Power Supplies      

Full Wave Rectifiers  | 2 | 3 | 4 |

Power supplies are used everywhere appliances are powered at voltages higher or lower than line voltage.

Most power supplies change voltages and  rectify AC into DC for use on electronic circuits.

Welders battery chargers are also power supplies that supply power at range that exceed our familiar appliances such as audio gear and computers.

Battery chargers that keep a charge on emergency lighting systems and electric fork lifts etc. are power supplies.


Power supplies combine our understanding of the components studied earlier.



AC is rectified into Pulsating full wave DC
> this type of output would be suitable for for a battery charger but not for much because of the waveform




A single diode will produce half wave
pulsating DC which
is inefficient because half of the wave is not captured





a 4 diode bridge configuration creates an efficient fullwave pulsating DC output which is efficient since the full wave is captured  



electrical energy is stored and released by the capacitor during each pulse in a way that smoothes out the peaks ....... more capacitance will create a smoother output with no ripple

Q -   why do some electronic circuits appear to shut down slowly even thought you have turned of the power (supply)??


Addition of a capacitor in parallel will act like a shock absorber

The pulsating wave form will be eliminated as the capacitance is increased

pure DC is achieved when all ripple has been eliminated

     FULL WAVE RECTIFIER with filtering      capacitor




increased capacitance will eliminate ripple


    FULL WAVE RECTIFIER with regulator

a larger capacitor will remove any ripple and the addition of a regulator will stabilize the voltage across various load current demands

proper voltage stability is very important to the operation of sophisticated electronic devices






a regulator will clamp the output voltage at a fixed level that will not vary when the load increases

( all unregulated power supplies experience a voltage drop under load)




the 7805 regulator will clamp the output voltage of this power supply at 5 V

a 7809 volt regulator will clamp output voltage at 9V


Here is a power adapter split open to expose the step-down transformer and diodes that make up the rectifier.

The filtering capacitor is not shown.


Can you identify the primary on the transformer?

How can you tell it is a step down transformer?