3.3 volts or 5 volts from 1.5 volt battery. HOW?

[btbass]

I need a cost driven circuit that can generate a supply for a micro from a 1.5 volt battery. The supply can be anywhere from 3 to 5 volts.
The current requirement is very low, 10 - 30mA.
Space is very limited, so I think a SOT-23 smps IC is the way to go.
Anybody done this or could suggest a low cost IC to use?
Your help would be appreciated.

 

[Audioguru]

Stepup circuits are simple. They have an oscillator that pulses a current into an inductor (or transformer). A voltage spike is produced when the current turns off. The spikes are filtered into a higher DC voltage.

Another way to boost a voltage is with a charge-pump IC. The ICL7660 is the old first one but there are newer ones with a higher output current.

Solar garden lights. A 1.2V battery is charged all day. The 3.5V LED is lighted by a simple voltage stepup circuit at night. But the LED current might be only 5mA or 10mA.

 

[btbass]

I have looked at charge pumps, but most of them have an inverted output voltage.
You can convert this to a positive votage using two diodes, but then the forward diode drop is too much at this level.
The charge pumps that give out a positive regulated voltage are too expensive.
Switchers are more efficient, I've just got to find the most cost effective one.

 

[Audioguru]

"The Joule Thief" is a popular voltage step-up circuit that is simple and small. Its output current is fairly low but it lights an LED when the battery cell has dropped to 1V.

 

[btbass]

My problem is space, the pcb is 16.5mm diameter and the height restriction is 3mm. A SOT-23 and Tant_B is about the biggest component I can fit.
The Inductor on the Joule Thief is to large.

 

[FvM]

Major analog companies (TI, National, Linear, Fairchildsemi) have some parts that basically fit your requirements (cost criterion may depend on...). Why not simply start to select a suitable device? I don't want to make a suggestion cause you're continously coming up with new requirements.

Regarding suggested single transistor inverter: You're free to design it with a smaller inductor, it's always an option, although no high efficiency should be expected.

 

[Audioguru]

If you want 3.5V at 30mA then a stepup circuit will need 1.5V at 84mA. The little 1.5V button cell might last for 2 seconds.