Regulators filters out ripple?

[TommyF]

How does a Linear or switching Regulator chip filter out ripple?

The ripple percentage is filtered out even more when it passes through a regulator chip. I don't see any filtering components inside a regulator chip to filter out ripple.

 

[davenn]

Hi there

putting your question into google I got

http://www.microchip.com/stellent/groups/designcenter_sg/documents/market_communication/en028091.pdf

see if it is of interest ... there were other links that may also help you

Dave

 

[TommyF]

yes it's called the PSRR

it eliminates the ripple so how

 

[davenn]

lets take the 78/79xx series linear reg

here's the block diag



The error amplifier using the reference voltage is going to do all it can to keep any variations in the output voltage to a minimum
it will compensate for variations in voltage on the input. And that is all ripple is ... a slight variation in the DC voltage


Dave

 

[TommyF]

Yes the error amplifier is a comparator , it compares the reference voltage with the output voltage. If there is an difference it will adjust the series pass transistor.

So it's not filtering out the ripple, it's leveling out the variations to keep it steady

 

[TommyF]

Some power supplies are low impedance and other power supplies are high impedance. What is the difference between them and when do you use a low impedance power and when do you use a high impedance power supply?

 

[davenn]

So it's not filtering out the ripple, it's leveling out the variations to keep it steady

and that also (as I said earlier) effectively filters out the ripple

do you really not understand what ripple is ?

 

[TommyF]

Yes it's Smoothing out the ripple by an error amplifier and the series pass transistor

LDO low drop out regulators use a series pass FET which has no voltage drop and other advantages which i don't know about.

 

[TommyF]

Each power supplies technology has different line or load regulation methods.

When I turn down the AC line voltage under 90VAC until the power supply turns off. The cutting off voltage is between 80vac to 90vac. I'm not sure what sets the cutting off voltage in a power supply.

 

[davenn]

I'm not sure what sets the cutting off voltage in a power supply.

probably mainly the combined component values selected in the design