This discussion covers a number of ways to generate 5v (and up to 10v) from 1 or 2 cells.
It also covers how to get 5v from a number of nearly flat cells and generating a voltage from solar cells.
Every project needs a power supply. It may be a single 1.5v cell or a  3v lithium cell. It may be a 9v battery or a set of 4 cells to get 6v.
It's wonderful if you can fit a battery and everything works perfectly, but there are lot of times when the voltage from the cells is not exactly the correct voltage. It may be too high or just not quite right. In addition, the voltage from a set of cells will drop as they get older and may create problems with reliable operation of the project.
What is needed is a REGULATED SUPPLY.
A regulated supply will deliver a fixed voltage, even though the cells are getting flat.
Imagine if you had a 9v battery that remained 9v, instead of dropping to 8v, 7v, 6v and finally dying.
The same with a 5v supply for a microcontroller project. Four cells produces 6v and this is too high for a micro. Adding a diode drops the voltage to 5v4 and as the cells start to get old, the voltage drops to less than 4v.
By adding one of our circuits, the voltage remains at 5v6 until the cells are at the end of their life.
These are the circuits you have been wanted for a long time.

Theory on how a POWER SUPPLY works can be found on Talking Electronics website.

CIRCUIT 1

5v3 to 10v OUTPUT
Q1 is a current amplifier
Q2 is an oscillator
Q3 is a signal inverter
Q4 is the output voltage detector

This circuit converts a 3v supply to 9v. It can take the place of a 9v battery and perform better and cost less.
The biggest problem with a 9v battery is the small amount of energy it contains.
This has been improved recently with the introduction of alkaline and lithium cells but you are paying a high price for theses types of batteries.
The cheapest battery contains manganese dioxide or ordinary "dry" cells, so called because they did not spill when tipped over. Customers thought the cell was "dry" and this is how it got its name.
But the problem with this type of cell is the voltage rapidly falls to less than 1.2v per cell and with 6 cells in series, this becomes about 7v.
As the voltage drops to any device such as a radio or amplifier, the current also drops and since the output power is a combination of these two, the performance drops appreciably.
Imagine if you could provide a constant 9v. The output of your project would remain high and the performance could be guaranteed.
This circuit is the answer.
It provides a regulated output of 9v from two AA or AAA cells and costs less than any of the 9v batteries on the market.
The only thing we cannot deliver is a very high current. Some of the lithium and alkaline batteries will deliver over 2amp for short periods of time and we cannot compete with this performance.
However we can compete with a standard 9v battery and deliver a constant current of up to 70mA with a voltage drop of less than 60mV.
9v batteries are rated a 330mAh at a discharge of 2mA. When the current increases to 50mA, the rating is 200mAh and at 100mA the rating is less than 100mAh. By using AA cells we can compete very favourably with these figures and provide a constant 9v output.
The clever part of the circuit is the current amplifying transistor driving the base of the second transistor.
This transistor allows the circuit to consume less than 10mA when idling (quiescent current) and draws over 250mA when delivering 70mA to the load. Without this transistor, the quiescent current would be 30mA.

HOW THE CIRCUIT WORKS
The circuit starts via the current supplied by the 100k turning on the third transistor via its base.
This turns on the first transistor and supplies current to the second transistor to turn it ON.
The voltage on the collector of Q2 drops and this pulls the 330p towards the 0v rail. This turns on the first transistor more and the two transistors keep turning on more and more until they cannot turn on any harder. The 330p is charging during this time and it continues to charge and as it becomes more-charged, the charging-current falls and this turns off the first transistor slightly.
This action turns off the second transistor slightly and the voltage on the right-side of the 330p rises and this reduces the charging current through the first transistor and very soon the first transistor is turned off more. This action turns off the second transistor.
The current through the inductor stops and the magnetic flux collapses and produces a voltage in the opposite direction.
This voltage flows through the 1N4148 diode and charges the 100u electrolytic. It also charges the 330p in the opposite direction via the 33k. When the high voltage from the inductor decays, the voltage on the right-hand plate of the 330p drops and this lowers the left-hand plate. This action turns on the first transistor and the two transistors begin to turn on again, assisted by the presence of the 33k.

5v to 10v REGULATED SUPPLY

As the voltage on the 100u increases, the voltage at the join of the 1k and 5k6 increases and when it reaches 0.65v, the fourth transistor begins to turn on. This action turns off the third transistor slightly and this has the effect of making the 33k a larger value.
This means the 330p is not charged as much during part of the cycle and during the next part of the cycle it does not turn on the first transistor as much.
This means the two transistors do not turn on as hard and thus the output voltage does not rise above a particular value.
This is how an exact voltage is produced on the output rail. It is accurately set by adjusting the 10k pot.
When a load is applied, the output voltage decreases and turns off Q4 slightly. This turns on Q3 slightly and allows the 330p to charge slightly more so that the two oscillator transistors "work harder."
The end result is more energy delivered by the inductor and the voltage is restored.
The output voltage can be maintained up to an output current of about 70mA. This is as much energy as the inductor can deliver. After this, the voltage drops off slightly when a higher current is required.
The circuit can be set to a minimum of 5v  and a maximum of 10v via the pot.

