PFC ncp1653 + ir2153D...any advantage of higher voltage with pfc ?

[papasteack2]

Hi,
I'm planning of doing a smps with a ncp1653 @66khz boost pfc, and a unregulated half bridge ir2153d smps for running a amp based on composite lme49720/lm3886 in bridged mode using remote sensing (amp name is bato mm) =>4 lm3886.
I've readen a lot of thread, here and on diyaudio...lot of datasheets too. Now, i need help to compile and understand everything. As a hobby, i want to do it myself, trying to do things well, and satisfying myself. I know it would be cheaper to buy one psu new.
My first question is about the voltage output of the pfc stage. At minimum, the worksheet of the ncp1653 allow it to output 375V. So would there be any advantage of running the half bridge converter with higher voltage? I know it would need higher voltage caps and mosfet... For primary cap, i plan to put 2x1000uf 250v low esr 105°C if running at 375v.
I've gotten the ncp1653 boost inductor. For the half bridge, i have some atx psu transformers. To get symetrical output, i'll probably run two identical transformers in parrallel.
I've read some advices on the web, telling to run atx psu transformer around 40khz. Does using two identical transformer in serie would allow to run higher frequency ? Would there be real advantage? It seems that higher frequency are easier to filter.
And finally, i see often inductors on secondaries. Inductors filter seems complicated to tweak. It seems to be better to put after rectifiers a LC filter...and not a CLC..don't understand for now. Maybe in few years, learning, i'll understand. For now, i need help. From what i've seen and understood, i would put a 7mh common mode 14A inductor and 7500uf x4 105°C low esr caps. CRC filter would be easier, but it seems me it loose the advantage of fast current supplying... For layout, i'll do as reference designs.
I go for simple half bridge topology because it seems me doable with my actual level.

Thanks for helping me cleaning my knowledge, explaning and sharing your own experience and knowledge !

(and sorry for my poor english !)

Damien

 

[MicrosiM]

I am not sure about your needs for the PFC stage at the input of the SMPS, it looks low power SMPS.

Combining PFC with SMPS wont be an easy task as many other guys expects, Thats because of one good reason, the quality of the LINE REGULATION of your PFC stage, specially when minimum load to maximum load appears at the PFC output.

Regarding the IR2153D, you can use it with PFC, just use one 450V capacitor for your PFC, and then split the voltage using 1uf 275V capacitors, this way you get the correct voltage for your SMPS.

And those inductors at the secondary of any SMPS, used for regulated SMPS. so in your case you will not be using them, I think!


But to keep things simple, I suggest you a simple SMPS for your amplifier without engaging the PFC stage now, as this may drive your project into longer road than you expect. and you may succeed very quickly.

Dont get disappointed from my advice, but I am just trying to give you some ideas to know where to start.

Regards

 

[papasteack2]

Thanks a lot, you're one of the forum users i'm looking at work a lot. The idea behind PFC stage is to get the protective features of the chip, and slow start-up during capacitor bank charging. And there is a 300w evaluation board for ncp1654, and everything to do exactly the same. Iv'e gotten the inductor recommanded as free sample. The excel worksheet allow to set the ripple by sizing the output capacitor. The only change i will made from the evaluating board are different EMI filters, and bigger output cap, and different brand parts. I'll use the same pcb layout. So I would say that pfc stage is probably the most easy part. Using only one 450V capacitor and spliting with 1uf 275v is so simple...i feel stupid not having though about it. Thanks a lot for the advice. But after looking at prices on mouser, it's not cheaper for the minimum quality of cap i want. The pfc stage for the moment would cost me 33€ with EMI filters AND high voltage cap bank.

For the ir2153d, there isn't such a thing as a evaluation board. There is a lot of shematic one the web, with some subtil change. As the 10k resistor from mosfet to "-". In the pfc stage, there is such a resistor. So i'm tempted to put those resistors for the smps two. I'm looking at each part. There are also some shematic using what i would call snubber on primary side of atx transformer...but it appears not so much often.
The common mode inductor i talk about on secondary of smps can be found in a lot of ir2153 schematic unregulated just google image ir2153. Using "high bandwith" amp (lm49720+lm3886 =>200khz), even if there's a very good psrr, from what i've readen a simple coil can easily kill 15db of rectifier noise, and correct me if i'm wrong, i can only be a benefit. And i'm only talking of 40khz fondamental. It can kill more of harmonics. And secondly, it act as energy storage two. There is a coilcraft online app to select a inductor, that allow to understand that for such "low" frequency, it need really high inductance... the 7mh common mode 10A inductor i found cost 5€. The thing i don't know is does the inductor would add ripple oscillating... With 4x7500uf ultra low esr 35V on output, the smps stage (without high voltage caps as i count them on pfc stage), would cost 35€. So full PSU would be around 70€ wich is not cheap, but still ok for hobby project for me.
The thing is that i've seen different way to proctect with ir2153 to get a slow start-up that seems all complicated and need tuning, whereas the pfc stage do all that stuff. And i've been really lucky to get the free sample boost inductor, so !

Between pfc and smps, what i'd like to know is does running the smps mosfet with higher than 400V...450-500v would have any benefit on the smps as it's just one resistor to change in the PFC boost stage. For smps stage I'm planning on using two 30A 650v 125mohms rsdon 219w mosfet IPP60R125C6, and two, or 4 (depending on trnasformer wiring) BYV32E-200 diodes. From what i've seen, it would be a lot more than enough.

I'll be soon ready to draw a shematic to get advices, and i'll put all links as soon as i have more time. Please correct me if i've said anything wrong. I'm compiling a lot of data seen on the web. For the moment,the only smps i've only done is a 80w step-down variable voltage smps using TI online power design tool, to cut polysteren foam with "hot wire", 100khz air-wired on the inductor in a atx box, it work like a charm.