12 V to 6 V linear regulator

How it works

The pass transistor drops the difference between the input and output voltage while carrying the load current. That makes the circuit straightforward, but the unused electrical power becomes heat.

Estimate dissipation as P ≈ (Vin − Vout) × I. Dropping 12 V to 6 V at 0.5 A produces about 3 W, so the original suggestion that this needs no heatsink is unreliable. A car’s running voltage can be higher still.

On the bench

Select the heatsink and transistor using safe-operating-area and thermal calculations. Do not assume the claimed 5 A is available without reviewing current limiting, cooling, wiring, and automotive input protection.

Resources & provenance

Rewritten from the original circuits/pos/h23n8m9_pos002.php page. Component values and historical performance claims have not been independently bench-tested. The circuit figures have had their watermarks removed.