role of optocoupler for biasing drain of amplifiers

[xvr]

That is absolutely the same as your initial schematic (just used 2 channel isolator).

> Could you give an intuition regarding how the diode and resistor act ?

They control open/close timings for MOSFET (almost the same as your initial schematic, but without capacitor)

You can safely drop all of them (just put small resistor, something about 20-200 Ohm, directly between output of UCC and MOSFET Gate)

[john23]

Hello ,according to the datasheet (photo shown in the link)I have to put 20V on the drain(which is the source of the NDT3055L mosfet) of the TGA2590 power amplifier that means i need to put
20V on the source of the mosfet.
You said that its a floating voltage without reference ,how do i make sure i have 20V on the source of the mosfet (drain of TGA2590) as shown in the diagram below.
Thanks.

https://www.qorvo.com/products/p/TGA2590-CP

https://ibb.co/SfNRtJy
https://ibb.co/xgF5VL0

[xvr]

Schematic is definitely wrong,
Remove V2 and connect VSSa/VSSB directly to Source of U2
Now V1 is your floating power, V4 - logic power, V5 - TGA2590 power.

[john23]

Hello, As i understand the component We have on the input Vcci_0 and INA pint which we get input
and the output which is desided low level from VSSA and high level from VDDA ,we can see it in the basic functionality of photo 1 link.If i Understand correctly your words we need to connect the mosfe gate and source to the mosfet .
In photo two i got a very high current(which says that my Vds and Vgs are too high),but we see that the mosfet opens.

In photo 3 I have connected the simulation as you told me ,but unfortunetly its not converging and freezes.
Why my simulation is freezes when i tried the configuration you reccomended?
Thanks.
LTSPICE simulation is attached and NDT3055L lib link spice model file.
photo 1:
https://ibb.co/6Jn2h0N

photo 2:
https://ibb.co/DKzMdXr

NDT3055L spice model:
https://www.onsemi.com/download/models/lib/ndt3055l.lib

UCC212 spice model link:

http://www.ti.com/litv/zip/slum649

[xvr]

Something very strange with your MOSFET connection. It has 2 pins for Drain, so on schematic 2 pins should be short. On your schema all 4 pins connected to different circuits. I can't say who is who on Spice model - there is no pin names, only Spice node numbers

[john23]

Hello XVR, I have tried to connect other mosfet but connecting VSS as you said just gives me very bad gliching result.
A schematics is shown below is it the proper way i should connect the driver to a mosfet?
Thanks.

[xvr]

Yes, connection is right, but result is very strange
Low pin of V1 should be connected to MOSFET source as well.
Try to add small resistor in gate of MOSFET (20 Ohm will be enough)

[john23]

Hello , the problem is that i dont know the exact power amplifier TGA2590 drain voltage if we connect it this way.
I need exactly 20V to know how it by the datasheet.

[xvr]

Power amplifier supply voltage has no relation to connection of V1. It will be defined by V5

BTW. Why not use P channel MOSFET? All isolated drivers and floating power supplies will gone avay.

[john23]

Hello , There is a logical problem
The source of the mosfet is connected to the drain of the amplifier.
The source of the mosfet is something floating :-)
I need the source to be 20V because its the drain of the amplifier.
So either my schemtics is wrong  and source of the mosfet is not connected to drain of the amplifier?
How do i make sure i get 20V to the drain of the amplifier?

[xvr]

That is exactly DB02S2415A used for. You still need it to power floating side of schematic

It"s V1 in Spice model

[john23]

Hello XVR,DB02S2415A outputs 15V voltage difference between the gate and the source of the mosfet(floating).
I need a solid 20V on the drain of the TGA2590 power amplifier with respect to the source of the power amplifier.
How the DB02S2415A does that?
Can you please draw so i could understand?
For the mosfet i understood the 15V difference  floating ,but how it helps us put 20V with respect to the TGA2590 source?
Thanks.

[xvr]

You need separate voltage source for it. It was labeled +24V in your first schematic

[john23]

Hello , there is a basic confusion I have.

We have a mosfet with 24V drain its VGS i getting plugged with 15V floating from  DB02S2415A floating difference.

But in my configuration as you see the drain of the power amplifier is the source of the mosfet.



So on one side we have the floating value of GIZ but on the other hand you said i should connect to the same node 24V to 20V converter I will try to build.

So we are connecting two different voltage potentials on the same node.

Arent they going to conflict which other?

Thanks.

[xvr]

You don't need 24V, it should be 20V. This is a amplifier power. You didn't specify power voltage for amplifier in first post, but label it as +24V, so I decided that your amplifier powered by 24V.
There are 3 voltage source in scheme in total: logic side power supply, floating power supply (from DC/DC) and amplifier power supply. That is all, bo more power supplies (no any +24V)

[john23]

Could you please draw the mosfet and amplifier with the devices ?
I am having trouble to imagine your words.

