larmar

modified 8 years ago

Almost 10MHz high cutoff—Voltage sample current sum—Avo-10V-V—AB output

175

01:52:38

The miracle of negative feedback!
Note: the app doesn't seem to like computing at or around f_hi: 100kHz works fine for me. 

published 8 years ago

schwenk

8 years ago

Very inspiring !

hurz

8 years ago

Looks like an audio amplifier but all in all quite some rubbish.

crake

8 years ago

You can achieve a similar frequency response with fewer transistors.

crake

8 years ago

So, is this a CB, CC, CB, class AB?

crake

8 years ago

I think I seen it now. CB, Cascode, Class AB.

larmar

8 years ago

You got it! It looks messy, I know: I'll just be happy to get it built and functional!

larmar

8 years ago

If you don't mind me asking, how would you make it with fewer transistors? Also, do you often encounter the error message: "Cannot Find Solution" or something similar in this app?

dannymarshall06

8 years ago

Yeah, a lot of times you can add a switch at the power source, leave the switch open when you start simulation, then close the switch, and it'll work.

dannymarshall06

8 years ago

Also, this circuit is really cool!

larmar

8 years ago

Nice tip Danny!

hurz

8 years ago

It changed a bit to the better since I watched it the first time. But what the hell are the transistor across the thermal compensating resistors at output connected as diodes?? They produce a hell of non linearity. There a lot more strange. Btw, the thermal compensating resistor with 14Ohm are quite high, more 1.5Ohm in this power class. Anyway, lets see were this is going to.

BillyT

8 years ago

It would be interesting to see this circuit built around the high percentage of unattainable resistor and capacitor values.

crake

8 years ago

@larmar try a CB, CC, CE with class AB output. You shouldn't need current sinks or sources either.

zorgrian

8 years ago

nobody does RF this way... not for real.com

crake

8 years ago

The class AB or the entire approach? I'm interested in RF, so any feedback would be great zorgrian.

crake

8 years ago

@larmar this isn't exactly what i was talking about before but, I'll post it just to show something similar can be done with less: http://everycircuit.com/circuit/6039672630542336

larmar

8 years ago

@crake That's exactly the configuration someone else made today! I might have to give that a try.

larmar

8 years ago

@hurz That was my attempt at short circuit protection, though I've heard there are several other methods. I like this way because it's intuitive: with a maximum desired current in mind, place a resistor, like the thermal runaway resistors of the AB output, such that the maximum current develops a potential, forward biasing the BE junction of the diode-connected transistor, and then consequently redirecting any over-current. I hope I explained that well, and I'd be interested in any other techniques you might know!

hurz

8 years ago

Ok, so you burn the transistors as fuse and wired as diode to then fall back to high 14Ohm thermal resistance which wont hurt?

larmar

8 years ago

Oh yeah, you're right about the resistors, way too high!

larmar

8 years ago

As far as the diode-connected transistors, that's me playing around, haha. Learn as you go!

hurz

8 years ago

Probably not to bad this idea,.if the transistor are not burned and strong enough. So what is the maximum they can take as Vbe 2V? 2V/14Ohm is about 140mA but probably far away from high power bilpoar transistors.. hmm think about a little more

hurz

8 years ago

You see what I mean?

larmar

8 years ago

Hmm, I've only ever used Si BJTs in any of my design, so I'm used to Vbe ~ .7V

larmar

8 years ago

I'm hoping to come across more designs making use of such things!

hurz

8 years ago

Check some more datasheets whats possible with Vbe or forward voltage drop at diodes

larmar

8 years ago

@crake, after looking at your circuit, I have a strong feeling that we have the same instructor, only your notes must be much better, because that circuit is clean!

crake

8 years ago

@larmar Thank you. Yes, I started thinking the same thing when I saw your circuit.

cspanbauer

8 years ago

I'm sure there are a few people on here that have the same instructor.

crake

8 years ago

I wonder how many?

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