F4 power amplifier

[cviller]

It might also be worth to check out these pairs (not sure how official):

2n5462/2n5459
or
j271/j310

First with high voltage and second with better transconductance.

[MiiB]

Now I've had some time to play with this little fine circuit in my simulater. First I had a hard time getting it to work and blamed it om my TL431 spice subcircuit. Later i found out that the 0.47 Ohm source resistors can't be 0.22 Ohm That is if you don't want to have 6 dB loss in the circuit.
I find the the way the 2 caps from the Jfet center bootstraps the output fets a stroke of genius. Thanks for shearing.

My question is regarding thermal tracking. Is this done by the TL431 or is it done by useing IRFP240 that dosen't seem to suffer as much from secondary breakdown.

[jacco vermeulen]

That Class A amps can only get colder still is very elegant,imo.
Why bother to stick a TL431 on a heatsink.

(shear it off)

[Nelson Pass]

Originally posted by MiiB
Now I've had some time to play with this little fine circuit in my simulater. First I had a hard time getting it to work and blamed it om my TL431 spice subcircuit. Later i found out that the 0.47 Ohm source resistors can't be 0.22 Ohm That is if you don't want to have 6 dB loss in the circuit.

My question is regarding thermal tracking. Is this done by the TL431 or is it done by useing IRFP240 that dosen't seem to suffer as much from secondary breakdown.

I can't imagine why .22 ohms wouldn't work.

As to the temperature compensation, the circuit drifts positive
on bias, so of course you set it at temperature, and it's fine.
If you want compensation, just put a thermistor in series with
the resistance between the + and control pins. When I do this
I usually use another resistor in parallel with the thermistor so
I can box its range better.

[mpmarino]

I ordered some 9240s and some jfets from Tech-Diy on Friday and they were in my mailbox today! Granted he's (?) in NJ and I'm right here in MA, but that's good service in my unhumble opinion.

-plug over

Now I will make an utter fool of myself (ahem, again). I have a question on this simple circuit that I should understand better, but don't

- Regarding the TL431, what exactly is it doing, and which way does it go in? I assume that the reference connects left (in schem), the anode connects neg, and the cathode connects pos. Am I right? Do I win the dunce prize?

[Babowana]

Originally posted by mpmarino


- Regarding the TL431, what exactly is it doing, and which way does it go in? I assume that the reference connects left (in schem), the anode connects neg, and the cathode connects pos. Am I right? Do I win the dunce prize?

I think you are right about the pins of Ref, K and A.
The reference voltage between Ref-pin and A-pin is 2.5V
whatever resistor value (at proper current level) is between
those two nodes. Then, you pay a peanut for the calculation
of the voltage at K ^^.

[jacco vermeulen]

Originally posted by mpmarino
which way does it go in?

Mark,

you can see the orientation of the TL431 on the board layouts.

In 1st grade HS chemistry class i learned OPA(grandpa) and HENK(origin of Hank) as memory clues for the electrolysis process.
Oxygen-Positive-Anode and Hydrogen-Negative-K(C)athode.
For electronic components i always think negative is where the current is drawn in, positive where it comes out. Retards Rule !
"What exactly is" doesn't count. You're disqualified too.

[mpmarino]

Thanks guys,

It makes sense to me now. For some reason the datasheet was clear as mud to me and I had a hard time picturing it at work in the circuit.

"What exactly is" doesn't count. You're disqualified too.

You've been waiting a couple days for that, haven't you

[Mad_K]

After inspecting the layout is seems to me that P1 is wired "backwards"? That is, you increase bias by turning it counter-clockwise? This assuming a standard 5K (Bourns?) single turn trimmer is used.

[jacco vermeulen]

Originally posted by mpmarino
For some reason

For some reason i don't get why there's not a uniform lead pattern for these devices, not even for same brand components.

National also manufactures the oldy LM335Z, besides the LM431.
Precision temperature sensor, but the +,- and Adjust leads are switched.
The LM335Z is a valuable friend for Class-A/Pretty-Pass amps, btw.

Months, if necessary !!