[xvr]

Your overall schematic is very over-complicated. You need just P channel MOSFET, one NPN bipolar transistor and a couple of resistors.
I will draw schematic...

All resistors values are taken approximately.

Q1 - your power MOSFET. Should have DrainToSource breakdown voltage > 20V. GateToSource also >20V. RDSon will determine voltage drop and power dissipation on MOSFET.
Q2 - any NPN transistor with CE > 20V and high enough Ic (100mA or more will be enough) - it will define turn on time of schematic. R2 limit Ic of Q2.
R1 used to discharge Q1 Gate, it will determine turn off time.
R3 determine Ib of Q2. Should be low enough to ensure Ic (with minimum h21e of Q2

[john23]

Hello I am trying to solve this riddle :-)
As shown in the diagram The output of DB02S2415A difference is 15V , this floating voltage supply goes into UCC5304DWVR which creates again a floating voltage for NDT3055L NMOS.
This floating voltage opens the NMOS and current goes threw from drain to source.
The problem starts with the parts that is not present in the schematics.
I need to connect TGA2590 power amplifier to J4 node. It needs 20V on the drain.
How do i make sure i have the desired 20V on that node and get the current of the NDT3055L(which was opened by the floating voltage of UCC5304DWVR)?
If there is some method i could use? because this floating voltage is confusing. i am used to this of voltage where each node has exact voltage with respect to some reference.
From the LTSPICE model I need some how to make 24V into 20V and make it pulsating open and close like the V2 because currently forsing steady 20V which is not good. is athere something that could be done?
Thanks.
 

[xvr]

In LTSpice schematic you again connect all 4 pins of MOSFET to different nets. I guess that one of them directly shot some MOSFET terminal to ground. There should not be.

As for 20V - power for your amplifier should be connected to terminal that in your schematic labeled 'After relay. 24V (ar)'. I don't know what relay was connected ant where, but definitely here should be connected just plain +20V. No any +24V from any relay should be used in final schematic.

In LTSpace change voltage of V1 to +20V and remove V3

> because this floating voltage is confusing. i am used to this of voltage where each node has exact voltage with respect to some reference.

Yes, but for flying voltage will be another reference - not common ground, as for all others.
If you want to see voltage on MOSFET gate set a probe to V(Gate)-V(Souce)

[john23]

Hello XVR, in the case below i conected two power amplifiers.
each of them needs to be 20V and 6A , and i get them by tuning the system with Vgs and Vds.

Is there a way to improve the circuit so my Vds  of the power amplifier could be tuned ?


Thanks.

[xvr]

Hello XVR, in the case below i conected two power amplifiers.
each of them needs to be 20V and 6A , and i get them by tuning the system with Vgs and Vds.

I'm not quite understand. You want to turn on/off 2 amplifier in parallel? On control both individually?
In any case Vgs and Vds is internals of switching schema and do not directly affect connected load (amplifiers). What you want to get?

[john23]

Hello XVR, I have 5 amplifier i need to power.Single and two pairs.
 I want both to be able to power a single amplifier and a pair from a single Vds and Vgs.
For that i need to tune the bias for my single amplifier and to tune sepratly for the pair.
Is there a clever way to tune to Vgs and Vds .
Its basicly a thing of a load.

[xvr]

> For that i need to tune the bias for my single amplifier and to tune sepratly for the pair.

Nothing. Your schematic do not depends of amplifier current (6A for single, 12A for pair), only for amplifier voltage. Voltage the same for both single and pair.
But you need 3 identical channel (including DC/DC and UCC) for control 3 independent subcircuit (1 single + 2 pair)

PS. Consider P channel MOSFETS from my previous post - your current schematic became monstrous 
PPS. Your currently selected MOSFET do not fit to your requirement: only 4A of Id and large Rdsonn - 0.1Ohm. Consider something more powerfull

[john23]

Hello XVR, Could you please reccomend me a PMOS model i could use?

Also , I have attached the two plots from NDT3055L mosfet.How do you see that its problematics , from the Vds sweep i can have 20A.
How do you see thats its limited to only 4A?


Thanks.

[xvr]

> How do you see thats its limited to only 4A?

It stated in its datasheet. LTSpice do not take in account physical limits of devices which it [LTSpice] simulate.

> Could you please reccomend me a PMOS model i could use?

You should firstly select REAL transistor, by its real parameters. Ids and Rdson firstly.

What maximum voltage drop on MOSFET you can tolerate? 0.1V (0.5% of Supply Voltage for AMP) will be acceptable?
And what budget limit for MOSFET? High power MOSFETs can be expensive 

SISS65DN-T1-GE3 (0.8 euro on Digikey). Gate maximum voltage is 20V , so additional zener should be used to protect Gate
FDS6681Z (1.49 euro). Gate maximum 25V, no zener needed