7805 Regulator IC Sourcing

Dear all,

Its not arduino related question. I posted the general electronic question here.

I have 7805 dc regulator 1A output 5v dc . Datasheet say Input voltage range 9V to 35V

I have Pulse transformer which gives 2 transformer output 12V 1 A and 12V 500ma

I am giving 12V1A source to run Micro-controller and relay operation & 12V 500ma given to another 7805 with isolated grounding to RS485 ckt.

My question here is weather 7805 can source by 12V 500mA??
when i gave 12V 500mA i used to get proper 5V but when loaded with IC like ADM2483 etc it wont allow

Is it make any difference.? weather current also matters here?? i have only ADM2483 driving ckt to drive it

Make sure to use a suitably large heatsink and/or fan. Use..... 7812.

As i told ,

I have 2 7805 regulator IC which is driven from common pulse transformer. where one 7805 is driven with 12V1A source and other 12V 500mA source. my final product is working with 12V 1A source and now i am adding additional isolated power supply for ADM2483

As soon as i add 7805 hardware wise i used to get proper 5V output but my final product stop working.

So my question here is .
i haven't made any changes only added 7805 regulator output to drive ADM2483 which require isolation grounding.

what made my hardware to stop working after adding another 7805 regulator . if i remove it its working normal.

12V1A used to drive micro controller , Relays. which is working fine

12V 500ma given only to drive ADM2483 from 7805.

weather since out put is 5V1A= 5W 12V500mA=6W enough to drive it or not??

Do you want to just use 7812 instead?

So my question here is .
i haven't made any changes only added 7805 regulator output to drive ADM2483 which require isolation grounding.

Did you add the recommended capacitors to both 7805s? Without the capacitors it can oscillate and you can get all kinds of strange problems. Or, maybe the ADM2483 is bad/shorted or maybe the 2nd 7805 is bad?

You can also get "strange problems" when they overheat. They are thermally protected so they rarely burn-out, but again they can oscillate or shut-down intermittently.

Is it make any difference.? weather current also matters here?? i have only ADM2483 driving ckt to drive it

Yes, but the ADM2483 doesn't use much current (normally).

Usually these linear regulator chips are limited by power/heat and in most applications you can't get the full-rated 1.5 Amps. A bigger heatsink or lower-applied voltage allows more current.

Power dissipated by the regulator (directly related to heat) is calculated as Voltage dropped across the regulator X Current through it.

The voltage from the power supply is (hopefully) constant but the actual current depends on the load (Ohm's Law). i.e. The 12V power supply isn't "putting out" 1A unless you happen to have a 12 Ohm load.

You've got 7V across the regulator, but unknown current.

AJITnayak:
weather since out put is 5V1A= 5W 12V500mA=6W enough to drive it or not??

That would work for a switching regulator (buck converter). Not for a linear regulator: for 1A out you need 1A in. That's also why the thing gets so hot: 7V drop @ 1A = 7W power dissipation. Without a big heat sink that'll mean smoke.

If you need 1A at 5V you're much better off with a buck converter.