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role of optocoupler for biasing drain of amplifiers

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yefj

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Hello,In the diagram sown below I have a MOSFET called NDT3055L, the mosfet sends the current into the Qorvo TGA2590-CP drain.
When we test the circuit the source of the mosfet is basically floating although when I will connect the amplifier to source then the QORVO amplifier will introduce a load to the source of the mosfet.
Somehow the optocoupler helps with the transition of the state when we don't have QORVO amplifier load on the source of the MOSFET.
What is the role of the optocoupler in this situation?
I'll be glad to have some analog design logic behind putting this component in this position.
Thanks.


TGA2590-CP - Qorvo

www.qorvo.com www.qorvo.com

1713358389211.png
 
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UPDATE:
Hello , I have simulated an identical device gate driver shown below.
As you can see my output pulse moves from VDDA to VSSA .
If this is going to a mosfet then i need to know what voltage goes into the the MOSFET.
given that DB02s2415A is that source of my driver how do I know what voltage potential goes into the gate and what into the source.

I know to simulate the interactionof this driver and the mosfet and if i dont know what ecactly are VDDA and VSSA then i will not know what will go into my MOSFET and my simulation could the opposite ofthe voltage that will drive this mosfet in reality?
Thanks.
1713794868131.png
1713794740990.png
 
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UPDATE:
Hello ,according to the datasheet I have to put 20V on the drain 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
1713871847246.png

1713871825392.png
 
Last edited:
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Hi,

yefj said:
You said that its a floating voltage without reference ,
Click to expand...
Who said this and where?
In my eyes every voltage needs a reference.

****
For me speaking ... it´s hard to help you, because I don´t get any feedback. I recommend things, I ask questions .. but all gets lost in space.
You don´t keep focussed on the probelm befroe, but with your next post you talk all about your new ideas ... but you don´t communicate with us.

****
Example: In post#13 I posted a "relay equivalent" for your MOSFET. No reaction at all. Maybe you don´t read my post, maybe you don´t understand how a rely works, maybe maybe maybe ... I don´t know because there is not feedback at all. I rate this that you are not interested in my posts.
And BTW: there´s nothing wrong when you are not interested in my post. That´s fine.
But if you want to discuss with me, then I expect to keep up a bidirectional communication. (like: referring to my text with your information/answers)


Klaus
 
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Circuit in #23 doesn't work because it misses the necessary floating power supply, as previously explained for UCC5340. A minor point, you apparently trying to use switch to drop the voltage from 24V to 20V. This doesn't work with a gate driver controlling the MOSFET.

An additional question regarding your schematic, what is pin 50? MOSFET has only 3 electrical terminals.

There's an open question from the start of this thread. What is the required switching speed? How is it determined?
 
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Hello Klaus, Yes you are tottaly correct i will try to focus.
From the datasheet of TGA2590 drain source resistance of the power amplifier is 20/6=3Ohms.
But my spice model is not logical.
How do i simulate the mosfet power amplifier anddriver together?
Thanks.
1714208035953.png

--- Updated ---

UPDATE:
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?
--- Updated ---

Update:
Hello ,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.
 
Last edited:
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Hello Klaus, if by relay you mean mosfet then Mosfet n-channel is on when Vgs>Vt and it could be in linear or saturation. and there is another condition with Vds.
 
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Hello Klaus ,of course with you :) i am maybe having trouble to undestand.
You said in post 13 a photo of mosfet relay and asked how it works.
I answered that. Why i didnt answer your question.
It simple mosfet :)

1714212713593.png
 
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Hi,

I see it´s getting difficult in communication. I ask to focus.
It´s a relay circuit. And I want you - for the time being - to forget about MOSFET.

May I ask for a sketch with (hand drawn)
* A 12V battery
* the 3-leg relay circuit of post#13
* a 21V Battery
* a 3 Ohms resistor

Nothing else.

Thank you.

Klaus
 
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Relay analogy shows that gate node must be biased xx volts above source potential to turn the switch on. It does not address switching speed, actual threshold voltage or transfer function.

Referring to the simplified equivalent circuit seems in so far appropriate as none of the circuits presented in this thread manages to set gate voltage correctly.
 
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Hello Klaus, by the definition shown below and the data you gave the hand written circuit is shown below.
Did i do it correctly?

Basic structure of mechanical relays​

Relay consists of a coil, which receives an electric signal and converts it to a mechanical action and contacts that open and close the electric circuit.

1714291622829.png
 
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Hi,

I did not ask for any connections ... nor GND. I wanted to do this later, step by step. Thus I wrote "nothing else"... and meant it seriously.
This is why I have to say sorry, I´m not the right person, because I´m not patient enough (I`m a bit stressd aout by other problems)

I tried this short step by short step, because I think it is important to do one step, then talk about whether it is correct, and in case it is not correct to fix it.
Then do the next step.

Don´t get mad at me by this: From what I see .. you think three steps ahead but miss to get the first one correctly ... and then one needs to correct three steps, while each of these three steps is a different topic.

I´m sorry for not being patient enough. Good luck.
Hopefully there are others that can teach you better than I can.

Klaus
 
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Update:

maybe baicly its like this? we put a voltage source dirrctly to that point
and the masofet has 29-20 Vgs pulse?but the 20V voltage source is constant that is the problem.
Thanks.

1714300756325.png
 
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