real life method to properly biasing an amplyfier

UPDATE 2:
Hello Brad, given the datasheet could you say why you cant see the TL431 supplying the needed current?
we supply Vg1 with -2.5V, what current it could sink under these circumstances?
Thanks.

yefj said:

given the datasheet could you say why you cant see the TL431 supplying the needed current?
we supply Vg1 with -2.5V, what current it could sink under these circumstances?

Click to expand...

The datasheet for TL431 limits it to 100mA and 1kHz.

The description of your amplifier IC tells how it can attain 400mA or so. Unless my understanding is wrong, the same Ampere level has to go down through the negative supply rail, and at any frequency possibly up to 10GHz. Application schematics show TL431 operating in positive territory, never negative. TL431 does not seem adequate for the job.

There are negative voltage regulators such as LM337, 7805, etc. Some are adjustable.

yefj said:

Hello ,I understand that the value of the load is irrelevant.
Whats relevant is the ability of the circuit bellow to sink current while keeping the desired -2.5V
When I swept RLoad for different value and i see that at some Rload values i get 8mA(twice the maximal rating)
How do i know that it will get enough current from my reference regular source ?
Could you say why exactly its not going to work,as i see it in the simation i get 8mA for -2.5V for 800 ohm load?
LTspice file is attached.
Thanks.

Click to expand...

If you say load is irrelevant then puzzle over poor design examples with load why is this relevant? Very illogical.

BradtheRad said:

The datasheet for TL431 limits it to 100mA and 1kHz.

The description of your amplifier IC tells how it can attain 400mA or so. Unless my understanding is wrong, the same Ampere level has to go down through the negative supply rail, and at any frequency possibly up to 10GHz. Application schematics show TL431 operating in positive territory, never negative. TL431 does not seem adequate for the job.

There are negative voltage regulators such as LM337, 7805, etc. Some are adjustable.

Click to expand...

Hello Brad, 400mA current consumption is the consumption of the VDD input as shown bellow.
The reference components are supplying current for Vg1 Vg2 not Vdd.(as shown below)
As i see it TL431 have nothing to do with the 400mA because they are not supplying for the Vdd.
Where am wrong in my logic?

I'm looking at datasheet instructions regarding VG1. Apply -2V first (to pin 13), then a couple steps later 'increase' to desired IDD. It's ambiguous whether it means to increase amplitude (further into negative polarity) or dial it closer to zero. It's uncertain how much Amperes comes from the positive supply (pin 2) and how much goes through the negative supply (pin 13).

Conventional operation suggests the amplifier draws some from positive and then a comparable amount from negative. (Perhaps as much as 1 Ampere peak). So to be on the safe side I recommend a more beefy regulator than TL431.

Until @jefj learns to design properly with functional I/O specs & block diagram 1st then detailed schematic 2nd, his questions seem to be irrelevant details

Idd = Iss