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Author Topic: RC Power Oscillator  (Read 21410 times)
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Posts: 337
Hi,

Will this circuit work as an power oscillator capable of pulsing
out approx. 5 Amps at 12 VDC?

GL.
   
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Posts: 1146
Did you simulate it in Spice already?  I use LTspice to check most of my circuits.


(I built an RC oscillator before, but it was symmetric. Both transistors had the RC network and were crossed with each other C to B.  Your oscillator, at face value, seems not to work, why?  well, think about how will the lower left capacitor discharge? What will you connect on the output?  )

EM


PS. This is what I built a while ago, and it worked great.  The output can also be taken from the other transistor and it will be 180 deg out of phase, so its complimentary, you can drive a push pull stage.
« Last Edit: 2013-03-21, 04:43:07 by EMdevices »
   
Sr. Member
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Posts: 337
Did you simulate it in Spice already?  I use LTspice to check most of my circuits.


(I built an RC oscillator before, but it was symmetric. Both transistors had the RC network and were crossed with each other C to B.  Your oscillator, at face value, seems not to work, why?  well, think about how will the lower left capacitor discharge? What will you connect on the output?  )

EM


PS. This is what I built a while ago, and it worked great.  The output can also be taken from the other transistor and it will be 180 deg out of phase, so its complimentary, you can drive a push pull stage.

EM,

Thanks for taking time to look at my circuit. I do not have a Spice simulator.
I have built (some long time ago) the standard oscillator you posted but this
oscillator does not meet my needs because of two tuning RC parts. I need
a oscillator that have just one R and one C to tune.

My thought for my oscillator is like this: At switch on there is no output so
the capacitor is not charged. This means the first transistor is not switched on.
The second transistor will switch on bringing the gate on the P-Type mosfet
low, thus switching on the output. Now the capacitor will charge and the
first transistor will switch on. This will swicth off the second transistor,
bringing the gate on the P-mosfet high again, thus switching off the mosfet.
Now the output is gone and the capacitor will discharge through
the base emitter diode on the first transistor, switching off the first transistor
again. The cycle repeats.  Now, by using a variable resistor in the RC network
will allow me to tune the frequency. That was the plan.

GL.
   

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You maybe use frequency part of this circuit, just thought it might help

Mike 8)


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Sr. Member
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Posts: 337
You maybe use frequency part of this circuit, just thought it might help

Mike 8)

Hi Mike,

Thank you for posting the nice OP amp based oscillator circuit.

GL.
   
Sr. Member
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Posts: 337
Hi,

Is there anybody on this forum that can help me running a sim on my circuit?

GL.
   
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Hi,

Is there anybody on this forum that can help me running a sim on my circuit?

GL.

Do you have ltspice? I've tried with BC546B, and IRF9640 instead of IRF9540N whose I have not the model. It doesn't work.

   

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GL,

EM was correct. The circuit you present can't oscillate but there are many possible solutions.

What is your target pulse rate frequency, duty cycle, etc.?

What components do you have available? ( 555 timers? op-amps?....PIC controllers with PWM output  ??? )


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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   
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It's turtles all the way down
Here is a simple FET based self oscillator that can work over fairly wide frequency range at considerable power. Proper phasing of the coils insures oscillation. I like simplicity. Tuning can be accomplished with a variable cap across L1.


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"Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy
   
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Same reply than in the other thread about a pulsing circuit:
For an easy power oscillator, I think that the simpler method is to use a MOSFET driver with a non-inverting input, for example the TC4420.
A simple or double RC circuit between the output and the input will trigger the oscillation and determine the frequency.
The TC4420 is cheap, has a small case (8 pins DIL), no need of external components, is able to output 6A with 25ns rise/fall time and is perfect to drive a possible power MOSFET. There is no need to bother with transistors when we see such little marvels...

