Hey falks,
I have a question to a voltage regulator in genereal (see attachment):
Does a voltage regulator consumes energy if no current is going throw ?
If yes: what kind of energy is it consumging, heat energy ?
According to the data sheet the quiescent current for that part is 2mA. This will be the current drawn from the input when the output is open circuit, used to bias up the regulator circuit. It consumes electrical energy and will turn it into heat.
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Thanks man, this is what I wanted to hear, thanks 
For most mobile application, that should works weeks and months on single battery, 2ma is a very large expense. The typical current consumption of a mobile device on batteries is a few to tens of microamperes, which is hundreds of times less than the leakage current of the regulator. This is the main reason. why mobile devices usually do not use regulators and voltage converters
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okay, can you give me an advice which regulator I should use ?
My aim is to drop the voltage from 6V to 5V. The Current flow is only 200mA. And here are the project details:
the first picture is showing a 230V-socket-plug. As you can see, there is already a power drop from 230V AC to 5V DC. The 230V-socket-plug is connected to the board (see picture 2) itself. The board needs 5V DC. It is a Wifi-Repeater.
So, my aim is to dissemble the socket-plug, because I only need the board itelf. I want to run the board with a 6V DC supply. So, which voltage regulator should I use ?
I guess, that the board already has capacitors to avoid voltage noise etc.
So battery operation isnt a requirement? https://www.aliexpress.com/item/1005003038609476.html?gatewayAdapt=Msite2Pc
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No, it is not. It has to be runned by a 6V Power Supply. So should I use the shown Buck Converter ? Thanks
An 7805 has a quiescent current of 4.3mA.
It is old technology, with a dropout voltage of 2volt.
It needs 7volt minimum to make a stable 5volt.
Buck converters also have a minimum dropout voltage, so read the datasheet.
Could be easier to just use a 1N4004 diode. They drop about 0.7volt.
Make sure your supply is regulated. A 6volt supply is uncommon, so it could be unregulated. If so, then it could be more than 6volt unloaded. Measure it...
Leo..
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It is worth noting that the sort of regulator you had pictured at the start of this thread would not be able to convert 6V to 5V, as it needs a voltage at least 1.5V to 2V higher at the input than the output is going to be.
To work with that sort of input voltage you need what is called a "low drop out" voltage regulator.
I forget to mention the possible noise..
So here my final questions:
Can I simply put a 5V DC input there ? And if yes: should I use the Buck converter, or der voltage regulator (post1) ?
It seems that the board has two buck converters. The WiFi processor likely runs on 3.3volt.
But who knows what the second buck converter is for...
If the plug only connects to the two buck converters, then powering it with 6volt could be ok.
Where exactly is that 6volt coming from.
Leo...
The power is coming from a normal power supply loke this...
https://www.ebay.de/itm/384954380726
So, you are saying that 6V from this example supply would be okay ?
Wait a Minute, my friend. I am gonna measure it out how much V is converted through the two buck conveerters. I am at work right now, so I will measure it out today evening. Now it's 1pm in Germany 
Okay, I have measured exactly on the pointing red line (see picture).
So, is a simple 1N4004 Diode enough ? Or should I use indeed, a voltage regulator (#post 1) ?
I'm curious to know, for what the 1.1V is needed.
That's a regulated supply. Universal voltage input (100-240) confirms this.
I would use that 1N4004 to be on the safe side. It also gives you reverse voltage protection.
Good detective work...
I now also see a third switching converter on the left.
Leo..
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Indeed, there is a third one
I am gonna sleep now. I will analyse it tomorrow. I will post my findings here...
Good night good man.
As I promised, here are my findings... (you have to zoom it)
Note: I have demolished the LAN-Connector on the bottom-center.
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