Using below circuit and LM317 constant current calculator you can design constant current source up to 1.5A, (recommended max output current is 1A). This circuit uses LM317 voltage regulator as current regulator. Because you can get constant current output without affecting input voltage and output load. Also typical load regulation about 0.1% for this. So this constant current regulator can use for led driver, battery charger, current limiter for your dc power supply and more.
| Parts List | |
| U1 | LM317 |
| R1 | Between 0.8Ω to 1250Ω |
You can use below LM317 constant current calculator to calculate R1 resistance and R1 wattage. LM317 IC need good heatsink when the output load is more than 500mA. During this experiment we use 2.5Ω resistor (1.5+1.0) to get 500mA output. As well as max input voltage for above circuit is 37V. Also input voltage should be greater than output load voltage + 4.25 V for good current regulation.
OUTPUT CURRENT = VREF/R1
VREF=1.25 for LM317
(Output current units – Ampere, R1 units – Ohms)
e.g. for R1=2.5Ω
Output current=1.25/2.5
=0.5A
LM317 online calculators
Finally You can use above LM317 constant current calculator for LM338 and LM350. Because LM338 max output current is 5A and LM350 max output current is 3A.
Also please go through below post for discover more LM317 circuits
LM317 REGULATED BATTERY CHARGER CIRCUIT