Hey experts,

im trying to construct a single transistor colpitts oscillator circuit using LC circuit as shown in the figure, to detect the change in frequency when varying the value of inductor

According to f=1/2*pi*(L*Ct)^1/2
Where Ct= C1*C2/C1+C2

so C1=C2=47ηF
and L1=47μH

Hence oscillating frequency should be 150 Khz

However, the circuit didnt oscillate when connecting it in bread board

i have tried many schematic circuits on the internet but it seems that the feedback circuit is not connected to the transistor (( amplifier circuit )) for some reason



may any of the great engineers help me connecting this circuit

 

The Completed Projects Forum is for Completed Projects only. It is meant to allow members to show plans for projects they built so other members can duplicate them if desired. New threads are also automatically moderated per Moderator review for this reason. Your thread does not belong in this forum, and was moved here.

 

Hello,

I found your thread in "the completed projects" forum, where it will stay invisible.
As the title says it is the showcase for members who have a completed project.

I moved it over here and made it visible to the others.

On the circuit, I do not see how the circuit is powered.

On this page of the EDUCYPEDIA you will find some links with schematics on the colpitts oscillator:
http://educypedia.karadimov.info/electronics/analogosciltypes.htm

Bertus

PS I noticed that some of the links do not work.
You can have a look in the internet archive if the pages are stored:
http://archive.org/web/web.php
You can copy the not working URL into the search-bar.

 

The plastic plug-in boards have a lot of capacitance between their terminals. That might be your problem.
Also, there is no power supply represented in the drawing.

 

The plastic plug-in boards have a lot of capacitance between their terminals. That might be your problem.
Also, there is no power supply represented in the drawing.

Nor are there any bias resitors. If you're going to post a schematic, please post the circuit you built. We can't help if we don't know what it is.

 

The plastic plug-in boards have a lot of capacitance between their terminals. That might be your problem.
Also, there is no power supply represented in the drawing.

Lots of parasitic inductance as well.

Is the OP trying to use this circuit to find the value of an inductor?

Please clarify all of the above please.

 

thank you guys for answering that quick, well my problem is the connection of the circuit !!

all of the circuit i constructed have a 5 v power supply from the collector and i tried both diagrammes shown below

#12 and brownout
as you can see in graph the values of c and l are different , however the bias resistor values are 10k for both and the load resistor is 50 , i didnt know how to get values for the dc blockers capacitors (C3 & C5 in 1st graph)
just to clarify im using BC107 transistor with the rl tank circuit to detect the change in oscillating frequency when varying the inductor value

 

bertus: sorry for choosing the wrong section ,, the website seems great and usefull, however my most wanted page there is not working even when using the internet archive web
but thanks anyway

 

its my uni's final year project and i tried my best to make the oscillator work but i failed ,, please guys i would appreciate it if someone try to find the problem here