LM7912 is a three-terminal negative 12 volts voltage regulator IC. Most of the applications need both positive and negative voltages for their operation. The negative voltages should be stable otherwise they can damage the circuit or reduce the life of components used in the circuit. Therefore, negative voltage regulators sever this application purpose. LM7912 IC is a negative voltage regulator supply negative voltages. It consists of three pins and has a fixed output voltage of -12V. It is used in case of fluctuating inputs to stable the output,
LM7912 Pinout Diagram
Pinout diagram shows that this negative 12 volts regulator has three pins such as input, output and ground pin.
Pin Configuration Description
It is a three-terminal device whose pin details are enlisted below.
|1||GROUND||The ground pin is connected to the ground of the circuit.|
|2||INPUT||The unregulated voltage signal is applied at the input pin. The range of input signal is 5V to 24V.|
|3||OUTPUT||A stable and regulated signal of fixed -12 voltage reflects at the output.|
LM7912 Block Diagram
The block diagram of the internal circuitry of LM7912 IC is given in the figure.
LM7912 Negative Voltage Regulator Features
- It has a fixed -12V output voltage
- The input voltage should lie in between -27V to -14.5V
- Protection circuits against short circuits and thermal overloads are incorporated inside this IC.
- Safe area protection is provided for output transistors.
- It has a high power supply rejection ratio and low noise.
- The output current is 1.5 A
- The output voltage tolerance is ± 4%.
- It has a low quiescent current which ensures good regulation.
Where to use it?
LM7912 IC is used in designing analog circuits which require negative voltages. You can use this IC to get -12 volts. Microcontrollers need a smooth and regulated voltage at the input to function smoothly. Therefore, LM7912 IC is used for generating smooth voltage. It is also useful in designing split power supplies and sensors. Most importantly, it can operate over 0 to 50 °C temperature range. Moreover, it is suitable for use in fixed voltage applications.
How to use the LM7912 Negative Voltage Regulator?
A basic circuit of this IC is mentioned below. It requires only two capacitors in performing a stable operation. One capacitor is connected at the input and the other at the output. They are used to filter noise. To avoid excessive power dissipation, they have a thermal overload protection system incorporated inside the IC.
Short circuit protection is provided to keep the current in limits otherwise it can damage the IC. Pin 2 is supplied with a negative input signal in a range of – 5V to – 24V. LM7912 consists of a pass transistor. The output current decreases when the voltage across this transistor increases. Therefore, safe area compensation is provided in order to compensate for the losses. The life of this device can be increased using heat sink which increases its power dissipation capability.
Negative -12 voltage regulator using LM7912
In this circuit, we apply a 14 volts dc at the input of 7912. Capacitors C1 and C2 are filter capacitors. These capacitors avoid voltage fluctuations at the input and output terminals. Greater the capacitor values less will be voltage fluctuations. But we always use optimum and easily available capacitor values.
We connect a voltmeter at the output to measure output voltage. As you can see from the circuit diagram that output is negative 12 volts.
This IC can be used in designing a dual symmetric voltage supply of 12V. The positive voltage regulator (LM7812) and negative voltage regulator (LM7912) is used in this project. The circuit diagram is given below.
Equivalent Negative Voltage Regulators
Sometimes, we are not able to find electronics components in the market, we can use alternative/ Equivalent regulators.
It is used in fixed voltage applications. Few applications of LM7912 IC are:
- It can be used as a reference or power voltage in analog and digital circuits and as a current source in some applications.
- LM7912 can design a dual regulated supply.
- This IC can design a current limiter in various applications.
- This highly stable regulator is used in highly sensitive light controllers
- It also has a protection circuit for output polarity-reversal.
LM7912 IC is available in only the TO-220 package. Dimensions and 2D diagram of this package is given below.