IC 79xx (7905, 7912, 7915, 7918) - Negative Voltage Regulator
79xx voltage regulators are very commonly used in electronic circuits. The main purpose of this IC is to supply required regulated negative voltage to the circuits. IC 79xx can supply a constant negative voltage output, in spite of any voltage fluctuations in its input voltage. It can be mainly found in the circuits in which integrated circuits that require +Vcc and – Vcc are used.
What Is a Voltage Regulator IC?
Voltage regulator IC can be defined as an integrated circuit that is capable of supplying a constant controlled output voltage which is not at all affected by the variations in input voltage provided that the variations are within the prescribed limits under specified atmospheric conditions. Voltage fluctuations may damage or reduce the life of circuit components. Usage of voltage regulator ICs helps in avoiding such events by maintaining voltage at the required levels.
IC 79xx is a three pin negative voltage controller IC. It is a small integrated circuit used in a circuit to supply a constant negative input voltage. The number 79 indicates that it is a negative voltage regulator and xx indicates the output voltage of the IC. ‘xx’ can be replaced by the controlled output voltage provided by the regulator, for example, if it is 7905, then the output voltage of the IC is -5 V. Similarly if it is 7912, then output voltage of the IC is -12 volts and so on. The name of the IC may vary based on the manufacturer as LM79xx, L79xx, MC79xx etc.
IC 79xx requires heat sink for its safe operation. Heat sink boosts heat dissipation therefore the life of the device can be extended.
79xx ICs and Output Voltages
79xx Pin out Configuration
Pin out Configuration of IC 79xx.
The pin out configuration of IC 79xx is shown in the diagram below.
- The pin 1 acts as the Ground terminal (0V).
- The pin 2 acts as the input terminal (5V to 24V).
- The pin 3 acts as the output terminal (constant regulated 5V).
IC 79xx is used in circuits as shown in the circuit. In order to improve stability two capacitors – C1 and C2 are used. The capacitor C1 is used only if the regulator is separated from filter capacitor by more than 3". It must be a 2.2 μF solid tantalum capacitor or 25μF aluminum electrolytic capacitor. The capacitor C2 is required for stability. Usually 1 μF solid tantalum capacitor is used. One can also use 25μF aluminum electrolytic capacitor. Values given may be increased without limit.
79xx Connection diagram
Similar to IC 79xx, IC 78XX is a three pin IC that gives a constant output voltage of +5V irrespective of the varying input voltages. The maximum value of input voltage that the IC can withstand is 24 volts.