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 R1 is precisely selected so as to maintain a safe 5 amp maximum current limit that can be withdrawn from the circuit.
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.
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.
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.
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.
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.