small smps with uc3844

[Eva]

I've got a nice continuous-mode approach :
- Primary inductance: 20uH (>30A sat.)
- Turn ratios: 2+2:1 (sec+secri)
- Operating frequency: 50Khz

Predicted steady state full load conditions (175W):
- Primary current sweeps from 21A to 28A during 11.86uS on-time.
- Secondary currents sweep from 7A to 5.25A during 8.13uS off-time (each).


I've also tried critical-conduction-mode :
- Primary inductance: 5uH (>50A sat.)
- Turn ratios 2+2:1
- Minimum frequency at full load: 28Khz (depends only on inductance).

Predicted steady state full load conditions (175W):
- Primary current sweeps from 0A to 49A during 20.9uS on-time.
- Secondary currents sweep from 12.3A to 0A during 14.3uS off-time (each).

[Tekko]

According to my multimeter i have had over 9A out from the thing with only 8A in Overtunity or busted multimeter ?? i had it between the rails and set on the high current 10A mode.

The fets i have used can do around 38A continous together and over 100A pulsed.

The transformer has the turns ratio of 3-4 turns primary and 9 turns secondary.

Eva, show me the proggy.

[Tekko]

Now i run the smps with a toroidial transformer and it actually appears to work better.

[-_nando-_]

Where is the schematics? They disappeared or what ?

I'm VERY INTERESTED in this topic, I NEED see the schematics and build this thing uahuahuahua..


Look !
Swithing Power Supply !

I dind't find it before open the topic , sorry !

Well, I'm learnig about theese supplies, and thank you all !


Sooo, can you guys send me the schematics? It appeared to have been removed by the admin or happend some error in the forum...

Here's my email, fuinhox@gmail.com I apreciate very much if you send me the prototypes



Thanks !!!

[Tekko]

All these 3842 and 3844 controllers i had have died, therefore i removed all the pics.

[Eva]

Have they failed? why?

By the way, this is my flyback calculation helper program. Yes, I know that it's GWBASIC so don't blame me... Lines 10 and 20 contain input parameters :

VP=primary voltage
TP=primary turns
VS=secondary voltage
TS=secondary turns
PIN=power level
F=operating frequency (zero for critical conduction mode)
LT=core Al value in Henries per turn^2

10 VP=12: TP=12: VS=35: TS=24: PIN=175
20 F= 50000!: LT=1.4E-07: REM F=0 for critical conduction mode
30 LP=LT*TP^2: LS=LT*TS^2
40 VTR=VS/TS: VRP=TP*VTR: DC=VRP/(VP+VRP)
45 IF F=0 THEN F=.5*LP*VP^2*DC^2/(LP^2*PIN):PRINT "f=";F
50 TON=DC/F: IRP=VP*TON/LP
60 EP=PIN/F: IF (.5*LP*IRP^2)>EP THEN TON=SQR(EP*LP^2/(.5*LP*VP^2))
70 TOFF=TON*(1-DC)/DC: IRP=VP*TON/LP:IRS=VS*TOFF/LS
80 I0P=(PIN/(.5*LP*F)-IRP^2)/(2*IRP)
90 I0S=(PIN/(.5*LS*F)-IRS^2)/(2*IRS)
95 IRMSP=SQR((LP/VP)*(((IRP+I0P)^3-I0P^3)/3)*F)
96 IRMSS=SQR((LS/VS)*(((IRS+I0S)^3-I0S^3)/3)*F)
100 PRINT "p:";INT(TON*1E+09)/1000!;"us",INT(I0P*1000!)/1000!;"A to",INT((I0P+IRP)*1000!)/1000!;"A",INT(IRMSP*1000!)/1000!;"A_rms"
110 PRINT "s:";INT(TOFF*1E+09)/1000!;"us",INT((I0S+IRS)*1000!)/1000!;"A to",INT(I0S*1000!)/1000!;"A",INT(IRMSS*1000!)/1000!;"A_rms"
120 PRINT INT(.5*LP*IRP^2*F*1000!)/1000!;"W discont.",INT(TON*F*1E+05)/1000!;"% duty"
130 PRINT INT(LP*1E+09)/1000!;"uH L pri"


And this is the output that it should produce with these parameters:

p: 11.864 us 21.052 A to 28.114 A 18.999 A_rms
s: 8.135 us 14.057 A to 10.526 A 7.866 A_rms
25.136 W discont. 59.322 % duty
20.16 uH L pri

The 'W discont.' rating is the power level at which the discontinuous to continuous mode transition happens.

It only supports one secondary winding, it's quite hard to calculate output RMS currents for multi-output flybacks since not all diodes conduct during all the off-time and complex load-sharing phenomena may be observed. However, two symmetrical outputs with balanced loading may be modelled as a single output carrying double the current, or providing double the voltage. Also, for calculation purposes, low power outputs may be neglected, or the highest power output may be assumed to deliver all the output power...

Enjoy

[Tekko]

Once again im planning a audio smps for 12v in, this time a PP one with SG2524 for controller.

Output criteria is split supply around 35v unloaded and 25-30v @ 2A per output rail under max load.

I plan on using two gate drive IC´s for driving 2-4 IRFP460 per side till i get hold of better fets.
This all i plan to use a hand drawn boar for where i solder the controller and gate drive ic´s SMD style as i dont have a drill.
The thing will prolly be something similar to Rod Elliot´s smps.

[Tekko]

Heres a schemo of what i was thinking about:

Would it work if some bypass caps were added around the IC´s ?