Leaky Voltage Regulators

[MoltenVoltage]

I have an ultra low power circuit which uses a 5-volt chip and draws less than 0.1 uA.

The problem is I want to run it off a 9-volt battery so I am using a 5-volt regulator (L78L05).

The current after the voltage regulator is still the same low value.  The problem is that the current going out of the battery and into the regulator is about 2.5mA.  I have a 10uF tank cap which doesn't seem to make any difference.

I think I know the answer, but is there any practical way to avoid this vampire current while still using a 9-volt battery?

Thanks!

[PRR]

A regulator needs power to set-up a reference, to compare it to the output, and possibly to drive the output power device. It is a many-stage amplifier, so needs power; there's also no zero-power way to build a solid voltage reference.

Google "micropower 5V regulator"

There's choices; in a quick look I found a 6uA typ 5V reg MAX663.

> draws less than 0.1 uA

That's very small.

Are you sure it isn't delivering some power to a load?

Stuff like that often is not fussy about supply voltage. Common CMOS will run on 4.5V to 15V. 9V straight is fine. So is three 1.5V cells, and AAA will last their shelf-life at 0.1uA. So will many "watch" and "hearing aid" cells. 3V Lithium can be had small, and two of those is 6V and years of life.

[MoltenVoltage]

Thanks for the reply, Paul.

It's based on a microcontroller that goes into sleep mode so it draws almost no current unless you ask it to do something.  I've been using AAA batteries but wanted a shorter solution to fit in a smaller enclosure and I assumed 9 volts was the answer.  I think your suggestion of a coin cell might be the answer since it can run on 3 volts.

Thanks again!

[Seljer]

Those regulators require a minimum load to work (go look at the LM317 datasheet). This is usually accomplished by dimensioning the feedback resistors that set the voltage to be small enough to let the minimum current through, regardless of what load you have connected. In the fixed voltage regulators this is already accomplished within the part.

So otherthan a micropower regulator, I'm guessing the simplest solution is a zener diode in the common "voltage regulator" setup (resistor from the power supply and zener diode to ground). If you only need microamperes you can make the resistor very large and the current even without the load very small. Or even just a zener diode in series with your voltage source.