Voltage Regulator Heat Calculator Formula
Understand the math behind the voltage regulator heat calculator. Each variable explained with a worked example.
Formulas Used
Power Dissipated
power_dissipated_w = (v_in - v_out) * load_current_aJunction Temperature
junction_temp = t_ambient + (v_in - v_out) * load_current_a * theta_jaTemperature Rise
temp_rise = (v_in - v_out) * load_current_a * theta_jaVariables
| Variable | Description | Default |
|---|---|---|
v_in | Input Voltage(V) | 12 |
v_out | Output Voltage(V) | 5 |
load_current_a | Load Current(A) | 0.5 |
theta_ja | Thermal Resistance (junction-ambient)(°C/W) | 50 |
t_ambient | Ambient 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.
- 01P = (12 - 5) x 0.5 = 3.5 W
- 02T_rise = 3.5 x 50 = 175C
- 03T_junction = 25 + 175 = 200C (exceeds limits!)
Frequently Asked Questions
What is a safe junction temperature?
Most ICs are rated for 125-150C maximum. Stay below with margin, ideally under 100C for reliability.
How to reduce junction temperature?
Add a heat sink, reduce input voltage, reduce current, improve airflow, or switch to a switching regulator.
What is thermal resistance?
Measured in C/W, it indicates temperature rise per watt of dissipation. Lower is better. Depends on package and heat sinking.
Ready to run the numbers?
Open Voltage Regulator Heat Calculator