12vdc from 120ac?

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lanchile

lanchile

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Joined 2008
#1
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.
 
#8
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
 
#9
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.
 
#11
Yes.
1) you could probably work with no more than 25/30mA.
Even if many Leds are lit, they can be wired in series, so current consumption does not add up.

2) in such tight spaces, SMPS is your friend, but even so, you may salvage some proper sized conventional transformer, from stuff such as, say, an old clock radio.
Or pull the SMPS from a dead DVD player or something.

3) you could make a passive VuMeter, where rectified audio voltage which already feeds the speaker, can be rectified and used to directly light Leds.
No need for a PSU.
 
#14
sofaspud said:
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
Click to expand...

Very nice sofaspud 😉. I am going to put it on my list of candidate for sure! Thanks!
 
#16
A regulated 12Vdc at a continuous 1A requires a 12Vac 2Aac transformer.
Unregulated needs 9Vac 2Aac for continuous duty. For cool running double the AC current ratings.

For an intermittent 1Apk and around 150mAdc continuous, then the current rating could be reduced to around 500mAac.
 
#17
sofaspud said:
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
Click to expand...

I know this threat is old but, that was exactly what I was looking for. Thank you😉
 
#18
DigitalJunkie said:
I tore down one of the white plug-in iPod/iPhone cube style chargers a while back,cause I was curious. They really pack it in that little cube! The only downside is that it's 5V output,not 12V.
Something similar could probably be found with some searching around the local thrift-store,or such.
Click to expand...

yes, I did it with a 12v charger, I took all the guts out to save even more room, it worked very well. the only problem was it gave me a lot of back noise since the ONLY place I have is near the potentiometer and it causes noise in the inputs.... for now I think I have to put it in hold. maybe until I get a bigger chassis and have more room. it is not important for me, it was just for look only. Thank you guys for all the ideas.😉
 
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