Power supply is source of power which supplies the load. Each and every instruments need power for its working. A different power supply is design for the each instrument. In electronics devices, they operated at low voltage power hence we design low voltage DC power supply. Broadly DC Power supply categories into two types.

  1. Unregulated DC power supply
  2. Regulated DC power supply

Unregulated DC power supply: – A supply which output voltage doesn’t constant is called unregulated power supply. Output voltage gets affected from the fluctuation of the input voltage.

Regulated DC power supply: – Regulated power supply maintains the output voltage constant if the fluctuation of input voltage occurs. A voltage regulator IC is used for the constant output.


Designing of power supply mean decided the each and every component functioning and how we choose their value. Therefore we start from the first essential component.

Transformer: – We know that transformer is two types, step up and step down, here we required low voltage transformer so we need a step down transformer.

Before designing the power supply we must be know two requirement, desired voltage and current. So here we select 12 V, 1 Amp.

Rectifier: – Rectifiers are divided into two types.

  1. Half wave rectifier
  2. Full wave rectifier
    1. Center tape rectifier
    2. Bridge rectifier

Half wave rectifier: – Half wave rectifier consist a diode. When AC power applied in it, diode conduct on the forward biased and gives the output in only half cycles. So the output voltage gets on and off. Hence this is not use practically in power supply it used only in clipping circuits.

Full wave rectifier: – Full wave rectifier provides continuous varying output. Diode is conduct both of AC cycles, full wave rectifier divided into two types

  1. A.    Center tape rectifier: – It consist two diodes, one diode work on the positive half cycle and another is work on the negative half cycles. The output voltage achieved full of the AC cycles. Practically center tape rectifier due to its consumed double peak inverse voltage.
  2. B.     Bridge rectifier: – It consist four diodes. The arrangement of four diodes is arrange that two diodes work on the positive half cycles and another two diodes are work on the negative bridge rectifier - Power Supplyhalf cycles. The output is achieved continuously. Advantage of bridge rectifier is that it PIV is same as the required voltage.

Filter Circuits: – Filer circuits smooth the ripple from the fluctuating DC signals. Filter network design from capacitor and inductor. Capacitor passes the AC signals and blocks the DC signals, so it connected parallel. Inductors remove the changes of the fluctuation and it passes the DC signals so it’s used series in the circuits.  By the help of capacitor and inductor we select the required T and π network. The value of capacitor design by the given formula

Vc = Vrms x 1.414

Here we design 12 V DC supply and value of transformer choose 12 V, so the transformer gives the 12 V RMS(Root Mean Square) value which is multiply from the root 2  that is 1.414 and output value should be 16.96 (approx 17 V). That means value of capacitor select greater than 17 volt.

Regulator Circuit: – Regulator network design from the regular IC or Zener diode. Voltage regulators IC are two types

  1. Positive voltage regulator (78xx Series)
  2. Negative voltage regulator (79xx Series)

Both type of regulator IC consist three terminals.

  1. Pin No. 1 used for the input voltage
  2. Pin No. 2 used for the ground
  3. Pin No. 3 used for the output terminals

A desirable value of regulator IC also available in market.  The last two digit indicates it output voltage. For example 5 volt voltage regulator IC is 7805, 12 volt voltage regulator IC is 7812 and so on.