7805 5V regulator trouble!

[Dominick22]

The 7805 I have is from radio shack and it is rated up to 35VDC.

It does sound like it would be easier just to get a different transformer, especially with my limited abilities.

Any ideas where I could find a 5V transformer?????

Thanks to everyone for the encouragement,
Dominick

 

[peranders]

A LM7805 needs 8 VAC at least and max around 24 VAC. This will give you 10-35 V DC after rectification and smoothing.

How much AC voltage do you have now?

Just wondering: What are you going to use the 5 volts for?

 

[neutron7]

if its just to power those digital voltmeters you could easilly just take the transformer out of an unused wallwart. 9 or 12 volt is pretty comon and would work great for you.

 

[Dominick22]

I am using a 12 Volt transformer from parts express right now!

I think the next thing I will try will be to lower the cap to 10 uf.

But I dont think that will make it kick on? So frustrating.
I thought this would be simple
Dominick

 

[neutron7]

your transformer must be center tapped and you are using the full 24 volts (2 x 12 volts)

is there 3 wires on the transformer secondary(output) then you will be able to still use the same one.

 

[anatech]

Dominick,
neutron7 is suggesting you use the same transformer in full wave. Your input cap should remain where you have it. Anything around 1,000 uF and in excess of your actual voltage plaus a saftey margin will work well.

The 10uF value is on the output of the regulator.

-Chris

 

[Dominick22]

ok--I will get the caps organized correctly. As far as the transformer goes:

There are 3 taps for the secondary. Which ones should I use for the 2 output leads?

The left and center one???
I am currently using the left and right one. I did not know there was a difference.

Thanks,
You guys are a big help!
Dominick

 

[anatech]

Hi Dominick,
Use a single diode from the left and right, cathodes connected together. The center tap goes to ground, the diode junction to the + of your cap. You should have about 1/2 the voltage you had now.

-Chris

 

[DJ Exprice]

Where is the filter cap , directly after rectifier between + and ground ?

No cap?! ZOMG. Thats gonna make everything a problem.
You will HAVE to add something there.

If that works, and end of problem, fine . But if not, you may want to try feeling the 7805 - cos if it gets hella hot, you need to bring the input amperage down...