Design and Simulation of  a 5V Voltage Regulator using Proteus

Since most Microcontrollers operate at 5 Volt DC, we need to design a power supply for it. Since the current required for most of the cases is not more than a few milli Ampere a 1 Ampere Supply would be just fine for most of the basic circuits. Hence we can use a Linear Dropout Regulator, which is not very efficient, but is simpler to use and it does suffice for our requirement.

Basic Flow-Chart of getting a +5Volt 1 Amp DC from 220 V AC:

Design Procedure:

Selecting a Suitable Transformer:

Since our power supply to be designed can supply a maximum of 1 Amp current, the transformer we choose must be able to supply it. Hence we choose a 12 Volt 1.5 Ampere transformer.

Choosing the bridge rectifier:

Again the bridge rectifier must allow the current range, so any Bridge rectifier with a 2 Amp or more current rating will suffice.

Smoothing Capacitor:

To smooth the output of the rectifier a reservoir capacitor is used - placed across the output of the reciter and in parallel with the load.. This capacitor charges up when the voltage from the rectifier rises above that of the capacitor and then as the rectifier voltage falls, the capacitor provides the required current from its stored charge.

It must fulfil two requirements:

1. The value must be chosen so that its time constant is very much longer than the time interval between the successive peaks of the rectified waveform:

Where:
C = value of capacitor in Farads
f = the ripple frequency - this will be twice the line frequency a full wave rectifier is used.
2. The ripple voltage after adding the capacitor must be in the allowable range of the next load.

For cases where the ripple is small compared to the supply voltage - which is almost always the case - it is possible to calculate the ripple from a knowledge of the circuit conditions:

In our case since we would be connecting a Voltage regulator, the input voltage ripple allowed, is 4 Volt, for our design using a 12 Volt transformer secondary voltage, which is enough to give a steady supply of 5 Volt upto 1 Ampere,

But since we will not be using our power supply for full load all the time, a 1000uF cap will do just fine. Moreover, most of the electrolytic caps have a 20% Tolerance which is more than enough to handle such abnormality for a short period of time.

Therefore we chose a 100uF Capacitor to be our smoothing capacitor.

Choosing a voltage Regulator:

A linear Dropout (LDO) Regulator is a device which keeps the output voltage constant, even if the input changes. Since we need a 5 Volt DC Supply, with a maximum current of 1 Ampere a CD7805 or an LM7805 will suffice.

An Important thing to note here is the input voltage must be in the allowable range, i.e. from about 1 Volt more than the output voltage to about 22 Volt. So for our case the allowable input voltage is from 6 Volt to 22 Volt, to get a Constant 5 Volt DC output voltage.

After figuring out all the components we need we simulated the circuit in Proteus Circuit Simulation Software, to verify whether our design is working. For testing purpose, we have taken an LED with a 220 Ω series resistor as the load, which takes about 13 mA load current.

The schematic of the simulation setup is given below.

The Simulated Waveforms as Observed: