Let’s calculate the voltage regulator efficiency impact on battery life and understand why LDO selection matters for IoT prototypes.
LDO Efficiency and Heat Dissipation
For an ESP32 weather station running from a 3.7V LiPo battery with a linear regulator (LDO) to 3.3V:
LDO efficiency: \[\eta_{\text{LDO}} = \frac{V_{\text{out}}}{V_{\text{in}}} = \frac{3.3\,\text{V}}{3.7\,\text{V}} = 0.892 \quad (89.2\%)\]
Power loss in regulator during active phase (80 mA load): \[P_{\text{loss}} = (V_{\text{in}} - V_{\text{out}}) \times I_{\text{load}} = (3.7 - 3.3) \times 0.080 = 0.032\,\text{W} = 32\,\text{mW}\]
Over 4.1 seconds active per 10-minute cycle: \(E_{\text{loss}} = 32\,\text{mW} \times 4.1\,\text{s} = 131\,\text{mJ}\)
Battery capacity wasted per day: \(144\,\text{cycles} \times 0.0036\,\text{mAh} = 0.52\,\text{mAh/day}\) (3.4% overhead)
Buck Converter Alternative: A 95% efficient buck converter: \[P_{\text{loss}} = P_{\text{out}} \times \frac{(1-\eta)}{\eta} = (3.3\,\text{V} \times 0.080\,\text{A}) \times \frac{0.05}{0.95} = 13.9\,\text{mW}\]
This is 2.3× lower loss than the LDO, extending battery life by ~2.5% annually. For a 131-day design, this adds ~3 days.
Trace Width for Power Delivery: The ESP32 draws 80 mA average. For a 3.3V trace on a PCB with 1 oz copper (35 µm thick):
Trace resistance: \[R_{\text{trace}} = \frac{\rho \times L}{A} = \frac{1.68 \times 10^{-8} \times 0.05}{(0.254 \times 10^{-3} \times 35 \times 10^{-6})} = 0.095\,\Omega\]
for a 5 cm long, 10 mil (0.254 mm) wide trace.
Voltage drop: \[V_{\text{drop}} = I \times R = 0.080 \times 0.095 = 7.6\,\text{mV} \quad \text{(acceptable, <1\% of 3.3V)}\]
But increasing to 200 mA (Wi-Fi TX burst): \(V_{\text{drop}} = 19\,\text{mV}\) (0.58% drop, still acceptable).
Rule of thumb: Use 20 mil (0.5 mm) traces for power lines carrying >100 mA to keep voltage drop below 0.5%.
