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strategy for turning bias poit for TGA2590

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yefj

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Hello,The TGA2590 needs 20V and 6A for proper functionality.In the schematics below its represented as 3Ohm resistor.
however when i need to bias two TGA2590 as shown in the end then my Vss lowers and Current threw it rises.
Which probably means i need to change the gate signal going to the gate of the mosfet or changing the drain voltage going to the mosfet.


Is there a way to take the out of the UCC component that goes as VGS into the mosfter and apply tuning mecahnism so the Vgs could change?
Thanks.


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Please clarify transistor pin assignment. NDT3055 has three terminals, not four.

Most likely we just see Rds voltage drop. NDT3055 has absolute maximum Id rating of 4A. Are you sure what you are trying to design here?

According to Edaboard rules, this post should be regularly appended to same topic thread https://www.edaboard.com/threads/ro...asing-drain-of-amplifiers.410706/post-1772928

But I see that it's almost fruitless up to now.
 
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Hello FVM , I use it in Pulsed mode not contiues.In continues i can get 25A.
Could you recommend power mosfet which could be better and deliver 20A?
Thanks.

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O.k, transistor rating is no problem for a short pulse as used in the test circuit. 0.7 V voltage drop has to be expected nevertheless. You should also consider that the real load includes bypass capacitors when selecting driver circuit and switch transistor.

Most standard MOSFET, Vds 30- 60 V, Id 10 - 20 A should fit. I'd use search engine of my preferred distributor.

NDT3055 symbol terminal 50 is still mysterious to me.
 
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How can i tune my VGS ?
is there a mechanism i could use i want to connect 2 or 1 TGA2590?
Thanks.
 
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Hello FVM,You said a very important thing which is the decoupling .
Where do you reccomend to put the decoupling capacitors, and what values to use?
my pulse is 500nsec 1u period 3n rise and fall time.
my amplifier is the load resistor of 3 ohms.
Thanks.

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Hello FVM,I Used resistor to simulate the rds. How do i update the capacitors shown in the diagram below into the simulation circuit?

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You would connect 200 nF parallel to 3 ohm equivalent load resistor.
Charging 200 nf to 20V in 20 ns needs 200 A, by the way.

I wonder if the amplifier is suited for fast Vd transient at all. Do you have application notes suggesting this operation.
 
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Hello FVM,where did you see in the data sheet that I need to connect 200nf in parralel.
Also how do you know that I need to charge 20 nf into 20v in 20ns ?
How did you get this time requirement ?
Thanks .
 
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1. Did you notice the C9 and C10 in the datasheet?
2. I was asking about intended pulse rise time for week or so without success. Now you specified 3 ns in post #6. 20 ns is a more realistic suggestion of mine. Pulsing 20V supply in 3 ns with 200 nF bypass capacitors would involve 1330 A current peak.

Bypass capacitors can be probably reduced for pulsed Vd operation.
 
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Hello FVM,I didnt know that.Could you specify the mathematical theory behind the words below?
or some manual i could use ?
Pulsing 20V supply in 3 ns with 200 nF bypass capacitors would involve 1330 A current peak.
Thanks.
 
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yefj said:
Pulsing 20V supply in 3 ns with 200 nF bypass capacitors would involve 1330 A current peak.
Click to expand...

--> Wikipedia --> Capacitor --> Current–voltage relation:

***********
Taking the derivative of this and multiplying by C yields the derivative form:
{\displaystyle I(t)={\frac {\mathrm {d} Q(t)}{\mathrm {d} t}}=C{\frac {\mathrm {d} V(t)}{\mathrm {d} t}}}

for C independent of time, voltage and electric charge.
***********

In words: If you want to charge a capacitor ... you need to put in current.
* The bigger the capacitor --> the higher the current
* the less time (for the same charge) -> the higher the current
* the more voltage --> the higher the current

thus I = C * delta_V / delta_t
Now in your case:
C = 200nF
delta_V = "from 0V to 20V" = 20V
delta_t = "within 3ns" = 3ns

Now you get I = 200nF * 20V / 3ns ...

THIS simply is what a capacitor does. It´s what makes a capacitor a capacitor.

Thus it´s highly recommended to be understood an known for anyone who works with a capacitor. (not only circuit designer).
I recommend to keep basic capacitor working principle in mind ... at least one should know "where" to find the information /formula and "how to use it".

*******

Charging a capacitor basically similar to "filling water into a bucket".

Klaus
 
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Hello Klaus, Very good eye opening answer :) i need 1333A to do that.
SO what are my options ?
i need to reduce the bypass capacitors? or just increase the rise time?

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yefj said:
SO what are my options ?
i need to reduce the bypass capacitors? or just increase the rise time?
Click to expand...
Reducing the capacitors is no option, since they are mandatory according the datasheet.
Others have already asked why you want to switch the power supply at all. (And with those parameters)
I guess I'm not alone with the opinion that it makes no sense at all.
Still you hide your ideas/informations.

Klaus
 
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Bypass capacitors of a microwave amplifier must not necessarily have higher capacitance than a few 100 pF up to nF. But the complete circuit must be designed for the intended operation. I don't even know if TGA2590 is suited for fast Vd pulsing, e.g. what's the value of internal coupling capacitance.

You never explained the purpose of fast Vd pulsing or the significance of planned rise time. We can't assess if it's usefull or even possible with this amplifier.
 
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