120vac to dual 12vdc/5vdc rectifier design? (low-current)
120vac to dual 12vdc/5vdc rectifier design? (low-current)
(OP)
First up, I'm fairly new to this aspect of things. Normally I'm the software designer, technician, etc, not the circuit designer. I'm quite eager to learn, and have done a good deal of reading and researching thus far. On the other hand, I have a healthy (fearful) respect for electricity, so I'm here to make sure I do it right. A cursory search didn't reveal anything here to me that I could be certain would work for my application.
Now, as I mentioned in the subject line, I'm looking to build a small rectifier for 120vac to both 12vdc and 5vdc. Whether that's one circuit or two that happen to be in the same enclosure is something I've yet to determine. I'm going for efficiency here, primarily for the sake of keeping heat generation as low as possible.
The goal:
Assuming this is feasible, the rectifier(s), microprocessor, etc listed below would all be contained within a single-width lightswitch receptacle. This particular receptacle is in an outside wall of a home, exchanging it with a larger receptacle isn't an option, and it is surrounded by blown fiberglass insulation. Heat control is key here. The space normally taken up by the control unit of a more complex light/dimmer switch is available here, as the dimmer switch being installed in place of it will be a simple trimmer potentiometer.
The 12vdc line would be used to power a yet-undetermined number of "rails" for lighting LEDs (1-7 rails total). These would originate in the receptacle, presumably attached via transistor to PWM pins on the microcontroller. At present these wires do not exist, do not have any specifications, and can be adjusted to fit any needs that may come up. One more "rail" would be present as a ground. This is in effect an indirect-exposure track lighting system for LEDs, with different wavelength LEDs available on separate tracks for independent control. The number of LEDs and exact power requirements of each are not yet known, I'd assume standard 20mA LEDs though.
The 5vdc line would be used to power a microprocessor to control the device. The microprocessor in question is a Teensy 2.0, which can technically function between ~2.4v-5.5v, but 5v would be optimum for CPU speed and general functionality. Under no circumstances would I expect this to draw more than 30mA, but I'd leave some room for error regardless. This is the biggest part that leaves me uncertain. I'm not sure exactly -how- stable the current has to be, how continuous, etc. If left to my own devices and research, I've proven to myself I'd overdesign this part, resulting in higher cost, danger to myself, and potential frustration. In the worst case, I'd just pick up a standard 120vac-5vdc USB charger, strip it down, and use it directly, but I don't learn anything from doing that, and I have a feeling there's a better option. By all means, correct me if I'm wrong here.
If I've left any pertinent detail out (if it's a known detail anyway), feel free to ask. There's no timeline I need to conform to here, no due date to speak of. Also, as it has come up before, I do have access to the circuit breaker and can run this on an isolated circuit initially (but only initially, not in final deployment) if needed as well.
As a final note, while I'd like to think it wouldn't be an issue here, if you're someone who is not willing to be patient with a novice of sorts, don't worry about responding. There are many other forums and mediums where I could listen to people instructing me to hire a professional or stay within my field.
Thanks in advance, everyone.
Now, as I mentioned in the subject line, I'm looking to build a small rectifier for 120vac to both 12vdc and 5vdc. Whether that's one circuit or two that happen to be in the same enclosure is something I've yet to determine. I'm going for efficiency here, primarily for the sake of keeping heat generation as low as possible.
The goal:
Assuming this is feasible, the rectifier(s), microprocessor, etc listed below would all be contained within a single-width lightswitch receptacle. This particular receptacle is in an outside wall of a home, exchanging it with a larger receptacle isn't an option, and it is surrounded by blown fiberglass insulation. Heat control is key here. The space normally taken up by the control unit of a more complex light/dimmer switch is available here, as the dimmer switch being installed in place of it will be a simple trimmer potentiometer.
The 12vdc line would be used to power a yet-undetermined number of "rails" for lighting LEDs (1-7 rails total). These would originate in the receptacle, presumably attached via transistor to PWM pins on the microcontroller. At present these wires do not exist, do not have any specifications, and can be adjusted to fit any needs that may come up. One more "rail" would be present as a ground. This is in effect an indirect-exposure track lighting system for LEDs, with different wavelength LEDs available on separate tracks for independent control. The number of LEDs and exact power requirements of each are not yet known, I'd assume standard 20mA LEDs though.
