12V High Current Power Supply

This schematic bellow is a simple 12V power supply capable of supplying up to 15A. Heatsinking is, as usual, necessary for both the bridge rectifier and the pass transistor (the use of a fan to increase cooling is highly recommended).

T1 - 230/12V 16A Transformer

D1 - GBPC25005 Bridge Rectifier

C1 - 2200uF 25V Electrolytic Capacitor

C2 - 470uF 25V Electrolytic Capacitor

R1 - 680Ω 1/4W Resistor

C3 - 10uF 25V Electrolytic Capacitor

Q1 - 2N3055 Power Transistor*

D2 - 5.1V Zener Diode

D3 - 7.5V Zener Diode

R2 - 1kΩ 1/4W Resistor

C4 - 10uF 16V Electrolytic Capacitor

C5 - 100nF 16V Mylar Capacitor

* Comes in TO-3 package

1.25V to 30V 5A Power Supply

When what's needed is a variable power supply with a greater current output the following circuit can easily solve this problem. Using the LM338 5A Adjustable Regulator (or the LM138 which enables current peaks of up to 12A) it is possible to obtain a regulable 1.25V to 30V output (approximately) at up to 5A. Due to excessive heating, effective heatsinking is mandatory. A large heatsink must be attached to the regulator and the use of a fan to blow air through the regulator is strongly recommended.

S1 - Toggle Switch
T1 - 230/24V 5A Transformer
D1 - 10A 50 PIV Bridge Rectifier
C1 - 470uF 50V Electrolytic Capacitor
U1 - LM138/LM338 5A Adjustable Regulator
R1 - 120Ω 1/2W Resistor
R2 - 5kΩ Potentiometer
C2 - 10uF 50V Electrolytic Capacitor
C3 - 100nF 50V Mylar Capacitor

Resistor Calculation

For those who have a hard time calculating the resistor values based on the color code, here is a simple table to make the task easier.

Color	1st Digit	2nd Digit	3rd Digit	Multiplier	Tolerance
Black	0	0	0	x1
Brown	1	1	1	x10
Red	2	2	2	x100
Orange	3	3	3	x1000
Yellow	4	4	4	x10000
Green	5	5	5	x100000
Blue	6	6	6	x1000000
Violet	7	7	7	x10000000
Gray	8	8	8	x100000000
White	9	9	9	x1000000000
Gold				x0.1	5%
Silver				x0.01	10%
None					20%

Current Source

Sometimes, instead of a regulated voltage source, what is needed is a fixed current source. This simple circuit solves this problem easily. Using the LM117/LM317 adjustable regulator, it's easy to build a 250mA current source, like the one in this circuit. With the component configuration bellow, the output of this circuit is 250mA with a maximum voltage output of approximately 12.6V. A large variety of current outputs is possible though and that can be achieved by switching the resistor R1 (the formula to calculate the resistor based on the desired current output I is R1=1.2/I).

T1 - 230/12V 1A Transformer

D1, D2, D3, D4 - 1N4004 Diode

C1 - 470uF 25V Electrolytic Capacitor

U1 - LM117/LM317 Adjustable Regulator

R1 - 4.8Ω 1W Resistor

+12/-12V DC Power Supply

This is another simple linear power supply, this time using a center tapped transformer and two linear voltage regulators to achieve a +12V/-12V DC output. A better ripple reduction for the negative regulator may be achieved by exchanging the capacitors.

T1 - 230/12/0/-12V 5A Center Tapped Transformer

D1, D2, D3, D4 - 1N4004 Diode

C1, C4 - 470uF 25V Electrolytic Capacitor

U1 - LM7812 Linear Voltage Regulator

U2 - LM7912 Negative Voltage Regulator

C2, C5 - 10uF 16V Electrolytic Capacitor

C3, C6 - 100nF 16V Mylar Capacitor

5V Linear Power Supply

This is a simple 5V DC output power supply using a transformer and a linear voltage regulator. The full-wave bridge is used to increase ripple reduction to capacitor C1, while this capacitor garantees a much more stable voltage to the linear regulator. The use of a heatsink attached to the linear regulator should be considered if there's a high voltage drop across it or if a higher output current is needed. This circuit is pretty simple and easy to build and is very useful when dealing with digital electronics, for instance, to power your microcontroller.

T1 - 230/8V 1A Transformer

D1, D2, D3, D4 - 1N4004 Diode

C1 - 470uF 25V Electrolytic Capacitor

U1 - LM7805 Linear Voltage Regulator

C2 - 10uF 16V Electrolytic Capacitor

C3 - 100nF 16V Mylar Capacitor

Source: National Semiconductor Application Note 556