as only a limited range of capacitors is available.)

given the oscillator frequency of multivibrator is approximate:
f=1/[0.693RB1C1+0.693RB2C2]

Thanks and i wish someone can teach me how to do calculation of this circuit.

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Have you tried using google?.

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Ya, i had try to search from google...but it didn't teach much how to calculate the capacitor and resistor value. Most of them just tell how it operate

 

See Nigel, many people have already tried Google without any luck so just asking them to use Google is pointless.

erictham83,
Did you find my link helpful?

I found it through Google, when I was helping someone else to find a function generator schematic. If typing in words like "astable multivibrator" isn't helpful then sometimes you can get better results if you try related searches like "signal generator" or maybe "square wave generator".

http://www.google.com/search?num=100...or&btnG=Search

http://www.google.com/search?num=100...erator&spell=1

http://www.google.com/search?client=...utf-8&oe=utf-8

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I would be more impressed if they tried using google first, and put a little work into it! - many of these posts can be answered by the first hit that google returns.

Presumably this is yet another school homework question?, and it's easier to ask than to do the work yourself!.

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I'm going to assume this is a homework problem. We are reluctant to do your homework here.
Selecting RB is the only real problem here. Since your instructor only gave you the minimum current gain (beta) for the linear region, and you need to select a value that will drive the transistor into saturation, I'm guessing that your instructor has given you a rule of thumb for this situation.
You also need to know about base-emitter voltage for a transistor which is biased ON. I can't believe your instructor would give you this problem without having given you these two pieces of information.
Selecting the capacitor value is simple algebra, once you have a value for RB. Surely you didn't sleep through algebra?

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Ron

 

I would too, but there again Googling is a skill and not everyone can do it and you do need to know exactly what you're looking for to find what you need and it's even harder if English isn't your first language.

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