LM7805

It depends on headroom and package. The LM7805 needs about 2 V of dropout at 1 A and comes in a TO-220 you must bolt down, so it suits 9 V to 24 V rails with copper or a heatsink available. The AMS1117-5.0 needs only about 1.1 V to 1.2 V and mounts in SOT-223, but its tab has to dump the same watts into a PCB pour. For a 5 V input from USB neither part works well — use a true low-dropout device such as the MCP1703, HT7550 or a micropower LDO with a sub-200 mV dropout.

Dissipation is (VIN - VOUT) x IOUT plus a few milliwatts of quiescent current. At 12 V in, 5 V out and 1 A that is 7 W. With TO-220 junction-to-ambient around 50 °C/W bare and a 125 °C junction limit at 25 °C ambient, you have a 100 °C budget, so 7 W already needs a heatsink of roughly 10 °C/W plus the interface. Reduce input voltage, split the drop across two regulators, or move to a switching converter — an LM2596 running the same job wastes only about 1.4 W.

Functionally no — the 78xx family is internally compensated and stable without an output capacitor. In practice always fit one: 0.1 µF to 0.33 µF ceramic at the input if the regulator sits more than about 150 mm from the supply filter, and 0.1 µF to 10 µF at the output for transient response and to stop the pass transistor ringing into long cable loads. If the input can be shorted while the output holds charge, add a reverse diode across input to output to protect the die.

Yes, in both cases with external parts. Lifting the ground pin with a resistor or Zener adds that voltage to the output, at the cost of a few milliamps of extra quiescent error, but regulation and short-circuit behaviour degrade — the LM317 is the proper adjustable solution. Current can be boosted with an external PNP pass transistor and a 0.2 Ω to 0.5 Ω sense resistor, but you then lose the internal current limit unless you add your own sensing.

They are the same circuit from different houses: onsemi MC7805, TI uA7805, ST L7805 and the generic LM7805 all follow the original Fairchild design with identical pinout (input, common, output) and 1 A rating. Differences are in grade suffixes, temperature range (0 °C to 125 °C commercial versus -40 °C for automotive NCV7805), tightness of line/load regulation and short-circuit current limit — TI lists 750 mA typical short-circuit current while onsemi B grades list 200 mA. Specify the exact manufacturer part number on the BOM to keep incoming inspection meaningful.

Three checks. First, marking: genuine parts are laser-etched with a crisp logo, part number and traceable date code, while fakes use ink that lifts with acetone on a cotton bud. Second, mechanics: the moulding should be matte with clean flash-free edges, the tab firmly bonded and the leads matte tin with a bright cross-section when nicked — re-tinned pulls look shiny and often show solder wicking. Third, electrical: load the sample at 1 A for ten minutes and measure output and case temperature. A remarked lower-rated die drifts below 4.75 V or exceeds the temperature rise you calculated. We sample-test every lot on a load bank and supply a certificate of conformance on request.

MOQ is 50 pcs loose or one tube (50 pcs) for TO-220, and 800 pcs on tape-and-reel for TO-263. In-stock lots ship in one to two business days; authorised onsemi and ST channel replenishment runs eight to fourteen weeks, longer during allocation.