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Author Topic: transformer less power supply  (Read 3657 times)
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joaler
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« on: January 03, 2008, 01:33:06 13:33 »

hai all

can anyone help me to design a transformerless powersupply for PIC mcu's?

jo
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shailesh5
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« Reply #1 on: January 03, 2008, 03:59:59 15:59 »

you can use a resistor in series with a non polarised capacitor then a zener ,at then end of the circuit with repect to ground its for AC use.

but its   DANGEROUS , i would recomend you to use an isolating transformer

shailesh
« Last Edit: January 03, 2008, 04:05:37 16:05 by shailesh5 » Logged
gtn
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« Reply #2 on: January 04, 2008, 08:33:38 08:33 »

Be careful It is dangerous, if you don't do it right. But it is possible See some data bellow. I tried the Microchip solution and it did work fine for my project.
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chen
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« Reply #3 on: January 04, 2008, 06:54:54 18:54 »

i think u should have look at powerintegration's powersupply ics.

www.powerint.com

especially tiny series.

chen..
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yobalzal
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« Reply #4 on: January 06, 2008, 05:04:06 17:04 »

Here's a simple schematic for one, just modify R2 and ZD3 as per your requirement.

Just be careful you are working with live voltages ...
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narc60
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« Reply #5 on: January 06, 2008, 05:42:25 17:42 »

yobalzal,

Is the FR resistor a special type (why the FR designation)?
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yobalzal
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« Reply #6 on: January 06, 2008, 05:59:36 17:59 »

FR is abbreviation of Fusible Resistor that works as resistor in normal condition and turned into fuse while abnormal current comes in.
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surachai
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« Reply #7 on: January 06, 2008, 07:44:22 19:44 »

hi yobalzal
   How much current can supply in your circuit?
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yobalzal
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« Reply #8 on: January 06, 2008, 08:33:16 20:33 »

You can draw easily upto 100 mA from this circuit, enough to drive any of your MCU application.
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darksky
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« Reply #9 on: January 06, 2008, 09:42:10 21:42 »

100 mA would need abig capacitor.  Don't forget the current goes down with voltage and frequency.

Capacitors can also have a big tolerance -20% or more.

Capacitor needs to be X or Y rated for this type of appliation.

I would never try to get more than 50 mA from this kind of supply.
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proton
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« Reply #10 on: January 07, 2008, 04:18:34 16:18 »

Design TIPS :-

Put a resistor RLimit and Capacitor in C1 (must be connected in parallel with a discharging resistor of about 220K...1Meg) in series with a bridge (If you want DC) then use a Zener to the required voltage then a filter capacitor.

I assume :

Input             230V AC at 50Hz
Output           10V DC at 100mA

RLimit is used only to protect all other components used from surge current.
RLimit should be selected such that maximum surge current cannot exeed the current capacity of any of the components used,That is zener,bridge,filter CAP,Series Cap C1.

Preferable values will be such that it will limit surge at 10 times the maximum DC output current.That is 1Amp

so R1 = 230 / 1Amp = 230 Ohms and 100mA * 100mA * 230Ohms = 2.3 Watts

Value of C1 can be found using C1 = 1 / 2 * PI * F * R

where R = 230V / 100mA = 2.3K

so,
     C1 = 1/ (2 * PI * 50 * 2300) = 1.383ufd NON Polar with a voltage rating of 230 / 0.707 = 325.3V + 10% margin.

Zener 's wattage should be such that it can handle the 1Amp maximum surge current

Zener's Wattage = Zener's Voltage * Maximum Current flowing through Zener.

The basic idea of this circuit is to use the AC impedance property of the C1 to limit the current just like any other resistor but without dissipating power.

If there will always be load then you may even remove the Zener.If you use half wave rectifier then you will get just half the current output.

I would not recomend this type of design since,

1.It does not isolate the mains.
2.It still dissipates power in RLimit

But it is weightless,simple and easy.

Proton
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blastronics
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« Reply #11 on: January 08, 2008, 02:28:37 02:28 »

hello!

i have ask the same question in other forum.
This will be very useful
http://ww1.microchip.com/downloads/en/appnotes/00954a.pdf

blastronics
 Cheesy
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spl
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« Reply #12 on: January 09, 2008, 06:50:42 06:50 »

I have try this rc regulate for my light switch  , it work fine ..But becareful after i use is for a long time
(about 1 year) some part can burn  Angry. So the transformer may be the simple choice . Undecided
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lek05134
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« Reply #13 on: January 10, 2008, 03:38:18 03:38 »

Look at this
ww1.microchip.com/downloads/en/AppNotes/00954A.pdf Wink
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joaler
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« Reply #14 on: January 11, 2008, 09:32:04 09:32 »

hai all

i know it's dangerous to yse the transformerless power supply
but the thing is that i want to reduce the cost and size
the system will be installed by me only to avoid any problems

jo
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donno
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« Reply #15 on: January 13, 2008, 06:40:29 06:40 »

Many fine solutions offered...but remember this important formula

         S.O.L.S=D.O.A.*Xp

(Short On Line Side =  Dead On Arrival x Number (of people))

Isolation transformers such as used in appliances, switch modes psu's etc. electrically Isolate the nasties
from the secondary side.

Any one of the fore mentioned solutions would be fine given some form of isolation is
provided from the mains.
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Kabron
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« Reply #16 on: January 13, 2008, 01:59:24 13:59 »

See my post here http://kazus.ru/forum/topic_9957-0-asc-100.html
In russian, but with all links and examples in Proteus and SwitcherCad.
It is a kind of very simple Pulse Power Supply.
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yangzy
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« Reply #17 on: January 15, 2008, 01:44:49 01:44 »

You can use LNK306 from PI.
It's a good solution for transformer less power supply.
http://rapidshare.com/files/83870720/lnktn_family_datasheetCN-LNK306.pdf
 Smiley
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Resonance
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« Reply #18 on: December 20, 2015, 11:38:00 11:38 »

I know this is an old topic, but it's a common requirement to have a non isolated power supply from the mains.
Here's a circuit I came across from a light dimmer which I've been messing with and simulated.
I think you should be able to get 10mA from it which is enough to be useful.

Welcome comments on this.

Posted on: December 20, 2015, 11:33:47 11:33 - Automerged

Yet another non-isolated mains power supply.
This time from an ST application note UM1597 user manual.
Quite a few components here. I haven't worked out fully the mode of operation so can't comment on it much.
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Some Anon Guy
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« Reply #19 on: December 20, 2015, 08:32:13 20:32 »

IMO, it seems silly to me to go down this path trying to save a couple dollars...
This transformer from mouser is $8.
http://www.mouser.com/ProductDetail/Triad-Magnetics/FS16-150/?qs=sGAEpiMZZMvwUzoUXIIvycT6np3HRZBQ1hwcG22b%2fio%3d

This was just a quick search.

life > $8

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bobcat1
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« Reply #20 on: December 27, 2015, 09:01:11 09:01 »

Hi

Why bother design a dangerous high voltage circuit where you can order a switch PSU fully encapsulated and isolated for less then 2 USD ?
see link below :

http://www.xt-xinte.com/?goods=detail&id=20328

All the best

Bobi
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