That sounds like it is loaded down more than 800 mA.

20 posts and still no schematic. Looks like the OP doesn't want a real answer..

ak

 

Hello,

As asked before, do you have the decoupling capacitors mounted?

Bertus

 

20 posts and still no schematic. Looks like the OP doesn't want a real answer..

ak

Cut him a bit of slack, he is either an early riser ( posted at 5am) or he lives on the other side of the big blue marble.

EDIT: but he did say a schematic is coming, but nothing yet.

 

Your regulator is probably fine.

From the Fairchild datasheet:
" Each type employs internal current limiting, thermal shut-down, and safe operating area protection."

This means that if your 7805 is still regulating, it is not too hot.

The maximum operating temperature is 125°C, water boils at 100°C, and it is unlikely you can hold your hand in boiling water for long at all

 

Your regulator is probably fine.

From the Fairchild datasheet:
" Each type employs internal current limiting, thermal shut-down, and safe operating area protection."

This means that if your 7805 is still regulating, it is not too hot.

The maximum operating temperature is 125°C, water boils at 100°C, and it is unlikely you can hold your hand in boiling water for long at all

125 deg where? On the heat sink or on the die itself? What counts?

 

125 deg where? On the heat sink or on the die itself? What counts?

It's the junction temperature that counts. At a dissipation of 5W, the temperature differential between case and junction is 25C.

The regulator has thermal protection, so it should be able to protect itself from over temperature.

 

It's the junction temperature that counts. At a dissipation of 5W, the temperature differential between case and junction is 25C.

The regulator has thermal protection, so it should be able to protect itself from over temperature.

The original poster mentioned that the output had dropped a bit to 4.90 V. Initially I took that as excessive current. Could it be over temp kicking in?

 

The original poster mentioned that the output had dropped a bit to 4.90 V. Initially I took that as excessive current. Could it be over temp kicking in?

Could normal operation, 4.8-5.2V according to the datasheet, or any combination of over temp, dropout/ripple, oscillation, ... After a couple dozen posts, we still don't have a schematic...

 

125 deg where? On the heat sink or on the die itself? What counts?

Obviously the chip only knows its own temperature so its the die temperature that counts.

 

you can drop supply voltage to reduce voltage drop across regulator. this will distribute load and your heat sink will be cooler. for example put power resistor or couple of diodes before regulator. also consider using SMPS, there is tons of cheap DC/DC regulators that will operate in wide range and will work with considerably larger output current without any heat.

 

Sry I didn't reply earlier. It was weekend & went on leave.

Schematic is same as @bertus put in post #22. Except i had additionally added 10uF at input & output also.

I was looking at http://www.tme.eu/gb/details/oki78sr-5_1.5-w36c/dcdc-converters/murata/oki-78sr-515-w36-c/ , it sounds good.

 

I have this type of heat sink, Aluminium(refererence for shape): http://www.amazon.in/Pure-Aluminium...ascsubtag=c82341c3-20fd-40a9-b576-9c6a2257dfd

Height of heat sink is around 50cm & width is 24 cm.

 

You should add 100nf caps to input and output