I have a problem with the Collpitts oscillator circuit that I'm using as my input stage for an inductive proximity sensor circuit. The idea is for me to build a metal detector and therefor I'm using that diagram to achieve that. I'm not getting any output on my output stage i.e. its not oscillating. I only get DC voltages because the amplifier is amplifying allright. Please give me a sollution. I did make the required coil and it gives me the correct inductance.

 

If the oscillator is working, then the positive feedback is not enough, Try to increase the gain in the osc stage. If you are using transistor type, then try changing to higher beta transistor.
regards,
sekar

 

Replying to Bongiwe's Apr 11, 10:53am query:

1) Which circuit are you using... Transistor? or Op-Amp?

2) What do you mean "amplifier is operating alright"?

3) Does your detection circuit consist of two C'c and an L arranged in a
Pi configuration? If so then amplication factor is dependent on ratio
of the two cap's.

4) Please provide circuit parameters!

Regards,
Phil Corso, PE
Boca Raton, FL
[[email protected]] ([email protected]) {[email protected]}

 

Either the gain is less than the losses or your feedback ratio is way wrong. Bias is a possibility although class C requires no bias. The
other alternative is a hartley oscillator, which see.

Regards

cww

 

I have two simple inductive prox. switches that you can use to develop yours.

Take a look at my page:

http://www.geocities.com/the_beijing_dragon