Advantage of using Low Dropout Regulator

[lilimike]

I was dismantling and old FTA receiver and came across an LM3940 Low Dropout Regulator which drops the voltage from 5 to 3.3 Volts.

Is there an advantage in using this type of regulator versus using a regular regulator?

Mike

 

[crutschow]

The advantage is that you can use a source voltage closer to the output voltage. That will minimize power dissipation in the regulator and improve efficiency.

If your source voltage is several volts above the output voltage, then there is no advantage to the low dropout design.

 

[lilimike]

Makes lots of sense,

Thanks for the explanation Carl.

Mike

 

[MRCecil]

Yes, in some cases. Less overhead is required. The LM3940 can deliver a regulated 3.3V output from a 5V supply, where a typical regulator requires 2.5-3V or more overhead.

 

[tvtech]

Low Dropout regulators are typically used where there is no "headroom to play with''. Anyone here remember that term??

For example: A raw, smoothed PSU that barely puts out the the required Voltage....never mind the stuff coming in...And it must still regulate the Output despite the Input Voltage..

Solar Panels are favourites. Why did I say that?

Essentially, they regulate the Output Voltage with minimal Power loss across the Series Transistor. Hence the term " low dropout"....

Minimal power loss with Regulation as well......someone is going to shoot me down here.

Bring it on. Sigh.

Never mind. I shot myself in the foot anyway.

Anyway. LM317T is around 2.5V. Low Dropout regulators are about quarter of that.

 

[Joe G]

sometimes using one will let you sneak in one more led on a led array

 

[creakndale]

I like using variable Low Drop Out (LDO) regulators with rechargeable NiMH battery packs.
For example:
Set the LDO regulator for 6.0V
Input is a series 6-cell NiMH pack which varies from 8.4V to 6.0V (or less if you're not careful and drain them too far).

Input 8.4V to 6.5V then output is 6.0V
Input 6.4V then output ~5.9V
Input 6.3V then output ~5.8V
Input 6.2V then output ~5.7V
Input 6.1V then output ~5.6V
Input 6.0V then output ~5.5V

Time to recharge.

creakndale

 

[bobledoux]

LDO's are more sensitive to capacitor selection. They can play havoc in circuits where a clean power supply is required--like analog to digital converters. Greater design care and experimentation may be required in these cases.

 

[MrAl]

Hello,

Oh yes, good point. That's mostly because of the PNP output stage structure unlike many other types of regulators. It's harder to compensate for every conceivable load.