Work out voltage regulator power loss instantly with clear inputs, formula shown and shareable results.
A linear regulator drops the excess voltage as heat: loss is (Vin - Vout) times load current, plus the quiescent current times input voltage. Efficiency is therefore roughly Vout/Vin, so dropping 12 V to 5 V wastes more than 40% of the input power whatever the load.
Linear regulator loss
P = (Vin - Vout) x Iload + Vin x Iq; efficiency approx Vout / Vin
Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.
When the drop is small, the current is low, or output noise must be very low — an LDO after a switcher is a common combination.
Because both output power and dissipation scale with current, so the ratio stays near Vout/Vin until quiescent current dominates at very light load.