150v 80Khz piezo driver amplifier

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#3
I already checked LM1875, 1876 and 3886 datasheets; with LM1876 and 3886 there is no problem that they have a bit under 100Khz but LM1876 they only say 70Khz power bandwidth..
But at this point i have a transformer calculation problem.
- First, i dont know detailed trafo calculations,
- Second, the trafo has to be 80Khz tuned
- Third, primary coil must have 8 ohm exact inductive load at 80Khz.
- Fourth, this trafo must handle at least 20W power.
And naturally i cannot calculate a working trafo that can realise that needs!
I know that, here is not place for trafo calculations but may anybody calculate that trafo for me?
Thanks a lot.
 
#8
No. Its for piezo ceramic motor driver. And i will use a signal generator to change frequency. So the amp must have 70-80Khz bandwidth at least.

2 chips which doubles the voltage swing.
Click to expand...
So if i use two LM3886 bridge and feed with +/-38v i can have 38x4=152v swing teorically. Is it? But i guess there is another problem that;
My piezo pads have 65pF capacitance. At this frequency (75Khz) it looks like short circuit from the amp output.. Do you think LM3886s can handle this?
 
#9
"........At this frequency (75Khz) it looks like short circuit ...."

How ? The reactance for 65pF at 75Khz is over 30 K ohms ! What am I missing ?

Your voltage swing with bridged mode is twice ( x 2 ) and not x 4.
It's power delivered which is x 4 ( voltage squared ).
 
#13
".... equals 38+38=76v not 154... Who gave that idea?
...." .................You indicated that in your earlier post 🙂

Do you require a sine wave signal ? If you could manage with a square wave , things might get much simpler .

At 100Khz maybe you could use a ferrite core transformer ??
 
#17
Here is another one .
http://www.lab-systems.com/products/amplifier/a303.html

Gives you an idea of what they are using in the market !

Looks like you can rig up a simple class B amp with MOSFET's in bridged mode. Should be simple and no need for transformers which can be a big pain in itself.

You want 150V pp. So each bridge should give 75 vpp.
With split supplies you need AT LEAST +/- 45 volts supplies. More to take into account supply drop on load and transistor losses.

Looks like 0.5 % distortion is OK. So a class B or 'almost on' biased transistors might be OK . I think !

Comments anyone ?
 
#19
1.) Do you need to be able to vary the output voltage ?

2.) Do you want a bandwidth form 70 kHz to 80 kHz or do you need from DC up to this frequency range?

If the voltage can be fixed AND the output signal is narrow-band (i.e. 70 to 80 kHz) then you could as well use a class-C output stage and the voltage-transformation can be done purely by the use of caps and inductors.

Regards

Charles
 
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