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LM317 / LM337 Voltage Regulator Calculator
Select regulator, enter desired output voltage or resistors for precise calculation.
🔽 LM317 (Positive)
🔼 LM337 (Negative)
📐 Circuit Diagram - R1 & R2 Location
🔴 R1 connected between OUTPUT and ADJUST
🔴 R2 connected between ADJUST and GROUND
📍 INPUT: Unregulated DC voltage (2V to 40V)
📍 OUTPUT: Regulated voltage (Vout = 1.25V × (1 + R2/R1))
🔴 R2 connected between ADJUST and GROUND
📍 INPUT: Unregulated DC voltage (2V to 40V)
📍 OUTPUT: Regulated voltage (Vout = 1.25V × (1 + R2/R1))
Calculates R2 using standard R1 (240Ω or 120Ω)
LM317: 240Ω (typical) | LM337: 120Ω (typical)
Modify to calculate voltage
⚠️ Vout = 1.25V × (1 + R2/R1) + Iadj·R2. Iadj ≈ 50μA negligible for accuracy.
LM317
5.00 V
Calculated Vout: 5.00 V
R2 for desired Vout: 720 Ω
Reference voltage (Vref): 1.25 V
Current through R1: ~5.21 mA
Standard Resistor Values (E12/E24)
| R1 (Ω) | R2 (Ω) | Vout LM317 (V) | Vout LM337 (V) |
|---|
📐 Basic formula: Vout = Vref × (1 + R2/R1) , with Vref = 1.25V (LM317/337).
For LM337 output voltage is negative: -Vout.
For LM337 output voltage is negative: -Vout.