Offline full-bridge SMPS… need help

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#1,101
I would like to second Luka's comment, and I would also like to thank all who shared in this thread.Info about my website is cedlabs.com and at this moment under construction because I had a lot of LLC converter notes that needed tidying up along with changing the theme.My plan is to have complete designs of Fullbridge offline,Halfbridge offline,Two switch forward as well as LLC info.All will have complete simulations using Ltspice along with detail explanations of closing the loop and zener feedback.I will allow others to post there designs as long as they are complete if they want.
chas1
 
#1,103
The first thought of any design should be its purpose and that goes double for any power supply because faults here can have catostrophic effects on the downstream load if not protected therefore if you are going to power your highend amp I would think you would also want a well designed power supply attached to it, however if its a lowend amp then you can relax the requirements on your supply design.All the info needed for a workable design is in the 110 pages that you read along with many don'ts.
 
#1,104
I just want to play around with pc psu parts first with a 50/100 vdc input from amp former.
I would like to build +/-50v at 5A on both rails psu to power my amp(200 wpc into 4ohms). Am currently using one channel but am planning to finish up the other channel then bridge the amp.
Regards Xeclipse.
 
#1,105
xeclipse said:
Can bjt's work to a fsw of 100khz? If yes,is there any changes in gate/base drive?
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I am not sure, i'm not into using them, I know they are good (very old bjt's) for 30-40k, some new ones, should be just fine for 100k probably

Incase of unregulated supply, is an inductor necessary? What about the % overwind in the secondary?
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with unregulated you shouldn't use it, since it will drop voltage under load. if your main trafo is build good, you can have "regulation" within 10% of no load voltage. But I find if I have PFC in front of it, that drop is almost none (diodes, traces, a bit of sagging, say 1-2% of no load)

I dont know if this is 'too wrong', but i tend to think that an optocoupler is not necessary in the fb loop since the pwm chip and the outputs are both in the secondary of the smps.
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In my smps, pwm and drive IC are both on primary side. But if they were on secondary, I couldn't use drive IC, but I could have gate trafo which would provide the insulation, that opto does when you have control on primary side

There was a mention of Chas1's 'project', maybe i mistook it for a website.
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Yes he started on one, did a loot of simulations and so on, maybe even made a working model, but its been some time since I last heard from him
 
#1,107
If you have one of out the latest PC supplies (ER type core set:note about 2 1/4 in tall)realizing a 500 watt supply should be no problem and I would use all of the pc supply including gate drv,transistors and etc.You should be able to raise freq to 50kHz with little effort.Primary winding is normally 42 turns(21 per layer?)Remove main transformer and place in a microwave along with a cup of water for about 2.5 to three minutes(don't put transformer in water palce at the side some distance away)The core should seperate easily(don't inhale fumes)after this three pins form the primary winding the center being the start of one and the termination of the other.Be careful with the coil former as it will break easily,carefully remove yellow tape to expose first layer of primary,cut lead at the start pin and unwind carefully to the center pin,try not to kink wire ,now the secondaries should be exposed,unwind all of these windings along with the shield, you should now have the other part of the primary covered by yellow tape,leave as is and place a couple of wraps of black tape if you don't have mylar,take a pair of #20 AWG of sufficent lenght and bifliar wind 9 turns and solder to availble pins,the center tap will be pulled out as orignal,now rewind the primary wire in the same direction as removed and solder to the orginal start pin and cover with two layers of black tape or mylar,you should have a transformer with 42 turns primary and 9 turns each secondary ,most of the parts can be reused and if you take your time you can reuse the pcb as is by removing some circuits and modifying others,time consuming but I have done it.
 
#1,110
pc psu

chas1 said:
If you have one of out the latest PC supplies (ER type core set:note about 2 1/4 in tall)realizing a 500 watt supply should be no problem and I would use all of the pc supply including gate drv,transistors and etc.You should be able to raise freq to 50kHz with little effort.Primary winding is normally 42 turns(21 per layer?)Remove main transformer and place in a microwave along with a cup of water for about 2.5 to three minutes(don't put transformer in water palce at the side some distance away)The core should seperate easily(don't inhale fumes)after this three pins form the primary winding the center being the start of one and the termination of the other.Be careful with the coil former as it will break easily,carefully remove yellow tape to expose first layer of primary,cut lead at the start pin and unwind carefully to the center pin,try not to kink wire ,now the secondaries should be exposed,unwind all of these windings along with the shield, you should now have the other part of the primary covered by yellow tape,leave as is and place a couple of wraps of black tape if you don't have mylar,take a pair of #20 AWG of sufficent lenght and bifliar wind 9 turns and solder to availble pins,the center tap will be pulled out as orignal,now rewind the primary wire in the same direction as removed and solder to the orginal start pin and cover with two layers of black tape or mylar,you should have a transformer with 42 turns primary and 9 turns each secondary ,most of the parts can be reused and if you take your time you can reuse the pcb as is by removing some circuits and modifying others,time consuming but I have done it.
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I have two units but they have small transformers and use two switch forward converters. I could use the gate drive transformer,transistors,diodes etc. I have another core (44x35x11 mm i cant identify), but it has an airgap almost 1mm. I read a post where a member sanded the outer legs to level up with the centre leg.
I like diy so i wont be buying assembled units (pfc) soon.
Regards, Xeclipse.
 
#1,113
I would try to find a better source for cores,if you can buy a couple of ETD44 core sets along with spring clips ,these will enable you to build a very stable supply for 500watts-1kw,The transformer along with proper design,contruction is the heart of smps,second gate drive,transformer frequency,feedback.As for pfc I only use that for LLC,not required for me but you can get the parts for 1150 type,irf provides pcb gerbers and for 500w shouldn't be a problem.Stay awayfrom gapped cores if you can...
 
#1,120
Grinding cores, you also need to polish them to make sure you don't have any jagged surfaces.Why would you want to grind a core set.The transformer from almost any 500watt or above PC power supply can be used for 400watts and above,also if you have two of these the transformer core can be used as the inductor for your 500watt pfc.
 
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