The quantity of current that flows to a load, or the item being powered, is controlled by a current limiting circuit that uses an LM317 or LM338 integrated circuit.
By carefully configuring these integrated circuits, voltage regulators can also function as current limiters.
An input voltage Vin from a power source enters the circuit.
Three pins are included on the LM317/LM338: input, output and adjust.
Vin is connected to the input pin.
Connected to the load that will receive a restricted current is the output pin Vout.
Circuit Working:
Parts List:
| Category | Item | Quantity | Notes |
|---|---|---|---|
| Resistor | Resistor Rx | 1 | |
| Semiconductors | IC LM317/LM338 | 1 | Choose either LM317 or LM338 based on your voltage and current requirements |
If you have specific values or additional components to include, feel free to provide more details!
The power source provides the input voltage Vin.
Three pins make up the LM317/LM338 IC: input, output, and adjust.
Vin is linked to the input pin.
The load, or the object that will receive the restricted current, is connected to the output pin Vout.
Connected between the adjust pin and the output pin is resistor Rx.
The current limit is determined by this resistor.
The following formula determines the current through the load and, thus the current limit:
ILIMIT = VREF / Rx
where,
- VREF is the LM317/LM338s internal reference voltage, which is normally 1.25V.
The voltage across Rx rises as the current passing through the load gets closer to the current limit established by Rx.
This voltage rise is detected by the LM317/LM338s adjust pin.
In order to maintain a constant voltage across Rx and consequently, a constant current through the load, the LM317/LM338 then lowers the output voltage Vout.
Essentially, the LM317/LM338 controls the current passing through the load by functioning as a variable resistor in a feedback loop.
Here are some additional points to consider:
To make sure that Rx can withstand the current passing through it without overheating, the value must be carefully selected.
The following formula may be used to determine the power wasted by :
P = I2 * R
where,
- I is current in amps, R is resistance in ohms, and P is power in watts.
The greatest output current that the LM317 and LM338 can manage is 1.5 amps and 5 amps, respectively.
The current rating of the LM317/LM338 being utilized will restrict the circuits capacity to limit current.
The graphic specifies a range for the value of Rx (0.8Ω to 1200Ω).
This is due to the possibility of improper operation of the LM317/LM338 if the voltage across the adjust pin is very high or low.
Advantages:
- Shields your load from high current, which might cause harm.
- Even in the event of a little input voltage fluctuation, produces a steady current.
How to Build:
To build a Simple Current Limiting Circuit using IC LM317/LM338 follow the below mentioned steps:
- Gather all the components as shown in circuit diagram above.
- Connect Adjust pin of LM317 IC to other end of resistor Rx which is also the current controlled output.
- Connect Vout pin of LM317 IC to current controlled output through resistor Rx.
- Connect Vin pin of IC LM317 to positive of input DC supply.
- Connect the negative terminal of the load to ground.
Safety Measures:
- The datasheet for the particular LM317 or LM338 you are using should always be consulted.
- Important details like voltage and current restrictions, temperature concerns, and any particular safety measures the manufacturer may have stated will be provided by this.
- Make sure the heat sink, capacitors and resistors you choose are rated for the voltages and currents your circuit will be using.
- Never give a component a higher grade than it deserves.
- The LM317/LM338 may produce heat during circuit operation, particularly at higher input and output voltages and currents.
- Examine your design and the datasheets thermal specifications carefully to see whether a heat sink is required.
- The IC wont overheat thanks to a heat sinks assistance in dissipating heat.
Conclusion:
An LM317/LM338 current limiting circuit is a useful tool for shielding your gadgets from high current.
You may construct and use this circuit efficiently by choosing your components wisely, taking safety precautions and being aware of the working principles.
When dealing with electronics, do not forget to emphasize safety precautions and refer to the datasheet for precise specifics.