High Voltage Linear Regulator

LR8 Resistor Calculator

Compute R1 and R2 for the Microchip LR8 adjustable regulator. Vout = 1.20 V · (1 + R2/R1) + I_adj·R2

V_REF = 1.20 V · I_adj ≈ 80 nA

Design Parameters

Input VoltageOptional — for dissipation check

R1 (Reference Resistor)Min 1000 Ω · typical 10 kΩ — fixed by you

Output Voltage1.2 V to 438 V

Load CurrentMax 25 mA (LR8N3)

Calculated Values

R1 (nearest E96)1.21 kΩ

R2 (ideal)283.78 kΩ

R2 (nearest E96)287.00 kΩ

Actual Vout285.851 V

Error+0.30 %

Vin − Vout15.00 V

Power Dissipation150 mW

Reference Circuit

   Vin ──[ IN  LR8  OUT ]──┬─────┬──────── Vout
              ADJ          │     │
               │         [ R1 ] ===  1 µF
               ├───────────┘     │
               │                 │
             [ R2 ]              │
               │                 │
              GND ───────────────┘

   Vout = 1.20 V · (1 + R2/R1) + Iadj · R2
   Iadj ≈ 80 nA  (typically negligible)

Vin max: 450 V

Vout range: 1.2 – 438 V

Iout max: 25 mA

Dropout: ~12 V