The article explains the pinout functions, and datasheet of a versatile low dropout voltage regulator IC KA378R12, and also presents a circuit diagram showing how to use the IC in practical applications.

A related question was asked by Mr. Jon, which inspired me to update this post. The question can be seen in the following paragraph:

Technical Specification

The reason I emailed you is about a Low Drop Out 12vdc voltage regulator. What I'm working on is a LED brake light assembly were the input voltage needs to be 11.5-12.5 vdc.

With a regular 12v regulator the drop out voltage is too high. It works ok when the vehicle is running producing 14.5 volts. With vehicle engine turned off the output voltage from these regulator IC drops to low. I was looking at the KA378R12CTU from Fairchild I included the data sheet. Do you have any other suggestions?

Thank You
Jon Richey

Circuit Analysis

Hi Jon, 

I think it's the perfect option that you have selected for fulfilling your requirement, please go ahead and use it for the application.

The Design

Coming back to our proposed low voltage dropout regulator IC KA378R12, it is quite similar to our ordinary 12V fixed regulator, such as 7812, or the 12V/5amp regulator version except the difference that this device is able  to produce a 12V output with an impressive low dropout of 0.5V.

The IC is a 12V voltage regulator capable of producing a fixed 12V output at a maximum 3 amp current, with a dropout of hardly 0.5V across its input and output terminals, meaning, even with a 12.5V as the input you can expect the output to produce a consistent and fixed 12V.

We can see that this IC has 4 pinouts instead of 3 which we usually find in other traditional regulator ICs, the functions of these pinouts can be understood from the following points:

Pinout Details

Pin#1 is the input pinout of the IC. A maximum of 35V DC can be applied on this pin.

Pin#2 is the output pinout of the IC. A 12V fixed low dropout output can be achieved across this pinout.

Pin#3 is the common ground pinout. The above discussed input and output voltages are referenced to this common ground pinout, meaning it forms the negative line for the input as well as the output voltages, and also the load

Pin#4 has the function of "output disable". This pin should be fed with a minimum of 2V to keep the output enabled and functioning, not exceeding 35V or the input supply level.

However a zero volt trigger or a ground connection on this pin will instantly render the output zero volt by disabling the IC.

Application Circuit Diagram

The basic circuit diagram using the above explained low drop 12V regulator KA378R12 can be witnessed in the following image:

Built-in Protections

Apart from the low dropout feature the IC also comes with a few outstanding and useful protection capabilities such as peak current protection, thermal shut-down, input over voltage protection, and output disable feature (already discussed previously).

Feedback from Mr. Jon

Hi Swagatam,

I'm using this regulator we discussed. But It's a fixed voltage regulator that's a tiny bit to high in voltage. My LED board is 12volts with a total amp draw of 1.50 amps. At 12.3v it creates to much heat. At 11.9v its perfect. Any suggestions on how to bring voltage down? Could I use a resistor to ground draw it down? Or would a switching regulator be a better alternative? If so could you point me in the direction of a schematic.

Thank You

Jon Richey

My Reply

Hi jon,

the IC is rated to handle 3 amps, therefore 1.5 amps should not be a problem for the mentioned IC

You can add a large heatsink to it for controlling the heat.

I can suggest you a switching regulator but that may involve complexities and many adjustments.


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