# Regarding LDO and Switching Regulator

#### sgr

Joined Jun 27, 2017
26
If the input voltage is 10V and Output voltage is 5V and Output current is 1Amp. and Lets consider 100% Efficiency. Then what is the Input current in case of LDO and what is the input current in case of switching regulator ?

#### Irving

Joined Jan 30, 2016
3,420
For LDO, Iout = Iin so efficiency cannot be more than 50%.

For switcher at 100%, eff, Iin = 0.5Iout,

#### Ya’akov

Joined Jan 27, 2019
7,419
Schoolwork must be posted in the Homework Help forum because the AAC rules limit the types of information that can be provided to students doing schoolwork.

#### BobTPH

Joined Jun 5, 2013
6,513
For LDO, Iout = Iin so efficiency cannot be more than 50%.

For switcher at 100%, eff, Iin = 0.5Iout,
To clarify, a buck converter will need 1A 50% of the time for an average current if 0.5A.

#### MrAl

Joined Jun 17, 2014
10,064
If the input voltage is 10V and Output voltage is 5V and Output current is 1Amp. and Lets consider 100% Efficiency. Then what is the Input current in case of LDO and what is the input current in case of switching regulator ?
Hi,

I think what you mean is not 100 percent efficiency but rather there are no coincidental losses. That makes the calculations simpler yet still get a decent understanding of how things work.

For example, if i have a circuit that has 2 amps output and 20 volts input, that doesnt mean the input gets 40 watts because there is usually some extra current needed for biasing and things like that, and also possibly some leakage currents. If we ignore those things, then we have what we often call the 'ideal' case, and then we might consider the input power to be 40 watts, at least for the time being. If we dont ignore those things then with an output of 2 amps and input of 20 volts the input current may actually be higher than 2 amps, like 2.2 amps, if there is no power converter as part of the circuit.

An LDO regulator is still a linear regulator so there will be extra losses in addition to the ideal case we calculate.