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Old 19th August 2014, 07:15 PM   #1
Sin Bin
 
Join Date: Apr 2014
Default Simple 20 volt DC from 220 AC circuit

Can anyone show me a VERY VERY BASIC idea /schematic ----on how to build
a simple bridge rectifier ---from a transformer 30 -0 30 ac out
--by very simple ---I mean no fancy IC ,S or complex circuits --
just a 20 DC from 30 V ac transformer --( 220 v AC in )
----do not want to include any lousy voltage regulator IC s that are not available
in the 3rd world --
just good ol diodes /capacitors please --
if impossible ---no problem !
will post a foto of the transformer ---was once used for a old TDA 140 watt guitar amp -- ( forgot the TDA #)
now I require 20 volt dc from it --
( printed on transformer as follows ) ---30 v --0 ----30 v---1.417 AMP
85 VA
nb ----no expert -- lotta hands on DIY experience---
prefer basic diagrams /sketches to complex un-fathomable-electronic jargon /theory
1.41 amps

Last edited by carl winter; 19th August 2014 at 07:31 PM. Reason: did not complete my question ! cut off !
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Old 19th August 2014, 08:12 PM   #2
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by carl winter View Post
----do not want to include any lousy voltage regulator IC s that are not available
in the 3rd world --
just good ol diodes /capacitors please --
I am afraid it is going to be difficult: peak rectification, whether half or full wave will yield more than 40V, average filtering with a choke (not included in your initial BOM) will give out 27V or so under load, and half-wave plus inductor filtering half of that.
In any case, you' ll be seriously distant from your target voltage.

Completely avoiding active components would probably be possible in theory, using clever fractional voltage rectifiers, but honestly a cheap active circuit, not necessarily an IC will be much less costly and easier to source.
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Old 19th August 2014, 08:16 PM   #3
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Regulated or unregulated?
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Old 19th August 2014, 08:38 PM   #4
Sin Bin
 
Join Date: Apr 2014
those voltage regulators I have seen on hundreds of bridge rect circuits ---are moon rocks here --take months to order from US supplies
all I want is some brave fella to post a simple schematic that ie possibly retro 60 /s
transistors --- mostly diodes
but its DIY ---I hate ic/s they are nightmares to handle /solder on home made circuits---
--hens teeth
there must be a circuit somewhere that's novice /idiot proof?
why is a " voltage regulator"
so necessary ---?--no -don,t answer that ---the quantum theory is way beyond
us laymen ----
I simply build a circuit --I do not delve into mathematical hieroglyphics --way too
complex --
all I want is a schematic with few parts --that works (not in theory ) but finger blistering practical application
the amp (TDA 2040---I built works ok 23 VOLTS ( 2 x 12 volt bulky heavy batteries) ---not nice
--that's why the TRANSFORMER /rectifier circuit is needed--
or is there a commercially available plug in 20 volt dc from ac adaptor unit --
available ? I doubt its cheap or small -probably cost a fortune /take 3 months to
import ---
ok thanks for the help ---
will keep looking
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Old 19th August 2014, 08:57 PM   #5
sreten is offline sreten  United Kingdom
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Join Date: Nov 2003
Location: Brighton UK
Hi,

19V ex laptop power supply will do the job.

rgds, sreten.
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Old 19th August 2014, 09:08 PM   #6
WSJ is offline WSJ  United States
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Location: GILROY, CA
For 20 V out use a 21 V zener. R1=1k, Q1=Darlington. Use large heat sink for Q1.

Click the image to open in full size.

Click the image to open in full size.

Last edited by WSJ; 19th August 2014 at 09:23 PM.
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Old 19th August 2014, 10:22 PM   #7
JMFahey is offline JMFahey  Argentina
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Location: Buenos Aires - Argentina
Quote:
Originally Posted by carl winter View Post
Can anyone show me a VERY VERY BASIC idea /schematic ----on how to build
a simple bridge rectifier ---from a transformer 30 -0 30 ac out
--by very simple ---I mean no fancy IC ,S or complex circuits --
just a 20 DC from 30 V ac transformer --( 220 v AC in )
----do not want to include any lousy voltage regulator IC s that are not available
in the 3rd world --

just good ol diodes /capacitors please --
if impossible ---no problem !
will post a foto of the transformer ---was once used for a old TDA 140 watt guitar amp -- ( forgot the TDA #)
now I require 20 volt dc from it --
( printed on transformer as follows ) ---30 v --0 ----30 v---1.417 AMP
85 VA
nb ----no expert -- lotta hands on DIY experience---
prefer basic diagrams /sketches to complex un-fathomable-electronic jargon /theory
1.41 amps
Quote:
those voltage regulators I have seen on hundreds of bridge rect circuits ---are moon rocks here --take months to order from US supplies
What you say is impossible, standard voltage regulators are easily available even in the 5th World, go figure.
WHERE do you actually live?
Unless you live *here*, of course:
Click the image to open in full size.
Quote:
I hate ic/s they are nightmares to handle /solder on home made circuits---
A 3 leg TO220 voltage regulator?
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Old 20th August 2014, 09:33 AM   #8
Sin Bin
 
Join Date: Apr 2014
Default TO 220 voltage regulator

thanku for enlightening me - only 3 legs! WONDERFUL!-assumed a the V REGULATOR was a
MILLIPEDE legged nightmare ( never seen one )
SO it resembles a power transistor ? that's great news !

still --it takes 2- - 3 month wait for snail mail to central Africa
but now I can at least solder with ease --16 legged IC ,s are hell with
my eyesight at 65 ---thanku ---so much!
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Old 20th August 2014, 09:49 AM   #9
Sin Bin
 
Join Date: Apr 2014
WSJ ---
you are the man ! ---exactly what I asked for --really appreciate!
a few questions ----
1 ------21 volt ZENER diode ----yes---( from old tv set)
2 -------Q1 = darlington pair transistors-?--or the 2N3055 power transistor? ( got a few from salvage of scrap)
as you have shown a 12volt DC bridge circuit --do I copy exact circuit shown?

or the same circuit using those above components?
I have the above 220volt ---12 volt AC transformer---
can you put all modifications in place on another schematic ----?
sorry ---gross amateur ---a bit lost here---
will scrap the 30 ac transformer---
rebuild the above circuit---
thanku so much ---really learnt another quantum leap!
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Old 20th August 2014, 10:10 AM   #10
Sin Bin
 
Join Date: Apr 2014
Default pc laptop supply

WOW --- thanku SRETEN--- so simple --I was blind! damn thing is in front of me !
Brighton to the rescue ! --brilliant !
had no idea my old PC supply was 19 volt ! ( should always read the fine print---) even then I assumed it was milliamps -----
2 . I amp ---astounding---
now I can scrap nasty bulky 24 volt lead weights( 4kilos)
for a small compact /lightweight solution --
so very grateful --

but I do intend building that rectifier circuit WSJ has so kindly
posted for me ----you guys are superstars for ideas --
( my innate curiosity has forced me to learn the hard way --))
after all --- this forum is called DIY --- SO --
despite Mr Faheys sarcasm -----(--Tom Hank,s Pacific island is a lot closer to USA than I am )--he has no idea what corrupt incompetent
3rd world customs / mail system can do to one,s parcels/composure!
will figure out how the rectifier circuit works --in practise
much more challenge involved in hands on ---instead of
easy to plug in sealed mysteries---
thanku all ---regards
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