# What is dropout voltage?

1. ## What is dropout voltage?

What is drop out voltage in voltage regulators? on every datasheet they give a graph of drop out voltage versus temperature... is it the minimum difference between input and output voltages?

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2. ## Re: What is dropout voltage?

The dropout voltage is defined as the minimum voltage drop required across the
regulator to maintain output voltage regulation ..

Regards,
IanP

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3. ## Re: What is dropout voltage?

i have saw a definition: the dropout voltage is defined as the minimum voltage when the output voltage has dropped 2% while sustain fixed output current

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4. ## Re: What is dropout voltage?

Hi Lucifre,
The DropOut Voltage in Linear Regulator Voltage depends on its characteristics, for example, in Regulators LMxxx it is 2V aprox. in Reg with Low DropOut Voltage it is <1V aprox.

If you need obtain a Power Supply with linear regulators, you should to do:

VOreq + Vdor + 2 Vd = Vmin wihout ripple
where:
VOreq is Voltage output required
Vdor is DropOut Voltage on IC regulator
Vd is dropouto across diode

rgds

5. ## Re: What is dropout voltage?

Originally Posted by IanP
The dropout voltage is defined as the minimum voltage drop required across the
regulator to maintain output voltage regulation ..

Regards,
IanP

could you introduce some useful books about LDO? thanks a lot!

Originally Posted by IanP
The dropout voltage is defined as the minimum voltage drop required across the
regulator to maintain output voltage regulation ..

Regards,
IanP
could you introduce some useful books to me ? thanks a lot!

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6. ## Re: What is dropout voltage?

Dropout voltage is the input-to-ouput differential voltage at which the circuit ceases to regulate against further reductions in input voltage;this point occurs when the input voltage approaches the output voltage. The below figure shows a typical LDO regulator circuit. In the dropout region, the PMOS pass element(assume output transistor is PMOS) is simply a resistor, and dropout is expressed in terms of its on-resitance(Ron).
Vdropout=Io×Ron

7. ## What is dropout voltage?

Drop out voltage is the minimum input/output differentialvoltage where the circuit just ceases to regulate.

8. ## What is dropout voltage?

Hi

huojinsi is correct.
For simplicity, there's nothing need to remember.
Just remind yourself, when the INPUT voltage close to OUTPUT voltage such that the PASS element changes from saturation to linear region, that is, the VDS(sat), this is AROUND the drop-out voltage. What does it mean?
The name already explains its meaning.
The input/output voltage difference when output ceases to regulate itself and then it DROPS OUT of the regulation.

9. ## Re: What is dropout voltage?

lTo: iuyonggen_1

https://www.edaboard.com/viewtopic.php?p=802274#802274

Success.

10. ## What is dropout voltage?

from the name, it is so easy to tell that is the diff of supply voltage and the output voltage. Things seem more difficult when VDD shrinks to 1.5v (+/- 10%) but you may need output 1.2v which big current output requirement

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11. ## What is dropout voltage?

the minimum difference required between input and output of ldo when it is regulating is dropout voltage

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