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Old 8th November 2013, 07:35 PM   #1
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Default 12vdc from 120ac?

I need to get approximately 12vdc from 120vac line. The problem is I do not have room to put a step-down transformer, a bridge rectifier and caps
I can use an external power supply but that is not my option. I have small space like 2x1x1 all in inches. I have to get this from power switch.
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Old 8th November 2013, 07:39 PM   #2
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What is the current requirement do you know?
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Old 8th November 2013, 07:42 PM   #3
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I would be happy with 1 amp!

I saw one circuit, but it uses 1 diode, 1 lightbulb and a capacitor! that light bulb it is way too big....!
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Old 8th November 2013, 08:18 PM   #4
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That space is small - and 1 A will provide a challenge. Sorry I don't have a solution - I'm sure someone clever will post some ideas though.
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Old 8th November 2013, 08:24 PM   #5
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I know it is not easy....well, for me lol! I guess someone can come up with a clever way to do it. Thanks
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Old 8th November 2013, 08:27 PM   #6
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Well, actually it is not the need for a 1amp current. I am building a VU meter using one LM3915 with 10 leds, I guess I can get away with 1/2 amp.
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Old 8th November 2013, 09:10 PM   #7
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gents, please remember, forum rules says your curcuit must have isolation from mains power


moderation
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Old 9th November 2013, 03:20 AM   #8
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You should have a better idea of the supply requirements to obtain a helpful response. A LM3915 and 10 LEDs shouldn't require half an amp. Less than 250mA seems more sensible; if all the LEDs stay lit at once you should redesign the meter!
Having said that, there may be a ready-made encapsulated module that you could use. Something like this VSK series from CUI found in Digikey's catalog
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Old 9th November 2013, 03:42 AM   #9
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The LM3915 has a mode where only the "peak" LED is powered at any time..."Dot Display" mode.

You could probably design the whole circuit to use less than 25 mA if you used this feature.

Hammond 161C10 might fit.
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Old 9th November 2013, 09:07 AM   #10
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About 2x1x1 inch sounds like space enough for a small switching-style wall wart (if you stripped off the casing)?
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