Making a simple variable power supply. Power supply applications. Ac and Dc current defintions. Half wave and full wave rectifier. Power supply circuit. Used tools. Working steps. Testing.

3. Power supply is a hardware component that
supplies power to an electrical device.
It receives power from an electrical outlet and
converts the current from AC (Alternating
Current) to DC (Direct Current)

5. It also regulates the voltage to an adequate amount,
which allows the device to run smoothly without
overheating.
The power supply an integral part of any computer or
any device and must function correctly for the rest of the
components to work.

6. Many electronic devices use external ones For Example
some Monitors and External Hard Drivers have power
supplies that reside outside the main unit.
These power supplies are connected directly to the cable
that plugs into the wall.
They often include another cable that connects the
device to the power supply.
Some power supplies, often called "AC adaptors," are
connected directly to the plug (which can make them
difficult to plug in where space is limited)

7. Switched-Mode Power Supply have applications in various
areas.
A switched-mode supply is chosen for an application
when its weight, efficiency, size, or wide input range
tolerance make it preferable to linear power supplies.

9. Personal Computer
Battery Charges
Central power Distribution
Vehicles
Customer Electronics
Lighting
Space Station

10. Switched-mode PSUs in domestic products such as Personal
Cpmputers often have universal inputs, meaning that they can
accept power from most Mains Electricity throughout the world,
with rated a Frequencies in the 50 - 60 Hz range and a voltage
range between 100 - 240 V AC(although a manual voltage range
switch may be required).
In practice they will operate from a much wider frequency range
and often from a Dc supply as well.
Most modern desktop and laptop computers also have a Voltage
Regulator Module which is a DC-DC converter on the motherboard
that step down the voltage from the power supply or the battery to
the CPU Core Voltage, which may need to be as low as 0.8 V for a
low voltage CPU to 1.2 - 1.5 V for a desktop CPU as of 2007.

11. Due to their high volumes, mobile phone chargers have
always been particularly cost sensitive.
Recently the demand for even lower no-load power
requirements in the application has meant that flyback
topology is being used more widely; primary-side sensing
flyback controllers are also helping to cut the bill of
materials (BOM) by removing secondary-side sensing
components such as optocouplers.

12. Modern power supplies have also increased greatly in their
complexity, and can supply very stable output voltages
controlled by feedback systems. Many power supply circuits
also contain automatic safety circuits to prevent dangerous
over voltage or over current situations.

13. In a basic power supply the input power
transformer has its primary winding
connected to the mains (line) supply.
A secondary winding, electro -
magnetically coupled but electricallyisolated from the primary is used to obtain
an AC voltage of suitable amplitude, and after further processing by the
PSU, to drive the electronics circuit it is to supply.

14. The transformer stage must be able to supply the current
needed.
As the transformer is likely to be the most costly item in
the power supply unit, careful consideration must be given
to balancing cost with likely current requirement.
There may also be a need for safety devices such as
thermal fuses to disconnect the transformer if overheating
occurs, and electrical isolation between primary and
secondary windings, for electrical safety.

15. Three types of silicon diode rectifier
circuit may be used, each having a
different action in the way that the AC
input is converted to DC.

16. A single silicon diode may be used to obtain a DC voltage from the AC
input as shown in Fig , This system is cheap but is only suitable for
fairly non-demanding uses.
The DC voltage produced by the single diode is less than with the other
systems, limiting the efficiency of the power supply, and the amount of
AC ripple left on the DC supply is generally greater.

17. You'll want to use a power diode such as a 1N4001 , they're extremely
common and can put up with a lot of abuse.
The side with the silver stripe matches the schematic symbol side that the
'arrow' in the diode symbol is pointing to.
That's the only direction that current can flow. The output is then chopped
in half so that the voltage only goes positive.
This will convert into

18. What we have now isnt really AC and isn't really DC, its this lumpy wave.
The good news is that it's only positive voltage'd now, which means its
safe to put a capacitor on it.
This is a 2200 microFarad (0.0022 Farad) capacitor, one leg has (-) signs
next to it, this is the negative side.
The other side is positive, and there should never be a voltage across is
so that the negative pin is 'higher' than the positive pin or it'll go POOF!

