LM7805 3A
Posted: Wed Dec 19, 2018 10:29 pm
It is worth using the regulator 7805 with 3A at 5V in QL instead of its original?
There is one reson why a higher current version of the 7805 was popular as a replacement for the original 7805 1A version, and this has nothing to do with the power consumption of the actual QL, as Dave pointed out - what happens is that additional peripherals load the 9V input voltage to the 7805.Dave wrote:No. There is zero benefit in increasing the capacity of the internal regulator.
All external expansions run off the 9v expansion port supply, so external expansions do not load the internal 5v voltage regulator. The modern internal expansions like QL-SD are so efficient they make an immeasurable difference to 7805 load.
In fact, replacing the 7805 with a larger one could create problems. If you have a short do you want 1 or 1.5A of current dumped through it, or 3-4 amps? It will also take the 3-4A 7805 longer to react to a short or over current situation and start to throttle, which could massively increase the amount of damage done while the magic smoke is being released.
If you want to cool that end of the QL, replace any 7805 with a 5v buck regulator. If it's ideally sized it would be around 1.2 to 1.5A.
DC/DC converter modules (switching regulators) are available that are “drop-in” replacements for 7805 series pass voltage regulators.Nasta wrote:2) Replace the regulator with a switching buck regulator. This type of a regulator acts similarly to what would be a DC transformer (for reference, a real transformer can only operate on AC). The efficiency is very high so very little excess heat is generated, to the point where a heatsink is not needed at all. Also, in many cases the switching regulators have a low dropout voltage and higher current capability, but this has to be a circuit rather than a component.