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transformer


Codyhtml
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hello for my security system project that i'm working on i need to use a wall transformer. because the ir leds that i will be uusing to trigger it will need to be on most the time or my system would be useless. so it would probably draw anout 100ma so batterys would be unreasonable. but the wall transformer i want to use is unregulated so how can i regulate it? it could work out with un regulated that the ir leds are running and voltage is right and then it gets triped sudenly there is like 600ma more curent flowing and the voltage drops to low for my warning lights and stuff to work as planed. even if it isent fully regulated it would be nice to have some kind of regulation.
but then again i was planing to use batterys until i realised how much i'd have to change /charge the batterys wait or would it be eayser to build a charge to charge some nicad batteres all the time?
thanks for ideas :)

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Guest SM2GXN

Hi Codyhtml!

Wall transformers are usually not ment to be taken apart, some of those got screw heads that need special tools.
What does the label say on your wall transformer, volts. watts, ma dc or ac?

Bjorn

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Hi Cody,
You don't need a regulator for a dumb IR LED but maybe if you are modulating it. If you modulate it then it will be cooler and you can use a cheap high gain very reliable 3-pins IR receiver module for better range and less interference.

I just measured my 6VDC/500mA wall-wart. It is rated for a 120VAC input and mine was 120.4VAC just now, but varies between 117VAC to 121.5VAC throughout the day:
No load: 9.82VDC.
50 0hm load (162mA): 8.1VDC with 0.5Vp-p of 120Hz ripple.
So my wall-wart can power many dumb LEDs if I adjust the value of the current-limiting resistor for each LED to match the output voltage of the wall-wart.

If your load is only 100mA then an 800mA or 1A wall-wart is much too big, a 200mA one would be fine. But its output voltage will be much higher than expected when it isn't fully loaded. ;D

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well i think i will be modulating it because i have tryed many different ways without modulating it and they didn't work so i've come to the conclusion that it will be better to modulate it and it should only draw <100ma when idle but when sombody trips it then i add about 100-200ma more so i guess just buy a 300 or or well i guess they only have a 700ma hmm so that would be like 400ma unneeded power hmm i'll think about this some more i have to leave so i can't think right now

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it would work to just have the transformer and just conect a voltage regulator to it like the
7806 to give me 6v that should be suficent but now my other question is i've designed my circuit around 6v it should be ok to run it on 5v shouldent it? the only thing that i can think that mabe would be affected would be a latch that i have but usually 1 volt won't make a difference will it? and my leds but they shouldent be hurt
my other question would be would it be bad to buy like a 12v wall transformer so i could use it for other things also or would that put alot of extra strain on the regulator

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Hi Cody,
Use a 7805 regulator since most things are spec'd to operate at 5V, but many shouldn't have a supply as high as 6V. The 7805 needs a DC input voltage from your DC adapter of at least 8V to regulate properly. If your DC adapter has an 8VDC output then the ripple in it reduces the minimum voltage fed to the 7805, and it won't regulate properly.

If your 5V load is 300mA, with a 12V DC adapter then the 7805 will heat with 12V minus 5V = 7V times 300mA = 2.1W and will need a small heatsink. ;D

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