The STMicroelectronics LD1085V is a single-output, positive adjustable linear regulator delivering up to 3 A continuous current. The output voltage is set with two external resistors from a 1.25 V reference up to 28.5 V, with a maximum input of 30 V. The 1.5 V maximum dropout at full 3 A load defines the minimum input-to-output headroom: a 5 V rail needs at least 6.5 V input to hold regulation. That matters when the input comes from a loosely regulated supply or a battery nearing end-of-discharge. PSRR is 72 dB at 120 Hz, which is a strong ripple-rejection figure for a 3 A adjustable part. It makes the LD1085V a candidate for post-regulator stages in audio equipment, precision analog supplies, or any rail where 100/120 Hz mains ripple needs attenuation.
Sizing the thermal budget
With 3 A output and a 1.5 V dropout, worst-case power dissipation is 4.5 W. The TO-220 package with a heatsink is mandatory at that level — the junction-to-ambient thermal resistance of a bare TO-220 (typically 50–60°C/W) would exceed the 125°C junction limit even at moderate ambient. Plan for a heatsink sized to keep junction temperature below 125°C across the operating range. It adds 30 mW to the dissipation budget at 3 V input, negligible compared to the load power, but worth noting in always-on or battery-backed designs where the regulator idles.
Protection features and temperature grade
Built-in over-current and over-temperature protection are included. The thermal shutdown prevents die damage during sustained overload or inadequate heatsinking, and the current limit folds back to protect the pass transistor. No separate high-temp variant is needed for these environments.
It is RoHS3 compliant.