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Old 24th December 2011, 07:09 AM   #1
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Default Low Quiescent current LDOs?

Hey all,

One of my projects involves powering a 5V circuit from a 9.9V battery.
I'm looking for the easiest and most power-effective way to drop those 9.9 Volts to 5V i.e. I don't want to reduce battery life more than necessary and space is a bit tight in there.

I did some research and saw many fixed voltage regulators out there that claim a very low quiescent current and, judging by the datasheets, most require only a small cap at the input and output.
They're supposed to be made for battery-powered/portable applications so I guess this will be the optimal way?

I should be OK with around 100mA of current and the quality of the supply is not a top priority, by the way (it's not an audio application but an auxiliary function).

Some examples of the LQC LDOs that I've come across:
ADP1720 | 50 mA, High Voltage, Micropower Linear Regulator | Linear Regulators | Power Management | Analog Devices
LM2936 - Ultra-Low Quiescent Current LDO Voltage Regulator
ON Semiconductor MC78LC: MicroPower Low Dropout Linear Voltage Regulator
TDA3664 :: NXP Semiconductors
Linear Regulators - Single Channel LDO - TPS76601 - TI.com

Any recommendations in specific?
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Old 24th December 2011, 07:31 AM   #2
Mooly is offline Mooly  United Kingdom
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Do you mean you need a 100ma continuously ? Ifso then with a current requirement of 100ma the quiescent current of a linear reg isn't really an issue. 0.1ma or 1ma or 5ma, it makes little difference when you are drawing 100ma.

If the 100ma is an intermittent load and most times the reg sits there not supplying anything then yes, quiescent current is important and there are micropower regs available.

The big problem is the efficiency (or lack of) in using series pass regulators. Switching supplies are far more energy efficient but come at the price of complexity.
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Old 24th December 2011, 07:34 AM   #3
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If I recall correctly, LDOs in general have higher quiescent current than their eg 78xx counterparts. How about something like the NatSemi LM2574 buck switcher? It has a standby mode with ~50uA QC. Possibly >80% efficiency delivering to your load.
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Old 24th December 2011, 07:40 AM   #4
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Quote:
Originally Posted by Mooly View Post
If the 100ma is an intermittent load and most times the reg sits there not supplying anything then yes, quiescent current is important and there are micropower regs available.
When there is no music playing, there is no load, so I'd consider it an intermittent load.
I'm mostly worried about heat because, from a quick check and being SMD LDO parts some can't handle the drop from 9.9V to 5V @ 100mA (at least without some sort of heatsinking).
I'll need to dig deeper into the datasheets to figure that one out.

Quote:
Originally Posted by sofaspud View Post
If I recall correctly, LDOs in general have higher quiescent current than their eg 78xx counterparts. How about something like the NatSemi LM2574 buck switcher? It has a standby mode with ~50uA QC. Possibly >80% efficiency delivering to your load.
Thanks, I'll check it out!
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Old 24th December 2011, 07:50 AM   #5
Mooly is offline Mooly  United Kingdom
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100ma, 5 volt, 300mv drop out,
NATIONAL SEMICONDUCTOR|LM2931AZ-5.0|V REG LDO +5.0V, 2931, TO-92-3 | CPC

Actually its similar to one in your link...
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