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Fixed Voltage Regulators


Here is a simple Fixed voltage regulator circuit using 7805 and 7905 voltage regulator ICs

Components Required:

1) Breadboard
2) 1Amps Fuse
3) 9 - 0 - 9 center tapped Transformer
4) 1N4007 diode = 4
5) 2200uf capacitor = 2
6) 100nf capacitor = 2
7) LM7805 Positive Voltage Regulator IC
8) LM7905 Negative Voltage Regulator IC

Explanation for Dual Voltage Regulator:
  • Connect the circuit as shown in the circuit diagram below.
  • The output of the center tapped transformer is AC voltage.
  • Voltage between the center and anyone of the other terminal gives +9Volt AC, Voltage between the two outer terminals gives +18Volt AC.
  • Connecting in center tapped pattern gives +9Volt AC across terminals 1 & 2 and gives -9Volt AC across terminals 3 & 2.
  • Four 1N4007 diode connected as shown below forms a bridge circuit which converts bidirectional AC into unidirectional DC.
  • The converted signal is not pure DC, it still consists of some AC signals.
  • The 2200uf capacitor is used as a filter, which allows only DC to pass through..
  • 78XX Voltage Regulators are used for Positive voltage values and 79XX Voltage Regulators are used for Negative voltage values.
  • Here i have used +5Volt and -5Volt Voltage Regulator ICs ie) 7805 and 7905.
  • 78XX and 79XX consists of three terminals namely unregulated input voltage, ground and regulated output voltage.
  •  +9Volt DC input goes to 7805 and -9Volt DC input goes to 7905, which gives +5Volt and -5Volt regulated DC output.
  • Output of the regulator produces noise which can be removed using 100nf capacitor, which acts as a filter.
Circuit Diagram:

 
Figure 1: Fixed Dual Voltage Regulator Circuit simulation made in Multisim


Explanation for Single Voltage Regulator:
  • Connect the circuit as shown in the circuit diagram below.
  • The output of the center tapped transformer is AC voltage.
  • Voltage between the center and anyone of the other terminal gives +9Volt AC, Voltage between the two outer terminals gives +18Volt AC.
  • Four 1N4007 diode connected as shown below forms a bridge circuit which converts bidirectional AC into unidirectional DC.
  • The converted signal is not pure DC, it still consists of some AC signals.
  • The 2200uf capacitor is used as a filter, which allows only DC to pass through..
  • 78XX Voltage Regulators are used for Positive voltage values and 79XX Voltage Regulators are used for Negative voltage values.
  • Here i have used +5Volt Voltage Regulator IC ie) 7805. Similarly we can replace 7805 with 7905 to get -5Volt regulated output.
  • 78XX consists of three terminals namely unregulated input voltage, ground and regulated output voltage.
  •  +9Volt DC input goes to 7805, which gives +5Volt regulated DC output.
  • Output of the regulator produces noise which can be removed using 100nf capacitor, which acts as a filter.
  • For other voltage values we can simply replace 7805 with the corresponding 78XX or 79XX Voltage Regulator ICs.
Circuit Diagram:

 

Figure 2: Fixed Single Voltage Regulator Circuit simulation made in Multisim


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