Class a amplifier

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wien

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I'm trying to connect a class A power amplifier to a circuit that has a resonance frequency of 110 kHz, has 11 v, and has almost no current. I'm trying to make about 10w of power by using the amplifier to make 1A of current. Vcc is trying to use 15v or 12v. Vcc uses 12v or 15v and please recommend resistance values for that

 

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Does it have to be Class A ?

Unless you make Rc a parallel resonant LC and remove Re you will find it hard to get 10W from that schematic and you would need a large heat sink on the transistor. Used in that configuration you probably also need an output coupling capacitor to block DC passing straight into the load.

I would suggest a Class B or AB push-pull output stage instead, it would be far more efficient for little extra complication.

Brian.
 
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What specifically is your load Z ? Specs and a description, is it capacitive,
inductive ....?

Is this a school test ?


Regards, Dana.
 

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Can A-level and A-level amplifiers be boosted to 10W?
 
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What specifically is your load Z ? Specs and a description, is it capacitive,
inductive ....?

Is this a school test ?


Regards, Dana.
 

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For your specs you can expect 8 ohm load impedance.

Select Rc about the same or 20% greater than your load impedance.

Try to eliminate or minimize Re value.

Drive the transistor so its average resistance gravitates to a value about the same as your load.

This creates output centered at 1/2 supply V.
 

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    wien

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danadakk said:
What specifically is your load Z ? Specs and a description, is it capacitive,
inductive ....?

Is this a school test ?


Regards, Dana.
Click to expand...
It's not a school exam, it's a circuit used for machines that need to be made in projects that schools do. I'm a high school student, so I'm new to circuits this time, so I don't know much about them yet. There's no specific frame, so I just need to make 10w. I'm not sure, so can you tell me what load Z is?
 

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Hi,

voltage, current, impedance.
You know Ohm´s law?

In my eyes it can´t work with
* 11W
* almost no current
* how do you think to "make" 1A
++++
What I don´t understand:
You talk about "a circuit that has a resonance frequency of 110 kHz, has 11 v, and has almost no current."
What is it?
Somehow I think about an RLC. But series, parallel?

So we know ther is a circuit with 11kHz resoanance. But is the electrical (amplified) signal also exactly the resonance frequency.
(To do so it needs to follow all tolerances and drifts "of the "mysterious cicuit"

You talk about "11V". What is it? 11V RMS, peak, peak-to-peak? Something else?
Same with "1A"

To me it´s all a riddle without any meaningful function / information / use..

Klaus
 

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Rather than play with circuits with no chance of working as you expect ( 110 kHz 1A from a TL072 into a Class A ), let's review your specs & tolerances so you ask questions about what you need to learn.

10Vac Units? Vp, Vpp, Vrms, Vavg These are all relative to how it is measured and what you need.
Tolerance = roughly ? variable ? or just managed to get? It is better to say tuneable or fixed with say X% tolerance. such as X= 10% or can you imagine a need for 1% ?
Freq = 110 kHz sine, Was this by accident when you were trying to get something else.
Quality = Different attributes are used for sine, square, triangle, sawtooth, stair-case and all these can be synthesized in circuits. e.g. specify f = ___ +/- ___ sine ___% total harmonic distortion (THD) or for square wave, < 1% asymmetry, for sawtooth ___% linear error.(gain, offset or curve) max
Environment = ? Indoor (Benign), Consumer temp range, Industrial temp Range, Military temp and mechanical environment. (shock & vibe)
Load = ? define RLC values Ohms, Henries, Farads with tolerances, then current in Amps can be computed. DC motors for example draw > 10x the start current as rated current and all inductors have a DC resistance or DCR. All Capacitors have an equivalent series resistance, or ESR.
Thermodynamics= Power dissipation max, Temp rise max, implies a heat sink required with thermal resistance 'C/W.

