using linear regulator in high voltage with pre-regulator

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johny_fv9a

Joined Feb 19, 2021
2
My structure is like this:
0-220 Vac——>full wave rectifier——>linear regulator——>microcontroller and led

Microcontroller and led are taking 20ma.My linear regulator is LD1086.Regulator can accept input voltage up to 30V.I dont want step down transformer.I need to pre regulator.And I need to 5V output without ripple in regulator.Can you help me?
 

dendad

Joined Feb 20, 2016
3,835
If this is directly connected to the mains, that is a very dangerous way to go. And it is against this site's rules I think.
Why do you not want to use a transformer?
An old cell phone power supply would work very well, and be a LOT safer.
 

DickCappels

Joined Aug 21, 2008
7,432
Direct connection to the mains is ok according to the User Agreement, and discussion of the same is allowed provided everything in done safely.

I agree an USB charger or cell phone charger would be a much better way to go because all of the safety work has already been done by professionals. I use such chargers often -my objective is not to build yet another power supply.
 

crutschow

Joined Mar 14, 2008
27,210
I agree with the above.
No reason to mess with the dangerous main's voltage without isolation when 5V wallworts are so common (and inexpensive if you have to buy one).
 

shortbus

Joined Sep 30, 2009
8,581
Direct connection to the mains is ok according to the User Agreement, and discussion of the same is allowed provided everything in done safely
When did this change? It, getting low voltage with out isolation, used to be forbidden here, and many threads were locked about doing it. As far as "provided everything in done safely", the TS hasn't proven that he can do it, since this is his first post.
 

Papabravo

Joined Feb 24, 2006
16,132
When did this change? It, getting low voltage with out isolation, used to be forbidden here, and many threads were locked about doing it. As far as "provided everything in done safely", the TS hasn't proven that he can do it, since this is his first post.
This policy changed at some point after the forum was acquired. It was at about the same time as automotive topics were allowed, I want to say 2017-2018 time frame.
 

dl324

Joined Mar 30, 2015
12,871
I don't know when or why it changed either, but I won't offer assistance in any threads with mains connections without isolation.
 

Thread Starter

johny_fv9a

Joined Feb 19, 2021
2
If this is directly connected to the mains, that is a very dangerous way to go. And it is against this site's rules I think.
Why do you not want to use a transformer?
An old cell phone power supply would work very well, and be a LOT safer.
because this is variable voltage.between 0-220Vac.also,why dangerous?I need to pre regulator
 

dendad

Joined Feb 20, 2016
3,835
What is your actual supply device and voltage range?
Is it the mains or a generator?
It is really hard to get 5V out with 0V in!
A "universal" mains input power supply, like most phone chargers, will work from a wide input voltage range.
And any voltage over about 50V can be dangerous. I'm particularly concerned as it sounds like you do not have much experience in electronics, and so you are dealing with potentially lethal voltages so you could quite easilly hurt yourself, or maybe worse, someone else.
Please, post more details of your project if you really want assistance.
 

Papabravo

Joined Feb 24, 2006
16,132
because this is variable voltage.between 0-220Vac.also,why dangerous?I need to pre regulator
Because line voltage can KILL you! Do you fancy being the winner of a Darwin Award?
The pre-regulator is not the way to go. It is too inefficient and you will be dissipating quite a bit of heat. What you want is an offline SMPS that goes straight to +5V
You wont be able to generate +5V from 0 VAC as has already been mentioned. In any SMPS you can reduce the ripple to undetectable levels with excellent transient response. This is not a good project for a beginner, so it might be best if you purchased a unit suitable for your needs.
 
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DickCappels

Joined Aug 21, 2008
7,432
The policy was changed a few months ago. The discussion revolved around the question of whether it was better to refuse to help novices dabbling in non-isolated power supplies or to help them do so safely.
 

andrewmm

Joined Feb 25, 2011
1,468
Regarding the advise and questions we ask on here,
if some one gives advise, and the user is injured,
what is our liability as posters ?
 

bertus

Joined Apr 5, 2008
21,364
Hello,

The User Agreement has been changed.
The restricted topics and safety rules have been split:
UA restricted safety.png
When the safety comes into play, we are allowed to close the thread with section 7 of the UA.

Bertus
 
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