Voltage Regulating

[Barry]

Hi all,
Excuse my ignorance. Is it possible to "over regulate " voltage or current? I have a 7805 regulator in my home made power supply and on my experimental board I use with my PIC experiments I also have a 7805 regulator. Is this o.k.?Can this regulator stay in the experimental board for when using a 9V battery for example? When using the power supply the voltage is now double regulated.( So much to learn and so little time! )
Thank you very much.
Barry.

 

[Nigel Goodwin]

Hi all,
Excuse my ignorance. Is it possible to "over regulate " voltage or current? I have a 7805 regulator in my home made power supply and on my experimental board I use with my PIC experiments I also have a 7805 regulator. Is this o.k.?Can this regulator stay in the experimental board for when using a 9V battery for example? When using the power supply the voltage is now double regulated.( So much to learn and so little time! )

No, it won't work - a regulator requires a certain higher voltage for it to work, probably about 7.5-8V for a 7805 (it's listed in the specs). If you only feed it from 5V the output will be too low and unregulated.

 

[Barry]

Thank you for your reply. Much appreciated.
Barry.

 

[Barry]

Hi,
Another quick question. Will it work if I supply the 7805 with 9V or 12V REGULATED DC supply or should one only use an unregulated supply voltage?
Thank you.
Barry.

 

[Johnson777717]

Another quick question. Will it work if I supply the 7805 with 9V or 12V REGULATED DC supply or should one only use an unregulated supply voltage?

You should be fine with a regulated or unregulated supply input to the 7805. As long as you're not pumping too much voltage into the 7805. Most 7805's will handle max 35 volts.

As you may know, regulators dissipate heat proportional to the volts that you are regulating off of a supply line. Thus, more heat is created running 25 volts into a 7805 than 9volts. So if you're running higher voltage for times greater than a couple of minutes, you may want to consider heat sinking the 7805.

probably about 7.5-8V for a 7805 (it's listed in the specs).

Hit the nail with the hammer there Mr. Goodwin. Minimum 7.5 is what National specs state.

 

[gerty]

Also don't forget proper filtering....

 

[Barry]

Hi all,
Thank you all for your inputs. Really appreciated.
I built a power supply with two outputs. One output is regulated +5V and the second output is regulated variable +5V to +17V. I built Nigel's main board and it also has a 7805 regulator, hence my silly questions.I just needed to find out if it was o.k. inputting regulated voltage into another regulator. I take the point of inputting at least 7.5V but would probably use +9V. Now I can really get to grips with Nigel's tutorials!
Thanks again for your help.
Barry.