Voltage Regulator Heat Calculator Formula

Understand the math behind the voltage regulator heat calculator. Each variable explained with a worked example.

Use the Voltage Regulator Heat Calculator

Formulas Used

Power Dissipated

power_dissipated_w = (v_in - v_out) * load_current_a

Junction Temperature

junction_temp = t_ambient + (v_in - v_out) * load_current_a * theta_ja

Temperature Rise

temp_rise = (v_in - v_out) * load_current_a * theta_ja

Variables

VariableDescriptionDefault
v_inInput Voltage(V)12
v_outOutput Voltage(V)5
load_current_aLoad Current(A)0.5
theta_jaThermal Resistance (junction-ambient)(°C/W)50
t_ambientAmbient Temperature(°C)25

How It Works

Linear Regulator Heat

Formulas

P = (V_in - V_out) x I_load

T_junction = T_ambient + P x Theta_JA

Keep junction temperature below the maximum rating (usually 125-150C). Use a heat sink to reduce thermal resistance.

Worked Example

12 V to 5 V regulator at 0.5 A, 50 C/W thermal resistance, 25C ambient.

v_in = 12v_out = 5load_current_a = 0.5theta_ja = 50t_ambient = 25
  1. 01P = (12 - 5) x 0.5 = 3.5 W
  2. 02T_rise = 3.5 x 50 = 175C
  3. 03T_junction = 25 + 175 = 200C (exceeds limits!)

Ready to run the numbers?

Open Voltage Regulator Heat Calculator