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Power Amplifier

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techie

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I need to adjust the output of an XR2206 freq gen producing sine wave
at max freq of 100 Hz to an transformer 6V > 220V on which secondary
an 10W asynchronic induction motor is connected.

Voltage output of an XR2206 is 3V and current is in mA.

I thought of using an AB class amplifier but im not sure would it be the best solution.

Thx.
 
A 'normal' audio amplifier should work fine, depending on the impedance of the transformer. You may have to design an amp to feed a lower impedance than normal, or use a different transformer and supply voltage.
 
I need to adjust the output of an XR2206 freq gen producing sine wave
at max freq of 100 Hz to an transformer 6V > 220V on which secondary
an 10W asynchronic induction motor is connected.

Voltage output of an XR2206 is 3V and current is in mA.

I thought of using an AB class amplifier but im not sure would it be the best solution.

Thx.
Most assuredly not. Class D if you insist on that technique. I actually think a PIC is tolerable for this... https://www.electro-tech-online.com/custompdfs/2008/10/msintro1.pdf

The sinewave tables work as well otherwise... you could just as easilly program them into a memory chip and just clock a counter to drive the address lines, but that really is getting involved.
 
Class D also has no real advantage over an amplifier that's continuously driven using a sinewave.
With full output at 10W, a class-D amplifier dissipates about 1.5W of heat.
With full output at 10W, a linear amplifier dissipates almost 10W of heat.
Therefore the class-D amplifier is cooler and uses less power supply current.
 
With full output at 10W, a class-D amplifier dissipates about 1.5W of heat.
With full output at 10W, a linear amplifier dissipates almost 10W of heat.
Therefore the class-D amplifier is cooler and uses less power supply current.

And is more complicated, and generally less reliable.

But, as far as I'm aware, a class AB amp is far more efficient than that.
 
Nearly all IC amplifiers have the same heat dissipation as their output power.
For a typical 10W into 8 ohms amplifier I looked at the datasheet for an LM1875 IC.
7.5W output, 7.5W dissipation (30V total supply).
13W output, 13W dissipation (40V total supply).
18W output, 18W dissipation (50V total supply).
25W output, 25W dissipation (60V total supply).
 

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Most IC amplifiers do not have bootstrapping so they have a high voltage loss.
A few amplifier ICs use bootstrap capacitors for higher output power (and better efficiency).
A "new" IC amplifier output stage advertises "rail-to-rail" without expensive bootstrap capacitors. The idle current is low and is class-AB.
 

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I'm still working on this and still having some difficulties.

- I cant get linear amplitude gain characteristic in an frequency band that i need
10Hz - 100Hz.
- Output is connected to an symmetrical input transformer and i can't tweak both amplifications (current and voltage) to a desired levels. I need about x2 voltage gain and >100 current gain (depending on amplifiers input stage.

The amp I'm trying to make should work in AB class.
 
I'm still working on this and still having some difficulties.

- I cant get linear amplitude gain characteristic in an frequency band that i need
10Hz - 100Hz.
It is easy to design or buy an amplifier with a flat response from almost DC to at least 70kHz.

Post the schematic you have so we can see what is messing up its frequency response. Probably the transformer can't work a low frequencies.
 
Here is how i was working from the start. Improvments step by step.
It was relativle ok for a normal transformer, except for the gains, but it got complicated with the symmetric input transformer.

Dont mind the resistor values, i was experimenting a lot with them so i just left defaults on pics here.

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Atm im stuck on modifying the desing for symmetric input transformer.

All comments and suggestions are most welcomed :)

Thx
 
Why did you post your schematics at ImageCrap instead of posting them here?

What is a "desing"? Is it Design?

Your circuits are from the '60ies. The 100 ohm resistors feeding the transformer steal all the output power.

The first circuit has the base of Q4 shorted to its collector so it is a piece of wire.
The remainder of the circuits are better but still very old.
 
I posted on imageshack because of a habit, next time i will post images here.

Yes is 'Design', i misspelled.

Well im trying to design an amp myself but there always something wrong with it :(
I managed to get everything working as it should be except for voltage gain.
I just cant get the appropriate voltage gain at the secondary of a transformer.
It should be 220V but max i get is 80mV peak to peak. :S

Any ideas how to fix the voltage gain?

If these designs are so old can you point out to me how are things done presently?
Post some links with modern designs of power amps that could be used in this case.
Maybe would be better to adopt an egzisting amp design than to try to make my own.
One of the reasons i started designing my own amp is that i just couldn't find any amps designed for symmetrical input transformer.

Thanks for help.
 
Your circuit does not have an input transformer. It has an output transformer. The transformer does not need a grounded center-tap.

10W at 6VRMS is 1.67A RMS. The peak current is 2.36A. The extremely old 2N1711 output transistor must pass the 2.36A of peak current but its max allowed current is only 500mA and the power through it will melt it. I didn't look at the datasheet for the 2N1132A but it is probably the same.

The 2.36A peak current must flow through the 100 ohm emitter resistors. Then they will create a voltage loss of 2.36A x 100 ohms= 236V each. You have only 12V so the 100 ohm resistors have values that are far too high. 0.47 ohm resistors will have a voltage loss of only 1.1V each.

The 2.36A peak output current from each output transistor requires a power transistor like a TIP31 and TIP32. Their minimum current gain at 2.36A is about 12 so the max base current is 197mA. But you have the value of the base resistor at 1k so it will produce only 3mA at the peak of the waveform instead of 197mA. Your schematic with darlington transistors might work.

Your schematic with darlington transistors had so many things wrong that I fixed it without a long explanation. Ask questions if you want.

Can you turn off the chicken pox dots that are all over your schematic?
 

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I tryed simulating the schematic you specified but i just couldn't get close to
0V DC at a specified point, and the output was always a distorted square wave with V+ peak pulled down to 0V.
So i tried modifying the schematic a bit and this is the best i could get.
But in any case output isn't what it should be.

Thx for help :)

pic1mod.JPG

pic1mod_osc.JPG
 
I changed my amplifier schematic slightly and sim'd it. My sim program doesn't have a PNP power transistor so I used little 2N4401 and 2N4403 output transistors instead. They are straining and are smoking. I increased the value of the 3.2 ohm load to 8 ohms to reduce the heat in these little transistors.

I adjusted R1 for 0VDC at the output and R6 is adjusted for a voltage gain of 1.25.
R3 is adjusted to eliminate crossover distortion.

The output transistors probably need series emitter resistors (0.47 ohms) for thermal stability and Q2 should be mounted on the heatsink of the output transistors for thermal tracking. Q1 might need a small value capacitor from collector to base to prevent the amplifier from oscillating at a high frequency.
 

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