Calling the Forward Converters Gurus - Please Help !!
I'm looking for help on building my forward converter. For people not knowing what a forward converter is, basically it's the modification of an AC-DC power suply into a DC-DC unit. There's a very extensive and old thread discussing the subject here:
Well, I've already read all the info on the above thread and also on marsjell's website , read some theory on transformers and am willing to begin the job. So I unmounted my ATX PSU and did tried to identify the parts of th PSU. For my surprise (and if I'm not wrong) there is a clear separation of the AC part of the PSU from the DC part. I handled to identify the transformer wich I will have to modify, but some things called my attention, and since I don't know much about electronics (did take basic electronics at University) I decided to ask for help of all the gurus that have already done this job and from other electronic gurus that always hang around here. I've taken some pictures to help me explain my doubts: (Please scroll down in order to check my questions written after the pics)
So, my doubts are the following :confused: :
1-. I've got 6 components (3 IC's, 2Transformers and 1 ??) joining the 2 parts (ac and dc) of my PSU. After removing them and re-winding the transformer will I just leave them out??? Is it going to work fine???
2-. I searched the internet for info on any of the 6 components above and found nothing. Does anybody have any idea of what those 3 Ic's do???
3-. My PSU has 2 transformers (as can be seen in the pic). So far I have only heard speaking of 1 transformer. What's the purpose of the smaller transformer??? I believe that I'll be working (re-winding) the bigger one).
4-. After building the circuit (I belive it's Presslab's circuit design that I have) and re-winding the transformer shall I connect the output of the transformer back to the PSU?? The circuit says that the output is 12v, 5v and 3.3v?? Do I connect it back to the PSU in order to regulate these voltages and obtain the negs??
Sorry if my questions seem to lame :( but I really need some help.
Thanks in advance,
Questions about the project
Well, yesterday I had prepared a very big post and when I pressed the "submit" button my computer crashed, so I'll try to resume here all the points that I had written yesterday. I'll be posting a lot of questions, some of them have already been asked but will be posted again since I haven't completely understood the answers given and expect Presslab to drop by, as well as the contribution of all the members of this forum. BTW I'm working with an ATX 150W PSU that has a switch on the rear for selection of the input voltage (115-240).
1-. I haven't been able yet to identify the optocouplers, so I don't know wich is the on/off and wich is the voltage. Worst of all, I have a third opto and don't know wich is it's function. Probably for the 5V stdby? (see the next point in order to understand this 5V stdby issu).
2-. I've got a second smaller transformer. Rob said that it might be for the 5V stdby and that makes a lot of sense after reading all the previous posts on this subject. My doubt here is: After I reap it off, I'll need a simple circuit for the 5V stdby won't I? Marsjell included this in his project but I don't really understand how this simple circuit connects to the secondary side of the PSU.
3-. I did some measurements before reaping of my transformer and found only 12V and 3.3V no 5V. Is this possible or did I measure something wrong?
4-. I reaped off my transformer and this is what I found:
Primary Side (3 Pins)
Pin 2 => 26 turns CCW (watching from Top to Bottom) doubled => Pin 1
Secondary Side (6 Pins)
Pin 2 => 5 turns CCW (watching from Top to Bottom) tripled => Pin 1
Pin 5 => 4 turns CCW (watching from Top to Bottom) tripled => Pin 3
Pin 6 => 4 turns CCW (watching from Top to Bottom) tripled => Pin 4
Back to Primary Side
Pin 3 => 26 turns CCW (watching from Top to Bottom) doubled => Pin 2
This is what I did:
Primary Side: Followed Arby's tutorial, so I made 3 coils, each having 3 turns of 18 gauge wire doubled up.
Secondary Side: Got a little bit confused about the pins and the polarity, so I just got the 22 gauge wire and wound up everything just like it was but with the double of turns so now it is:
Pin 2 => 10 turns CCW (watching from Top to Bottom) tripled => Pin 1
Pin 5 => 8 turns CCW (watching from Top to Bottom) tripled => Pin 3
Pin 6 => 8 turns CCW (watching from Top to Bottom) tripled => Pin 4
Here I have a lot of questions: What kind of glue should I use to join back the two parts of the transformer's core? I thought of using loctite's crazy glue but since I may need to apart it again for rewinding it (if something is not OK) maybe this is not a good choice. Since I'm having some trouble finding some of the PWM circuit, I would like to know how can I test the transformer alone? Where should I connect the voltage and what result should I expect? Where shall I do the measurings?
Well guys I believe this is a pretty long post for today, I'll probably be posting some more questions and maybe some photos of the transformer mod (if needed) some other day.
Components for PWM Circuit
Arby made a post on the original thread asking:
No body answered, neither did he ask again. May I assume that the answer to both questions is yes?
Resistors - Normal 1/4 watt metal film resistors good?
Capacitors - 100V, electrolytic fine?
I'll keep on posting.