   
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@Exn
Quote
For an easy power oscillator, I think that the simpler method is to use a MOSFET driver with a non-inverting input, for example the TC4420.
A simple or double RC circuit between the output and the input will trigger the oscillation and determine the frequency.
The TC4420 is cheap, has a small case (8 pins DIL), no need of external components, is able to output 6A with 25ns rise/fall time and is perfect to drive a possible power MOSFET. There is no need to bother with transistors when we see such little marvels...

I would agree 100% and there are so many new IC's that building circuits from the ground up has almost become a thing of the past. There are also integrated oscillator drivers having a mosfet driver and a built in oscillator section requiring only two external components. As well a person can now buy a miscrocontroller IC not much bigger than a postage stamp for under $10 which can replace whole circuit boards and has a degree of flexibility which was unimaginable 10 years ago.

It's a very exciting time to be in electronics.

AC


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Maybe I'm just a purist but I think ION's suggestion is the best.

The TC4420 is an excellent driver but the idea of using it for much more than a simple audio oscillator will get you into trouble.

Positive feedback on this device can be a real design problem. If you ever have one take-off on its own you'll learn what I mean. Many variables will govern the frequency, amplitude, wave shape and noise content of this thing as an oscillator for much more than audio signals.

The same problems abound when using any device beyond suggested usage. Too many integral functions and devices can really mess a project. - Integral diodes, pull-up/down resistors, capacitance, unpublished I/O inter-coupling - it goes on.

For the best control and flexibility just use a PIC to drive a TC4420 or some similar device or simple mosfet output stage.


---------------------------
"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   
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It's turtles all the way down
Maybe I'm just a purist but I think ION's suggestion is the best.

The TC4420 is an excellent driver but the idea of using it for much more than a simple audio oscillator will get you into trouble.

Positive feedback on this device can be a real design problem. If you ever have one take-off on its own you'll learn what I mean. Many variables will govern the frequency, amplitude, wave shape and noise content of this thing as an oscillator for much more than audio signals.

The same problems abound when using any device beyond suggested usage. Too many integral functions and devices can really mess a project. - Integral diodes, pull-up/down resistors, capacitance, unpublished I/O inter-coupling - it goes on.

For the best control and flexibility just use a PIC to drive a TC4420 or some similar device or simple mosfet output stage.

Agreed, I could have posted other circuits with higher gain drive devices, but with a low gain single transistor setup you have less a chance of spurious oscillation due to a poor breadboard, as I see most of the youtube posters have. (flying clipleads, plugboards, no attention to a careful build or layout).

I suggest to anyone trying to build a wideband oscillator, please read the ARRL handbook and acquaint yourself with good build practices.

It is not that I am incapable of making things complex, it is that I am ashamed to offer more than is necessary, especially when adequate specifications / requirements are not posted with the request.


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"Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy
   

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The ARRL Handbook should be a prerequisite for any electronics hobbyist - not just rag chewers and brass pounders  O0


---------------------------
"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   
Group: Guest
...
It's a very exciting time to be in electronics.
...

Electronics has always been the only industry that has never disappointed me!
From the tubes up to the power mosfets, from the germanium transistors to the GaAs FET, from the firsts TTLs to the µproc, it's never over, what an exciting and funny evolution!

   
Group: Guest
...
The TC4420 is an excellent driver but the idea of using it for much more than a simple audio oscillator will get you into trouble.

Positive feedback on this device can be a real design problem. If you ever have one take-off on its own you'll learn what I mean. Many variables will govern the frequency, amplitude, wave shape and noise content of this thing as an oscillator for much more than audio signals.
...

I agree that a very stable frequency or duty cycle won't be easy to get. But it's a general rule of power oscillators, they are not designed for that. For example induction heaters or microwave ovens have unstable frequencies.
The input signal for the TC4420 can be very low, using a negligible power in comparison with the output power, so it will not influence the output. The output can also easily be isolated from the load with a MOSFET, and so the load will not much inluence the reaction circuit. Such a circuit should be relatively stable for its simplicity.

Even in a small "lab", one doesn't use power oscillators but a frequency generator followed by an amplifier if we need power. It's the solution that I suggest.



   
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