CONSTRUCTION
The core of the inductor (transformer) is obtained from a 10mH inductor but any core of the same size can be used.
Remove the original winding.
Wind 70 turns of 0.25mm wire (or any near size) enamelled wire to fill the bobbin and solder the ends to the two pins connected to the bobbin.
The components can be assembled on a small piece of matrix board. 

CIRCUIT 2
5v REGULATED SUPPLY FROM 3v
This circuit will produce a 5v regulated output from 2 cells (3v). The output current is limited to 50mA  but will be ideal for many microcontroller circuits.
The output voltage is set to 5v by the 3k9 and 560R resistors, making up a voltage divider network.

CIRCUIT 3
5v FROM OLD CELLS
This circuit takes the place of a 78L05 3-terminal regulator. It produces a constant 5v  @ 100mA. You can use any old cells and get the last of their energy. Use an 8-cell holder. The voltage from 8 old cells will be about 10v and the circuit will operate down to about 7.5v. The regulation is very good at 10v, only dropping about 10mV for 100mA current flow (the 78L05 has 1mV drop).  As the voltage drops, the output drops from 5v on no-load to 4.8v and 4.6v on 100mA current-flow. The pot can be adjusted to compensate for the voltage-drop.

The regulator connected to a 12v battery pack	The regulator connected to a 9v battery
	The battery snap plugs into the pins on the 5v regulator board with the red lead going to the negative output of the board as the battery snap is now DELIVERING voltage to the circuit you are powering.   A close-up of the regulator module

CIRCUIT 4
1.5v to 5v PHONE CHARGER
Sometimes it is better to use something that is already available, rather than trying to re-invent the wheel. This is certainly the case with this project. You could not buy the components for the cost of the complete phone charger and extension leads.
The circuit will deliver 70mA at 5v and if a higher current is drawn, the voltage drops slightly.
These chargers were originally priced at $30.00 !!    Contact Talking Electronics for the supplier.

The AA case and 4 adapter leads  - cost: $3.00!!

The LED and 1u capacitor can be clearly seen in this photo.


 

FIXED POWER SUPPLIES USING 5v REGULATOR



78L05 Surface mount 5v  100mA Regulator

CIRCUIT 6
POWER SUPPLIES - ADJUSTABLE
The LM317 regulators are adjustable and produce an output from 1.25 to about 35v. The LM317T regulator will deliver up to 1.5amp.

 ADJUSTABLE POWER SUPPLIES USING REGULATOR

CIRCUIT 7
POWER SUPPLIES - ADJUSTABLE using 7805
The 7805 range of regulators are called "fixed regulators" but they can be turned into adjustable regulators by "jacking-up" their output voltage. For a 5v regulator, the output can be 5v to 30v.

ADJUSTABLE POWER SUPPLIES USING 5v REGULATOR

CIRCUIT 8
POWER SUPPLIES - ADJUSTABLE from 0v
The LM317 regulator is adjustable from 1.25 to about 35v. To make the output 0v to 35v, two power diodes are placed as shown in the circuit. Approx 0.6v is dropped across each diode and this is where the 1.25v is "lost."

ADJUSTABLE from 0v USING 2 DIODES

CIRCUIT 9
POWER SUPPLY TO DRIVE A WHITE LED
A white LED requires about 3.6v to illuminate and this circuit will produce very good illumination from a single cell:

CIRCUIT 10
5v Regulated Solar Power Supply
This project uses the 1.2v rechargeable battery and solar panel from a Solar Garden Light. These lights can be bought for less than $5.00 in most $2.00 shops or similar shops that sell general household items.
We are also using the housing for this project as we could not buy the case, battery and panel for $5.00 in an electronics shop.
It is incredible that a solar panel, rechargeable battery and plastic housing can be bought for less than $5.00!
We have already described the operation of the Solar Circuit, but unfortunately it cannot be used to generate a voltage higher than about 4v, so a new design had to be created. The circuit we have designed is shown above and provides a regulated 5v output @ 10mA. If a higher current is drawn, the output voltage will drop. At 15mA, the output voltage drops to 4v.
This supply has been specially designed for a microcontroller project, but it will also work for circuits such as amplifiers, FM transmitters etc.
All the components and PC board: $11.00   
0.5v @ 200mA solar cells $2.50 each 
0.5v @ 100mA solar cells $1.50 each 
Order the kit and/or solar cells from Talking Electronics

5v Regulated Solar Power Supply Circuit

CIRCUIT 11
5v from a Hand Cranked Generator
When the handle is turned fairly quickly, the output of the motor produces a maximum of 5.5v and has a current under short-circuit conditions of about 400mA. This project is fully described HERE and shows how to increase the voltage of the generator by adding 100 turns to each pole of the generator and this will increase its charging current to a 3.6v Li Ion battery.

The diode and LED connected
to the generator

Wind-up Torch/Radio

THE HAND-CRANKED TORCH - charging current 175mA
(after the modification)

Close-up of the 3.6v Li Ion 450mAhr cell