Fooling around w/one of Colin's circuits (3V-9V converter)

colin55 said:

You can replace a 9v battery with this circuit.
The output is about 10.4v on no load and 9.6v @30mA output.
The advantage is the voltage stays over 9v for the life of the cells.
A normal 9v battery drops to 7v very quickly.
The output voltage is set to 9-10v by the 6k8 and 390R resistors. The 470R gives the circuit an idling current of about 20mA. The spikes are about 75mV.
**broken link removed**

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Colin.....

Would 4.5V from 1.5V be possible?

I have an old HP28s calc that wants 3 Ncells for 4.5V. I'd much rather run it it with 1 AAA 1.5V alkaline due to the cost & availability of N cells were I live. Radio Shack wants 6 USD for a pair!

I can get 6 AAA (equiv.) from one 9 V alkaline for about 3 USD.... 0.50 USD per AAA/alkaline or a buck per pair ...a 3 x savings.

Using 1 AAA would give me the remaining batt space (about 125% AAA volume) to build the circuit. The batt. compartment cylinders are 12mm wide x 60mm and 12mm by 30mm holding the 3, 12 x 30mm N cells. . So the AAA will occupy 44mm of the 60mm tube and I still have another 30mm tube free.

Can it be done?

A 9V battery has six AAAA cells inside, not AAA cells. A skinny AAAA alkaline cell has a capacity of only 460mAh, an AAA cell is 1000mAh and an AA cell is 2500mAh. So an AAAA cell will not last long.

For 5v, the voltage divider should be 3k9 and 560R