This five-watt LED driver uses the IC LM338 to safely light a four-watt LED in a constant current circuit mode.
As is well known, the integrated circuit LM338 is an extremely flexible device for managing voltages and current quantities.
Circuit Working
The LM338 configuration in the given concept is intended for an automatic current control.
In particular, white LEDs require a precisely measured input, and practically, the current flowing to them needs to be tightly regulated.
It ensures that the output's current is constantly tracked by the ADJ pin and is never permitted to exceed the preset level established by the 0.6 Ohm resistor through the connection of its ADJ pin to the output.
Because this LM338 can readily drive one to five one-watt LEDs, each with its own current-limiting resistor, it can sustain at least three amps of current.
It is possible to play around with different values for the current limiting resistors in order to increase the brightness levels of the LEDs. Despite this, anything lower than fifty Ohms is not worth attempting since it may permanently harm the LEDs.
Understanding the Circuit Design
A regulated DC power source that can provide 12 volts at three amps or higher might be used as the input for the LM 338 integrated circuit.
For best results, the IC LM 338 must be installed on a heatsink.
A 1N5408 rectifier diode is suitable for the intended use if the input diode has a 3 amp rating.
A 12 volt battery, such as one from a vehicle, may be used as the input if the circuit is meant to run outside.
The suggested 4 watt LED driver circuit is therefore particularly well suited for lighting up car interiors, such as with a roof light or other fixture.
Calculating the Limiting Resistor
Assuming only one 4 watt LED is connected, the resistor value may be chosen using the formula R = 1.25/LED current.
Here, LED current = 4/3.3 = 1.21A
Therefore R = 1.25/1.21 = about 1 ohm (0.6 is not correct)
R watts = 1.25 x 1.21 = 1.5 or 2 watt
for 4 nos 1 watt LEDs, total current is 300mA
Therefore R = 1.25/0.3 = 4 ohms
Circuit Diagram
Parts List
| Component | Specification |
|---|---|
| LM338 IC | Voltage Regulator IC (1 piece) |
| LEDs (1 watt, 350 mA) | 1 watt, 350 mA (4 pieces) |
| Resistor (0.6 Ω, 1 watt) | 0.6 Ω, 1 watt (1 piece) |