Originally Posted by Hero999

I still hope you sign up, we're a bit short of really active members who post loads.

Then perhaps you've made a mistake with the simulation settings/models.

Could you please post a scheenshot.

.

Ok I signed up, here is a link to my first post:
http://www.stop-microsoft.org/bbs/in...=12082.new#new

As far as simulation is concerned, I will post a screen shot after I rebuild the circuit (didn't save sorry). This might take a while as I have no acess to internet from home (school time only).

Thank you for your help!

Great.

I like your signiture by the way.

Do you understand negative feedback in the booster now?

I'll try simulating it in LTSpice.

Originally Posted by Hero999

Great.

I like your signiture by the way.

Do you understand negative feedback in the booster now?

I'll try simulating it in LTSpice.

Yes, seems clear at this point.

Thanks!

Oh, and please visit Most random videos in chit chat section
Most Random Videos

I am sure you will find some funny videos there...

Oh and there are a lot of quotes from Joseph Stalin. Some can be scary...

“Death solves all problems - no man, no problem.”

“A single death is a tragedy, a million is a statistic.”

“When we hang the capitalists they will sell us the rope” (LOLZ I LOVE THIS ONE!)

“If the opposition disarms, well and good. If it refuses to disarm, we shall disarm it ourselves.”

"Education is a weapon whose effects depend on who holds it in his hands and at whom it is aimed.”

"Mankind is divided into rich and poor, into property owners and exploited and to abstract oneself from this fundamental division and from the antagonism between poor and rich means abstracting oneself from fundamental facts”

Originally Posted by Hero999

Q5 and the diodes forms a current regulator that biases Q6 (a high gain common emitter amplifier).

Hero, I think you had a brain fart here. Q6 is an emitter follower with a voltage gain of slightly less than one.

You're right and Q5 is the constant current load for it.

I've just simulated it in LTSpice and it works perfectly.

Originally Posted by Hero999

You're right and Q5 is the constant current load for it.

I've just simulated it in LTSpice and it works perfectly.

I'm guessing that his transducer needs to be driven at ≈40kHz. The amplifier's response as drawn is about 1.3dB down at 40kHz. It also slews at about 12V/usec, meaning you can only get about 100V p-p at 40kHz out of it, even with no load. Sinewave simulation shows lots of distortion at 40kHz with 80V p-p output. The output of the LT1001 is a triangle wave under these conditions.
If 40kHz is not the target frequency, then never mind!
There are probably things that can be done to improve this performance.

It can be fixed by doing the following:

• Use a faster op-amp.
  
• Reduce R12 to increase the voltage gain of the buffer and put less strain on the op-amp, be careful too higher gain will cause oscillation.
  
• Reduce the compensation cacitor values, again watch out for oscillation.

Hi there,


Hmmmm, did somebody say 120 volts at 1.2 amps? This is got PWM written
all over it. Anything linear is going to eat up lots of power reproducing
sine waves, unless square waves are acceptable of course, but then rise
and fall times have to be carefully considered also. MOSFET's anyone?
They are quite efficient for rectangular waves.

In any case, calculate the power lost in the output transistors
before deciding on a particular design and go from there.

The problem is to build a decent class D amplifier, the switching frequency needs to be much higher the the bandwidth, for 40kHz the switching frequency would need to be 320kHz minimum.

on1aag,
Regarding the transistors: I just used the higest Vce transistors on LTSpice, I agree they need to be rated to at least 300V.

Originally Posted by Hero999

You're right and Q5 is the constant current load for it.

I've just simulated it in LTSpice and it works perfectly.

Q3 is upside down.

Originally Posted by on1aag

Maybe it's a symmetrical transistor ?

on1aag.

It turns into a low-beta transistor when you swap emitter and collector.

.model 2N5401 PNP(Is=21.48f Xti=3 Eg=1.11 Vaf=100 Bf=132.1 Ne=1.375 Ise=21.48f Ikf=.1848 Xtb=1.5 Br=3.661 Nc=2 Isc=0 Ikr=0 Rc=1.6 Cjc=17.63p Mjc=.5312 Vjc=.75 Fc=.5 Cje=73.39p Mje=.3777 Vje=.75 Tr=1.476n Tf=641.9p Itf=0 Vtf=0 Xtf=0 Rb=10 Vceo=150 Icrating=600m mfg=Fairchild)

The simulation oscillates when you place the transistor correctly.

Originally Posted by Hero999

It can be fixed by doing the following:

• Use a faster op-amp.
  
• Reduce R12 to increase the voltage gain of the buffer and put less strain on the op-amp, be careful too higher gain will cause oscillation.
  
• Reduce the compensation cacitor values, again watch out for oscillation.

Sounds good. I will do that along with a minor change to the emitter - follower circuit. I would like to use Darlington pair. Doing so I need to add 2 more diodes. The signal frequency will be varied from 6Hz - 60Hz so I probably won't have any issues with gain roll-off. I never dealt with switching amplifiers or components before so I doubt I can design a Class D amplifier at this point. So I will just stick to linear for now.

Thank you for your help.