I have a 240v ac - 22v dc plug in transformer lying about.

If i used it in place of the transformer and bridge rectifier would the circuit still work?

(i know i will only be able to get a max of 22v and not 24v)

Thanks

 

hi Mike,
It would still work, as you say a lower maximum voltage out.
E
I assume your mains supply is ~240Vac.?

 

This is what i have, Do you think this will be suitable?

 

Due to the minimum dropout voltage across the LM317, the maximum output voltage will only be about 20V with a 22V input.

 

The photo shows that it can accept 100-240 Volts input which makes it most likely to be a switched mode supply without the mains isolating transformer shown in your schematic. These can be problematic due to some not having the output fully isolated from the input.
Check for any resistance (continuity) reading between the plug pins and the output connector.

 

hi M,
Your Adaptor says DC, please confirm.?
E

 

hi M,
Your Adaptor says DC, please confirm.?
E

Its AC to Dc....??

 

OK, so the bridge rectifier in your original circuit is not required.

EDIT:
I would say the two 1000uF caps is an overkill for a nominal 800mA
Use just one.

 

Oh ok, Do you think the 800mA is a little low for an adjustable power supply for my projects?

 

I would say for bread board projects, 800mA would be OK.
If you are considering driving motors etc, you may need 2 to 5 amps.
What are the projects.?

 

Not sure on the projects but could be things like driving motors....

Better look for another power supply...

 

Over the gretz bridge rectifier you have "1.2V" dropout, so after it you have "22.8V" plus the transformer is not perfect it might be "23V" not "24V", so "22V" is ok if its an AC to DC adapter. But I dont know if its good for prolong use. Normally a transfomer has to be picked properly, because if it heats up it will break. As for the projects, depends what you are doing. "800mA" can be enough but you have to calculate it for your project.

 

Would something like this be ok?

http://www.ebay.co.uk/itm/24V-5A-12...472256?hash=item1a243301c0:g:sf4AAOSwHsRYEd~p

 

That would be OK, but you must consider the LM317's current and heat dissipation limitations,


EDIT:
You will find as you build more complex projects you will require more than one PSU.

 

Another option is i have this lying around also:

 

Not sure on the spec tho....

Came from a Philips portable cd player

 

Sorry Mike, I cannot identify that txr.??

 

Whats your distance from Portsmouth.??

 

im in littlehampton

 

Hi,
I have loads of electronic items I am trying to pass on, for free, to someone who could make good use of it.
E