Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Does linear regulator need Cin and Cout.....will it go unstable if nto used?

Status
Not open for further replies.
T

treez

Guest
Hello,

Does the LM3480 linear regulator require input and output caps to assure stability?

**broken link removed**

...the datasheet does not speak of this capacitance and stability.




....if you loof at the LT3082 linear regulator, the datasheet speaks at great length about the need for the LT3082 to have adequate input and output caps or esle there will be instability.
http://cds.linear.com/docs/Datasheet/3082f.pdf

So is the LM3480 just more immune to instability, or is the LM3480 datasheet just lacking in detail?
 

For the price of two capacitors I wouldn't risk leaving them out. Inside these linear regulators there is a high gain error amplifier and like all amplifiers they can easily become unstable if unwanted feedback paths appear, such as on their supply lines. There should at least be a capacitor on the input side to prevent this, one on the output is less essential but may increase stability as well.

Brian.
 

Hello treez,

the input and output capacitators are necessary to protect the regulator circuits against oszillation.

This regulators have high gain error amplifiers inside, and they are very sensitive against oszillation. So they need the capacitators.

The output capacitor also reduce the noise.

Regards

Rainer
 

These 2 capacitors are known generally as BY PASS (a capacitor that provides low impedance over certain (high) frequencies) capacitors. Meaning any transient on the input or output line may create false behavior of the device so these capacitors provide a path to ground for them.
The following link gives nice explanation on Bypass capacitors.
**broken link removed**
 

The datasheet does strongly hint that capacitors should be used.
  • The typical application circuit shows Cin = Cout = 0.1uF
  • The PSRR curves show the effect of using different capacitors
  • All the other typical performance characteristics assume Cin = Cout = 0.1uF
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
On our board the output 100n cap comes after a 100R series resistor and they dont report problems with LM3480
 

Hello treez,

On our board the output 100n cap comes after a 100R series resistor and they dont report problems with LM3480
Click to expand...
be happy, that you have no problems.:smile:

I have other experiance, because about a bad soldering point at the output capacitator. So I have to search for serveral hours, before I find the bad point. The measuring tip of my oscillosscope stops the oscillation about his capacity.

Regards

Rainer
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top