I also cannot understand what size capacitor and resistor I am supposed to use for the relaxation oscillator. How do you know to use 3300uF capacitor and 1Kohm resistor?

 

Actually, I have not. I am a total beginner. Please tell me more, if you would. I will look into it.

Hi,

When a capacitor charges, it follows a rule like this:
Vc=Vcc*(1-e^(-t/RC))

where Vc is the cap voltage,
Vcc the power supply voltage (or other DC voltage V),
t is time,
RC is R*C,
e is the base of the natural log system e=2.71828...

What this tells us is that the voltage across the cap starts to rise quickly but then slows down as time progresses until it reaches almost the full voltage.

The current though during that time is:
iC=(V/R)*e^(-t/RC)

and that starts out at max current V/R and gradually diminishes over time.

The first circuit you posted can be analyzed with these ideas in mind, while the second circuit we have to know the breakdown voltage of the transistor.

 

hi V,
Check this link for Capacitor Charge/Discharging.
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capdis.html

E

 

hi V,
Check this link for Capacitor Charge/Discharging.
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capdis.html

E

Hi there Eric,

That's a good link i think. I would have included some graphs too but got a little lazy

A capacitor charging graph would help too i think.

 

OK. I get it. A capacitor charges quickly at first then slowly, in an arc. But how do you know to use a 3300uF capacitor?