The article explains the pinout functions, and datasheet of a versatile low dropout (LDO) 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.
Hai sir…
How to use pin no 4…
Need any resistor or direct dc..
LM78 series many o/p available 5,6,9,12,24v is same availabe in this KA378R12C model ic
Hi Kesava, it can be connected directly without any resistor.
the above IC comes only with 12V as far as I know…
The regulator comes in many different voltages and also adjustable. 3.3, 5, 8, 9, 12vdc and 1.25-32vdc adjustable with 35v max input.
http://www.mouser.com/Fairchild-Semiconductor/Semiconductors/Power-Management-ICs/Voltage-Regulators-Voltage-Controllers/LDO-Voltage-Regulators/_/N-5cgac?P=1z0zlebZ1z0z63x
Thanks for updating the info for us Jon…appreciate it.
Hello Mr swagatam good day.. I have a problem..pls do help.. I have an electric guitar which if plug it on the amplifier, the noise is there. If I touch the string the noise minimize automatically. Can you pls help me what to put to the string so that the noise will gone?
Hi Mark, it seems your amplifier is not properly grounded, make sure the ground line of the amplifier is clamped to the chassis or the enclosure and the power supply ground is also clamped with the chassis, and if possible wire the chassis with your home earthing line, also make sure that your guitar body is also connected with this ground line.
Hi, I am looking at your regulator circuit that uses the IC KA378R12 regulator.
I have a 12vdc solar system that runs from about 12.7vdc to 14.5 vdc during the day.
I need to have as near to 12vdc output as possible and thought this circuit would be perfect.
I intend using 47uF 50v electrolytic capacitors for C1 and C0. However I am not too sure what value that resistor should be to get the required minimum 2v to keep the circuit running.
An Ohm value and rating would be great.
Any suggestions would be appreciated, thanks
Hi, you can use this IC for the mentioned purpose, the 2V is the minimum requirement for keeping the output switched ON. You can connect this pin#4 with the input pin#1 of the IC directly so that it is held at the input voltage level and ensures an enabled output as long as the input voltage is active.
Hi
I have another question about that KA378R12 regulator.
Do I need a heat sink for this device and if so how big?
I intend running it near to it’s max 3amps and therefore assume I would need one.
In fact I will be using five of the devices. four of them will power two cameras, each camera using about 350mA, possibly no heat sink required here.
The last one will be powering my DVR which uses up to about 2 amps again the question about heat sinks applies.
Although the IC has an internal thermal protection, a heatsink would allow the IC to work efficiently, so yes it is required. The size will need to be checked with some experimentation, I would recommend a finned type 3 x 3 inch heatsink, that should do the job.
at 350mA also a heatsink may be required, however it will need to checked practically, if the heat is manageable then no need to add it.