Power Supply load - help :(

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sehtat

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I have been working on a universal power supply prototype as my final year project using the IRIS4009 aiming to produce a 12V, 1A output.

As far as my test run goes, a voltage test at the output without any load connected gives me around 10.8-11.6V which seems fine to me.

But the weird part happens when I attempt to attach a small value resistor (from a few to tenths of ohms), the output voltage at the load just drops down to zero, giving totally no output. But when I take away the load, the output slowly rises back to 10.8-11.6v.

So, I don't really understand which part of the circuit, whether is the feedback, primary side or secondary side giving me the trouble. Does anyone have any clue which part is it to blame, and how to pin-point which component went wrong? And is it possible that using the wrong parameters for the circuit caused it?

Thanks.
 
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Small resistor = high current = high load.

When a supply has to supply too much current, it's voltage output drops (since it can only put out so much power). Your power supply is too weak.

I= V/R = 12V/(0.1) = 120A >> 1A therefore your supply is way too weak.

The highest load your supply can drive is 12ohms since that will draw 1A.
 
I have tried 11ohms and 5ohms resistor load as well, but I can't seem to get any output from my oscilloscope. Any clue? Or might it be the feedback loop's problem? Thanks again.
 
Sehtat, if you can't read the schematic that you posted, neither can we.
 
Why does the ordinary 12V/1A power supply use so many parts?
Why is the schematic saved as a fuzzy JPG file type instead of a very clear GIF or PNG file type?
Why is the image over at ImageShack instead of being attached here?
 
sehtat said:
Image link fixed, sorry for the trouble
Click to expand...
It's still impossible to read some of the part numbers.
You are obviously testing with loads that exceed the maximum current output capability. Are you expecting to get reduced voltage output?
Have you tested it with a more reasonable load, like 20 ohms?
 
It might be a boost voltage converter that has only 3V for its input. The schematic doesn't say its input voltage.

The OP disappeared and took away his fuzzy schematic.
 
Thanks for the tremendous help everyone.
I'm new to this forum and wasn't aware of the image uploading function which has caused a lot of inconvenience to everyone, deeply sorry for that.

audioguru: Thanks for the help. And to explain why I'm using so much parts is because I'm relatively new in designing electric/electronic stuff, and I referred to IR's Flyback power supply design guide to help me through it. Means I really have minimal knowledge of practical know-how's, still trying to explore and learn new stuff.

Ron H: I'll try to test as you taught. Previously I tried to test with two 22hm: 10watts resistors in parallel, and another time I tested with two 10hm: 10 watts resistors in parallel. Did I test with the wrong load? Please advise.
 

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Btw, I'm trying to produce a prototype board which allows universal input(85-265Vac) and produces a 12V 1A DC output. The high frequency transformer I made has pri turns 60, sec 7, aux 9. My friend suspects something might be wrong in my voltage control loop.

And thanks again for all the feedback and help. I still have a lot to learn from you all gurus.
 
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You said it is a 12V/1A power supply. Then Ohm's Law says its minimum load resistance is 12 ohms.

You overloaded it with two 22 ohms resistors in parallel which is a total resistance of only 11 ohms. The current would try to be 12V/11 ohms= 1.09A.

You also overloaded it with two 10 ohms resistors in parallel which is a total resistance of only 5 ohms. The current would try to be 12V/5 ohms= 2.4A.

Thanks for attaching a very clear GIF schematic.
 
Thanks for the enlightenment audioguru, it seems that I have even missed out the basics that I should have not.

Another question, is how do I know for each particular capacitor part, whether a ceramic/electrolytic is more suitable? I only know that ceramics are more suitable for high freq and electrolytics are for low freq. Take my schematic's C7 and C8 as an example, which type of capacitors are the better choice? What are the effects if I use the wrong type? Thanks.
 
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You can look at the online catalog from any electronic parts distributor to see which capacitors are available in which types.

C7 is only 56pf. Many ceramic capacitors are only 56pF. The lowest value electrolytic capacitor I have ever seen is nearly 10,000 times more than the value of only 56pF.

C8 is 47uF. Many electrolytic capacitors are 47uF. The highest value for a ceramic capacitor I have ever seen is 1uF which is 1/47th of the value of a 47uF electrolytic capacitor.
 
It would be helpful if you posted links to the datasheets of the parts represented by the yellow rectangles, and also to the IR flyback design guide.
 
Some of the parts are stripped out from other boards(eg. line filter) And I know some parts I just chosen a far more greater rating which I ever needed(a noob's 1st time), hope I don't get flamed for those. And the high-frequency transformer is self-constructed......
 

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Some updates with my recent test:
Tested with a larger load (22hm: ; 100hm: and 68hm: . All 5W resistors).
Yet, the output voltage still drops to zero when I measured the voltage across the resistor.

Still working out with the matter now, so any advice or guidance is welcomed. Possible components failure? Or some problem with my circuit(eg. feedback loop failure)?

Thanks again all.
 
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But what I'm puzzled is, the larger the load I put in, the higher the output becomes(starting around 500hm:, and increasing it to ~22khm: where I get the maximum output voltage).

This basically means my output voltage is unregulated, which is not something I had expected(I'm designing a regulated power supply prototype in the 1st place)

I need some help on this matter @@
 

Here is a tip,

If you suspect feedback, why dont you follow the signal around the loop to verify it. For a given load (light) you can determine what the duty cycle should be and check it. See if the output of your transformer is correct. Then record the feedback signal back to the controller. Possibly the controller is in some mode of operation whcih you are not expecting.
 
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