This can be expanded or simplified. But the bottom line is to engineer something means to define is measurement qualities and limitations and all the quantity assumptions like power, voltage, temperature and impedance. For questions, it is good to state your limitations on tools, experience and preferences to learn for better answers. Like is this just for simulation fun, prototype or hobby or future profession.

This may seem boring, but engineering needs to be data-driven with specs and tolerances.

However , I can see a dozen things go wrong with this circuit, I made for you. For your amusement.



Maybe all you care about is finding a current amplifier that works better than Class A.
If you can read schematics, look at discrete audio power amps.
 
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The load Z is the impedance of the load, what the 10W is driving. Is it an ultrasonic
transducer, a motor, a speaker, a lamp, a led, what is the 10W amplifier used for
other than creating heat (its 10W will ultimately appear as heat in some form).


Regards, Dana.
 

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Thank you for always doing your best to answer questions. I learn a lot thanks to you.
--- Updated ---

I'm going to make a receiver for a magnetic resonance wireless transmitter circuit. So I used a Winbridge oscillator to make a circuit with a resonance frequency of 110 kHz and 11V at 110 kHz as shown in the picture above. But my goal is to transmit 10W, so I need 1A of current. The purpose of this circuit is to transmit power.
 
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The purpose is not clear.

Is this to transfer power or data or both? i.e WPT

What units? 1A rms? What about frequency tolerance?
Show a block diagram with signal parameters.

Do you already have a magneto resonant antenna pair?

If you have a high Q, then you can drive it with a square wave FET like a power supply.
 
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It's only for transmitting power. It transmits in a resonant magnetic coupling method. I haven't made antenna pairs yet. My role in the project is to make a transmitter, so I don't know the antenna, but when I make a transmitter circuit, I decided to make the antenna accordingly.
 

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OK but you said "I'm going to make a receiver" Rx what ? power or data?
If you research Wireless Power Transfer or WPT, you will find thousands of research articles on magneto resonant loop antennae with high-current film capacitors and transmitter-receivers. You might find one more useful by choosing keywords to add to the search.


The oscillator is the "easy" part, so not much is said about this.
The choice of configurations, power driver and antenna tuning is the tricky part.

Magnetically Coupled Resonance WPT: Review of Compensation Topologies, Resonator Structures with Misalignment, and EMI Diagnostics

Magnetically coupled resonance wireless power transfer systems (MCR WPT) have been developed in recent years. There are several key benefits of such systems, including dispensing with power cords, being able to charge multiple devices simultaneously, and having a wide power range. Hence, WPT...
www.mdpi.com



If you hit a "paywall", often the title can be found on www.Researchgate.com , which is free.
e.g. transmit coils
 

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I made a mistake. I make a transmitter.
--- Updated ---


This is an example of a transmitter made by someone else. This person also used an oscillator and then an amplifier.
 

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I can guarantee that is not class A !
Why do you specify class A, for WPT there is no need for conduction over the full cycle or great linearity.
Incidentally, the schematic in post #15 seems to connect R4 wrongly, my guess is the top and wiper should not have a link across them. I'm not sure D1 is useful either.

Brian.
 

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Also, the D1 is clearly reversed.
It ought to convert a bipolar sine to a unipolar positive biased sine wave with a diode -ve clamp.
The pot appears to bias ineffectively the peak gate voltage during conduction. However, the square law effect (Vgs-Vt)² adds distortion making the sine oscillator a poor choice in the 1st place when a square wave osc can be more accurate and efficient with a high Q series resonator.

Overall, not a great implementation but without specs, it doesn't matter.
 

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Hi,

and R4... is connected as variable load.

this is another example why not to use random circuits from the internet. There is so much nonsense around.
As Tony already mentioned .. there are many really good solutions. Look for reliable sources like
* semiconductor manufacturers
* universities
* reputable engineers

these documents usually also give informations like
* theory of operation
* formulae
* part selection
* and so on.

Klaus
 

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