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Design oscillator circuit!

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khtnthanh

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HI all! I'm a student, I have a problem! I want to design a oscillator circuit at 50khz frequency.

what should I do? use a transistor or op-amp circuit and a positive feedback!
and may use give me some name of a transistor or op-amp

please help me!

any help will be grate!
Thank you so much!:)
 
Last edited:

Try this, its called Hartley Oscillator quite simple in fact !!!

Circuit.png

Simulation.png
 
khtnthanh said:
HI all! I'm a student, I have a problem! I want to design a oscillator circuit at 50khz frequency.
what should I do? use a transistor or op-amp circuit and a positive feedback!
and may use give me some name of a transistor or op-amp
Click to expand...

Since you are a beginner I strongly would recommend to use an opamp based oscillator because of the following reasons:
It is easy to understand and it is simpler to design (if compared with transistor-based structures) as long as you know the well-known oscillation condition from Barkhausen.
More than that - it has a very low output impedance - thus a load does not influence the oscillation.
As you probably know - one of the most common oscillator topologies is the WIEN type.
But be aware that for an oscillating frequency of 50 kHz you need an opamp with a gain-bandwidth-product of (at least) several MHz.
But this shouldn`t be a problem today.
 
Last edited:
HI all! I'm a student, I have a problem! I want to design a oscillator circuit at 50khz frequency.

what should I do? use a transistor or op-amp circuit and a positive feedback!
and may use give me some name of a transistor or op-amp

please help me!

any help will be grate!
Thank you so much!
Click to expand...
Hi
If you're going to design it yourself , as LvW mentioned , the best choice is op amp based wien bridge oscillator . but if you just need it's circuit , i think a transistor based oscillator would be suitable because it won't need simultaneous supply , it's price will be lower and you can increase it's out put amplitude up to each value that you need .
but as i think it is your first time to design an oscillator i think that op amp based oscillator is the best choice .

Best Wishes
Goldsmith
 
thank! all! but if a real circuit! how many prolems are the best importance?? the problem with transistor and op-amp!
 

khtnthanh said:
thank! all! but if a real circuit! how many prolems are the best importance?? the problem with transistor and op-amp!
Click to expand...

My recommendation: Search via Google for "Wien oscillator". You will find a lot of links and a lot of information how the circuit looks like.
 
oscillator.png
Thank alot!
but may you help me again! the frequency is not good! the frequency that I need is 50khz!
when I simulate with my circuit the frequency I recieved is about 20khz! I don't known why?
help me!
any help will be great!
Thanh
 

but may you help me again! the frequency is not good! the frequency that I need is 50khz!
when I simulate with my circuit the frequency I recieved is about 20khz! I don't known why?
help me!
any help will be great!
Click to expand...
Hi Thanh
I think if you change your op amp with something like TL072 or LF356 or any other better opamps the result would be better !
Best Wishes + Good Luck
Goldsmith
 
Thanh, as mentioned in my post#3 you need another opamp with a GBW of at least 5 MHz and sufficient slew rate. A 741 cannot be used for your task.
More than that, check your amplitude control circuitry (diodes). Where does it comes from?
 
LvW! I don't understand what u mean! this is Vout result of mine!

Vo = V(D1n4002) * (3*R8*C1*s + R8*R8 + c1*c1*S*s) / (R8*R8) + (C1*C1*s*s))
V(D1n4002) is threshold voltage!

is it true??please help me!
Thank!
Thanh
 
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khtnthanh said:
LvW! I don't understand what u mean! this is Vout result of mine!

Vo = V(D1n4002) * (3*R8*C1*s + R8*R8 + c1*c1*S*s) / (R8*R8) + (C1*C1*s*s))
V(D1n4002) is threshold voltage!

is it true??please help me!
Thank!
Thanh
Click to expand...

I don`t know where this strange formula comes from. Certainly, it is false. For example you add squared resistors (R8*R8) with squared conductances (sC1*sC1).
Why didn`t you follow my advice to google for WIEN oscillator?
You will see that the negative feedback path normally consists of three resistors and two anti-parallel diodes.

R2=R21(with diodes in parallel)+R22 between output node and inv. input ( example: R21=0.2k, R22=1.9k)
R1=1k (inv. input to ground).

Thus, for a safe start of oscillations the gain is (1+R2/R1)=1+2.1=3.1.
When the diodes are conducting the gain automatically is reduced to 1+2=3 .
 

but the current throught only one of two circuit of (D1, D2, R3) or (D3, D4, R4) at every period of time! so the other like seem a huge impedance!

thank! Lvw
 
Last edited:

khtnthanh said:
but there is only one of two series of (D1, D2, R3), (D3, D4, R4) the current throught at any point of time! so the other has a huge impedance!
Click to expand...

Sorry, I don`t get the meaning of your reply.
 

but the current throught only one of two circuit of (D1, D2, R3) or (D3, D4, R4) at every period of time! so the other like seem a huge impedance!
Click to expand...
Hi again
I think it is a good idea that you prevent from confusing sentences . can you please explain what you mean exactly ?
Best Wishes !
Goldsmith
 

I'm sorry goldsmith. it is difficult for me to explain because of my english skill.
I have simple idea is when two resistor(r1, r2) in parallel. if r1>> r2 the value of (r1//r2) ~= R2.

Thank you!
Thanh
 

khtnthanh said:
I'm sorry goldsmith. it is difficult for me to explain because of my english skill.
I have simple idea is when two resistor(r1, r2) in parallel. if r1>> r2 the value of (r1//r2) ~= R2.
Thank you!
Thanh
Click to expand...

OK - now I know what you mean. But I am afraid, your understanding is not correct.
For each half wave only one chain is "open" due to the diodes (R3 or R4). Both resistors (R3 and R4) never will act in parallel!
This means that the gain always will be larger than 3 and there is no amplitude stabilization at all.
When you follow the concept as outlined in my post#11 the oscillator should work.
 
Hi,to generate square wave,it's possible to comprise with an inverter,a resistor,a capacitor;pls refer to typical inverter oscillator.
For generate sin wave,it's also able to comprise with an inverter,a resistor,two capacitor,one crystal;refer to typical microcontroller datasheet.
 

khtnthanh said:
HI all! I'm a student, I have a problem! I want to design a oscillator circuit at 50khz frequency.
Click to expand...

do you want square wave or sine wave ? or some other type of wave - triangle, sawtooth most common.
 

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