need little help with smps

[uglykid]

hi all.

im new in here, and now i need a little help.i have make a little smps with irs2153d controller, at the moment i use a transformer from a pc atx the frekvens is 50khz and i use a ligthbulb 12v 100w as load. when i connect the lightbulb to the secundare of trafo i have 12v full load on bulb but when i connect the lightbulb to the recitifer after caps (1000uf) and choke the voltage drops about 2,5 volts but there is still 12volts on the secundare of the trafo, so my ? is, is it the brigderecitifer ( 4*byv79e) or what is wrong...

and sorry for my bad english..

ls.

 

[LAJ]

Here's the answer!

The problem is your rectifier bridge. Its not working at 50KHz. This is a common problem in all SMPSes. It may be designed for 60 (or 50) Hz. Now for some more bad news. It will check good on an ohmmeter. You will need a bridge designed for "high speed".

 

[pjp]

You will need a bridge designed for "high speed".

He stated he's using byv79e diodes - they're 20ns. So that's not the problem.

O.P. Specify your choke.

 

[uglykid]

hi again.

my choke is a amidon t130-2 and 30uh.

i have done a test and when i connect the bulb to the secondary of the trafo i got 11.7 volts and when i connect to the dc side i got 10.4 volt i think it´s ok because where is a voltage drop over each recitifier o.6-o.7 volt or am i total wrong...

LS

 

[pjp]

I think everything is ok.

As I understand it, your transformer is putting out 11.7V AC, which is equal to 16.5V DC.
The diode you are using has a 0.8V-1V Vf, so in a bridge configuration you lose 1.6V-2V (2 diodes in series), and 30uH @50kHz should lose another couple of volts.