[SOLVED] Problem with accurate frequency generation

[aandavan]

Hi,

I am generating a 40KHz frequency with the help of a astable multivibrator circuit. I got one circuit in that they are using R1 as 4k and a variable resisitor connected in series to that R1 and R2 as 18K and C1 as 680PF . By using that its working.
I used one RC calculator and i calculated the alternate resistor value.I used R1 as 47ohm and R2 as 147ohm and C1 as .1microfarad. By using that value its not getting that correct frequency. Anyone help me please...........

 

[melc]

Re: Frequency Generation

I'm affraid you have to post the entirely schematic with component names and values.

 

[IanP]

Re: Frequency Generation

In theory you are right: 47Ω, 147Ω .. bla .. bla .. bla ..
On the other hand, these values are unrealistically low, so, don't expect these circuits to work with them ..

To give you a hint, if β of contemporary BJT is easily >250 to source/sink its collector current of 1mA you need its base current to be somewhere in µAs region ..
Just start with resistances of 1kΩ, and more, and you will be fine ..

Regards,
IanP