5V Power Supply using 7805 Voltage Regulator with Design

LM7805 - Pin Diagram

5V Power Supply using 7805 Voltage Regulator with Design

In most of our electronic products or projects we need a power supply for converting mains AC voltage to a regulated DC voltage. For making a power supply designing of each and every component is essential. Here I’m going to discuss the designing of  regulated 5V Power Supply.

Let’s start with very basic things the choosing of components

Component List :

  1. Step down transformer
  2. Voltage regulator
  3. Capacitors
  4. Diodes

Let’s get into detail of rating of the devices :

Voltage regulator :

As we require a 5V we need LM7805 Voltage Regulator IC.

7805 IC Rating :

  • Input voltage range 7V- 35V
  • Current rating Ic = 1A
  • Output voltage range   VMax=5.2V ,VMin=4.8V 
LM7805 - Pin Diagram

LM7805 – Pin Diagram

Transformer :

Selecting a suitable transformer is of great importance. The current rating and the secondary voltage of the transformer is a crucial factor.

  • The current rating of the transformer depends upon the current required for the load to be driven.
  • The input voltage to the 7805 IC should be at least 2V greater than the required 2V output, therefore it requires an input voltage at least close to 7V.
  • So I chose a 6-0-6 transformer with current rating 500mA (Since 6*√2 = 8.4V).

NOTE : Any transformer which supplies secondary peak voltage up to 35V can be used but as the voltage increases size of the transformer and power dissipation across regulator increases.

Rectifying circuit :

The best is using a full wave rectifier

  • Its advantage is DC saturation is less as in both cycle diodes conduct.
  • Higher Transformer Utilization Factor (TUF).
  • 1N4007 diodes are used as its is capable of withstanding a higher reverse voltage of 1000v whereas 1N4001 is 50V
Center Tap Full Wave Rectifier

Center Tap Full Wave Rectifier

Capacitors :

Knowledge of Ripple factor is essential while designing the values of capacitors

It is given by

  • Y=1/(4√3fRC)  (as the capacitor filter is used)

1. f= frequency of AC ( 50 Hz)

2. R=resistance calculated

R= V/Ic   

V= secondary voltage of transformer

  •      V=6√2=8. 4
  •      R=8.45/500mA=16.9Ω standard 18Ω chosen

3. C= filtering capacitance

We have to determine this capacitance for filtering


Vac-rms = Vr/2√3

Vdc= VMax-(Vr/2)

Vr= VMax- VMin

  •   Vr = 5.2-4.8 =0. 4V
  •    Vac-rms = .3464V
  •    Vdc = 5V
  •     Y=0 .06928

Hence the capacitor value is found out by substituting the ripple factor in Y=1/(4√3fRC)

Thus, C= 2314 µF and  standard 2200µF is chosen

Datasheet of 7805 prescribes to use a 0.01μF capacitor at the output side to avoid transient changes in the voltages due to changes in load and a 0.33μF at the input side of regulator to avoid ripples if the filtering is far away from regulator.

Circuit Diagram

5V Power Supply Circuit using 7805 Voltage Regulator

5V Power Supply Circuit using 7805 Voltage Regulator

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  • rusman


    thanks for the post.

    when calculating R it should not be from secondary transformer since during discharge current direction is into the load.

    so R = Vc / load into current via 7805.

    do you agree ?

  • arjun shinde

    thanks for giving specification of ICs 7805

  • Johanan Prime

    hi there. im trying to design this in the Multisim program but i am unable to obtain the desired 5V output. instead, I am getting a constant 0.926pV output. I’ve tried changing the component values but I’m unable to obtain the expected result.

  • 7805 is a proven voltage regulator. You will get it for sure. Try in hardware.

  • Nidheesh

    Whether the output will be 5V 1A DC?

  • Yes, 7805 maximum output capacity is 1A. So you should always use a current below it. And the current rating of the transformer also matters.

  • giridhar

    where have u used the 18k resistor?

  • giridhar

    18ohm, sorry

  • It is the assumed load resistance.