Readers are advised to proceed with the construction of the presented circuits only after understanding the concepts from the core. Not adhering to this can lead to failures and frustrations.

Search This Blog

Loading...

Sunday, April 1, 2012

IC LM338 Application Circuits - Explained in Simple Words

The IC LM338 by TEXAS INSTRUMENTS, is a versatile IC which can be wired in numerous different ways for obtaining high quality power supply circuit configuartions.
The following circuit examples simply depict few of the very interesting useful power supply circuits using this IC.


Let's study each circuit diagram in details:


Simple Adjustable Voltage Power Supply Circuit

The first circuit shows the typical wiring format done around the IC. The circuit provides an adjustable output right from 1.25V to the maximum applied input voltage which shouldn't be more than 35 vots.

R2 is used for varying the output voltage continuously.


Simple 5 Amp Regulated Power Supply Circuit

This circuit produces an output that may be equal to the input supply voltage but the current is well regulated and can never exceed the 5 Amp mark. R1 is precisely selected so as to maintain a safe 5 amp maximum current limit that can be withdrawn from the circuit.

15 Amp, Variable Voltage Regulator Circuit

The IC LM 338 alone is specified for handling a maximum of 5 Amp of current, however if the IC is needed to handle higher currents, in the region of 15 amps, it can well be modified to produce that much of current with the appropriate modifications as shown below. The circuit utilizes three IC LM338 for the intended implementations with output voltage that's adjustable as explained for the first circuit. R8 is used for the voltage adjustment operations.

Digitally Adjustable Power Supply Circuit:

In the above designs, the power supply utilized a pot for implementing the voltage adjustment procedure, the below given design incorporates discrete transistors which can be digitally triggered separately for obtaining the relevant voltage levels at the outputs. The collector resistance values are chosen in an incremental order so that a correspondingly varying voltages can be selected and becomes available through the external triggers.



Light Controller Circuit

Other than power supplies, LM338 can also be used as a light controller. The circuit shows a very simple design where a phototransistor replaces the resistor which normally acts as the component for adjusting the output voltage. The light which needs to be controlled is powered by the output of the IC and its light is allowed to fall on this phototransistor. As the light increases the value of the photo-transistor decreases which in turn pulls the ADJ pin of the IC more toward the ground, forcing the output voltage to decrease which also decreases the light illumination, maintaining a constant glow on the lamp.

Current Controlled Power Supply Citcuit:

The next circuit shows a super simple wiring with the IC LM338 whose ADJ pin is connected to the output after a current sensing preset. The value of the preset determines the maximum amount of current that becomes permissible through the IC at the output.


12V Current Controlled Battery Charger Circuit

The circuit below can be used to charge a 12 volt lead acid battery safely. The resistor Rs may be selected appropriately for determining the desired level of current for the connected battery. R2 can be adjusted for obtaining other voltages for charging other categories of batteris.


Slow Turn ON Output Power Supply

Some sensitive electronic circuits require a slow start rather than the usual instant start. The inclusion of C1 makes it sure that the output from the circuit rises gradually to the set maximum level ensuring the intended safety to the connected circuit.


Heater Controller Circuit

IC LM338 can also be configured for controlling temperature of a certain parameter like a heater. Another important IC LM334 is used as the sensor which is connected across the ADJ and ground of the IC LM338. If the heat from the source tends to increase above the predetermined threshold, the sensor lowers its resistance  correspondingly, forcing the output voltage of LM338 to fall, subsequently decreasing the voltage to the heater element.




10 Amp Regulated Power Supply Circuit

The following circuit shows another circuit whose current is restricted to 10 amps, that means the output can be made suitable for high current rated loads, the voltage is adjustable as usual via the pot R2.

Adjusting Many LM338 modules via a Single Control

The given circuit shows a simple configuration which can be used for controlling the outputs of many LM338 power supply modules simultaneously though a single pot.






10 comments:

  1. good day sir,

    regarding the 12V Current Controlled Battery Charger Circuit, can is use rectified DC from a motorcycle as V_in?

    if possible, what voltage of the capacitor would you recommend? is it ok to use 1/4w for all resisitors?

    thank you.

    Regards

    ReplyDelete
    Replies
    1. Good day Jhunix, yes you can use the motorcycle alternator input after rectification, but it should not exceed 35V.

      Use 10uF/50V at the input and 100uF/25V at the output of the IC.

      Delete
    2. Can i use LM317 or any equivalent IC replacing LM338? because I can't find LM338 in any electronic/electrical store here in or place.

      Delete
    3. 317 will charge only upto 10AH batteries not above that.

      Delete
  2. sir some times 7805 get short circuits & it gives 12v output how i save my mobile from 12v output
    give your reply

    ReplyDelete
    Replies
    1. prashant, 78XX ICs are internally short circuit protected, they will never get shorted unless tampered intentionally. Even if this happen, the cell phone is protected against upto 12V supplies and will simply show"not charging"

      Delete
  3. good day sir. i wat to build a powersupply with lm338 but i want to be able to adjust the curent to not just the voltage i saw a schematic above with a simple curent limiting circuit.but if i make that circuit how can i adjust the voltage not just the curent?

    ReplyDelete
    Replies
    1. good day,

      please refer to the first diagram in the following link:

      http://homemadecircuitsandschematics.blogspot.in/2012/11/3-watt-5-watt-led-dc-to-dc-constant.html

      Replace the transistor with a Darlington pair (two BC547) and replace the base resistor with a 10k pot. The slider arm will go to ground while the two ends across base and 0.6 ohm resistor.

      this pot can be used for setting the current limits.

      Delete
  4. hello sir
    how to find R1 values(ohms,watts) for current controlled power supply . i am using 12v 80ah battery and need output current : 3.5 amp to drive led array of 30 * 1 watt leds

    ReplyDelete
    Replies
    1. hello aashish, please go through the following article, it has all the required info in it:

      http://homemadecircuitsandschematics.blogspot.in/2013/06/universal-high-watt-led-current-limiter.html

      Delete

Readers are requested not to include external links while commenting. For consulting a diagram, upload it on Google Drive and provide the link here.