lm7805 capacitors!!

SMUGangsta said:

Hi

sorry to dig up an old thread, but i just have a quick question and this is very relevent - I am building a relay box/power supply/square wave generator.

I plan on having 230v IEC mains plug on the back, through a fuse, transformer to 15v, bridge rectifier (with the filter caps earlier in the thread).

Now on to the question, I want to have a 7805 drawing 200mA, a 7805 capable of drawing 1A, and a 7812 capable of drawing 1A.

What size of capacitor would be suitable to use as the storage cap (the one that goes after the rectifier before the regulator. I have a few 2200uF and a few 4700uF. would any of these (or a combination) be suitable for this, if not what would?

The load on 1 of the 7805's and the 7812 may be switched on and off regularly.

I have all the smaller caps for use with the regulators.

Thanks

Click to expand...

SMUGangsta said:

I guess the idea is to use the Power Resistor is used to dissipate some of the power, helping the 7805 by not having to dump as much to regulate to 5v.

I have a few boxes of 10watt power resistors in various values, can you suggest a value that may be suitable.

I doubt that I will ever draw the full current from them, but as its a 'tool' im building, i dont really know what i'll be plugging into it - but it might as well be able to handle itss full rated capacity.

It is going in a rather large project box (A4 roughly, by about 100mm tall) so there is plenty space for heatsink and for a fan if neccisary.

Click to expand...

tech_vaibhav_eee said:

i am using 7805 regulator for getting 5v voltage...in its datasheet it says that we have to connect a capacitor between Vi and ground pin and another capacitor between Vo and ground pin...why are these capacitors required and can the regulator without these capacitors??

Click to expand...