The 5vdc line would be used to power a microprocessor to control the device. The microprocessor in question is a Teensy 2.0, which can technically function between ~2.4v-5.5v, but 5v would be optimum for CPU speed and general functionality. Under no circumstances would I expect this to draw more than 30mA, but I'd leave some room for error regardless. This is the biggest part that leaves me uncertain. I'm not sure exactly -how- stable the current has to be, how continuous, etc. If left to my own devices and research, I've proven to myself I'd overdesign this part, resulting in higher cost, danger to myself, and potential frustration. In the worst case, I'd just pick up a standard 120vac-5vdc USB charger, strip it down, and use it directly, but I don't learn anything from doing that, and I have a feeling there's a better option. By all means, correct me if I'm wrong here.
If I've left any pertinent detail out (if it's a known detail anyway), feel free to ask. There's no timeline I need to conform to here, no due date to speak of. Also, as it has come up before, I do have access to the circuit breaker and can run this on an isolated circuit initially (but only initially, not in final deployment) if needed as well.
As a final note, while I'd like to think it wouldn't be an issue here, if you're someone who is not willing to be patient with a novice of sorts, don't worry about responding. There are many other forums and mediums where I could listen to people instructing me to hire a professional or stay within my field.
Thanks in advance, everyone.





RE: 120vac to dual 12vdc/5vdc rectifier design? (low-current)
Mike Halloran
Pembroke Pines, FL, USA
RE: 120vac to dual 12vdc/5vdc rectifier design? (low-current)
TTFN
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RE: 120vac to dual 12vdc/5vdc rectifier design? (low-current)
RE: 120vac to dual 12vdc/5vdc rectifier design? (low-current)
TTFN
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RE: 120vac to dual 12vdc/5vdc rectifier design? (low-current)
If this is a design that you or your company will be selling, then it is even more important that you benefit from the experience and technology offered by National Semiconductor, Linear Technology, Maxim and other companies. The "fire" isn't that big. If you light a fire on your own, it may quickly get out of your hands.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: 120vac to dual 12vdc/5vdc rectifier design? (low-current)
Next, you should figure out what kind of LED light array you need to make useful landscaping lighting or outside "mood" lighting. There is no point designing a controller that can handle a 10 LED light array and then finding out that 10 of those LED's are basically useless due to producing so little light.
I expect you will want to use some higher voltage level under 50VDC and a fairly simple unregulated or poorly regulated supply. Then, use the LED's in series or series/parallel to allow the higher voltage and use the microcontroller to regulate the current to the LED's via PWM.
Overall, it's very wrong to be designing a power supply for something that doesn't exist. You can't build the power supply until you know what power requirements these LED strings will have. Typically, you come up with the circuit you want and then design a power supply for it. Sometimes, you will prototype a circuit with a lab power supply and then build the production supply later.
RE: 120vac to dual 12vdc/5vdc rectifier design? (low-current)
The space requirement is
nearly impossibleextremely challenging. The seven additional connectors is going to be an issue. Also, there are Code issues with AC and low voltage sharing a box.The chassis size will have to be the same as a 'device', not the size of the box itself. There are a multitude of solid state gadgets that fit into electrical boxes like a switch. Many of these gadgets have microprocessors and so on. You could probably learn a lot by purchasing several examples and opening them up for your analysis.
RE: 120vac to dual 12vdc/5vdc rectifier design? (low-current)
Not sure what they might be. There are roughly a dozen manufacturers of light and appliance switches that contain low voltage electronics, X10, Insteon/SmartHome, Intermatic, Wayne Davis, Leviton, etc., to name a few.
TTFN

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RE: 120vac to dual 12vdc/5vdc rectifier design? (low-current)
Corrected -^
Of course the gadget itself can and does contain low voltages sealed within it. But based only on the examples I've seen, there seems to be a trend of keeping the low voltage wiring out of the AC box.
(It's an assumption on my part that it's in the Code.)
RE: 120vac to dual 12vdc/5vdc rectifier design? (low-current)
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RE: 120vac to dual 12vdc/5vdc rectifier design? (low-current)
I just want to say now, as a first experience here, clear, honest, concise answers as you've given are fairly rare in most mediums. I appreciate it greatly. I'll be back to ask more when the time comes that I need it. Thanks everyone.