This is a simple 5volt power supply circuit using ic regulator type 7805. This circuit can be paired with Running LEDs circuit II in the Fun circuit category or even digital ic circuits. Input ranges from 8 Volts to 18 Volts DC. This circuit has a LED as an indication, if the power supply turns on.
Part list :

• R1 = 1K, ¼-watt
• C1 = 1000 µf, 35 volt
• C2 = 10 µf, 35 volt
• C3 = 0.01 µf or larger ceramic disc capacitor
• D2 & D3 = silicon rectifier diodes
• U1 = 7805 +5 volt voltage regulator IC
• D1 = miniature red LED.

Input voltage may also be from a 12 volt battery.

A switched-mode power supply (switching-mode power supply, SMPS, or just switcher) is an electronic power supply that incorporates a switching regulator in order to be highly efficient in the conversion of electrical power. Like other kinds of power supplies, an SMPS transfers power from a source like the electrical power grid to a load (e.g., a individual computer) whilst converting voltage and current characteristics. An SMPS is usually employed to efficiently supply a regulated output voltage, generally at a level diverse from the input voltage. Unlike a linear power supply, the pass transistor of a switching mode supply switches very quickly (typically between 50 kHz and 1 MHz) between full-on and full-off states, which minimizes wasted energy. Voltage regulation is supplied by varying the ratio of on to off time. In contrast, a linear power supply should dissipate the excess voltage to regulate the output. This higher efficiency will be the chief benefit of a switched-mode power supply.

Switching regulators are utilized as replacements for the linear regulators when greater efficiency, smaller size or lighter weight are needed. They are, nevertheless, far more complex, their switching currents can trigger electrical noise problems if not cautiously suppressed, and simple designs might have a poor power factor.

Explanation

A linear regulator provides the desired output voltage by dissipating excess power in ohmic losses (e.g., in a resistor or inside the collector-emitter region of a pass transistor in its active mode). A linear regulator regulates either output voltage or current by dissipating the excess electric power inside the form of heat, and hence its maximum power efficiency is voltage-out/voltage-in given that the volt difference is wasted. In contrast, a switched-mode power supply regulates either output voltage or existing by switching ideal storage elements, like inductors and capacitors, into and out of distinct electrical configurations. Ideal switching elements (e.g., transistors operated outside of their active mode) have no resistance when “closed” and carry no present when “open”, and so the converters can theoretically operate with 100% efficiency (i.e., all input power is delivered to the load; no power is wasted as dissipated heat).

For instance, if a DC source, an inductor, a switch, and also the corresponding electrical ground are placed in series and the switch is driven by a square wave, the peak-to-peak voltage of the waveform measured across the switch can exceed the input voltage from the DC source. This is since the inductor responds to adjustments in current by inducing its own voltage to counter the alter in current, and this voltage adds to the source voltage even though the switch is open. If a diode-and-capacitor combination is placed in parallel to the switch, the peak voltage might be stored in the capacitor, and also the capacitor can be used as a DC source with an output voltage greater than the DC voltage driving the circuit. This increase converter acts like a step-up transformer for DC signals. A buck-boost converter works in a similar manner, but yields an output voltage which is opposite in polarity to the input voltage. Other buck circuits exist to boost the average output existing having a reduction of voltage.

In an SMPS, the output present flow depends on the input power signal, the storage elements and circuit topologies utilised, and also on the pattern used (e.g., pulse-width modulation with an adjustable duty cycle) to drive the switching elements. Normally, the spectral density of these switching waveforms has energy concentrated at fairly high frequencies. As such, switching transients, like ripple, introduced onto the output waveforms could be filtered with tiny LC filters.

Advantages and disadvantages

The major advantage of this approach is higher efficiency simply because the switching transistor dissipates little power when it is outside of its active region (i.e., when the transistor acts like a switch and either has a negligible voltage drop across it or a negligible existing by way of it). Other positive aspects include smaller size and lighter weight (from the elimination of low frequency transformers which have a high weight) and lower heat generation because of greater efficiency. Disadvantages consist of higher complexity, the generation of high-amplitude, high-frequency energy that the low-pass filter must block to prevent electromagnetic interference (EMI), along with a ripple voltage at the switching frequency and also the harmonic frequencies thereof.

Extremely low cost SMPSs may couple electrical switching noise back onto the mains power line, causing interference with A/V equipment connected to the same phase. Non-power-factor-corrected SMPSs also trigger harmonic distortion.

The sample of switching power supply: 5V DC / 10A Offline Switching Power Supply

Schematic diagram:

PCB layout:

The circuit featured regulated output, short circuit safe, and with current limiter.

Check out the fully explanation in this page:

http://www.electronics-lab.com/projects/power/002/index.html

This power supply circuit can supply high current for your electronic project. Transistor 2N3055 is the main component which will increase the current level.

Notes:

1. D1 should be rated at about one volt higher than then desired output of the supply. A half watt diode will do.

2. Q1 can be a transistor similar to the 2N3055. I chose the 2N3055 for it’s availability and power handling (150 watts).

3. T1 should be about 5 volts higher than the desired output of the supply, and rated for about one amp more of current. The voltage overhead is required by the regulator section. The extra current is to keep the transformer from over heating.

4. The choice of BR1 will depend on the voltage and current of your transformer. The rectifier should be rated for 50 volts more than the transformer, and 5 amps more than the transformer.

5. The value of R1 will be smaller when supplying high currents. Expiriment until you get what you need.

6. Heatsink and fans are absolutely necessary!

This power supply will stabilize the voltage, both the positive voltage and negative voltage. IC 7815 will stabilize  positive voltage +15V and IC 7915 will stabilize the negative voltage -15V.

If you need stabilized 15 V output, you should choose transformer output around 18-24V AC and use IC 7815 and 7915. If you need stabilized 6V output, you sould choose transformer output arround 9V-15V and use IC 7806/7906.

Circuit Description:
This amplifier uses a dual 20 Volt power supply and delivers 15 watts RMS into an 8 ohm load. Q1 operates in common emitter, the input signal being passed to the bias chain consisting of Q8, Q9, D6, D13 and D14. Q8 and Q9 provide a constant current through the bias chain to minimize distortion, the output stage formed by a discrete darlington pair (Q2,Q4) and (Q7,Q11). The last two transistors are power transitors, specifically the 2N3055 and MJ2955. The 7.02K resistor, R16 was made using a series combination of a 4.7K, 680 Ohms, and two 820 Ohms. The 1.1K resistor, R3 was made using a 100 Ohms and a 1K resistor. You can use this circuit with any walkman or CD player since it is designed to take a standard 500mv RMS signal.

You can adjust the output voltage from 0V up to 12V with variable resistor R2. This circuit can handle a 1 ampere current. The 317 must have a heat sink. The charger output is 6V, you can use the charger to charge your mobile phone battery.
Here the PCB layout:

Electronic parts list:

Semiconductor:
LM 317 – 1pc
LED – 1pc
1N 4001 – 8pcs

Capacitors:
25V/470uF – 1pc
25V/10 uF – 1pc

Resistors:
1k, 1/2W – 1pc
220R, 1/2W – 1pc
5kR Potentiometer – 1pc

Others:
1Ampere, Multi-tap Transformer – 1pc
AC Chord – 1pc
Casing – 1pc
#22 Stranded Wire – 3m
Heatsink for TO220