1. What is the LM317 Current Calculator?

The LM317 current calculator helps determine the output current of an LM317 voltage regulator when used as a constant current source. The calculation is based on the reference voltage and the resistance value.

2. How Does the Calculator Work?

The calculator uses the LM317 current equation:

Where:

• \( I_{out} \) — Output current (A)
• \( V_{ref} \) — Reference voltage (typically 1.25V)
• \( R \) — Resistance value (Ω)

Explanation: The LM317 maintains a constant 1.25V reference voltage between the output and adjust terminals, creating a constant current through resistor R.

3. Importance of Current Calculation

Details: Accurate current calculation is crucial for designing power supplies, LED drivers, and battery chargers using the LM317 as a constant current source.

4. Using the Calculator

Tips: Enter the reference voltage (typically 1.25V) and the resistance value in ohms. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical V_ref for LM317?
A: The typical reference voltage is 1.25V between the output and adjust terminals.

Q2: What is the maximum current LM317 can provide?
A: The LM317 can provide up to 1.5A, but proper heat sinking is required for higher currents.

Q3: How accurate is this current source?
A: The accuracy depends on the tolerance of the reference voltage (typically ±1%) and the resistor tolerance.

Q4: Can I use this for LED driving?
A: Yes, the LM317 makes an excellent constant current source for driving LEDs.

Q5: What power rating should the resistor have?
A: The resistor power rating should be at least P = I²R to avoid overheating.