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Power supply mod

kiyoukan

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I have a compact wall power supply.
rated at 5.1v 2a
i have it opened up and have been looking at schematics to learn what i might adjust to turn this into a 7.5V around 1a (Cant be less than 750ma).
What might i replace to get the results i am looking for?
not best pic but a pic





I think i could get it if you could tell me to trace from where to where to find what needs to be changed, also whats the formula for this?
I am almost sure its just switch out a resistor or 2 but no idea what ones.
 
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if you must use that one then i think it is the regulator chip that you change, other then that it would be the large transformer, it would be easier and cheaper buying the one above off ebay
 

Gryphon

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Probably best to get another one rather than mess with this one.
Also have you tested its output or are you stating its rated output. I have found in some
cases that these little wall warts put out more voltage than what their sticker says. I've
had 9V wall warts put out 12V and 12V ones put out nearly 15V!
 

Benm

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Take a look at any chips on the board, including the one mounted on the heatsink (could be a transistor, cant tell from the pics). If you can find a datasheet for the regulator chip its probably not that hard to identify which resistor divider sets the output voltage and mod accordingly.

Considering the prices of these things i don't know if its worth the effort, but its probably doable.

Unloaded voltages of these wall warts are often higher than rated. Try to measure with a small load (220 ohm resistor or something) connected so that it has something to regulate against.
 
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i used an old pc fan i think... or it might've been a small motor. still came up as 16v under load (dodgy :D)
 

HIMNL9

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Being a switching PSU with a fixed output, there is a good probability that the transformer is dimensioned for the minimum voltage required for get the 5V from the regulation circuit without too much unhelpful heat dissipation ..... anyway ..... you can try to check one thing (but BEWARE about the AC section, ok ?)

Cannot be precise from these pics ..... anyway ..... i see that this circuit is a common configuration with an optocoupler (the small black square component with 4 pins), that block the AC oscillator when the output voltage rise over the threshold, and free it when it fall down it ..... this MAY mean (just a possibility) that the transformer can give you more voltage ..... usually, this configuration is controlled from a small 3-pins IC (it looks like a common plastic transistor, but is an IC), that take the output voltage from a dividing resistor network, and trigger the opto when the value go over the threshold level ..... if so, you need to locate the resistor network that take the voltage from the exit, and try to increase a littke bit the value of the "hot side" resistor .....

A LITTLE BIT, ok ? ..... better, changing it with a resistor with a trimmer in serie, and starting to slowly increase it til you see if the voltage reach the level that you need before the PSU goes in unstable mode ot start to do strange noises or "buzz/whistle" noises .....

Just as example, if you find that the resistor network connected to the control IC have a 500 ohm on the "cold" side (from the input pin and the ground), and a 1000 ohm on the "hot" side (from the input pin and the positive), you can try to add, in serie to the 1000 ohm one, a 1000 ohm trimmer, then, powering it with a load (a 12V lamp can be enough) and a multimeter connected , start to rotate it slowly, til the DMM shows the value that you need ..... anyway remember, if in the process, you see that the output becomes "unstable" or the PSU start to make some strange loud, then stop, it means that the PSU cannot reach the voltage that you need, and insisting can burn or blow it .....

If you decide to try this, ALWAYS SAFETY FIRST ..... remember that most of the circuits in the PSU are directly connected to the live AC power, you need to be cautious to not touch anything or short-circuit anything ..... if you have some plastic gloves, better also use them ..... never think "it's just a wall PSU, there's no danger" ..... working with switching PSUs, there's always a danger, if the work is not done in the right way .....
 

kiyoukan

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I thank you fro the information.
As for my camera thats my web cam. not to bad for a web cam.
Yes i know these things are dangerous and i do plan on wearing gloves as in my last ac project i lost all the hair on my arm and most feeling in it for a few hours.
 

bobhaha

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Yes i know these things are dangerous and i do plan on wearing gloves as in my last ac project i lost all the hair on my arm and most feeling in it for a few hours.
Been there done that.... Moving a faulty washing machine to get to the power plug... not fun :D
 

Gryphon

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I have only been biten by flash caps, i don't even wanna know what the mains feels like
 

kiyoukan

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well 110s arnt too bad but if you happen to be working on a wire while holding a metal pipe and a 220 line decides to find its way onto the same pipe...
Well you hand is no longer yours it griped the pipe and refused to let go so a couple of good kick's and tipping the ladder over and knowing i am to weak to hold myself up i fell to the ground. thank god no one was showering...
I could see it now...
"Son what's wrong?
I farted and the shower blew up! "
 

HIMNL9

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Well, experiments are always good ..... only remember that, for end in this way:



You don't need any special adapter like this one:



Distraction is more than enough :p :crackup: :crackup: :crackup:
 




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