# Homework Help: Colpitts oscillator

1. Aug 11, 2011

### logearav

1. The problem statement, all variables and given/known data

http://www.circuitstoday.com/colpitts-oscillator
2. Relevant equations

Dear Members,
Kindly go through this link. I read Capacitors block DC then how can the supply voltage Vcc
which is essentially DC can charge the capacitors of the tank circuit? Kindly help members

3. The attempt at a solution

2. Aug 11, 2011

### ehild

The capacitor blocks current when it is charged to the equilibrium voltage, but it gets charged. Also, when two capacitors are connected in series to a voltage source, both of them get charged.

ehild

3. Aug 12, 2011

### logearav

i dont understand sir

4. Aug 12, 2011

### ehild

See attached figure. Will the capacitor C2 get charged? What is the charge on each capacitor if C1=2 μF , C2=3 μF and C3=3 μF, and E=10 V if the voltage source has been connected for a long time?

ehild

#### Attached Files:

• ###### sercap.JPG
File size:
3.2 KB
Views:
59
5. Aug 13, 2011

### logearav

Sir,
According to the formula q = c/v the charge stored in c1 = 20 micro farad and for c2 and c3 it is 30 micro farad

6. Aug 13, 2011

### ehild

Capacitance is charge over voltage, so the charge is q=CV. And the charge is the same on all capacitors, the resultant capacitance multiplied by the voltage of the source.
Anyway, the capacitor is charged by the DC source, does not it?

ehild

7. Aug 13, 2011

### logearav

sir, how can we say charge is same on all the capacitors. because q = cv, so c1 has 20 micro coulomb and c2, c3 has 30 micro coulomb charge.
But when the capacitors are connected in series, charges are same. i am confused though i got the concept of capacitors are charged by DC

8. Aug 13, 2011

### ehild

9. Aug 14, 2011

### logearav

I got it now sir. Thanks a lot for your link and detailed explanation.