Hi, I'm trying my hand at making a power supply for a project that requires +5v +12v +33v, I would like anyone who may be able to help, to have a look at my schematic and board layout and see if there is any problems with it or any way it could be improved upon, I have tried to smooth the voltage before the bridge rectifiers and reduce the ripple after the voltage rectifiers, this is important for the final destination of the power supplies, this is my first attempt of designing such a project, but i have made several other projects from schematics and circuits web pages. any advice or suggestions would be most wellcome.
many thanks in advance for anyone willing to assist.

 

Hello, Welcome
About ur project, did you take the current requirements into account.
by the way..it would be wise to separate the high voltage ground form the low voltage ground.

I see that you have used series pass tr to increase the current provided.
Where did you actually get "those" diagrams?

 

Hi R!f@@,

The transformer is 3VA and the +33v bridge 3.05VA the 5v and 12v bridge is 1.5VA
I used the datasheets for the regulators, and a "texas instruments" paper on reducing ripple. to make up the schematic. I will seperate the high and low grounds as you advise, thanks

 

at 240VAC, a 3VA transformer will provide you with just a little more than 10 milliamp from your AC wall outlet. If your circuit tries to produce more current than the transformer can handle it will heat up then catch on fire.

I'm saying that it is a VERY small transformer for a power supply project.

You should get a much beefier one.

 

Te me your setup look very dodgy. What is the schematic source? Because it is drawn very confusing. Take a look at my pdf file. That should give you the correct start.

 

hi kermit2 thanks for advise what VA rating would you suggest?

 

It will depend on how much current your application need. So how much current do you plan to draw from your supply

 

Something with a VA rating close to, but bigger than, the VA rating (combined) of your outputs. If you want 5v at 5A then that's 25VA right there, if you have other outputs then add those in. Transformer with 35VA rating would be a good for a 25VA output. 10-20% more than the circuit gives out maximum.

Too big and you will have poor regulation and waste money on the extra copper and steel. Transformers are most efficient when operated close to the rating, but not over it.

 

Hi t06afri. thanks for the schematic "starter" its certainly neater than my effort, i used Target 3001 to make it. My trans has 2 15v sec6ndaries

 

I knew it...OP just had a schema and he wanted to go with that

 

R!f@@ i dont undersand your remarks! I used a schematic program to draw my project from scratch using ideas from datasheets

 

Hi t06afri. thanks for the schematic "starter" its certainly neater than my effort, i used Target 3001 to make it. My trans has 2 15v sec6ndaries

It is the same. Think about it as pin 9 and 7 are solder to gether. That would also be the correct approach for your design, given that you will use a transformer equal to TR1 in your schematics

 

What is ur budget OP

 

t06afri understood, so i would ideally like 350 milliamps on 5 & 12v and 1amp on 33v would a torroid be more suitable?

 

R!f@@ no particular budget i have a well stocked components & parts inventory collected over many years!

 

OK dhen...define ur load requirements..

Meaning that what you will be powering using that supply

 

the 33v is to power a tv type Uhf tuner, the 5 & 12v are to power the signal processing unit i do not believe either require excessive currents

 

I know what you trying to do...

33V is used as the tuning voltage in TV's which uses analog tuners.
and the 5V & 12V are the logic and audio supplies.

If that is the case..33V will need couple of mA, but the 5V and 12V load requirements must calculated from what u already have

 

yes that is correct, so going back to my circuit do you think it is fundamentally correct? Or should there be aditions, substitutions or otherwise?

 

It the 33V is just a few mA then 25-35 VA is fine for the transformer, if you want 1 amp for the 33V then you have to go up to 50-65 VA for the transformer. Final selection should be based on total current draw for the circuit at a worst case input voltage and temperature situation ( voltage sags in input AC would make higher peak current in the transformer primary.)