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IC 79xx (7905, 7912, 7915, 7918): Negative Voltage Regulator

I am an electrical and automation engineer specialized in LV switchgear design and process automation.

This is the IC 7912.

This is the IC 7912.

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?

A 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

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.

What Does the Name Mean?

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 the 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

IC NumberOutput Voltage

7905

-05 Volts

7912

-12 Volts

7915

-15 Volts

7918

-18 Volts

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).

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).

Pin Out Configuration of IC 79xx

The pin out configuration of IC 79xx is shown in the diagram above.

  • 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).
This is the 79xx connection diagram.

This is the 79xx connection diagram.

Connection Diagram

IC 79xx is used in circuits as shown in the circuit above. 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 a 1 μF solid tantalum capacitor is used. One can also use a 25μF aluminum electrolytic capacitor. Values given may be increased without limit.

IC 78XX

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.

Quiz

For each question, choose the best answer. The answer key is below.

  1. Why is 7905 used in a circuit?
    • To Step up voltage
    • To Step down voltage
    • To improve Voltage regulation
    • To obtain regulated negative voltage
  2. What does xx in 79xx indicate?
    • Family name
    • Input voltage
    • Output voltage
    • Temperature withstand capability
  3. Which is the input terminal of 7905?
    • Pin 1
    • Pin 2
    • Pin 3
    • None of the above
  4. Which is the output terminal of 7905?
    • Pin 1
    • Pin 2
    • Pin 3
    • None of the above
  5. What is the output voltage of 7812?
    • 5 volts
    • 7 volts
    • 12 volts
    • 8 volts

Answer Key

  1. To obtain regulated negative voltage
  2. Output voltage
  3. Pin 2
  4. Pin 3
  5. 8 volts

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Comments

Shakeel Ahmad on November 16, 2018:

Good job

OSBERT JOEL C (author) from CHENNAI on February 14, 2018:

Approx. 2A max. But the value varies up on manufacturers. Kindly refer the item datasheets for further details.

MASTEROFTECHNOLOGY on November 03, 2015:

Very useful and easy to understand.Thanks.

OSBERT JOEL C (author) from CHENNAI on May 15, 2014:

DDE, Thank you.

OSBERT JOEL C (author) from CHENNAI on May 15, 2014:

CyberShelley, Thank you so much

Devika Primić from Dubrovnik, Croatia on May 15, 2014:

A great insight to this hub so in detail and an educational one. Thank you for following me. Voted up!

Shelley Watson on May 13, 2014:

Interesting technical article. Voted up, interesting and useful

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