regulator capacitor logic

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yefj

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Hello, I have a basic regulator shown below. I use LT1084 instead of LD1084 and As you can see the simulator works great without capacitors.
I understand that capacitors are used to filter out the noise from power supply.

I have a circuit which uses a lot of capacitors both near input and output as shown in the photo in the end.
1.The network starts with polarised capacitor as shown in the blue arrow, why polarized?
2.why we have two networks both input and ouput?
3.I know how to simulation AC filter responce. how can i know based on the networks to what purpose they where planned for?
Thanks.


LD1084:

LD1084V pdf, LD1084V Description, LD1084V Datasheet, LD1084V view ::: ALLDATASHEET :::

LD1084V Datasheet, LD1084V datasheets, LD1084V pdf, LD1084V integrated circuits : STMICROELECTRONICS - 5A LOW DROP POSITIVE VOLTAGE REGULATOR ADJUSTABLE AND FIXED ,alldatasheet, Datasheet, Datasheet search site for Electronic Components and Semiconductors, integrated circuits, diodes, triacs and...
pdf1.alldatasheet.com

LT1084:

LT1084 pdf, LT1084 Description, LT1084 Datasheet, LT1084 view ::: ALLDATASHEET :::

LT1084 Datasheet, LT1084 datasheets, LT1084 pdf, LT1084 integrated circuits : LINER - 3A, 5A, 7.5A Low Dropout Positive Fixed Regulators ,alldatasheet, Datasheet, Datasheet search site for Electronic Components and Semiconductors, integrated circuits, diodes, triacs and other semiconductors.
pdf1.alldatasheet.com




 

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@yefj, you wont be using traditional capacitors at 10 Ghz, in fact this pretty much tells
the story (SRF = self resonant freq) :

How to Select High-Frequency Capacitors for RF Circuits

High-frequency capacitors are sometimes used in RF circuits, but they only work in specific instances and must account for the PCB layout.
resources.pcb.cadence.com





Quality Multi-Layer High-Q Capacitors from Johanson Technology

Johanson Technology is your source for High Frequency Ceramic Solutions.
www.johansontechnology.com

Hopefully you have a network analyzer to evaluate your layout and performance and
components.


Regards, Dana.
 

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Hello , regarding the output current of the LD1084 device.(data sheet shown below)
I dont have a SPICE model to test it.
from the datasheet shown bellow the output current can be 5A which will totally burn my device.
In the data sheet they give me a formula for the output voltage.
so inorder to know how much current will to the load i need to know the input resistance of the load device?
maybe there is some link between the R1 and R2 to the output current?
Thanks.


 

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Hi,

there is no link between R1 and R2 and the output current. Those resistors are the so-called feedback network defining the output voltage. A voltage regulator with a fixed output voltage has this resistors inside the package.

Keep in mind the LD1084 provides up to 5A. How much current goes into your load (sinked by the load) depends on its impedance e.g. a 10k resistor will for sure not sink 5A (only with an output voltage of 50kV ).

What is connect at the output? I assume some some active components e.g. amplifiers. If so check the datasheet regarding its current consumption.

BR
 

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