actually i dont really know smps well, so, anyone know how to do this practically?

Posted on 2003-10-23 06:47:21 by dion
Yes, what do you need to know? I am a smps designer.
Posted on 2003-10-23 11:48:01 by VVV
raising ampere :)
Posted on 2003-10-24 06:00:40 by dion
I am sorry, I don't understand the question.

If you mean increase the output current capability, you will have to post the schematic first.
Posted on 2003-10-24 20:42:30 by VVV
yes, sorry, i use a stupid english term. i mean increase the current.

the schematic? i must draw it first.
but is there any generic solution to do that?
i face with many smps device here to repair. i know that i must learn the preliminary, uhm... could you teach me, VVV, all 'bout smps?

ahh, i want to change the voltage too, if possible (had seen someone did it).

Posted on 2003-10-25 03:14:29 by dion
Yes, I can tell you a few things about spms. This cannot be done in a few posts, though. Maybe one day I will write a tutorial.
There is a very good book about smps, called "Switch-mode power supply design", by Abraham I. Pressmann. To my opinion, this is best book on smps. You should only spend the money on it if you are planning on designing smps.

You can also go to the ON Semi website and look for application notes on smps. Also, the Texas Instruments website is a good source of information. Try looking for the Unitrode (TI purchased them) power supply design seminars. These are held annually, and I think the materials for past seminars are now posted on the website. I will look for some good links.

As for changing the current and the voltage, that is fairly easy to do. I would not encourage it, though. You are only repairing the power supplies. You should not change the parameters, since the parts (switching transistors, transformers and chokes) cannot generally take more than 20% overload). If it appears the output current is not enough, then you still have a defective component inside.

Changing the voltage should also be done with caution.

If you really want to do these changes, you will need to post the schematic.
Posted on 2003-10-28 11:28:45 by VVV
As promised, here are a few links. Don't worry about things you do not really understand. First try to get an idea as to how smps operate.

There are two very basic topologies, which you should get familiar with: the boost and the buck topopogy.
All other topologies are derived: the flyback is a boost derived topology. The forward, push-pull, half-bridge and full-bridge are all buck derived topologies. Here are links to the boost and buck. Try to understand just the basics, don't worry about subtle details.

And here is another link from ON Semi, that describes the use of the popular TL494.

There are other links, just do a search on the web.

You should understand that the difference between AC/DC and DC/DC converters is mainly the presence of the input rectifier+filter and isolation. In other respects they work exactly the same way.
Posted on 2003-10-29 11:57:49 by VVV
reading now...

btw, seeing that book at amazon, US$79, but the shipping fee is greater than that (about US$100) :(
what a burdensome for me :(
Posted on 2003-10-30 05:35:03 by dion
As I said before, if you are not going to design any smps, do not spend the money on the book. Read whatever you can on the web
Here is another link: Start with the tutorial.

Also, maybe Amazon has a book on repairing smps, which could be cheaper, but still provide a lot of info.
And feel free to post questions about things you do not understand. I'll try to answer them the best I can.
Posted on 2003-10-30 11:43:27 by VVV

This is Power integrations

But I will tell you that if the power demands are low you can just use a capacitor to couple the AC to your board and rectify it as if it were a large Xformer. If you are interested in cheap design as we all must be now, then you must deterine the anmount of current needed. You can use TRIACs driven by DC to control total AC if desired.
Posted on 2003-11-06 18:40:12 by mrgone
I STRONGLY advise against any direct connection between the AC mains and your circuit board.
First of all it is your SAFETY that you should be concerned about.

Always use separation, such as a transformer. For most home projects you should be able to use commercially available AC adapters.
Regulators after that will solve most of your projects' power demands.
Posted on 2003-11-07 11:40:13 by VVV
thanks for replies ;)

mrgone+VVV, as you talk about it, i remember to ask a related question.

1. what is smps disadvantageous?

2. i use smps on my workbench, to switch it on/off, as you guys already know, i sometimes need to do it very frequently. the problem is, every time the smps on, its voltage was rising to its peak then resolved to the 5V(i see it on it's 7segment display). sometimes, it can be at around 8V, and i was afraid it can destroy my boards. what can i do with this?
Posted on 2003-11-08 04:50:07 by dion
1. The smps main disadvantages are the complexity and the cost.

2. This is a powerup overshoot problem. I don't know if it's possible for you to post the schematic. If you could post the schematic, I could suggest some fixes. Is this a commercial P/S ? Can you at least describe it?
Posted on 2003-11-10 11:39:33 by VVV
Hi, dion,

Here is a link to a free web seminar hosted by National Semiconductor. It's about their line of SimpleSwitchers, but it can help you understand a few things. It will start with a review of the basic topologies. (See event # 2).
I get these invitations regularly. This is the latest that came in this morning. And you too can register to receive them by e-mail from National.
Which reminds me that National's website also has interesting stuff on P/S, although mostly on the SimpleSwitchers.
Posted on 2003-11-11 11:21:21 by VVV
One more link to lots of good stuff on smps. I almost abandoned the thought of writing a tutorial.
Posted on 2003-11-12 11:31:27 by VVV

One more link to lots of good stuff on smps. I almost abandoned the thought of writing a tutorial.

Thats an excellent link... wish i had it handy when i was learning switched mode power supplies ;)
Posted on 2003-11-13 00:42:40 by NaN

Is this a commercial P/S ? Can you at least describe it?

yes, lot of them are WEI-YA model WY-03

uhm... about NatSemi events, i had register, but i can not see any video :(
how they manage the online video??

yes, thanks for the nice link, VVV.
Posted on 2003-11-14 19:05:07 by dion
Sorry, I am not familiar with those P/S and I cannot find anything on the web. You'll have to post the schematics.

Generally for webinars you need RealOne player to view videos and a relatively fast connection. Here is the link to RealOne, from where you can download the free player:,
Posted on 2003-11-17 11:35:43 by VVV
Originally posted by dion
sometimes, it can be at around 8V, and i was afraid it can destroy my boards. what can i do with this?

The easiest way to force this to happen is to find the reference voltage the SMPS is using to measure it's output voltage against. Break the trace between the reference and the error amp, and place some sort of voltage delay there. A properly chosen RC might even work.

The idea here is to slow the reference down at turn-on, then let it slowly ramp back up to normal. This should kill any overshoot you see, at the expense of a longer turn-on time.
Posted on 2003-11-21 15:21:38 by Ernie
oahh.. thanks Ernie, i just think about that way somehow :grin:
btw, long time no see you around, where have you been these time?
Posted on 2003-11-24 05:48:18 by dion