300W , 250KHZ with 2 Switch Forward Converter

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ahoss2000

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two switch forward converter

I have to design a low cost 300W (90-264VAC) power factor corrected single output (+24V) with small PCB. I have chosen Forward Conveter. Calculations shows an EER28-L core can barely do this.

I am looking for some suggestions or comments.
 

forward converter

I would advice you a half-brige with MC33368 PFC.
I guess in single-ended converter the reliability will be a problem.
 

two switch forward

hi,

you can use PFC+ "one switch forward converter" topology with ML4800(FAN4800,ML4824) or PFC+"two switch" with some additions. please look at the application notes from fairchild. i think there is an example with "two switch"

i designed an one switch forward converter 24V 10A, with UC3845 (no PFC). i used E42/20 core as transformer. it worked well.

regards
 

2 switch forward

Hi,

What freq. did you have your single switch 24V @10A operating? Looks like 50-80KHZ based on the core size. I am familiar with ML4810. I have been recently using UCC28514 PFC combo IC.

I do not have any experience with half bridge, but coming off of PFC, does it need to have the capacitor divider? Thanks.
 

one switch forward converter

hi,

my freq was 90kHz. i used a boost converter for PFC and one switch forward converter for PWM.

regards
 

forward converter topology

Hi,

Did you use a reset winding or just a RCD snubber? Was it difficult to pass the EMC class B?
 

application notes fan4800

hi,

i used both reset winding and snubber. i didnt try to pass EMC, you have to try and see it.
 

2 switch forward converter

the requirements for your smps are similar with the LCD TV smps. most of them use 24V at 4-12A. take a look at fairchild, ON semi, TI, ST reference designs, there are a lot of them. most of them have PFC and use LLC HB topology for main converter which have quite high efficiency and low EMI, but the transformer will be bigger than on the other topologies. for your required power, a minimum EE42 or ER4540. i designed some smps, and for this power level, i would choose LLC unless i have specific request to use other topology or the space is too small to fit the transformer.
 

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