120V AC to 12V DC
Hi guys I just wanted to know if anyone knows of a good and cheap way of building a 120v AC to 12v DC converter. I want just a small one to run a pair of LED like these.
Here
I found a schematic here Here but it looks quite heavy duty. I am just looking for a small one and cheap to build, can anyone help me on this please.
Thank You
Sammy
Last edited by sammy004; 7th February 2009 at 08:30 PM.
Just buy a wall adapter.
The link you posted is for a 12VDC to 120 VAC inverter, not what you wanted!Originally Posted by sammy004
The cheapest and simplest way, would be to walk into a thrift store and buy a wall wart which may cost a dollar or so.
You could build one with a 120V - 12V transformer, rectifier, a LM7812 regulator and a couple of caps. Your cost would be about 20 bux or so...
All that typing, and Bill beat me with a simple line.
Last edited by BeeBop; 7th February 2009 at 08:49 PM.
LOL and any cheap wall adapter can run a couple of LEDs
That circuit that you found is for going the opposite way to what you want.
You want a 12 V power supply rated at 3 A or more, if you are running two of those. (The data sheet says 1.5 A max).
PYRAMID POWER SUPPLY:PYRAMID 12 VOLT REGULATED DC POWER SUPPLY PS4KX would be fine.
Igloo Kool Mate Universal 120v Adapter - Toys "R" Us is a switch-mode design and will be a lot lighter.
Thanks guys for the great advice I will try to look for a wall plug.
As you may know...
Make sure the wall adapter is DC output, and be careful to get the polarity (+/-) right!
And it is one that DOES NOT WORK.The link you posted is for a 12VDC to 120 VAC inverter, not what you wanted!
The polarity of its capacitors is backwards so they blow up.
The emitter-base diodes of the transistors have avalanche breakdown so the capacitors also blow up even if their polarity is corrected.
The base current of the transistors is way too low for an inverter.
Its output is about 50V at 25W.
Uncle $crooge
You're good. That base-emitter junction can only handle about -7V or so, and those polarized caps are backwards at best. You work with that circuit before?
How about this... add a pair of base-emitter diodes and flip the caps around. Diodes in reverse to the base-emitter junction work like a charge-pump, protect the base and the caps from inverse voltage, increase the average charge to drive those unimpressive 2N3055's to higher wattage.
I saw the circuit at electronics-lab but the original is at aaroncake.net. Aaron has two very long threads about how guys tried many things to make it work but nobody did.
A simple square-wave inverter needs a half-decent oscillator like a CD4047 then some paralled output transistor for high current.
A CD4047 probably won't drive Mosfets properly because its outputs do not have any dead time, they switch at exactly the same time. One Mosfet turns on when the other is still turning off and the shoot-through current will be too high.
On Aaron Cake's site we discussed a modified sine-wave inverter (actually a modified square-wave) with PWM for voltage regulation.
Uncle $crooge
115v to 12vdc
Hi all, I am looking to build a pwm for a hydrogen unit with 3 cells, the input needs to be 115v ac input and the dc for the pwm hookup for the unit it will draw about 3 amps.
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