Quiescent current

Hi,

I bought this voltage regultor ua7808 -> http://www.ti.com/lit/ds/symlink/ua7808.pdf

I wanna know it's quiescente current, I mean, the current is consumes when I have this MOSFET connected to GND and INPUT but I am not connecting it to the OUTPUT. How many current does it use when the OUTPUT pin is disconnected?

Cannot be determined from that datasheet as far as I can see.

Thank you, so I will not waste time on it anymore! Should I assume it's 0?

Should I assume it's 0?

That would be wrong. What is the point?

I don't know. Do you have a multimeter with a mA range? Can you measure it? It may vary with the input voltage that is applied.
Usually the regulators with a really low quescient current will tout that in the datasheet.
That design is pretty old, 1975, so maybe not so low.

What are you using 8V for?

batata004:
Hi,

I bought this voltage regultor ua7808 -> http://www.ti.com/lit/ds/symlink/ua7808.pdf

I wanna know it's quiescente current, I mean, the current is consumes when I have this MOSFET connected to GND and INPUT but I am not connecting it to the OUTPUT. How many current does it use when the OUTPUT pin is disconnected?

Some data sheets reckon typical current drawn by 7808 when unloaded is around 3 to 4 milliAmp. It'll depend on input voltage.

Its called bias current in the datasheet, 4.3mA, max = 8mA, for the 7808

I dont have a multimeter, I will find someone who does and measure it :slight_smile: I was assuming it would be 0 cause if they didnt care about saying about it, maybe they assumed it would be insignificatly low, but probabl I am wrong about this too.

Great, so it's 8ma! It's something that I need to consider in my project! I am powering an RC RADIO with 6v with a permanent connection to my lipo battery so this chip converts 12v -> 6v -> radio.

12volt to 6volt with a linear regulator.
Then the regulator draws the same current as the radio, plus the idle current of the regulator (usually <=5mA for a 78xx).
If a simple linear regulator is a wise choise or not depends on the current draw of the “RC RADIO”. Both idle and active.

Some micro-power switching regulators have a low “no load” draw. This one is 0.2mA.

Switching regulators are basically power converters. Lower voltage is higher current.
If your 6volt device draws 200mA (1.2watt), then your 12volt battery draw is only 100mA (1.2watt).
Practically it will be more like 110-120mA, because of losses.
Leo…

batata004:
I dont have a multimeter, I will find someone who does and measure it :slight_smile: I was assuming it would be 0 cause if they didnt care about saying about it, maybe they assumed it would be insignificatly low, but probabl I am wrong about this too.

Low quiescent current is an extremely important characteristic that is considered for low power operations, such as when running off a small battery or from an unreliable power source like solar, so a regulator designed with low Q will make that the banner spec, like this MCP1810 from Microchip that has Ultra-Low Quiescent Current LDO Regulator right in the top bar, and the very first bullet point on the page is its insane 20 nA quiescent current.

Less Q is a good thing, so any marketer that buried an amazing spec like 0 Q current in the middle of some table in the data sheet would probably get a stern talking to from their boss pretty quickly.