circuit design for a simple 120vac to 12vdc linear power supply?
Im new to electronics, can someone help me with a simple linear power supply to convert household 120 vac to 12vdc. I know ill need some sort of 120v-12v transformer, then a full wave rectifier using diodes, and a capacitor filter to smooth it out. This is for a simple electronics project in which i will only power a LED. Would i really need a voltage regulator component? can i achieve a smooth enough dc signal for my purpose with a high RC time constant on the capacitor filter. please help. I have search for many designs but i see various changes on them. if someone cam provide me with some insight, and the basic design with some values to achieve a near 12 v transformer, i would be really grateful.
- Mark GLv 49 years ago
NNNNNNNnnnnnnnnnnnaaaaaaaahhhhhh!!!! Other guy making things to be super complex! first than any thing else, LED's are designed from the ground up to use only 3V, You can use 12 ! but you will be having to buy at least one 100 oHm resistor! to bring down the resistance at the level of the LED!
U can buy LED's that are rigged from the factory to use 12V, but you will pay ten times as much just because they solder the resistor for you. The bridge rectifier is a good Idea! but expensive, you can use a single Diode, on one of the leads! that will give you a clean polarity! No need for capacitors or any thing else!
Now if you don't have any of this electronic components! and you are going to buy them any way ! just buy one transformer one diode and one potentiometer of 100 ohm and as many LED's as you may want! all of this is available on Radio Shack! and make sure you buy a really small transformer! about the size of a tangerine, ask the people on radio shack to connect the power cord for you! in that way you will be safe from electrocution.
Good luck and have fun!
- R TLv 79 years ago
No, you don't need a regulator for just an LED. However you will need some resistors to limit the current into the LED. Otherwise, you have outlined the makings of a basic linear power supply. I would also put a fuse in the line on the primary side of the transformer.Source(s): Broadcast Engineer for 30+ years
- EdithLv 45 years ago
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An LED can be operated from 120V AC if a rectifier is used to protect it from excessive reverse voltage. Adding a filter capacitor would be a good idea (value to be determined by experiment; preferably, an oscilloscope would be used to assist in this). Some time ago, I disassembled a dead LED nightlight. It has a full-wave bridge rectifier (4 separate diodes) in it. I think that says a lot in favour of your concept of a power supply for each LED. A way to immediately achieve your objective would be to use 120V indicator lamps (either incandescent or neon). Incandescent lamps are easily available in various colours: 4 or 5 watt holiday lights are plentiful. [Lamp colouring kits can be obtained, but they are very expensive.] Neon panel lamps are available in a few colours, including blue, but they can be costly. I think you should find some way to have the lamp drivers trigger the LEDs in a common circuit so that you wouldn't need to use a separate supply for each LED. To wit: The optocouplers you mention are solid-state relays, intended to make a low-voltage control circuit activate line-powered items. If you used a few of them to control the outdoor lights, the low-voltage triggering circuit indoors could also drive the LEDs directly.
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