Need to know suitable value of capcacitor for my PCB

[Prohor]

I have a Transformer : 35 v ac output for 220v AC 50 hz input.

Target: 45 to 51 dc output

Will be used in : audio amplifier

I have a pcb like image bellow:

1. I need to know what would be suitable value of capacitors beside these diodes?
2. Electronics shopkeeper told me that it will reduce noise during power switch on off if I use these 4 capacitors, it that true?
3. what would be best diodes for this pcb considering 50 volts output? [ in original datasheet, DBA 40C bridge Diode used , what was a 4.0A Single-Phase Bridge Rectifier]

I am still in learning process of electronics, please help.

 

[Minder]

0.01μf Disc ceramic, 400vw
M.

 

[davenn]

Target: 45 to 51 dc output

and if you are really going for that output voltage then you need 63V or greater electro caps
and depending of expected current drain you may need more than 4700uF
rule of thumb = 1000uF per amp

 

[Bluejets]

That board looks like a split supply....i.e. V+ ...V- .....Common (grd)

 

[(*steve*)]

For the diodes use 1N5408.

 

[Prohor]

and if you are really going for that output voltage then you need 63V or greater electro caps
and depending of expected current drain you may need more than 4700uF
rule of thumb = 1000uF per amp

Yes, datasheet of stk4231 also has a requirements of 10000uF caps, I am going to use 10000uF 63V.
Thank you for your reply.

 

[Prohor]

That board looks like a split supply....i.e. V+ ...V- .....Common (grd)

Yes,..it is. Thanks

 

[Prohor]

For the diodes use 1N5408.

I think 1N5408 is a 3.0 Amp diode. If I use 4.0 Amp- would it better?
[the reason I am thinking for 4.0Amp diode is in the datasheet of stk 4231, power supply unit used "DBA 40C bridge Diode" , what was a 4.0A Single-Phase Bridge Rectifier ]

 

[(*steve*)]

Well, the other three diodes are 1N5408, so you'll have to replace all 4 of them.

 

[Prohor]

Well, the other three diodes are 1N5408, so you'll have to replace all 4 of them.

Yes, I am thinking to replace all of them.

 

[(*steve*)]

What current is your transformer rated for? Alternatively, what is it's VA rating?

The reason I ask is that the max DC current you should draw is 70% of the rated AC current.

 

[(*steve*)]

Here is an example of the sort of diode which may be suitable.

http://www.digikey.com/product-detail/en/diodes-incorporated/6A10-T/6A10DICT-ND/8819

Without knowing where you are it's a bit pointless to suggest something specific as I don't want to send you on a wild goose chase for something that just happens not to be available where you are.

 

[Prohor]

What current is your transformer rated for? Alternatively, what is it's VA rating?

The reason I ask is that the max DC current you should draw is 70% of the rated AC current.

Thanks a lot for your reply. I have a transformer build locally with the order specified:
input voltage: 220-230v, 8 Amp, 35v output.

I received from them:
2 input wire for 220v ac input and 2 pair of wires output for 35v ac each in the secondary. I wanted two separate 50/51v DC voltage output with the support of min.-7 amp. I have tested it in amplifier for about 2 hours and worked well without producing much heat.

The reason I am making every steps clear from this forum is "Getting and matching clear concept" and learn the best combination for this amplifier. I have completed my graduation from Computer Science and Engineering but now somehow I have got some electrical / electronics student of Diploma
They are keen about this project. Before I have to go for them, I need to know every steps clear myself first.

Re: for your last post, Yes, I have found 6Amp 1000v diode online before posting this thread in EP. Can you guide me how to a link- how to select Diode and it's amp according to secondary output,please?

 

[(*steve*)]

If each winding if rated at 8A, then the max continuous current you can draw from the DC supply is about 5.5A, however the nature of many amplifiers if that they draw power from each rail alternately.

Also it is very common for amplifiers to have somewhat underrated power supplies because music tends not to demand continuous high power unless your signal is a single frequency or the amplifier is driven deeply into clipping.

 

[Prohor]

and if you are really going for that output voltage then you need 63V or greater electro caps
and depending of expected current drain you may need more than 4700uF
rule of thumb = 1000uF per amp

I did not find exactly 63V, 10000uf for my stk4231 ic's power supply. Instead I found 100v, Rubycon cap. Can I use 100v, when my output dc would be 51v?

 

[(*steve*)]

Yep. Any voltage greater than 51 volts will be fine. Usually we like a bit of margin, so 63V (a common voltage rating) is what was suggested. Higher voltage capacitors may be physically larger but as long as they fit they will do fine.

 

[Prohor]

Yep. Any voltage greater than 51 volts will be fine. Usually we like a bit of margin, so 63V (a common voltage rating) is what was suggested. Higher voltage capacitors may be physically larger but as long as they fit they will do fine.

Thank you.