5- POWER SUPPLY WITH IC REGULATOR
A regulated power supply used to require a fairly complex circuit but the introduction of special ICs has made matters much simpler.
The secondary voltage from the transformer (it must be an isolating transformer but most are) is full-wave rectified by the diodes and then smoothed by capacitor C1. The voltage here is unregulated and has AC ripple superimposed upon it. The IC removes this and gives an almost ripple free, stable DC voltage. C2 and C3 must sited close to the regulator to prevent any loss of performance due to high frequency instability. Note that the capacitor and common lead from the IC should be wired to the same point, this helps to reduce instability and hum problems that can occur due to poor layout.
The 78XX series of regulators, which come in a TO220 package generally, can supply 500mA.Therefore the maximum power dissipated in them is probably going to be 500mA times the voltage difference between the input and output terminals. This might mean that the regulator has to dissipate 5W of heat, therefore an adequate heat sink must be used. The 78XX series is current limited, which means that if the maximum current is exceeded, the output voltage drops towards 0V. The regulator is thus short-circuit protected as long as proper heat sinking is provided.
