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aphpic
Joined: 01 Sep 2004
Posts: 3
Location: Basingstoke UK
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| Simple circuit 240v AC to power PIC |
 Posted: Mon Jan 10, 2005 9:19 am |
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Dear group
Some while ago I read about a simple circuit that used a couple of diodes and resisters to tap off mains AC (it may have been 120 volts) to 5 volts DC, to power a PIC. It wasn’t the original posted question but I have tried searching without luck (one link was the Microchip site but searching there got me nowhere). Does this ‘ring any bells’ with anyone?
Thanks in advance. |
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Ttelmah
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| Re: Simple circuit 240v AC to power PIC |
| Posted: Mon Jan 10, 2005 10:15 am |
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| aphpic wrote: | Dear group
Some while ago I read about a simple circuit that used a couple of diodes and resisters to tap off mains AC (it may have been 120 volts) to 5 volts DC, to power a PIC. It wasn’t the original posted question but I have tried searching without luck (one link was the Microchip site but searching there got me nowhere). Does this ‘ring any bells’ with anyone?
Thanks in advance. |
This is a 'can of worms'. You can build a simple potential divider, add a diode to rectify the voltage, and a capacitor to smooth it, and _for a fixed load_, you have a reasonable voltage. However there are a huge number of 'caveats'. If the incoming voltage changes, so will the output. If the output load changes, so will the voltage. The circuit provides no isolation, so is potentially lethal. For a given output power, about 20* this, has to be dissipated in the dropper resistors.
You can cure the first two problems by adding a zener. There are also a number of IC's designed for powering devices like triac dimmers, that have 90% of the parts in one package, and provide better regulation (Harris used to do one). Some of these also cure the third problem, by using a switching FET, instead of the discrete resistors (look at the 'VIPer12A', for an example of such a circuit.
However if you have to ask the question of how to do this, I'd say _use an isolated supply_. The safety this gives, both to 'life and limb', and to the parts involved (as soon as you connect to an external component, you have to consider how this is going to affect the processor inputs/outputs), is almost incalculable. There are dozens of 'monoblock' supplies on the market, some as small as a matchbox, containing complete transformers and regulation, that these provide the easiest way to power a PIC.
Best Wishes |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Mon Jan 10, 2005 11:57 am |
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Microchip has several good application notes on transformerless power supplies: AN954 Transformerless Power Supplies: Resistive and Capacitive discusses the advantages and disadvantages of both approaches.
TB008 Transformerless Power Supply discusses a capacitive approach.
Please Note that all these circuits can only deliver a small current (10mA max @ 5V) and because they are connected directly to the mains they are very dangerous. Only use these kind of circuits when cost and size are extremely critical and no part of the circuit can be touched by the user.
I agree with Ttelmah and recommend to use a transformer based circuit whenever possible. |
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newguy
Joined: 24 Jun 2004
Posts: 1907
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| Posted: Mon Jan 10, 2005 12:24 pm |
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Not too long ago I took my coffee maker apart to see what its supply looked like. This is a 120V 60Hz North American unit.
Not too sure what the secret to posting a picture is.... I have a .pdf of the schematic. Email me if you want it. |
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aphpic
Joined: 01 Sep 2004
Posts: 3
Location: Basingstoke UK
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| Thank you |
| Posted: Mon Jan 10, 2005 1:27 pm |
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| Thank you for the information, I now have some reading and thinking to do. The 2 Microchip docs are what I saw before. |
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BitHead
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| Yes indeed! |
| Posted: Wed May 10, 2006 7:32 pm |
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It is absolutely possible it run a PIC on direct 240V ac @ 900amps.
Diodes, resistors and capacitors are not need as they can be simulated
in software. In fact, most of you hardware people don't know
anything can be substituted software. I've managed to make a PIC10f220
do 470GIPS (470 giga instructions per second). An intel xenon can't come close to that performance.
Perpetual motion and over unity efficiency is perfectly possible in software. |
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Guest
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| Posted: Thu May 11, 2006 4:54 am |
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| Quote: |
It is absolutely possible it run a PIC on direct 240V ac @ 900amps.
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may be too much beer ? |
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Guest
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| Posted: Thu May 11, 2006 4:56 am |
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It is absolutely possible it run a PIC on direct 240V ac @ 900amps.
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...may be too much beer ?  |
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treitmey
Joined: 23 Jan 2004
Posts: 1094
Location: Appleton,WI USA
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| Posted: Thu May 11, 2006 8:32 am |
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BitHead is going to get someone killed.
Page 1 of spec say all instructions are 1uS except branch
1uS/inst. thus 1,000,000 inst/sec max. not 470E9inst/sec
http://ww1.microchip.com/downloads/en/DeviceDoc/41270B.pdf
is this a form of sarcasm that I am not getting?
Last edited by treitmey on Thu May 11, 2006 8:53 am; edited 5 times in total |
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rnielsen
Joined: 23 Sep 2003
Posts: 852
Location: Utah
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| Posted: Thu May 11, 2006 8:42 am |
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| Quote: | | It is absolutely possible it run a PIC on direct 240V ac @ 900amps. |
I've done something similar to that a few times. The only problem is that I've not quite figured out how to keep the magic smoke from escaping after about 3 micro-seconds after power is applied. He must have perfected that procedure.
Ronald |
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Humberto
Joined: 08 Sep 2003
Posts: 1215
Location: Buenos Aires, La Reina del Plata
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| Posted: Thu May 11, 2006 8:57 am |
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| Quote: |
I've managed to make a PIC10f220
do 470GIPS (470 giga instructions per second). An intel xenon can't come close to that performance.
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I've managed to make an LM555 to run at 475 THerz (475 Tera Hertz)
After BitHead explains to us how it did it, I will explain yours how I obtained it.  |
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Storic
Joined: 03 Dec 2005
Posts: 182
Location: Australia SA
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treitmey
Joined: 23 Jan 2004
Posts: 1094
Location: Appleton,WI USA
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| Posted: Thu May 11, 2006 4:01 pm |
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The first sentence says that this is run through a current limiting resistor.
That makes all the difference.
**I like the note on the schematic..Danger Electrocution Hazard 
Last edited by treitmey on Thu May 11, 2006 4:45 pm; edited 1 time in total |
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rnielsen
Joined: 23 Sep 2003
Posts: 852
Location: Utah
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| Posted: Thu May 11, 2006 4:25 pm |
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I just had a thought. Hmmm, haven't had one of those in a while. 
If you were to completely encapsulate the circuit the magic smoke might be able to be contained and keep stray electrons from jumping around that could cause those nasty electrocutions.
Ronald |
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Humberto
Joined: 08 Sep 2003
Posts: 1215
Location: Buenos Aires, La Reina del Plata
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| Posted: Thu May 11, 2006 6:07 pm |
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**I like the note on the schematic..Danger Electrocution Hazard
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haven't had one of those in a while
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Ronald you would know, usually you can read this warning in the backing of an electric chair...
I like the encapsulation theory. 
Humberto |
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