19. One thing that can be done to reduce the ripple/capacitor size by
half is to use a full wave rectifier instead of a half wave.
A full wave rectifier uses 4 diodes arranged in a peculiar way so
that it both lets the positive voltage through and manages to 'flip
over' the negative voltages into positive.

20. So now we get
As you can see, there are twice as many humps - there isnt that
"half the time, no voltage" thing going on.
This means we can divide the calculated capacitor size to half of
what it was in the previous.
Full wave rectifier is way better than a
half wave
In general, you're unlikely to see an
AC/DC converter that uses a half wave
as the cost of the diodes makes up for
the saving in capacitor size and cost!

21. The full wave bridge rectifier uses four diodes arranged in a bridge circuit
to give full wave rectification without the
need for a centre-tapped transformer.
An additional advantage is that, as two
diodes (effectively in series) are
conducting at any one time, the diodes
need only half the reverse breakdown
voltage capability of diodes used for
The bridge rectifier can be built from separate diodes or a combined bridge
rectifier can be used.
half and conventional full wave rectification.

22. Current Flow on the
Positive Half Cycle
Current Flow on the
Negative Half Cycle
The current paths on positive and negative half cycles of the input wave
It can be seen that on each half cycle, opposite pairs of diodes conduct,
but the current through the load remains in the same polarity for both
half cycles.

23. A typical power supply filter circuit can be
best understood by dividing the circuit into
two parts, the reservoir capacitor and the low
pass filter.
Each of these parts contributes to removing
the remaining AC pulses, but in different
ways.

24. A voltage regulator generates a fixed output
voltage of a preset magnitude that remains
constant regardless of changes to its input
voltage or load conditions.
There are two types of voltage regulators
linear and switching.

25. A linear regulator employs an active (BJT or MOSFET)
pass device (series or shunt) controlled by a high gain
differential amplifier.
It compares the output voltage with a precise reference
voltage and adjusts the pass device to maintain a
constant output voltage

26. A switching regulator converts the dc input voltage to a
switched voltage applied to a power MOSFET or BJT switch.
The filtered power switch output voltage is fed back to a circuit
that controls the power switch on and off times so that the
output voltage remains constant regardless of input voltage or
load current changes.

28. Step 1: Things that you will need...
Piece of veroboard
Four 1N4001 diodes
LM7812 regulator
Transformer that has an output of 14v -
35v AC with an output current between
100mA to 1A, depending how much
power you will need. (I found a 16v
200mA transformer in a broken alarm
clock.)
1000uF - 4700uF capacitor
1uF capacitor
Two 100nF capacitors
Jumper wires
Heatsink (optional)

29. Step 2: And the tools...
•Soldering iron
•Wire cutters
•Wire strippers
•A thing you can cut veroboard tracks.
•Hot glue (To hold components down and make the power supply physically
strong and sturdy.)
•And some other tools that you might find helpful.

30. Step 3: Schematic and others...
If you are going to pull out about 1 A from this power supply, you will
need a heatsink for the regulator, otherwise it will generate very high
temperatures and possibly burn out...
However, if you are just going to pull out a few hundred mA (lower than
500mA) from it, you won't need a heatsink for the regulator, but it may get
a little bit warm.
Also, heres the schematic...
I also add in an LED to make sure the power supply is working. You can
add in an LED if you want.

31. Step 4: Make it!

32. Step 5: Test it!
After you had built your power supply, test it with your multimeter to make
sure they are no solder bridges.
After you tested it, put it in a plastic box or something to protect you from
shocks.
But do not operate the power supply like I did, it is very dangerous
because of the mains voltage on the transformer, you or somebody will get
badly shocked!
# My power supply has 11.73v output, not too bad, I don't need it to be
exactly 12v..

33. Step 6: Done...