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LM7912 Negative Voltage Regulator | 12v Power Supply Circuit

negative voltage regulator IC (U2) regulates the -Ve input and provides a second output. The ground (GND) serves as a common reference.
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LM7912 Negative Voltage Regulator | 12v Power Supply Circuit

12v negative voltage regulator - Electronic Project


The power supply adapter from Raspberry Pi and the USB supply of Arduino was more than enough. But after some time my curiosity pushed me to consider other power supply methods, and after creating more projects I was forced to make considerations about different or if possible adjustable DC power supply sources. Especially when you finish your design you will definitely want to build a more permanent version of your project, and for that, you will need to consider how to go about providing a power supply to it. In this Tutorial, I will explain how you can create your own linear power supply with widely used or affordable voltage regulators IC (LM78XX, LM3XX, PSM-165, etc.). You will learn about their functionality or implementation for your own projects.

You should consider in your design that the logic level of the voltages needs to be regulated very precisely. For example for devices with TTL of the voltage, the supply voltage needs to be between 4.75 and 5.25 volts, otherwise, any voltage deviation will cause the logic of the components to stop working correctly or even destroy your components. In contrast to the logic level of the devices, the power supply for the motors, LEDs, and other electronic components can deviate in a wide range. Additionally, you must consider the current flow requirements of the project. Especially motors could cause the current draw to fluctuate and you need to design your power supply to accommodate the “worst case” situation where every motor is operated at full capacity.

A single linear voltage regulator IC (U2) from the 79xx series negative voltage regulators is utilized here to regulate the unregulated DC voltage to a negative voltage. Usually, this IC is used in series with the -Ve input of the terminal. You can find the minimum required input voltage to operate the negative voltage regulator ICs in the 79xx series datasheet. On the other hand, the negative voltage regulator IC (U2) regulates the -Ve input or provides a second output. The ground (GND) serves as a common reference for both outputs. This way the circuit diagram provides +Ve & -Ve dual DC outputs continuously.

Diagram of 12V Fixed Negative Voltage Regulator:

12v negative voltage regulator

Hardware Required for this Project:

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Working Principle of 12v Power Supply Circuit:

This type of linear regulator has a 2 V dropout of the voltage, as a result with a 5V output at 1A, you need to have at least 2.5 V DC head voltage (i.e., 5V + 2.5V = 7.5V DC input).With the increase of the voltage difference between the input and output voltage - the power supply dissipation increases as well. Meaning, for example, while a 7 volts source regulated to 5 volts delivering 1 amp would dissipate two- watts through the linear regulator, a 12 V DC source regulated to 5 volts delivering the same current flow would dissipate 5 watts, making the regulator only 50 % efficient. The next important parameter is the “Thermal of the Resistance” in units of °C/W (°C per Watt).

This parameter indicates the number of degrees the chip will heat up above the ambient air temperature, per each watt of power supply it must dissipate. Simply multiply the calculated power supply dissipation by Thermal Resistance and that will tell you how much that linear regulator will heat up under that amount of power supply. The 78XX voltage regulators are 3-pin devices available in a number of different packages, from large power supply transistor packages (T220) to tiny surface mount devices it is a positive voltage of the regulator. The 79XX series is the equivalent negative voltage of the regulators.

The 78XX series of regulators provide fixed regulation of the voltages from 5 to 24 V. The last two digits of the IC part number denote the output of the voltage of the device. This means, for example, a 7805 is a positive 5-volt regulator, or a 7812 is a positive 12-volt regulator. These voltage of regulators are straightforward – connect L8705 and a couple of electrolytic capacitors across the input or output, and you build a simple voltage regulator for 5 V Arduino projects. The important step is to check the datasheets for the pin-outs or manufacturer recommendations.

The manufacturer recommendation for the smoothing capacitors is CInput = 0.33 µF or COutput = 0.1 µF, but the general practice is 100 µF capacitor on the input and the output It is a good solution for the worst-case scenario, and the capacitors help to cope with sudden fluctuations or transients in the supply. In case the supply falls below the threshold of two V- the capacitors will stabilize the supply to ensure that this does not happen. If your project does not have such transients, then you could run with the manufacturer's recommendations. A simple linear voltage regulator circuit diagram is just an L7805 voltage regulator and two capacitors, but we can upgrade this circuit diagram to create a more advanced power supply with some level of protection or visual indication.

They must be voltage-rated for the output of the voltage but should be high enough to suit the input for a little margin of safety (e.g., 16 25 V). They really depend on the type of load you expect and can be left out for a pure DC load, but 100uF for C1 and C2, and 1uF for C4 (and C3) would be a good start. when the circuit diagram is powered LED lights are ON otherwise look for some failures in your circuit. Most voltage regulators have protection circuitry that protects chips from overheating and if it gets too hot, it drops the output voltage and therefore limits the output current flow so that the device is not destroyed by the heat. Voltage regulators in TO-220 packages also have a mounting hole for the heatsink attachment, or I will suggest that you should definitely use it to attach a good industrial heatsink.

Frequently Asked Questions

What is the introduction of a series voltage regulator?

The operation of a series voltage regulator is dependent upon the variable of the component that is connected to the load. When the resistance of the variable of the component is changed, the voltage drop across the component also changes. Using this technique when the voltage across the load remains the same.

What is the function of negative voltage?

Similarly, a positive voltage causes conventional current flow to flow from the positive node to the reference node, and a negative voltage causes current flow to flow from the reference node to the negative node.

What is a negative voltage?

Negative voltage just means it is negative relative to a reference point (usually ground). ie: If you took a 9V battery and connected its positive terminal to the ground while leaving the negative terminal open or then measured between its negative terminal and ground you would measure -9V.

How does a 12v voltage regulator work?

A voltage regulator generates a fixed output voltage of a preset magnitude that remains constant regardless of changes to its input of the voltage or load conditions. There are two types of voltage regulators: linear or switching.

How is the negative voltage generated?

A common way to generate a negative voltage has been to use an operational amplifier (op amp) to invert the output of a positive precision of the voltage. This approach typically requires a positive reference, the op-amp, or two supply rails to generate the negative output.

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