9V multimeter powered from single AA battery

Hi! Another 9V battery was dead in my 830 multimeter. I've used this situation to make some modifications. I have a lot of half empty AA and AAA batteries, so I decided to power up multimeter from 1.1V (fresh AA/AAA have 1.5V).

Here is a simple DC-DC step-up converter.

First R2 opens Q1. Q1 opens Q2. Current flows through primary winding of inductor. C1 works as posiive feedback and put transistors to saturation. After inductor current exceedes saturation current of Q2 volatge at Q2 increases and C1 forcing Q1 to close. Inductor works as auto-transformer 1 to 3 (in my case) and outputs stored energy through D1. C1 is recharging, Q1,Q2 are opened again and so on.

After output voltage exceeds Vd2+Q1Vbe Q1 is forced to close.

Output voltage ripple is high, but seems that multmeter works fine.

Click on any image for full size

C1 may be 220-680pF. PNP transistor may be BC557 (8550, etc.), higher hfe is better. NPN must have low saturation voltage.
Transformer is center-tapped inductor, 50+150 turns of 0.1mm (AWG 38) enamelled copper wire. Core was taken from PSU output filter inductor. Ferrite ring will work too. Please note: inductor parameters depends on used ferrite core. Some adjustments may be needed depending on used transistors, inductor and input voltage.
I've added 22uF input capacitior (not shown on schematic).

PCB is really simple. I don't attach PCB file, because you may want to use another elements with different size or pinout.

Also I added power switch (I didn't want to cut traces on multimeter's PCB) and simple LCD backlight (2 SMD LED's and resistor in series).

AA battery is longer than 9V battery, so I had to cut multimeter's case to fit battery and converter PCB.

LCD backlight in action.

Backlight also shows if multimeter is powered up. Battery is almost empty, TV remote doesn't work with it, but multimeter works OK.